Lazy Load

Package gopacket provides packet decoding for the Go language. gopacket contains many sub-packages with additional functionality you may find useful, including: Also, if you're looking to dive right into code, see the examples subdirectory for numerous simple binaries built using gopacket libraries. Minimum go version required is 1.5 except for pcapgo/EthernetHandle, afpacket, and bsdbpf which need at least 1.7 due to x/sys/unix dependencies. gopacket takes in packet data as a []byte and decodes it into a packet with a non-zero number of "layers". Each layer corresponds to a protocol within the bytes. Once a packet has been decoded, the layers of the packet can be requested from the packet. Packets can be decoded from a number of starting points. Many of our base types implement Decoder, which allow us to decode packets for which we don't have full data. Most of the time, you won't just have a []byte of packet data lying around. Instead, you'll want to read packets in from somewhere (file, interface, etc) and process them. To do that, you'll want to build a PacketSource. First, you'll need to construct an object that implements the PacketDataSource interface. There are implementations of this interface bundled with gopacket in the gopacket/pcap and gopacket/pfring subpackages... see their documentation for more information on their usage. Once you have a PacketDataSource, you can pass it into NewPacketSource, along with a Decoder of your choice, to create a PacketSource. Once you have a PacketSource, you can read packets from it in multiple ways. See the docs for PacketSource for more details. The easiest method is the Packets function, which returns a channel, then asynchronously writes new packets into that channel, closing the channel if the packetSource hits an end-of-file. You can change the decoding options of the packetSource by setting fields in packetSource.DecodeOptions... see the following sections for more details. gopacket optionally decodes packet data lazily, meaning it only decodes a packet layer when it needs to handle a function call. Lazily-decoded packets are not concurrency-safe. Since layers have not all been decoded, each call to Layer() or Layers() has the potential to mutate the packet in order to decode the next layer. If a packet is used in multiple goroutines concurrently, don't use gopacket.Lazy. Then gopacket will decode the packet fully, and all future function calls won't mutate the object. By default, gopacket will copy the slice passed to NewPacket and store the copy within the packet, so future mutations to the bytes underlying the slice don't affect the packet and its layers. If you can guarantee that the underlying slice bytes won't be changed, you can use NoCopy to tell gopacket.NewPacket, and it'll use the passed-in slice itself. The fastest method of decoding is to use both Lazy and NoCopy, but note from the many caveats above that for some implementations either or both may be dangerous. During decoding, certain layers are stored in the packet as well-known layer types. For example, IPv4 and IPv6 are both considered NetworkLayer layers, while TCP and UDP are both TransportLayer layers. We support 4 layers, corresponding to the 4 layers of the TCP/IP layering scheme (roughly anagalous to layers 2, 3, 4, and 7 of the OSI model). To access these, you can use the packet.LinkLayer, packet.NetworkLayer, packet.TransportLayer, and packet.ApplicationLayer functions. Each of these functions returns a corresponding interface (gopacket.{Link,Network,Transport,Application}Layer). The first three provide methods for getting src/dst addresses for that particular layer, while the final layer provides a Payload function to get payload data. This is helpful, for example, to get payloads for all packets regardless of their underlying data type: A particularly useful layer is ErrorLayer, which is set whenever there's an error parsing part of the packet. Note that we don't return an error from NewPacket because we may have decoded a number of layers successfully before running into our erroneous layer. You may still be able to get your Ethernet and IPv4 layers correctly, even if your TCP layer is malformed. gopacket has two useful objects, Flow and Endpoint, for communicating in a protocol independent manner the fact that a packet is coming from A and going to B. The general layer types LinkLayer, NetworkLayer, and TransportLayer all provide methods for extracting their flow information, without worrying about the type of the underlying Layer. A Flow is a simple object made up of a set of two Endpoints, one source and one destination. It details the sender and receiver of the Layer of the Packet. An Endpoint is a hashable representation of a source or destination. For example, for LayerTypeIPv4, an Endpoint contains the IP address bytes for a v4 IP packet. A Flow can be broken into Endpoints, and Endpoints can be combined into Flows: Both Endpoint and Flow objects can be used as map keys, and the equality operator can compare them, so you can easily group together all packets based on endpoint criteria: For load-balancing purposes, both Flow and Endpoint have FastHash() functions, which provide quick, non-cryptographic hashes of their contents. Of particular importance is the fact that Flow FastHash() is symmetric: A->B will have the same hash as B->A. An example usage could be: This allows us to split up a packet stream while still making sure that each stream sees all packets for a flow (and its bidirectional opposite). If your network has some strange encapsulation, you can implement your own decoder. In this example, we handle Ethernet packets which are encapsulated in a 4-byte header. See the docs for Decoder and PacketBuilder for more details on how coding decoders works, or look at RegisterLayerType and RegisterEndpointType to see how to add layer/endpoint types to gopacket. TLDR: DecodingLayerParser takes about 10% of the time as NewPacket to decode packet data, but only for known packet stacks. Basic decoding using gopacket.NewPacket or PacketSource.Packets is somewhat slow due to its need to allocate a new packet and every respective layer. It's very versatile and can handle all known layer types, but sometimes you really only care about a specific set of layers regardless, so that versatility is wasted. DecodingLayerParser avoids memory allocation altogether by decoding packet layers directly into preallocated objects, which you can then reference to get the packet's information. A quick example: The important thing to note here is that the parser is modifying the passed in layers (eth, ip4, ip6, tcp) instead of allocating new ones, thus greatly speeding up the decoding process. It's even branching based on layer type... it'll handle an (eth, ip4, tcp) or (eth, ip6, tcp) stack. However, it won't handle any other type... since no other decoders were passed in, an (eth, ip4, udp) stack will stop decoding after ip4, and only pass back [LayerTypeEthernet, LayerTypeIPv4] through the 'decoded' slice (along with an error saying it can't decode a UDP packet). Unfortunately, not all layers can be used by DecodingLayerParser... only those implementing the DecodingLayer interface are usable. Also, it's possible to create DecodingLayers that are not themselves Layers... see layers.IPv6ExtensionSkipper for an example of this. By default, DecodingLayerParser uses native map to store and search for a layer to decode. Though being versatile, in some cases this solution may be not so optimal. For example, if you have only few layers faster operations may be provided by sparse array indexing or linear array scan. To accomodate these scenarios, DecodingLayerContainer interface is introduced along with its implementations: DecodingLayerSparse, DecodingLayerArray and DecodingLayerMap. You can specify a container implementation to DecodingLayerParser with SetDecodingLayerContainer method. Example: To skip one level of indirection (though sacrificing some capabilities) you may also use DecodingLayerContainer as a decoding tool as it is. In this case you have to handle unknown layer types and layer panics by yourself. Example: DecodingLayerSparse is the fastest but most effective when LayerType values that layers in use can decode are not large because otherwise that would lead to bigger memory footprint. DecodingLayerArray is very compact and primarily usable if the number of decoding layers is not big (up to ~10-15, but please do your own benchmarks). DecodingLayerMap is the most versatile one and used by DecodingLayerParser by default. Please refer to tests and benchmarks in layers subpackage to further examine usage examples and performance measurements. You may also choose to implement your own DecodingLayerContainer if you want to make use of your own internal packet decoding logic. As well as offering the ability to decode packet data, gopacket will allow you to create packets from scratch, as well. A number of gopacket layers implement the SerializableLayer interface; these layers can be serialized to a []byte in the following manner: SerializeTo PREPENDS the given layer onto the SerializeBuffer, and they treat the current buffer's Bytes() slice as the payload of the serializing layer. Therefore, you can serialize an entire packet by serializing a set of layers in reverse order (Payload, then TCP, then IP, then Ethernet, for example). The SerializeBuffer's SerializeLayers function is a helper that does exactly that. To generate a (empty and useless, because no fields are set) Ethernet(IPv4(TCP(Payload))) packet, for example, you can run: If you use gopacket, you'll almost definitely want to make sure gopacket/layers is imported, since when imported it sets all the LayerType variables and fills in a lot of interesting variables/maps (DecodersByLayerName, etc). Therefore, it's recommended that even if you don't use any layers functions directly, you still import with:

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package pointer implements Andersen's analysis, an inclusion-based pointer analysis algorithm first described in (Andersen, 1994). A pointer analysis relates every pointer expression in a whole program to the set of memory locations to which it might point. This information can be used to construct a call graph of the program that precisely represents the destinations of dynamic function and method calls. It can also be used to determine, for example, which pairs of channel operations operate on the same channel. The package allows the client to request a set of expressions of interest for which the points-to information will be returned once the analysis is complete. In addition, the client may request that a callgraph is constructed. The example program in example_test.go demonstrates both of these features. Clients should not request more information than they need since it may increase the cost of the analysis significantly. Our algorithm is INCLUSION-BASED: the points-to sets for x and y will be related by pts(y) ⊇ pts(x) if the program contains the statement y = x. It is FLOW-INSENSITIVE: it ignores all control flow constructs and the order of statements in a program. It is therefore a "MAY ALIAS" analysis: its facts are of the form "P may/may not point to L", not "P must point to L". It is FIELD-SENSITIVE: it builds separate points-to sets for distinct fields, such as x and y in struct { x, y *int }. It is mostly CONTEXT-INSENSITIVE: most functions are analyzed once, so values can flow in at one call to the function and return out at another. Only some smaller functions are analyzed with consideration of their calling context. It has a CONTEXT-SENSITIVE HEAP: objects are named by both allocation site and context, so the objects returned by two distinct calls to f: are distinguished up to the limits of the calling context. It is a WHOLE PROGRAM analysis: it requires SSA-form IR for the complete Go program and summaries for native code. See the (Hind, PASTE'01) survey paper for an explanation of these terms. The analysis is fully sound when invoked on pure Go programs that do not use reflection or unsafe.Pointer conversions. In other words, if there is any possible execution of the program in which pointer P may point to object O, the analysis will report that fact. By default, the "reflect" library is ignored by the analysis, as if all its functions were no-ops, but if the client enables the Reflection flag, the analysis will make a reasonable attempt to model the effects of calls into this library. However, this comes at a significant performance cost, and not all features of that library are yet implemented. In addition, some simplifying approximations must be made to ensure that the analysis terminates; for example, reflection can be used to construct an infinite set of types and values of those types, but the analysis arbitrarily bounds the depth of such types. Most but not all reflection operations are supported. In particular, addressable reflect.Values are not yet implemented, so operations such as (reflect.Value).Set have no analytic effect. The pointer analysis makes no attempt to understand aliasing between the operand x and result y of an unsafe.Pointer conversion: It is as if the conversion allocated an entirely new object: The analysis cannot model the aliasing effects of functions written in languages other than Go, such as runtime intrinsics in C or assembly, or code accessed via cgo. The result is as if such functions are no-ops. However, various important intrinsics are understood by the analysis, along with built-ins such as append. The analysis currently provides no way for users to specify the aliasing effects of native code. ------------------------------------------------------------------------ The remaining documentation is intended for package maintainers and pointer analysis specialists. Maintainers should have a solid understanding of the referenced papers (especially those by H&L and PKH) before making making significant changes. The implementation is similar to that described in (Pearce et al, PASTE'04). Unlike many algorithms which interleave constraint generation and solving, constructing the callgraph as they go, this implementation for the most part observes a phase ordering (generation before solving), with only simple (copy) constraints being generated during solving. (The exception is reflection, which creates various constraints during solving as new types flow to reflect.Value operations.) This improves the traction of presolver optimisations, but imposes certain restrictions, e.g. potential context sensitivity is limited since all variants must be created a priori. A type is said to be "pointer-like" if it is a reference to an object. Pointer-like types include pointers and also interfaces, maps, channels, functions and slices. We occasionally use C's x->f notation to distinguish the case where x is a struct pointer from x.f where is a struct value. Pointer analysis literature (and our comments) often uses the notation dst=*src+offset to mean something different than what it means in Go. It means: for each node index p in pts(src), the node index p+offset is in pts(dst). Similarly *dst+offset=src is used for store constraints and dst=src+offset for offset-address constraints. Nodes are the key datastructure of the analysis, and have a dual role: they represent both constraint variables (equivalence classes of pointers) and members of points-to sets (things that can be pointed at, i.e. "labels"). Nodes are naturally numbered. The numbering enables compact representations of sets of nodes such as bitvectors (or BDDs); and the ordering enables a very cheap way to group related nodes together. For example, passing n parameters consists of generating n parallel constraints from caller+i to callee+i for 0<=i<n. The zero nodeid means "not a pointer". For simplicity, we generate flow constraints even for non-pointer types such as int. The pointer equivalence (PE) presolver optimization detects which variables cannot point to anything; this includes not only all variables of non-pointer types (such as int) but also variables of pointer-like types if they are always nil, or are parameters to a function that is never called. Each node represents a scalar part of a value or object. Aggregate types (structs, tuples, arrays) are recursively flattened out into a sequential list of scalar component types, and all the elements of an array are represented by a single node. (The flattening of a basic type is a list containing a single node.) Nodes are connected into a graph with various kinds of labelled edges: simple edges (or copy constraints) represent value flow. Complex edges (load, store, etc) trigger the creation of new simple edges during the solving phase. Conceptually, an "object" is a contiguous sequence of nodes denoting an addressable location: something that a pointer can point to. The first node of an object has a non-nil obj field containing information about the allocation: its size, context, and ssa.Value. Objects include: Many objects have no Go types. For example, the func, map and chan type kinds in Go are all varieties of pointers, but their respective objects are actual functions (executable code), maps (hash tables), and channels (synchronized queues). Given the way we model interfaces, they too are pointers to "tagged" objects with no Go type. And an *ssa.Global denotes the address of a global variable, but the object for a Global is the actual data. So, the types of an ssa.Value that creates an object is "off by one indirection": a pointer to the object. The individual nodes of an object are sometimes referred to as "labels". For uniformity, all objects have a non-zero number of fields, even those of the empty type struct{}. (All arrays are treated as if of length 1, so there are no empty arrays. The empty tuple is never address-taken, so is never an object.) An tagged object has the following layout: The T node's typ field is the dynamic type of the "payload": the value v which follows, flattened out. The T node's obj has the otTagged flag. Tagged objects are needed when generalizing across types: interfaces, reflect.Values, reflect.Types. Each of these three types is modelled as a pointer that exclusively points to tagged objects. Tagged objects may be indirect (obj.flags ⊇ {otIndirect}) meaning that the value v is not of type T but *T; this is used only for reflect.Values that represent lvalues. (These are not implemented yet.) Variables of the following "scalar" types may be represented by a single node: basic types, pointers, channels, maps, slices, 'func' pointers, interfaces. Pointers: Nothing to say here, oddly. Basic types (bool, string, numbers, unsafe.Pointer): Currently all fields in the flattening of a type, including non-pointer basic types such as int, are represented in objects and values. Though non-pointer nodes within values are uninteresting, non-pointer nodes in objects may be useful (if address-taken) because they permit the analysis to deduce, in this example, that p points to s.x. If we ignored such object fields, we could only say that p points somewhere within s. All other basic types are ignored. Expressions of these types have zero nodeid, and fields of these types within aggregate other types are omitted. unsafe.Pointers are not modelled as pointers, so a conversion of an unsafe.Pointer to *T is (unsoundly) treated equivalent to new(T). Channels: An expression of type 'chan T' is a kind of pointer that points exclusively to channel objects, i.e. objects created by MakeChan (or reflection). 'chan T' is treated like *T. *ssa.MakeChan is treated as equivalent to new(T). *ssa.Send and receive (*ssa.UnOp(ARROW)) and are equivalent to store Maps: An expression of type 'map[K]V' is a kind of pointer that points exclusively to map objects, i.e. objects created by MakeMap (or reflection). map K[V] is treated like *M where M = struct{k K; v V}. *ssa.MakeMap is equivalent to new(M). *ssa.MapUpdate is equivalent to *y=x where *y and x have type M. *ssa.Lookup is equivalent to y=x.v where x has type *M. Slices: A slice []T, which dynamically resembles a struct{array *T, len, cap int}, is treated as if it were just a *T pointer; the len and cap fields are ignored. *ssa.MakeSlice is treated like new([1]T): an allocation of a *ssa.Index on a slice is equivalent to a load. *ssa.IndexAddr on a slice returns the address of the sole element of the slice, i.e. the same address. *ssa.Slice is treated as a simple copy. Functions: An expression of type 'func...' is a kind of pointer that points exclusively to function objects. A function object has the following layout: There may be multiple function objects for the same *ssa.Function due to context-sensitive treatment of some functions. The first node is the function's identity node. Associated with every callsite is a special "targets" variable, whose pts() contains the identity node of each function to which the call may dispatch. Identity words are not otherwise used during the analysis, but we construct the call graph from the pts() solution for such nodes. The following block of contiguous nodes represents the flattened-out types of the parameters ("P-block") and results ("R-block") of the function object. The treatment of free variables of closures (*ssa.FreeVar) is like that of global variables; it is not context-sensitive. *ssa.MakeClosure instructions create copy edges to Captures. A Go value of type 'func' (i.e. a pointer to one or more functions) is a pointer whose pts() contains function objects. The valueNode() for an *ssa.Function returns a singleton for that function. Interfaces: An expression of type 'interface{...}' is a kind of pointer that points exclusively to tagged objects. All tagged objects pointed to by an interface are direct (the otIndirect flag is clear) and concrete (the tag type T is not itself an interface type). The associated ssa.Value for an interface's tagged objects may be an *ssa.MakeInterface instruction, or nil if the tagged object was created by an instrinsic (e.g. reflection). Constructing an interface value causes generation of constraints for all of the concrete type's methods; we can't tell a priori which ones may be called. TypeAssert y = x.(T) is implemented by a dynamic constraint triggered by each tagged object O added to pts(x): a typeFilter constraint if T is an interface type, or an untag constraint if T is a concrete type. A typeFilter tests whether O.typ implements T; if so, O is added to pts(y). An untagFilter tests whether O.typ is assignable to T,and if so, a copy edge O.v -> y is added. ChangeInterface is a simple copy because the representation of tagged objects is independent of the interface type (in contrast to the "method tables" approach used by the gc runtime). y := Invoke x.m(...) is implemented by allocating contiguous P/R blocks for the callsite and adding a dynamic rule triggered by each tagged object added to pts(x). The rule adds param/results copy edges to/from each discovered concrete method. (Q. Why do we model an interface as a pointer to a pair of type and value, rather than as a pair of a pointer to type and a pointer to value? A. Control-flow joins would merge interfaces ({T1}, {V1}) and ({T2}, {V2}) to make ({T1,T2}, {V1,V2}), leading to the infeasible and type-unsafe combination (T1,V2). Treating the value and its concrete type as inseparable makes the analysis type-safe.) Type parameters: Type parameters are not directly supported by the analysis. Calls to generic functions will be left as if they had empty bodies. Users of the package are expected to use the ssa.InstantiateGenerics builder mode when building code that uses or depends on code containing generics. reflect.Value: A reflect.Value is modelled very similar to an interface{}, i.e. as a pointer exclusively to tagged objects, but with two generalizations. 1. a reflect.Value that represents an lvalue points to an indirect (obj.flags ⊇ {otIndirect}) tagged object, which has a similar layout to an tagged object except that the value is a pointer to the dynamic type. Indirect tagged objects preserve the correct aliasing so that mutations made by (reflect.Value).Set can be observed. Indirect objects only arise when an lvalue is derived from an rvalue by indirection, e.g. the following code: Whether indirect or not, the concrete type of the tagged object corresponds to the user-visible dynamic type, and the existence of a pointer is an implementation detail. (NB: indirect tagged objects are not yet implemented) 2. The dynamic type tag of a tagged object pointed to by a reflect.Value may be an interface type; it need not be concrete. This arises in code such as this: pts(eface) is a singleton containing an interface{}-tagged object. That tagged object's payload is an interface{} value, i.e. the pts of the payload contains only concrete-tagged objects, although in this example it's the zero interface{} value, so its pts is empty. reflect.Type: Just as in the real "reflect" library, we represent a reflect.Type as an interface whose sole implementation is the concrete type, *reflect.rtype. (This choice is forced on us by go/types: clients cannot fabricate types with arbitrary method sets.) rtype instances are canonical: there is at most one per dynamic type. (rtypes are in fact large structs but since identity is all that matters, we represent them by a single node.) The payload of each *rtype-tagged object is an *rtype pointer that points to exactly one such canonical rtype object. We exploit this by setting the node.typ of the payload to the dynamic type, not '*rtype'. This saves us an indirection in each resolution rule. As an optimisation, *rtype-tagged objects are canonicalized too. Aggregate types: Aggregate types are treated as if all directly contained aggregates are recursively flattened out. Structs: *ssa.Field y = x.f creates a simple edge to y from x's node at f's offset. *ssa.FieldAddr y = &x->f requires a dynamic closure rule to create The nodes of a struct consist of a special 'identity' node (whose type is that of the struct itself), followed by the nodes for all the struct's fields, recursively flattened out. A pointer to the struct is a pointer to its identity node. That node allows us to distinguish a pointer to a struct from a pointer to its first field. Field offsets are logical field offsets (plus one for the identity node), so the sizes of the fields can be ignored by the analysis. (The identity node is non-traditional but enables the distinction described above, which is valuable for code comprehension tools. Typical pointer analyses for C, whose purpose is compiler optimization, must soundly model unsafe.Pointer (void*) conversions, and this requires fidelity to the actual memory layout using physical field offsets.) *ssa.Field y = x.f creates a simple edge to y from x's node at f's offset. *ssa.FieldAddr y = &x->f requires a dynamic closure rule to create Arrays: We model an array by an identity node (whose type is that of the array itself) followed by a node representing all the elements of the array; the analysis does not distinguish elements with different indices. Effectively, an array is treated like struct{elem T}, a load y=x[i] like y=x.elem, and a store x[i]=y like x.elem=y; the index i is ignored. A pointer to an array is pointer to its identity node. (A slice is also a pointer to an array's identity node.) The identity node allows us to distinguish a pointer to an array from a pointer to one of its elements, but it is rather costly because it introduces more offset constraints into the system. Furthermore, sound treatment of unsafe.Pointer would require us to dispense with this node. Arrays may be allocated by Alloc, by make([]T), by calls to append, and via reflection. Tuples (T, ...): Tuples are treated like structs with naturally numbered fields. *ssa.Extract is analogous to *ssa.Field. However, tuples have no identity field since by construction, they cannot be address-taken. There are three kinds of function call: Cases 1 and 2 apply equally to methods and standalone functions. Static calls: A static call consists three steps: A static function call is little more than two struct value copies between the P/R blocks of caller and callee: Context sensitivity: Static calls (alone) may be treated context sensitively, i.e. each callsite may cause a distinct re-analysis of the callee, improving precision. Our current context-sensitivity policy treats all intrinsics and getter/setter methods in this manner since such functions are small and seem like an obvious source of spurious confluences, though this has not yet been evaluated. Dynamic function calls: Dynamic calls work in a similar manner except that the creation of copy edges occurs dynamically, in a similar fashion to a pair of struct copies in which the callee is indirect: (Recall that the function object's P- and R-blocks are contiguous.) Interface method invocation: For invoke-mode calls, we create a params/results block for the callsite and attach a dynamic closure rule to the interface. For each new tagged object that flows to the interface, we look up the concrete method, find its function object, and connect its P/R blocks to the callsite's P/R blocks, adding copy edges to the graph during solving. Recording call targets: The analysis notifies its clients of each callsite it encounters, passing a CallSite interface. Among other things, the CallSite contains a synthetic constraint variable ("targets") whose points-to solution includes the set of all function objects to which the call may dispatch. It is via this mechanism that the callgraph is made available. Clients may also elect to be notified of callgraph edges directly; internally this just iterates all "targets" variables' pts(·)s. We implement Hash-Value Numbering (HVN), a pre-solver constraint optimization described in Hardekopf & Lin, SAS'07. This is documented in more detail in hvn.go. We intend to add its cousins HR and HU in future. The solver is currently a naive Andersen-style implementation; it does not perform online cycle detection, though we plan to add solver optimisations such as Hybrid- and Lazy- Cycle Detection from (Hardekopf & Lin, PLDI'07). It uses difference propagation (Pearce et al, SQC'04) to avoid redundant re-triggering of closure rules for values already seen. Points-to sets are represented using sparse bit vectors (similar to those used in LLVM and gcc), which are more space- and time-efficient than sets based on Go's built-in map type or dense bit vectors. Nodes are permuted prior to solving so that object nodes (which may appear in points-to sets) are lower numbered than non-object (var) nodes. This improves the density of the set over which the PTSs range, and thus the efficiency of the representation. Partly thanks to avoiding map iteration, the execution of the solver is 100% deterministic, a great help during debugging. Andersen, L. O. 1994. Program analysis and specialization for the C programming language. Ph.D. dissertation. DIKU, University of Copenhagen. David J. Pearce, Paul H. J. Kelly, and Chris Hankin. 2004. Efficient field-sensitive pointer analysis for C. In Proceedings of the 5th ACM SIGPLAN-SIGSOFT workshop on Program analysis for software tools and engineering (PASTE '04). ACM, New York, NY, USA, 37-42. http://doi.acm.org/10.1145/996821.996835 David J. Pearce, Paul H. J. Kelly, and Chris Hankin. 2004. Online Cycle Detection and Difference Propagation: Applications to Pointer Analysis. Software Quality Control 12, 4 (December 2004), 311-337. http://dx.doi.org/10.1023/B:SQJO.0000039791.93071.a2 David Grove and Craig Chambers. 2001. A framework for call graph construction algorithms. ACM Trans. Program. Lang. Syst. 23, 6 (November 2001), 685-746. http://doi.acm.org/10.1145/506315.506316 Ben Hardekopf and Calvin Lin. 2007. The ant and the grasshopper: fast and accurate pointer analysis for millions of lines of code. In Proceedings of the 2007 ACM SIGPLAN conference on Programming language design and implementation (PLDI '07). ACM, New York, NY, USA, 290-299. http://doi.acm.org/10.1145/1250734.1250767 Ben Hardekopf and Calvin Lin. 2007. Exploiting pointer and location equivalence to optimize pointer analysis. In Proceedings of the 14th international conference on Static Analysis (SAS'07), Hanne Riis Nielson and Gilberto Filé (Eds.). Springer-Verlag, Berlin, Heidelberg, 265-280. Atanas Rountev and Satish Chandra. 2000. Off-line variable substitution for scaling points-to analysis. In Proceedings of the ACM SIGPLAN 2000 conference on Programming language design and implementation (PLDI '00). ACM, New York, NY, USA, 47-56. DOI=10.1145/349299.349310 http://doi.acm.org/10.1145/349299.349310 This program demonstrates how to use the pointer analysis to obtain a conservative call-graph of a Go program. It also shows how to compute the points-to set of a variable, in this case, (C).f's ch parameter.

Package lingua accurately detects the natural language of written text, be it long or short. Its task is simple: It tells you which language some text is written in. This is very useful as a preprocessing step for linguistic data in natural language processing applications such as text classification and spell checking. Other use cases, for instance, might include routing e-mails to the right geographically located customer service department, based on the e-mails' languages. Language detection is often done as part of large machine learning frameworks or natural language processing applications. In cases where you don't need the full-fledged functionality of those systems or don't want to learn the ropes of those, a small flexible library comes in handy. So far, the only other comprehensive open source library in the Go ecosystem for this task is Whatlanggo (https://github.com/abadojack/whatlanggo). Unfortunately, it has two major drawbacks: 1. Detection only works with quite lengthy text fragments. For very short text snippets such as Twitter messages, it does not provide adequate results. 2. The more languages take part in the decision process, the less accurate are the detection results. Lingua aims at eliminating these problems. It nearly does not need any configuration and yields pretty accurate results on both long and short text, even on single words and phrases. It draws on both rule-based and statistical methods but does not use any dictionaries of words. It does not need a connection to any external API or service either. Once the library has been downloaded, it can be used completely offline. Compared to other language detection libraries, Lingua's focus is on quality over quantity, that is, getting detection right for a small set of languages first before adding new ones. Currently, 75 languages are supported. They are listed as variants of type Language. Lingua is able to report accuracy statistics for some bundled test data available for each supported language. The test data for each language is split into three parts: 1. a list of single words with a minimum length of 5 characters 2. a list of word pairs with a minimum length of 10 characters 3. a list of complete grammatical sentences of various lengths Both the language models and the test data have been created from separate documents of the Wortschatz corpora (https://wortschatz.uni-leipzig.de) offered by Leipzig University, Germany. Data crawled from various news websites have been used for training, each corpus comprising one million sentences. For testing, corpora made of arbitrarily chosen websites have been used, each comprising ten thousand sentences. From each test corpus, a random unsorted subset of 1000 single words, 1000 word pairs and 1000 sentences has been extracted, respectively. Given the generated test data, I have compared the detection results of Lingua, and Whatlanggo running over the data of Lingua's supported 75 languages. Additionally, I have added Google's CLD3 (https://github.com/google/cld3/) to the comparison with the help of the gocld3 bindings (https://github.com/jmhodges/gocld3). Languages that are not supported by CLD3 or Whatlanggo are simply ignored during the detection process. Lingua clearly outperforms its contenders. Every language detector uses a probabilistic n-gram (https://en.wikipedia.org/wiki/N-gram) model trained on the character distribution in some training corpus. Most libraries only use n-grams of size 3 (trigrams) which is satisfactory for detecting the language of longer text fragments consisting of multiple sentences. For short phrases or single words, however, trigrams are not enough. The shorter the input text is, the less n-grams are available. The probabilities estimated from such few n-grams are not reliable. This is why Lingua makes use of n-grams of sizes 1 up to 5 which results in much more accurate prediction of the correct language. A second important difference is that Lingua does not only use such a statistical model, but also a rule-based engine. This engine first determines the alphabet of the input text and searches for characters which are unique in one or more languages. If exactly one language can be reliably chosen this way, the statistical model is not necessary anymore. In any case, the rule-based engine filters out languages that do not satisfy the conditions of the input text. Only then, in a second step, the probabilistic n-gram model is taken into consideration. This makes sense because loading less language models means less memory consumption and better runtime performance. In general, it is always a good idea to restrict the set of languages to be considered in the classification process using the respective api methods. If you know beforehand that certain languages are never to occur in an input text, do not let those take part in the classifcation process. The filtering mechanism of the rule-based engine is quite good, however, filtering based on your own knowledge of the input text is always preferable. There might be classification tasks where you know beforehand that your language data is definitely not written in Latin, for instance. The detection accuracy can become better in such cases if you exclude certain languages from the decision process or just explicitly include relevant languages. Knowing about the most likely language is nice but how reliable is the computed likelihood? And how less likely are the other examined languages in comparison to the most likely one? In the example below, a slice of ConfidenceValue is returned containing those languages which the calling instance of LanguageDetector has been built from. The entries are sorted by their confidence value in descending order. Each value is a probability between 0.0 and 1.0. The probabilities of all languages will sum to 1.0. If the language is unambiguously identified by the rule engine, the value 1.0 will always be returned for this language. The other languages will receive a value of 0.0. By default, Lingua uses lazy-loading to load only those language models on demand which are considered relevant by the rule-based filter engine. For web services, for instance, it is rather beneficial to preload all language models into memory to avoid unexpected latency while waiting for the service response. If you want to enable the eager-loading mode, you can do it as seen below. Multiple instances of LanguageDetector share the same language models in memory which are accessed asynchronously by the instances. By default, Lingua returns the most likely language for a given input text. However, there are certain words that are spelled the same in more than one language. The word `prologue`, for instance, is both a valid English and French word. Lingua would output either English or French which might be wrong in the given context. For cases like that, it is possible to specify a minimum relative distance that the logarithmized and summed up probabilities for each possible language have to satisfy. It can be stated as seen below. Be aware that the distance between the language probabilities is dependent on the length of the input text. The longer the input text, the larger the distance between the languages. So if you want to classify very short text phrases, do not set the minimum relative distance too high. Otherwise Unknown will be returned most of the time as in the example below. This is the return value for cases where language detection is not reliably possible.

Package gopacket provides packet decoding for the Go language. gopacket contains many sub-packages with additional functionality you may find useful, including: Also, if you're looking to dive right into code, see the examples subdirectory for numerous simple binaries built using gopacket libraries. gopacket takes in packet data as a []byte and decodes it into a packet with a non-zero number of "layers". Each layer corresponds to a protocol within the bytes. Once a packet has been decoded, the layers of the packet can be requested from the packet. Packets can be decoded from a number of starting points. Many of our base types implement Decoder, which allow us to decode packets for which we don't have full data. Most of the time, you won't just have a []byte of packet data lying around. Instead, you'll want to read packets in from somewhere (file, interface, etc) and process them. To do that, you'll want to build a PacketSource. First, you'll need to construct an object that implements the PacketDataSource interface. There are implementations of this interface bundled with gopacket in the gopacket/pcap and gopacket/pfring subpackages... see their documentation for more information on their usage. Once you have a PacketDataSource, you can pass it into NewPacketSource, along with a Decoder of your choice, to create a PacketSource. Once you have a PacketSource, you can read packets from it in multiple ways. See the docs for PacketSource for more details. The easiest method is the Packets function, which returns a channel, then asynchronously writes new packets into that channel, closing the channel if the packetSource hits an end-of-file. You can change the decoding options of the packetSource by setting fields in packetSource.DecodeOptions... see the following sections for more details. gopacket optionally decodes packet data lazily, meaning it only decodes a packet layer when it needs to handle a function call. Lazily-decoded packets are not concurrency-safe. Since layers have not all been decoded, each call to Layer() or Layers() has the potential to mutate the packet in order to decode the next layer. If a packet is used in multiple goroutines concurrently, don't use gopacket.Lazy. Then gopacket will decode the packet fully, and all future function calls won't mutate the object. By default, gopacket will copy the slice passed to NewPacket and store the copy within the packet, so future mutations to the bytes underlying the slice don't affect the packet and its layers. If you can guarantee that the underlying slice bytes won't be changed, you can use NoCopy to tell gopacket.NewPacket, and it'll use the passed-in slice itself. The fastest method of decoding is to use both Lazy and NoCopy, but note from the many caveats above that for some implementations either or both may be dangerous. During decoding, certain layers are stored in the packet as well-known layer types. For example, IPv4 and IPv6 are both considered NetworkLayer layers, while TCP and UDP are both TransportLayer layers. We support 4 layers, corresponding to the 4 layers of the TCP/IP layering scheme (roughly anagalous to layers 2, 3, 4, and 7 of the OSI model). To access these, you can use the packet.LinkLayer, packet.NetworkLayer, packet.TransportLayer, and packet.ApplicationLayer functions. Each of these functions returns a corresponding interface (gopacket.{Link,Network,Transport,Application}Layer). The first three provide methods for getting src/dst addresses for that particular layer, while the final layer provides a Payload function to get payload data. This is helpful, for example, to get payloads for all packets regardless of their underlying data type: A particularly useful layer is ErrorLayer, which is set whenever there's an error parsing part of the packet. Note that we don't return an error from NewPacket because we may have decoded a number of layers successfully before running into our erroneous layer. You may still be able to get your Ethernet and IPv4 layers correctly, even if your TCP layer is malformed. gopacket has two useful objects, Flow and Endpoint, for communicating in a protocol independent manner the fact that a packet is coming from A and going to B. The general layer types LinkLayer, NetworkLayer, and TransportLayer all provide methods for extracting their flow information, without worrying about the type of the underlying Layer. A Flow is a simple object made up of a set of two Endpoints, one source and one destination. It details the sender and receiver of the Layer of the Packet. An Endpoint is a hashable representation of a source or destination. For example, for LayerTypeIPv4, an Endpoint contains the IP address bytes for a v4 IP packet. A Flow can be broken into Endpoints, and Endpoints can be combined into Flows: Both Endpoint and Flow objects can be used as map keys, and the equality operator can compare them, so you can easily group together all packets based on endpoint criteria: For load-balancing purposes, both Flow and Endpoint have FastHash() functions, which provide quick, non-cryptographic hashes of their contents. Of particular importance is the fact that Flow FastHash() is symetric: A->B will have the same hash as B->A. An example usage could be: This allows us to split up a packet stream while still making sure that each stream sees all packets for a flow (and its bidirectional opposite). If your network has some strange encapsulation, you can implement your own decoder. In this example, we handle Ethernet packets which are encapsulated in a 4-byte header. See the docs for Decoder and PacketBuilder for more details on how coding decoders works, or look at RegisterLayerType and RegisterEndpointType to see how to add layer/endpoint types to gopacket. TLDR: DecodingLayerParser takes about 10% of the time as NewPacket to decode packet data, but only for known packet stacks. Basic decoding using gopacket.NewPacket or PacketSource.Packets is somewhat slow due to its need to allocate a new packet and every respective layer. It's very versatile and can handle all known layer types, but sometimes you really only care about a specific set of layers regardless, so that versatility is wasted. DecodingLayerParser avoids memory allocation altogether by decoding packet layers directly into preallocated objects, which you can then reference to get the packet's information. A quick example: The important thing to note here is that the parser is modifying the passed in layers (eth, ip4, ip6, tcp) instead of allocating new ones, thus greatly speeding up the decoding process. It's even branching based on layer type... it'll handle an (eth, ip4, tcp) or (eth, ip6, tcp) stack. However, it won't handle any other type... since no other decoders were passed in, an (eth, ip4, udp) stack will stop decoding after ip4, and only pass back [LayerTypeEthernet, LayerTypeIPv4] through the 'decoded' slice (along with an error saying it can't decode a UDP packet). Unfortunately, not all layers can be used by DecodingLayerParser... only those implementing the DecodingLayer interface are usable. Also, it's possible to create DecodingLayers that are not themselves Layers... see layers.IPv6ExtensionSkipper for an example of this. As well as offering the ability to decode packet data, gopacket will allow you to create packets from scratch, as well. A number of gopacket layers implement the SerializableLayer interface; these layers can be serialized to a []byte in the following manner: SerializeTo PREPENDS the given layer onto the SerializeBuffer, and they treat the current buffer's Bytes() slice as the payload of the serializing layer. Therefore, you can serialize an entire packet by serializing a set of layers in reverse order (Payload, then TCP, then IP, then Ethernet, for example). The SerializeBuffer's SerializeLayers function is a helper that does exactly that. To generate a (empty and useless, because no fields are set) Ethernet(IPv4(TCP(Payload))) packet, for exmaple, you can run: If you use gopacket, you'll almost definitely want to make sure gopacket/layers is imported, since when imported it sets all the LayerType variables and fills in a lot of interesting variables/maps (DecodersByLayerName, etc). Therefore, it's recommended that even if you don't use any layers functions directly, you still import with:

Package gopacket provides packet decoding for the Go language. gopacket contains many sub-packages with additional functionality you may find useful, including: Also, if you're looking to dive right into code, see the examples subdirectory for numerous simple binaries built using gopacket libraries. Minimum go version required is 1.5. gopacket takes in packet data as a []byte and decodes it into a packet with a non-zero number of "layers". Each layer corresponds to a protocol within the bytes. Once a packet has been decoded, the layers of the packet can be requested from the packet. Packets can be decoded from a number of starting points. Many of our base types implement Decoder, which allow us to decode packets for which we don't have full data. Most of the time, you won't just have a []byte of packet data lying around. Instead, you'll want to read packets in from somewhere (file, interface, etc) and process them. To do that, you'll want to build a PacketSource. First, you'll need to construct an object that implements the PacketDataSource interface. There are implementations of this interface bundled with gopacket in the gopacket/pcap and gopacket/pfring subpackages... see their documentation for more information on their usage. Once you have a PacketDataSource, you can pass it into NewPacketSource, along with a Decoder of your choice, to create a PacketSource. Once you have a PacketSource, you can read packets from it in multiple ways. See the docs for PacketSource for more details. The easiest method is the Packets function, which returns a channel, then asynchronously writes new packets into that channel, closing the channel if the packetSource hits an end-of-file. You can change the decoding options of the packetSource by setting fields in packetSource.DecodeOptions... see the following sections for more details. gopacket optionally decodes packet data lazily, meaning it only decodes a packet layer when it needs to handle a function call. Lazily-decoded packets are not concurrency-safe. Since layers have not all been decoded, each call to Layer() or Layers() has the potential to mutate the packet in order to decode the next layer. If a packet is used in multiple goroutines concurrently, don't use gopacket.Lazy. Then gopacket will decode the packet fully, and all future function calls won't mutate the object. By default, gopacket will copy the slice passed to NewPacket and store the copy within the packet, so future mutations to the bytes underlying the slice don't affect the packet and its layers. If you can guarantee that the underlying slice bytes won't be changed, you can use NoCopy to tell gopacket.NewPacket, and it'll use the passed-in slice itself. The fastest method of decoding is to use both Lazy and NoCopy, but note from the many caveats above that for some implementations either or both may be dangerous. During decoding, certain layers are stored in the packet as well-known layer types. For example, IPv4 and IPv6 are both considered NetworkLayer layers, while TCP and UDP are both TransportLayer layers. We support 4 layers, corresponding to the 4 layers of the TCP/IP layering scheme (roughly anagalous to layers 2, 3, 4, and 7 of the OSI model). To access these, you can use the packet.LinkLayer, packet.NetworkLayer, packet.TransportLayer, and packet.ApplicationLayer functions. Each of these functions returns a corresponding interface (gopacket.{Link,Network,Transport,Application}Layer). The first three provide methods for getting src/dst addresses for that particular layer, while the final layer provides a Payload function to get payload data. This is helpful, for example, to get payloads for all packets regardless of their underlying data type: A particularly useful layer is ErrorLayer, which is set whenever there's an error parsing part of the packet. Note that we don't return an error from NewPacket because we may have decoded a number of layers successfully before running into our erroneous layer. You may still be able to get your Ethernet and IPv4 layers correctly, even if your TCP layer is malformed. gopacket has two useful objects, Flow and Endpoint, for communicating in a protocol independent manner the fact that a packet is coming from A and going to B. The general layer types LinkLayer, NetworkLayer, and TransportLayer all provide methods for extracting their flow information, without worrying about the type of the underlying Layer. A Flow is a simple object made up of a set of two Endpoints, one source and one destination. It details the sender and receiver of the Layer of the Packet. An Endpoint is a hashable representation of a source or destination. For example, for LayerTypeIPv4, an Endpoint contains the IP address bytes for a v4 IP packet. A Flow can be broken into Endpoints, and Endpoints can be combined into Flows: Both Endpoint and Flow objects can be used as map keys, and the equality operator can compare them, so you can easily group together all packets based on endpoint criteria: For load-balancing purposes, both Flow and Endpoint have FastHash() functions, which provide quick, non-cryptographic hashes of their contents. Of particular importance is the fact that Flow FastHash() is symmetric: A->B will have the same hash as B->A. An example usage could be: This allows us to split up a packet stream while still making sure that each stream sees all packets for a flow (and its bidirectional opposite). If your network has some strange encapsulation, you can implement your own decoder. In this example, we handle Ethernet packets which are encapsulated in a 4-byte header. See the docs for Decoder and PacketBuilder for more details on how coding decoders works, or look at RegisterLayerType and RegisterEndpointType to see how to add layer/endpoint types to gopacket. TLDR: DecodingLayerParser takes about 10% of the time as NewPacket to decode packet data, but only for known packet stacks. Basic decoding using gopacket.NewPacket or PacketSource.Packets is somewhat slow due to its need to allocate a new packet and every respective layer. It's very versatile and can handle all known layer types, but sometimes you really only care about a specific set of layers regardless, so that versatility is wasted. DecodingLayerParser avoids memory allocation altogether by decoding packet layers directly into preallocated objects, which you can then reference to get the packet's information. A quick example: The important thing to note here is that the parser is modifying the passed in layers (eth, ip4, ip6, tcp) instead of allocating new ones, thus greatly speeding up the decoding process. It's even branching based on layer type... it'll handle an (eth, ip4, tcp) or (eth, ip6, tcp) stack. However, it won't handle any other type... since no other decoders were passed in, an (eth, ip4, udp) stack will stop decoding after ip4, and only pass back [LayerTypeEthernet, LayerTypeIPv4] through the 'decoded' slice (along with an error saying it can't decode a UDP packet). Unfortunately, not all layers can be used by DecodingLayerParser... only those implementing the DecodingLayer interface are usable. Also, it's possible to create DecodingLayers that are not themselves Layers... see layers.IPv6ExtensionSkipper for an example of this. As well as offering the ability to decode packet data, gopacket will allow you to create packets from scratch, as well. A number of gopacket layers implement the SerializableLayer interface; these layers can be serialized to a []byte in the following manner: SerializeTo PREPENDS the given layer onto the SerializeBuffer, and they treat the current buffer's Bytes() slice as the payload of the serializing layer. Therefore, you can serialize an entire packet by serializing a set of layers in reverse order (Payload, then TCP, then IP, then Ethernet, for example). The SerializeBuffer's SerializeLayers function is a helper that does exactly that. To generate a (empty and useless, because no fields are set) Ethernet(IPv4(TCP(Payload))) packet, for example, you can run: If you use gopacket, you'll almost definitely want to make sure gopacket/layers is imported, since when imported it sets all the LayerType variables and fills in a lot of interesting variables/maps (DecodersByLayerName, etc). Therefore, it's recommended that even if you don't use any layers functions directly, you still import with:

Extensible Go library for creating fast, SSR-first frontend avoiding vanilla templating downsides. Creating asynchronous and dynamic layout parts is a complex problem for larger projects using `html/template`. This library tries to simplify overall setup and process. Let's go straight into a simple example. Then, we will dig into details, step by step, how it works. Kyoto provides a set of simple net/http handlers, handler builders and function wrappers to provide serving, pages rendering, component actions, etc. Anyway, this is not an ultimative solution for any case. If you ever need to wrap/extend existing functionality, library encourages this. See functions inside of nethttp.go file for details and advanced usage. Example: Kyoto provides a way to define components. It's a very common approach for modern libraries to manage frontend parts. In kyoto each component is a context receiver, which returns it's state. Each component becomes a part of the page or top-level component, which executes component asynchronously and gets a state future object. In that way your components are executing in a non-blocking way. Pages are just top-level components, where you can configure rendering and page related stuff. Example: As an option, you can wrap component with another function to accept additional paramenters from top-level page/component. Example: Kyoto provides a context, which holds common objects like http.ResponseWriter, *http.Request, etc. See kyoto.Context for details. Example: Kyoto provides a set of parameters and functions to provide a comfortable template building process. You can configure template building parameters with kyoto.TemplateConf configuration. See template.go for available functions and kyoto.TemplateConfiguration for configuration details. Example: Kyoto provides a way to simplify building dynamic UIs. For this purpose it has a feature named actions. Logic is pretty simple. Client calls an action (sends a request to the server). Action is executing on server side and server is sending updated component markup to the client which will be morphed into DOM. That's it. To use actions, you need to go through a few steps. You'll need to include a client into page (JS functions for communication) and register an actions handler for a needed component. Let's start from including a client. Then, let's register an actions handler for a needed component. That's all! Now we ready to use actions to provide a dynamic UI. Example: In this example you can see provided modifications to the quick start example. First, we've added a state and name into our components' markup. In this way we are saving our components' state between actions and find a component root. Unfortunately, we have to manually provide a component name for now, we haven't found a way to provide it dynamically. Second, we've added a reload button with onclick function call. We're using a function Action provided by a client. Action triggering will be described in details later. Third, we've added an action handler inside of our component. This handler will be executed when a client calls an action with a corresponding name. It's highly recommended to keep components' state as small as possible. It will be transmitted on each action call. Kyoto have multiple ways to trigger actions. Now we will check them one by one. This is the simplest way to trigger an action. It's just a function call with a referer (usually 'this', f.e. button) as a first argument (used to determine root), action name as a second argument and arguments as a rest. Arguments must to be JSON serializable. It's possible to trigger an action of another component. If you want to call an action of parent component, use $ prefix in action name. If you want to call an action of component by id, use <id:action> as an action name. This is a specific action which is triggered when a form is submitted. Usually called in onsubmit="..." attribute of a form. You'll need to implement 'Submit' action to handle this trigger. This is a special HTML attribute which will trigger an action on page load. This may be useful for components' lazy loading. With this special HTML attributes you can trigger an action with interval. Useful for components that must to be updated over time (f.e. charts, stats, etc). You can use this trigger with ssa:poll and ssa:poll.interval HTML attributes. This one attribute allows you to trigger an action when an element is visible on the screen. May be useful for lazy loading. Kyoto provides a way to control action flow. For now, it's possible to control display style on component call and push multiple UI updates to the client during a single action. Because kyoto makes a roundtrip to the server every time an action is triggered on the page, there are cases where the page may not react immediately to a user event (like a click). That's why the library provides a way to easily control display attributes on action call. You can use this HTML attribute to control display during action call. At the end of an action the layout will be restored. A small note. Don't forget to set a default display for loading elements like spinners and loaders. You can push multiple component UI updates during a single action call. Just call kyoto.ActionFlush(ctx, state) to initiate an update. Kyoto provides a way to control action rendering. Now there is at least 2 rendering options after an action call: morph (default) and replace. Morph will try to morph received markup to the current one with morphdom library. In case of an error, or explicit "replace" mode, markup will be replaced with x.outerHTML = '...'.

Package gopacket provides packet decoding for the Go language. gopacket contains many sub-packages with additional functionality you may find useful, including: Also, if you're looking to dive right into code, see the examples subdirectory for numerous simple binaries built using gopacket libraries. Minimum go version required is 1.5. gopacket takes in packet data as a []byte and decodes it into a packet with a non-zero number of "layers". Each layer corresponds to a protocol within the bytes. Once a packet has been decoded, the layers of the packet can be requested from the packet. Packets can be decoded from a number of starting points. Many of our base types implement Decoder, which allow us to decode packets for which we don't have full data. Most of the time, you won't just have a []byte of packet data lying around. Instead, you'll want to read packets in from somewhere (file, interface, etc) and process them. To do that, you'll want to build a PacketSource. First, you'll need to construct an object that implements the PacketDataSource interface. There are implementations of this interface bundled with gopacket in the gopacket/pcap and gopacket/pfring subpackages... see their documentation for more information on their usage. Once you have a PacketDataSource, you can pass it into NewPacketSource, along with a Decoder of your choice, to create a PacketSource. Once you have a PacketSource, you can read packets from it in multiple ways. See the docs for PacketSource for more details. The easiest method is the Packets function, which returns a channel, then asynchronously writes new packets into that channel, closing the channel if the packetSource hits an end-of-file. You can change the decoding options of the packetSource by setting fields in packetSource.DecodeOptions... see the following sections for more details. gopacket optionally decodes packet data lazily, meaning it only decodes a packet layer when it needs to handle a function call. Lazily-decoded packets are not concurrency-safe. Since layers have not all been decoded, each call to Layer() or Layers() has the potential to mutate the packet in order to decode the next layer. If a packet is used in multiple goroutines concurrently, don't use gopacket.Lazy. Then gopacket will decode the packet fully, and all future function calls won't mutate the object. By default, gopacket will copy the slice passed to NewPacket and store the copy within the packet, so future mutations to the bytes underlying the slice don't affect the packet and its layers. If you can guarantee that the underlying slice bytes won't be changed, you can use NoCopy to tell gopacket.NewPacket, and it'll use the passed-in slice itself. The fastest method of decoding is to use both Lazy and NoCopy, but note from the many caveats above that for some implementations either or both may be dangerous. During decoding, certain layers are stored in the packet as well-known layer types. For example, IPv4 and IPv6 are both considered NetworkLayer layers, while TCP and UDP are both TransportLayer layers. We support 4 layers, corresponding to the 4 layers of the TCP/IP layering scheme (roughly anagalous to layers 2, 3, 4, and 7 of the OSI model). To access these, you can use the packet.LinkLayer, packet.NetworkLayer, packet.TransportLayer, and packet.ApplicationLayer functions. Each of these functions returns a corresponding interface (gopacket.{Link,Network,Transport,Application}Layer). The first three provide methods for getting src/dst addresses for that particular layer, while the final layer provides a Payload function to get payload data. This is helpful, for example, to get payloads for all packets regardless of their underlying data type: A particularly useful layer is ErrorLayer, which is set whenever there's an error parsing part of the packet. Note that we don't return an error from NewPacket because we may have decoded a number of layers successfully before running into our erroneous layer. You may still be able to get your Ethernet and IPv4 layers correctly, even if your TCP layer is malformed. gopacket has two useful objects, Flow and Endpoint, for communicating in a protocol independent manner the fact that a packet is coming from A and going to B. The general layer types LinkLayer, NetworkLayer, and TransportLayer all provide methods for extracting their flow information, without worrying about the type of the underlying Layer. A Flow is a simple object made up of a set of two Endpoints, one source and one destination. It details the sender and receiver of the Layer of the Packet. An Endpoint is a hashable representation of a source or destination. For example, for LayerTypeIPv4, an Endpoint contains the IP address bytes for a v4 IP packet. A Flow can be broken into Endpoints, and Endpoints can be combined into Flows: Both Endpoint and Flow objects can be used as map keys, and the equality operator can compare them, so you can easily group together all packets based on endpoint criteria: For load-balancing purposes, both Flow and Endpoint have FastHash() functions, which provide quick, non-cryptographic hashes of their contents. Of particular importance is the fact that Flow FastHash() is symmetric: A->B will have the same hash as B->A. An example usage could be: This allows us to split up a packet stream while still making sure that each stream sees all packets for a flow (and its bidirectional opposite). If your network has some strange encapsulation, you can implement your own decoder. In this example, we handle Ethernet packets which are encapsulated in a 4-byte header. See the docs for Decoder and PacketBuilder for more details on how coding decoders works, or look at RegisterLayerType and RegisterEndpointType to see how to add layer/endpoint types to gopacket. TLDR: DecodingLayerParser takes about 10% of the time as NewPacket to decode packet data, but only for known packet stacks. Basic decoding using gopacket.NewPacket or PacketSource.Packets is somewhat slow due to its need to allocate a new packet and every respective layer. It's very versatile and can handle all known layer types, but sometimes you really only care about a specific set of layers regardless, so that versatility is wasted. DecodingLayerParser avoids memory allocation altogether by decoding packet layers directly into preallocated objects, which you can then reference to get the packet's information. A quick example: The important thing to note here is that the parser is modifying the passed in layers (eth, ip4, ip6, tcp) instead of allocating new ones, thus greatly speeding up the decoding process. It's even branching based on layer type... it'll handle an (eth, ip4, tcp) or (eth, ip6, tcp) stack. However, it won't handle any other type... since no other decoders were passed in, an (eth, ip4, udp) stack will stop decoding after ip4, and only pass back [LayerTypeEthernet, LayerTypeIPv4] through the 'decoded' slice (along with an error saying it can't decode a UDP packet). Unfortunately, not all layers can be used by DecodingLayerParser... only those implementing the DecodingLayer interface are usable. Also, it's possible to create DecodingLayers that are not themselves Layers... see layers.IPv6ExtensionSkipper for an example of this. As well as offering the ability to decode packet data, gopacket will allow you to create packets from scratch, as well. A number of gopacket layers implement the SerializableLayer interface; these layers can be serialized to a []byte in the following manner: SerializeTo PREPENDS the given layer onto the SerializeBuffer, and they treat the current buffer's Bytes() slice as the payload of the serializing layer. Therefore, you can serialize an entire packet by serializing a set of layers in reverse order (Payload, then TCP, then IP, then Ethernet, for example). The SerializeBuffer's SerializeLayers function is a helper that does exactly that. To generate a (empty and useless, because no fields are set) Ethernet(IPv4(TCP(Payload))) packet, for example, you can run: If you use gopacket, you'll almost definitely want to make sure gopacket/layers is imported, since when imported it sets all the LayerType variables and fills in a lot of interesting variables/maps (DecodersByLayerName, etc). Therefore, it's recommended that even if you don't use any layers functions directly, you still import with:

Extensible Go library for creating fast, SSR-first frontend avoiding vanilla templating downsides. Creating asynchronous and dynamic layout parts is a complex problem for larger projects using `html/template`. Library tries to simplify this process. Let's go straight into a simple example. Then, we will dig into details, step by step, how it works. Kyoto provides a simple net/http handlers and function wrappers to handle pages rendering and serving. See functions inside of nethttp.go file for details and advanced usage. Example: Kyoto provides a way to define components. It's a very common approach for modern libraries to manage frontend parts. In kyoto each component is a context receiver, which returns it's state. Each component becomes a part of the page or top-level component, which executes component asynchronously and gets a state future object. In that way your components are executing in a non-blocking way. Pages are just top-level components, where you can configure rendering and page related stuff. Example: As an option, you can wrap component with another function to accept additional paramenters from top-level page/component. Example: Kyoto provides a context, which holds common objects like http.ResponseWriter, *http.Request, etc. See kyoto.Context for details. Example: Kyoto provides a set of parameters and functions to provide a comfortable template building process. You can configure template building parameters with kyoto.TemplateConf configuration. See template.go for available functions and kyoto.TemplateConfiguration for configuration details. Example: Kyoto provides a way to simplify building dynamic UIs. For this purpose it has a feature named actions. Logic is pretty simple. Client calls an action (sends a request to the server). Action is executing on server side and server is sending updated component markup to the client which will be morphed into DOM. That's it. To use actions, you need to go through a few steps. You'll need to include a client into page (JS functions for communication) and register an actions handler for a needed component. Let's start from including a client. Then, let's register an actions handler for a needed component. That's all! Now we ready to use actions to provide a dynamic UI. Example: In this example you can see provided modifications to the quick start example. First, we've added a state and name into our components' markup. In this way we are saving our components' state between actions and find a component root. Unfortunately, we have to manually provide a component name for now, we haven't found a way to provide it dynamically. Second, we've added a reload button with onclick function call. We're using a function Action provided by a client. Action triggering will be described in details later. Third, we've added an action handler inside of our component. This handler will be executed when a client calls an action with a corresponding name. It's highly recommended to keep components' state as small as possible. It will be transmitted on each action call. Kyoto have multiple ways to trigger actions. Now we will check them one by one. This is the simplest way to trigger an action. It's just a function call with a referer (usually 'this', f.e. button) as a first argument (used to determine root), action name as a second argument and arguments as a rest. Arguments must to be JSON serializable. It's possible to trigger an action of another component. If you want to call an action of parent component, use $ prefix in action name. If you want to call an action of component by id, use <id:action> as an action name. This is a specific action which is triggered when a form is submitted. Usually called in onsubmit="..." attribute of a form. You'll need to implement 'Submit' action to handle this trigger. This is a special HTML attribute which will trigger an action on page load. This may be useful for components' lazy loading. With this special HTML attributes you can trigger an action with interval. Useful for components that must to be updated over time (f.e. charts, stats, etc). You can use this trigger with ssa:poll and ssa:poll.interval HTML attributes. This one attribute allows you to trigger an action when an element is visible on the screen. May be useful for lazy loading. Kyoto provides a way to control action flow. For now, it's possible to control display style on component call and push multiple UI updates to the client during a single action. Because kyoto makes a roundtrip to the server every time an action is triggered on the page, there are cases where the page may not react immediately to a user event (like a click). That's why the library provides a way to easily control display attributes on action call. You can use this HTML attribute to control display during action call. At the end of an action the layout will be restored. A small note. Don't forget to set a default display for loading elements like spinners and loaders. You can push multiple component UI updates during a single action call. Just call kyoto.ActionFlush(ctx, state) to initiate an update. Kyoto provides a way to control action rendering. Now there is at least 2 rendering options after an action call: morph (default) and replace. Morph will try to morph received markup to the current one with morphdom library. In case of an error, or explicit "replace" mode, markup will be replaced with x.outerHTML = '...'.

Package gopacket provides packet decoding for the Go language. gopacket contains many sub-packages with additional functionality you may find useful, including: Also, if you're looking to dive right into code, see the examples subdirectory for numerous simple binaries built using gopacket libraries. Minimum go version required is 1.5. gopacket takes in packet data as a []byte and decodes it into a packet with a non-zero number of "layers". Each layer corresponds to a protocol within the bytes. Once a packet has been decoded, the layers of the packet can be requested from the packet. Packets can be decoded from a number of starting points. Many of our base types implement Decoder, which allow us to decode packets for which we don't have full data. Most of the time, you won't just have a []byte of packet data lying around. Instead, you'll want to read packets in from somewhere (file, interface, etc) and process them. To do that, you'll want to build a PacketSource. First, you'll need to construct an object that implements the PacketDataSource interface. There are implementations of this interface bundled with gopacket in the gopacket/pcap and gopacket/pfring subpackages... see their documentation for more information on their usage. Once you have a PacketDataSource, you can pass it into NewPacketSource, along with a Decoder of your choice, to create a PacketSource. Once you have a PacketSource, you can read packets from it in multiple ways. See the docs for PacketSource for more details. The easiest method is the Packets function, which returns a channel, then asynchronously writes new packets into that channel, closing the channel if the packetSource hits an end-of-file. You can change the decoding options of the packetSource by setting fields in packetSource.DecodeOptions... see the following sections for more details. gopacket optionally decodes packet data lazily, meaning it only decodes a packet layer when it needs to handle a function call. Lazily-decoded packets are not concurrency-safe. Since layers have not all been decoded, each call to Layer() or Layers() has the potential to mutate the packet in order to decode the next layer. If a packet is used in multiple goroutines concurrently, don't use gopacket.Lazy. Then gopacket will decode the packet fully, and all future function calls won't mutate the object. By default, gopacket will copy the slice passed to NewPacket and store the copy within the packet, so future mutations to the bytes underlying the slice don't affect the packet and its layers. If you can guarantee that the underlying slice bytes won't be changed, you can use NoCopy to tell gopacket.NewPacket, and it'll use the passed-in slice itself. The fastest method of decoding is to use both Lazy and NoCopy, but note from the many caveats above that for some implementations either or both may be dangerous. During decoding, certain layers are stored in the packet as well-known layer types. For example, IPv4 and IPv6 are both considered NetworkLayer layers, while TCP and UDP are both TransportLayer layers. We support 4 layers, corresponding to the 4 layers of the TCP/IP layering scheme (roughly anagalous to layers 2, 3, 4, and 7 of the OSI model). To access these, you can use the packet.LinkLayer, packet.NetworkLayer, packet.TransportLayer, and packet.ApplicationLayer functions. Each of these functions returns a corresponding interface (gopacket.{Link,Network,Transport,Application}Layer). The first three provide methods for getting src/dst addresses for that particular layer, while the final layer provides a Payload function to get payload data. This is helpful, for example, to get payloads for all packets regardless of their underlying data type: A particularly useful layer is ErrorLayer, which is set whenever there's an error parsing part of the packet. Note that we don't return an error from NewPacket because we may have decoded a number of layers successfully before running into our erroneous layer. You may still be able to get your Ethernet and IPv4 layers correctly, even if your TCP layer is malformed. gopacket has two useful objects, Flow and Endpoint, for communicating in a protocol independent manner the fact that a packet is coming from A and going to B. The general layer types LinkLayer, NetworkLayer, and TransportLayer all provide methods for extracting their flow information, without worrying about the type of the underlying Layer. A Flow is a simple object made up of a set of two Endpoints, one source and one destination. It details the sender and receiver of the Layer of the Packet. An Endpoint is a hashable representation of a source or destination. For example, for LayerTypeIPv4, an Endpoint contains the IP address bytes for a v4 IP packet. A Flow can be broken into Endpoints, and Endpoints can be combined into Flows: Both Endpoint and Flow objects can be used as map keys, and the equality operator can compare them, so you can easily group together all packets based on endpoint criteria: For load-balancing purposes, both Flow and Endpoint have FastHash() functions, which provide quick, non-cryptographic hashes of their contents. Of particular importance is the fact that Flow FastHash() is symmetric: A->B will have the same hash as B->A. An example usage could be: This allows us to split up a packet stream while still making sure that each stream sees all packets for a flow (and its bidirectional opposite). If your network has some strange encapsulation, you can implement your own decoder. In this example, we handle Ethernet packets which are encapsulated in a 4-byte header. See the docs for Decoder and PacketBuilder for more details on how coding decoders works, or look at RegisterLayerType and RegisterEndpointType to see how to add layer/endpoint types to gopacket. TLDR: DecodingLayerParser takes about 10% of the time as NewPacket to decode packet data, but only for known packet stacks. Basic decoding using gopacket.NewPacket or PacketSource.Packets is somewhat slow due to its need to allocate a new packet and every respective layer. It's very versatile and can handle all known layer types, but sometimes you really only care about a specific set of layers regardless, so that versatility is wasted. DecodingLayerParser avoids memory allocation altogether by decoding packet layers directly into preallocated objects, which you can then reference to get the packet's information. A quick example: The important thing to note here is that the parser is modifying the passed in layers (eth, ip4, ip6, tcp) instead of allocating new ones, thus greatly speeding up the decoding process. It's even branching based on layer type... it'll handle an (eth, ip4, tcp) or (eth, ip6, tcp) stack. However, it won't handle any other type... since no other decoders were passed in, an (eth, ip4, udp) stack will stop decoding after ip4, and only pass back [LayerTypeEthernet, LayerTypeIPv4] through the 'decoded' slice (along with an error saying it can't decode a UDP packet). Unfortunately, not all layers can be used by DecodingLayerParser... only those implementing the DecodingLayer interface are usable. Also, it's possible to create DecodingLayers that are not themselves Layers... see layers.IPv6ExtensionSkipper for an example of this. As well as offering the ability to decode packet data, gopacket will allow you to create packets from scratch, as well. A number of gopacket layers implement the SerializableLayer interface; these layers can be serialized to a []byte in the following manner: SerializeTo PREPENDS the given layer onto the SerializeBuffer, and they treat the current buffer's Bytes() slice as the payload of the serializing layer. Therefore, you can serialize an entire packet by serializing a set of layers in reverse order (Payload, then TCP, then IP, then Ethernet, for example). The SerializeBuffer's SerializeLayers function is a helper that does exactly that. To generate a (empty and useless, because no fields are set) Ethernet(IPv4(TCP(Payload))) packet, for example, you can run: If you use gopacket, you'll almost definitely want to make sure gopacket/layers is imported, since when imported it sets all the LayerType variables and fills in a lot of interesting variables/maps (DecodersByLayerName, etc). Therefore, it's recommended that even if you don't use any layers functions directly, you still import with:

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are can be easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy function. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package gopacket provides packet decoding for the Go language. gopacket contains many sub-packages with additional functionality you may find useful, including: Also, if you're looking to dive right into code, see the examples subdirectory for numerous simple binaries built using gopacket libraries. Minimum go version required is 1.5 except for pcapgo/EthernetHandle, afpacket, and bsdbpf which need at least 1.7 due to x/sys/unix dependencies. gopacket takes in packet data as a []byte and decodes it into a packet with a non-zero number of "layers". Each layer corresponds to a protocol within the bytes. Once a packet has been decoded, the layers of the packet can be requested from the packet. Packets can be decoded from a number of starting points. Many of our base types implement Decoder, which allow us to decode packets for which we don't have full data. Most of the time, you won't just have a []byte of packet data lying around. Instead, you'll want to read packets in from somewhere (file, interface, etc) and process them. To do that, you'll want to build a PacketSource. First, you'll need to construct an object that implements the PacketDataSource interface. There are implementations of this interface bundled with gopacket in the gopacket/pcap and gopacket/pfring subpackages... see their documentation for more information on their usage. Once you have a PacketDataSource, you can pass it into NewPacketSource, along with a Decoder of your choice, to create a PacketSource. Once you have a PacketSource, you can read packets from it in multiple ways. See the docs for PacketSource for more details. The easiest method is the Packets function, which returns a channel, then asynchronously writes new packets into that channel, closing the channel if the packetSource hits an end-of-file. You can change the decoding options of the packetSource by setting fields in packetSource.DecodeOptions... see the following sections for more details. gopacket optionally decodes packet data lazily, meaning it only decodes a packet layer when it needs to handle a function call. Lazily-decoded packets are not concurrency-safe. Since layers have not all been decoded, each call to Layer() or Layers() has the potential to mutate the packet in order to decode the next layer. If a packet is used in multiple goroutines concurrently, don't use gopacket.Lazy. Then gopacket will decode the packet fully, and all future function calls won't mutate the object. By default, gopacket will copy the slice passed to NewPacket and store the copy within the packet, so future mutations to the bytes underlying the slice don't affect the packet and its layers. If you can guarantee that the underlying slice bytes won't be changed, you can use NoCopy to tell gopacket.NewPacket, and it'll use the passed-in slice itself. The fastest method of decoding is to use both Lazy and NoCopy, but note from the many caveats above that for some implementations either or both may be dangerous. During decoding, certain layers are stored in the packet as well-known layer types. For example, IPv4 and IPv6 are both considered NetworkLayer layers, while TCP and UDP are both TransportLayer layers. We support 4 layers, corresponding to the 4 layers of the TCP/IP layering scheme (roughly anagalous to layers 2, 3, 4, and 7 of the OSI model). To access these, you can use the packet.LinkLayer, packet.NetworkLayer, packet.TransportLayer, and packet.ApplicationLayer functions. Each of these functions returns a corresponding interface (gopacket.{Link,Network,Transport,Application}Layer). The first three provide methods for getting src/dst addresses for that particular layer, while the final layer provides a Payload function to get payload data. This is helpful, for example, to get payloads for all packets regardless of their underlying data type: A particularly useful layer is ErrorLayer, which is set whenever there's an error parsing part of the packet. Note that we don't return an error from NewPacket because we may have decoded a number of layers successfully before running into our erroneous layer. You may still be able to get your Ethernet and IPv4 layers correctly, even if your TCP layer is malformed. gopacket has two useful objects, Flow and Endpoint, for communicating in a protocol independent manner the fact that a packet is coming from A and going to B. The general layer types LinkLayer, NetworkLayer, and TransportLayer all provide methods for extracting their flow information, without worrying about the type of the underlying Layer. A Flow is a simple object made up of a set of two Endpoints, one source and one destination. It details the sender and receiver of the Layer of the Packet. An Endpoint is a hashable representation of a source or destination. For example, for LayerTypeIPv4, an Endpoint contains the IP address bytes for a v4 IP packet. A Flow can be broken into Endpoints, and Endpoints can be combined into Flows: Both Endpoint and Flow objects can be used as map keys, and the equality operator can compare them, so you can easily group together all packets based on endpoint criteria: For load-balancing purposes, both Flow and Endpoint have FastHash() functions, which provide quick, non-cryptographic hashes of their contents. Of particular importance is the fact that Flow FastHash() is symmetric: A->B will have the same hash as B->A. An example usage could be: This allows us to split up a packet stream while still making sure that each stream sees all packets for a flow (and its bidirectional opposite). If your network has some strange encapsulation, you can implement your own decoder. In this example, we handle Ethernet packets which are encapsulated in a 4-byte header. See the docs for Decoder and PacketBuilder for more details on how coding decoders works, or look at RegisterLayerType and RegisterEndpointType to see how to add layer/endpoint types to gopacket. TLDR: DecodingLayerParser takes about 10% of the time as NewPacket to decode packet data, but only for known packet stacks. Basic decoding using gopacket.NewPacket or PacketSource.Packets is somewhat slow due to its need to allocate a new packet and every respective layer. It's very versatile and can handle all known layer types, but sometimes you really only care about a specific set of layers regardless, so that versatility is wasted. DecodingLayerParser avoids memory allocation altogether by decoding packet layers directly into preallocated objects, which you can then reference to get the packet's information. A quick example: The important thing to note here is that the parser is modifying the passed in layers (eth, ip4, ip6, tcp) instead of allocating new ones, thus greatly speeding up the decoding process. It's even branching based on layer type... it'll handle an (eth, ip4, tcp) or (eth, ip6, tcp) stack. However, it won't handle any other type... since no other decoders were passed in, an (eth, ip4, udp) stack will stop decoding after ip4, and only pass back [LayerTypeEthernet, LayerTypeIPv4] through the 'decoded' slice (along with an error saying it can't decode a UDP packet). Unfortunately, not all layers can be used by DecodingLayerParser... only those implementing the DecodingLayer interface are usable. Also, it's possible to create DecodingLayers that are not themselves Layers... see layers.IPv6ExtensionSkipper for an example of this. By default, DecodingLayerParser uses native map to store and search for a layer to decode. Though being versatile, in some cases this solution may be not so optimal. For example, if you have only few layers faster operations may be provided by sparse array indexing or linear array scan. To accomodate these scenarios, DecodingLayerContainer interface is introduced along with its implementations: DecodingLayerSparse, DecodingLayerArray and DecodingLayerMap. You can specify a container implementation to DecodingLayerParser with SetDecodingLayerContainer method. Example: To skip one level of indirection (though sacrificing some capabilities) you may also use DecodingLayerContainer as a decoding tool as it is. In this case you have to handle unknown layer types and layer panics by yourself. Example: DecodingLayerSparse is the fastest but most effective when LayerType values that layers in use can decode are not large because otherwise that would lead to bigger memory footprint. DecodingLayerArray is very compact and primarily usable if the number of decoding layers is not big (up to ~10-15, but please do your own benchmarks). DecodingLayerMap is the most versatile one and used by DecodingLayerParser by default. Please refer to tests and benchmarks in layers subpackage to further examine usage examples and performance measurements. You may also choose to implement your own DecodingLayerContainer if you want to make use of your own internal packet decoding logic. As well as offering the ability to decode packet data, gopacket will allow you to create packets from scratch, as well. A number of gopacket layers implement the SerializableLayer interface; these layers can be serialized to a []byte in the following manner: SerializeTo PREPENDS the given layer onto the SerializeBuffer, and they treat the current buffer's Bytes() slice as the payload of the serializing layer. Therefore, you can serialize an entire packet by serializing a set of layers in reverse order (Payload, then TCP, then IP, then Ethernet, for example). The SerializeBuffer's SerializeLayers function is a helper that does exactly that. To generate a (empty and useless, because no fields are set) Ethernet(IPv4(TCP(Payload))) packet, for example, you can run: If you use gopacket, you'll almost definitely want to make sure gopacket/layers is imported, since when imported it sets all the LayerType variables and fills in a lot of interesting variables/maps (DecodersByLayerName, etc). Therefore, it's recommended that even if you don't use any layers functions directly, you still import with:

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json //This package implements three Handlers that add debugging information to the //context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's //an example that adds the source file and line number of each logging call to //the context. // // h := log.CallerFileHandler(log.StdoutHandler) // log.Root().SetHandler(h) // ... // log.Error("open file", "err", err) // //This will output a line that looks like: // // lvl=eror t=2014-05-02T16:07:23-0700 msg="open file" err="file not found" caller=data.go:42 // //Here's an example that logs the call stack rather than just the call site. // // h := log.CallerStackHandler("%+v", log.StdoutHandler) // log.Root().SetHandler(h) // ... // log.Error("open file", "err", err) // //This will output a line that looks like: // // lvl=eror t=2014-05-02T16:07:23-0700 msg="open file" err="file not found" stack="[pkg/data.go:42 pkg/cmd/main.go]" // //The "%+v" format instructs the handler to include the path of the source file //relative to the compile time GOPATH. The github.com/go-stack/stack package //documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package gopacket provides packet decoding for the Go language. gopacket contains many sub-packages with additional functionality you may find useful, including: Also, if you're looking to dive right into code, see the examples subdirectory for numerous simple binaries built using gopacket libraries. gopacket takes in packet data as a []byte and decodes it into a packet with a non-zero number of "layers". Each layer corresponds to a protocol within the bytes. Once a packet has been decoded, the layers of the packet can be requested from the packet. Packets can be decoded from a number of starting points. Many of our base types implement Decoder, which allow us to decode packets for which we don't have full data. Most of the time, you won't just have a []byte of packet data lying around. Instead, you'll want to read packets in from somewhere (file, interface, etc) and process them. To do that, you'll want to build a PacketSource. First, you'll need to construct an object that implements the PacketDataSource interface. There are implementations of this interface bundled with gopacket in the gopacket/pcap and gopacket/pfring subpackages... see their documentation for more information on their usage. Once you have a PacketDataSource, you can pass it into NewPacketSource, along with a Decoder of your choice, to create a PacketSource. Once you have a PacketSource, you can read packets from it in multiple ways. See the docs for PacketSource for more details. The easiest method is the Packets function, which returns a channel, then asynchronously writes new packets into that channel, closing the channel if the packetSource hits an end-of-file. You can change the decoding options of the packetSource by setting fields in packetSource.DecodeOptions... see the following sections for more details. gopacket optionally decodes packet data lazily, meaning it only decodes a packet layer when it needs to handle a function call. Lazily-decoded packets are not concurrency-safe. Since layers have not all been decoded, each call to Layer() or Layers() has the potential to mutate the packet in order to decode the next layer. If a packet is used in multiple goroutines concurrently, don't use gopacket.Lazy. Then gopacket will decode the packet fully, and all future function calls won't mutate the object. By default, gopacket will copy the slice passed to NewPacket and store the copy within the packet, so future mutations to the bytes underlying the slice don't affect the packet and its layers. If you can guarantee that the underlying slice bytes won't be changed, you can use NoCopy to tell gopacket.NewPacket, and it'll use the passed-in slice itself. The fastest method of decoding is to use both Lazy and NoCopy, but note from the many caveats above that for some implementations either or both may be dangerous. During decoding, certain layers are stored in the packet as well-known layer types. For example, IPv4 and IPv6 are both considered NetworkLayer layers, while TCP and UDP are both TransportLayer layers. We support 4 layers, corresponding to the 4 layers of the TCP/IP layering scheme (roughly anagalous to layers 2, 3, 4, and 7 of the OSI model). To access these, you can use the packet.LinkLayer, packet.NetworkLayer, packet.TransportLayer, and packet.ApplicationLayer functions. Each of these functions returns a corresponding interface (gopacket.{Link,Network,Transport,Application}Layer). The first three provide methods for getting src/dst addresses for that particular layer, while the final layer provides a Payload function to get payload data. This is helpful, for example, to get payloads for all packets regardless of their underlying data type: A particularly useful layer is ErrorLayer, which is set whenever there's an error parsing part of the packet. Note that we don't return an error from NewPacket because we may have decoded a number of layers successfully before running into our erroneous layer. You may still be able to get your Ethernet and IPv4 layers correctly, even if your TCP layer is malformed. gopacket has two useful objects, Flow and Endpoint, for communicating in a protocol independent manner the fact that a packet is coming from A and going to B. The general layer types LinkLayer, NetworkLayer, and TransportLayer all provide methods for extracting their flow information, without worrying about the type of the underlying Layer. A Flow is a simple object made up of a set of two Endpoints, one source and one destination. It details the sender and receiver of the Layer of the Packet. An Endpoint is a hashable representation of a source or destination. For example, for LayerTypeIPv4, an Endpoint contains the IP address bytes for a v4 IP packet. A Flow can be broken into Endpoints, and Endpoints can be combined into Flows: Both Endpoint and Flow objects can be used as map keys, and the equality operator can compare them, so you can easily group together all packets based on endpoint criteria: For load-balancing purposes, both Flow and Endpoint have FastHash() functions, which provide quick, non-cryptographic hashes of their contents. Of particular importance is the fact that Flow FastHash() is symetric: A->B will have the same hash as B->A. An example usage could be: This allows us to split up a packet stream while still making sure that each stream sees all packets for a flow (and its bidirectional opposite). If your network has some strange encapsulation, you can implement your own decoder. In this example, we handle Ethernet packets which are encapsulated in a 4-byte header. See the docs for Decoder and PacketBuilder for more details on how coding decoders works, or look at RegisterLayerType and RegisterEndpointType to see how to add layer/endpoint types to gopacket. TLDR: DecodingLayerParser takes about 10% of the time as NewPacket to decode packet data, but only for known packet stacks. Basic decoding using gopacket.NewPacket or PacketSource.Packets is somewhat slow due to its need to allocate a new packet and every respective layer. It's very versatile and can handle all known layer types, but sometimes you really only care about a specific set of layers regardless, so that versatility is wasted. DecodingLayerParser avoids memory allocation altogether by decoding packet layers directly into preallocated objects, which you can then reference to get the packet's information. A quick example: The important thing to note here is that the parser is modifying the passed in layers (eth, ip4, ip6, tcp) instead of allocating new ones, thus greatly speeding up the decoding process. It's even branching based on layer type... it'll handle an (eth, ip4, tcp) or (eth, ip6, tcp) stack. However, it won't handle any other type... since no other decoders were passed in, an (eth, ip4, udp) stack will stop decoding after ip4, and only pass back [LayerTypeEthernet, LayerTypeIPv4] through the 'decoded' slice (along with an error saying it can't decode a UDP packet). Unfortunately, not all layers can be used by DecodingLayerParser... only those implementing the DecodingLayer interface are usable. Also, it's possible to create DecodingLayers that are not themselves Layers... see layers.IPv6ExtensionSkipper for an example of this. As well as offering the ability to decode packet data, gopacket will allow you to create packets from scratch, as well. A number of gopacket layers implement the SerializableLayer interface; these layers can be serialized to a []byte in the following manner: SerializeTo PREPENDS the given layer onto the SerializeBuffer, and they treat the current buffer's Bytes() slice as the payload of the serializing layer. Therefore, you can serialize an entire packet by serializing a set of layers in reverse order (Payload, then TCP, then IP, then Ethernet, for example). The SerializeBuffer's SerializeLayers function is a helper that does exactly that. To generate a (empty and useless, because no fields are set) Ethernet(IPv4(TCP(Payload))) packet, for exmaple, you can run: If you use gopacket, you'll almost definitely want to make sure gopacket/layers is imported, since when imported it sets all the LayerType variables and fills in a lot of interesting variables/maps (DecodersByLayerName, etc). Therefore, it's recommended that even if you don't use any layers functions directly, you still import with:

Package gopacket provides packet decoding for the Go language. gopacket contains many sub-packages with additional functionality you may find useful, including: Also, if you're looking to dive right into code, see the examples subdirectory for numerous simple binaries built using gopacket libraries. Minimum go version required is 1.5. gopacket takes in packet data as a []byte and decodes it into a packet with a non-zero number of "layers". Each layer corresponds to a protocol within the bytes. Once a packet has been decoded, the layers of the packet can be requested from the packet. Packets can be decoded from a number of starting points. Many of our base types implement Decoder, which allow us to decode packets for which we don't have full data. Most of the time, you won't just have a []byte of packet data lying around. Instead, you'll want to read packets in from somewhere (file, interface, etc) and process them. To do that, you'll want to build a PacketSource. First, you'll need to construct an object that implements the PacketDataSource interface. There are implementations of this interface bundled with gopacket in the gopacket/pcap and gopacket/pfring subpackages... see their documentation for more information on their usage. Once you have a PacketDataSource, you can pass it into NewPacketSource, along with a Decoder of your choice, to create a PacketSource. Once you have a PacketSource, you can read packets from it in multiple ways. See the docs for PacketSource for more details. The easiest method is the Packets function, which returns a channel, then asynchronously writes new packets into that channel, closing the channel if the packetSource hits an end-of-file. You can change the decoding options of the packetSource by setting fields in packetSource.DecodeOptions... see the following sections for more details. gopacket optionally decodes packet data lazily, meaning it only decodes a packet layer when it needs to handle a function call. Lazily-decoded packets are not concurrency-safe. Since layers have not all been decoded, each call to Layer() or Layers() has the potential to mutate the packet in order to decode the next layer. If a packet is used in multiple goroutines concurrently, don't use gopacket.Lazy. Then gopacket will decode the packet fully, and all future function calls won't mutate the object. By default, gopacket will copy the slice passed to NewPacket and store the copy within the packet, so future mutations to the bytes underlying the slice don't affect the packet and its layers. If you can guarantee that the underlying slice bytes won't be changed, you can use NoCopy to tell gopacket.NewPacket, and it'll use the passed-in slice itself. The fastest method of decoding is to use both Lazy and NoCopy, but note from the many caveats above that for some implementations either or both may be dangerous. During decoding, certain layers are stored in the packet as well-known layer types. For example, IPv4 and IPv6 are both considered NetworkLayer layers, while TCP and UDP are both TransportLayer layers. We support 4 layers, corresponding to the 4 layers of the TCP/IP layering scheme (roughly anagalous to layers 2, 3, 4, and 7 of the OSI model). To access these, you can use the packet.LinkLayer, packet.NetworkLayer, packet.TransportLayer, and packet.ApplicationLayer functions. Each of these functions returns a corresponding interface (gopacket.{Link,Network,Transport,Application}Layer). The first three provide methods for getting src/dst addresses for that particular layer, while the final layer provides a Payload function to get payload data. This is helpful, for example, to get payloads for all packets regardless of their underlying data type: A particularly useful layer is ErrorLayer, which is set whenever there's an error parsing part of the packet. Note that we don't return an error from NewPacket because we may have decoded a number of layers successfully before running into our erroneous layer. You may still be able to get your Ethernet and IPv4 layers correctly, even if your TCP layer is malformed. gopacket has two useful objects, Flow and Endpoint, for communicating in a protocol independent manner the fact that a packet is coming from A and going to B. The general layer types LinkLayer, NetworkLayer, and TransportLayer all provide methods for extracting their flow information, without worrying about the type of the underlying Layer. A Flow is a simple object made up of a set of two Endpoints, one source and one destination. It details the sender and receiver of the Layer of the Packet. An Endpoint is a hashable representation of a source or destination. For example, for LayerTypeIPv4, an Endpoint contains the IP address bytes for a v4 IP packet. A Flow can be broken into Endpoints, and Endpoints can be combined into Flows: Both Endpoint and Flow objects can be used as map keys, and the equality operator can compare them, so you can easily group together all packets based on endpoint criteria: For load-balancing purposes, both Flow and Endpoint have FastHash() functions, which provide quick, non-cryptographic hashes of their contents. Of particular importance is the fact that Flow FastHash() is symmetric: A->B will have the same hash as B->A. An example usage could be: This allows us to split up a packet stream while still making sure that each stream sees all packets for a flow (and its bidirectional opposite). If your network has some strange encapsulation, you can implement your own decoder. In this example, we handle Ethernet packets which are encapsulated in a 4-byte header. See the docs for Decoder and PacketBuilder for more details on how coding decoders works, or look at RegisterLayerType and RegisterEndpointType to see how to add layer/endpoint types to gopacket. TLDR: DecodingLayerParser takes about 10% of the time as NewPacket to decode packet data, but only for known packet stacks. Basic decoding using gopacket.NewPacket or PacketSource.Packets is somewhat slow due to its need to allocate a new packet and every respective layer. It's very versatile and can handle all known layer types, but sometimes you really only care about a specific set of layers regardless, so that versatility is wasted. DecodingLayerParser avoids memory allocation altogether by decoding packet layers directly into preallocated objects, which you can then reference to get the packet's information. A quick example: The important thing to note here is that the parser is modifying the passed in layers (eth, ip4, ip6, tcp) instead of allocating new ones, thus greatly speeding up the decoding process. It's even branching based on layer type... it'll handle an (eth, ip4, tcp) or (eth, ip6, tcp) stack. However, it won't handle any other type... since no other decoders were passed in, an (eth, ip4, udp) stack will stop decoding after ip4, and only pass back [LayerTypeEthernet, LayerTypeIPv4] through the 'decoded' slice (along with an error saying it can't decode a UDP packet). Unfortunately, not all layers can be used by DecodingLayerParser... only those implementing the DecodingLayer interface are usable. Also, it's possible to create DecodingLayers that are not themselves Layers... see layers.IPv6ExtensionSkipper for an example of this. As well as offering the ability to decode packet data, gopacket will allow you to create packets from scratch, as well. A number of gopacket layers implement the SerializableLayer interface; these layers can be serialized to a []byte in the following manner: SerializeTo PREPENDS the given layer onto the SerializeBuffer, and they treat the current buffer's Bytes() slice as the payload of the serializing layer. Therefore, you can serialize an entire packet by serializing a set of layers in reverse order (Payload, then TCP, then IP, then Ethernet, for example). The SerializeBuffer's SerializeLayers function is a helper that does exactly that. To generate a (empty and useless, because no fields are set) Ethernet(IPv4(TCP(Payload))) packet, for example, you can run: If you use gopacket, you'll almost definitely want to make sure gopacket/layers is imported, since when imported it sets all the LayerType variables and fills in a lot of interesting variables/maps (DecodersByLayerName, etc). Therefore, it's recommended that even if you don't use any layers functions directly, you still import with:

Extensible Go library for creating fast, SSR-first frontend avoiding vanilla templating downsides. Creating asynchronous and dynamic layout parts is a complex problem for larger projects using `html/template`. Library tries to simplify this process. Let's go straight into a simple example. Then, we will dig into details, step by step, how it works. Kyoto provides a simple net/http handlers and function wrappers to handle pages rendering and serving. See functions inside of nethttp.go file for details and advanced usage. Example: Kyoto provides a way to define components. It's a very common approach for modern libraries to manage frontend parts. In kyoto each component is a context receiver, which returns it's state. Each component becomes a part of the page or top-level component, which executes component asynchronously and gets a state future object. In that way your components are executing in a non-blocking way. Pages are just top-level components, where you can configure rendering and page related stuff. Example: As an option, you can wrap component with another function to accept additional paramenters from top-level page/component. Example: Kyoto provides a context, which holds common objects like http.ResponseWriter, *http.Request, etc. See kyoto.Context for details. Example: Kyoto provides a set of parameters and functions to provide a comfortable template building process. You can configure template building parameters with kyoto.TemplateConf configuration. See template.go for available functions and kyoto.TemplateConfiguration for configuration details. Example: Kyoto provides a way to simplify building dynamic UIs. For this purpose it has a feature named actions. Logic is pretty simple. Client calls an action (sends a request to the server). Action is executing on server side and server is sending updated component markup to the client which will be morphed into DOM. That's it. To use actions, you need to go through a few steps. You'll need to include a client into page (JS functions for communication) and register an actions handler for a needed component. Let's start from including a client. Then, let's register an actions handler for a needed component. That's all! Now we ready to use actions to provide a dynamic UI. Example: In this example you can see provided modifications to the quick start example. First, we've added a state and name into our components' markup. In this way we are saving our components' state between actions and find a component root. Unfortunately, we have to manually provide a component name for now, we haven't found a way to provide it dynamically. Second, we've added a reload button with onclick function call. We're using a function Action provided by a client. Action triggering will be described in details later. Third, we've added an action handler inside of our component. This handler will be executed when a client calls an action with a corresponding name. It's highly recommended to keep components' state as small as possible. It will be transmitted on each action call. Kyoto have multiple ways to trigger actions. Now we will check them one by one. This is the simplest way to trigger an action. It's just a function call with a referer (usually 'this', f.e. button) as a first argument (used to determine root), action name as a second argument and arguments as a rest. Arguments must to be JSON serializable. It's possible to trigger an action of another component. If you want to call an action of parent component, use $ prefix in action name. If you want to call an action of component by id, use <id:action> as an action name. This is a specific action which is triggered when a form is submitted. Usually called in onsubmit="..." attribute of a form. You'll need to implement 'Submit' action to handle this trigger. This is a special HTML attribute which will trigger an action on page load. This may be useful for components' lazy loading. With this special HTML attributes you can trigger an action with interval. Useful for components that must to be updated over time (f.e. charts, stats, etc). You can use this trigger with ssa:poll and ssa:poll.interval HTML attributes. This one attribute allows you to trigger an action when an element is visible on the screen. May be useful for lazy loading. Kyoto provides a way to control action flow. For now, it's possible to control display style on component call and push multiple UI updates to the client during a single action. Because kyoto makes a roundtrip to the server every time an action is triggered on the page, there are cases where the page may not react immediately to a user event (like a click). That's why the library provides a way to easily control display attributes on action call. You can use this HTML attribute to control display during action call. At the end of an action the layout will be restored. A small note. Don't forget to set a default display for loading elements like spinners and loaders. You can push multiple component UI updates during a single action call. Just call kyoto.ActionFlush(ctx, state) to initiate an update. Kyoto provides a way to control action rendering. Now there is at least 2 rendering options after an action call: morph (default) and replace. Morph will try to morph received markup to the current one with morphdom library. In case of an error, or explicit "replace" mode, markup will be replaced with x.outerHTML = '...'.

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package gopacket provides packet decoding for the Go language. gopacket contains many sub-packages with additional functionality you may find useful, including: Also, if you're looking to dive right into code, see the examples subdirectory for numerous simple binaries built using gopacket libraries. Minimum go version required is 1.5. gopacket takes in packet data as a []byte and decodes it into a packet with a non-zero number of "layers". Each layer corresponds to a protocol within the bytes. Once a packet has been decoded, the layers of the packet can be requested from the packet. Packets can be decoded from a number of starting points. Many of our base types implement Decoder, which allow us to decode packets for which we don't have full data. Most of the time, you won't just have a []byte of packet data lying around. Instead, you'll want to read packets in from somewhere (file, interface, etc) and process them. To do that, you'll want to build a PacketSource. First, you'll need to construct an object that implements the PacketDataSource interface. There are implementations of this interface bundled with gopacket in the gopacket/pcap and gopacket/pfring subpackages... see their documentation for more information on their usage. Once you have a PacketDataSource, you can pass it into NewPacketSource, along with a Decoder of your choice, to create a PacketSource. Once you have a PacketSource, you can read packets from it in multiple ways. See the docs for PacketSource for more details. The easiest method is the Packets function, which returns a channel, then asynchronously writes new packets into that channel, closing the channel if the packetSource hits an end-of-file. You can change the decoding options of the packetSource by setting fields in packetSource.DecodeOptions... see the following sections for more details. gopacket optionally decodes packet data lazily, meaning it only decodes a packet layer when it needs to handle a function call. Lazily-decoded packets are not concurrency-safe. Since layers have not all been decoded, each call to Layer() or Layers() has the potential to mutate the packet in order to decode the next layer. If a packet is used in multiple goroutines concurrently, don't use gopacket.Lazy. Then gopacket will decode the packet fully, and all future function calls won't mutate the object. By default, gopacket will copy the slice passed to NewPacket and store the copy within the packet, so future mutations to the bytes underlying the slice don't affect the packet and its layers. If you can guarantee that the underlying slice bytes won't be changed, you can use NoCopy to tell gopacket.NewPacket, and it'll use the passed-in slice itself. The fastest method of decoding is to use both Lazy and NoCopy, but note from the many caveats above that for some implementations either or both may be dangerous. During decoding, certain layers are stored in the packet as well-known layer types. For example, IPv4 and IPv6 are both considered NetworkLayer layers, while TCP and UDP are both TransportLayer layers. We support 4 layers, corresponding to the 4 layers of the TCP/IP layering scheme (roughly anagalous to layers 2, 3, 4, and 7 of the OSI model). To access these, you can use the packet.LinkLayer, packet.NetworkLayer, packet.TransportLayer, and packet.ApplicationLayer functions. Each of these functions returns a corresponding interface (gopacket.{Link,Network,Transport,Application}Layer). The first three provide methods for getting src/dst addresses for that particular layer, while the final layer provides a Payload function to get payload data. This is helpful, for example, to get payloads for all packets regardless of their underlying data type: A particularly useful layer is ErrorLayer, which is set whenever there's an error parsing part of the packet. Note that we don't return an error from NewPacket because we may have decoded a number of layers successfully before running into our erroneous layer. You may still be able to get your Ethernet and IPv4 layers correctly, even if your TCP layer is malformed. gopacket has two useful objects, Flow and Endpoint, for communicating in a protocol independent manner the fact that a packet is coming from A and going to B. The general layer types LinkLayer, NetworkLayer, and TransportLayer all provide methods for extracting their flow information, without worrying about the type of the underlying Layer. A Flow is a simple object made up of a set of two Endpoints, one source and one destination. It details the sender and receiver of the Layer of the Packet. An Endpoint is a hashable representation of a source or destination. For example, for LayerTypeIPv4, an Endpoint contains the IP address bytes for a v4 IP packet. A Flow can be broken into Endpoints, and Endpoints can be combined into Flows: Both Endpoint and Flow objects can be used as map keys, and the equality operator can compare them, so you can easily group together all packets based on endpoint criteria: For load-balancing purposes, both Flow and Endpoint have FastHash() functions, which provide quick, non-cryptographic hashes of their contents. Of particular importance is the fact that Flow FastHash() is symmetric: A->B will have the same hash as B->A. An example usage could be: This allows us to split up a packet stream while still making sure that each stream sees all packets for a flow (and its bidirectional opposite). If your network has some strange encapsulation, you can implement your own decoder. In this example, we handle Ethernet packets which are encapsulated in a 4-byte header. See the docs for Decoder and PacketBuilder for more details on how coding decoders works, or look at RegisterLayerType and RegisterEndpointType to see how to add layer/endpoint types to gopacket. TLDR: DecodingLayerParser takes about 10% of the time as NewPacket to decode packet data, but only for known packet stacks. Basic decoding using gopacket.NewPacket or PacketSource.Packets is somewhat slow due to its need to allocate a new packet and every respective layer. It's very versatile and can handle all known layer types, but sometimes you really only care about a specific set of layers regardless, so that versatility is wasted. DecodingLayerParser avoids memory allocation altogether by decoding packet layers directly into preallocated objects, which you can then reference to get the packet's information. A quick example: The important thing to note here is that the parser is modifying the passed in layers (eth, ip4, ip6, tcp) instead of allocating new ones, thus greatly speeding up the decoding process. It's even branching based on layer type... it'll handle an (eth, ip4, tcp) or (eth, ip6, tcp) stack. However, it won't handle any other type... since no other decoders were passed in, an (eth, ip4, udp) stack will stop decoding after ip4, and only pass back [LayerTypeEthernet, LayerTypeIPv4] through the 'decoded' slice (along with an error saying it can't decode a UDP packet). Unfortunately, not all layers can be used by DecodingLayerParser... only those implementing the DecodingLayer interface are usable. Also, it's possible to create DecodingLayers that are not themselves Layers... see layers.IPv6ExtensionSkipper for an example of this. As well as offering the ability to decode packet data, gopacket will allow you to create packets from scratch, as well. A number of gopacket layers implement the SerializableLayer interface; these layers can be serialized to a []byte in the following manner: SerializeTo PREPENDS the given layer onto the SerializeBuffer, and they treat the current buffer's Bytes() slice as the payload of the serializing layer. Therefore, you can serialize an entire packet by serializing a set of layers in reverse order (Payload, then TCP, then IP, then Ethernet, for example). The SerializeBuffer's SerializeLayers function is a helper that does exactly that. To generate a (empty and useless, because no fields are set) Ethernet(IPv4(TCP(Payload))) packet, for example, you can run: If you use gopacket, you'll almost definitely want to make sure gopacket/layers is imported, since when imported it sets all the LayerType variables and fills in a lot of interesting variables/maps (DecodersByLayerName, etc). Therefore, it's recommended that even if you don't use any layers functions directly, you still import with:

Extensible Go library for creating fast, SSR-first frontend avoiding vanilla templating downsides. Creating asynchronous and dynamic layout parts is a complex problem for larger projects using `html/template`. Library tries to simplify this process. Let's go straight into a simple example. Then, we will dig into details, step by step, how it works. Kyoto provides a simple net/http handlers and function wrappers to handle pages rendering and serving. See functions inside of nethttp.go file for details and advanced usage. Example: Kyoto provides a way to define components. It's a very common approach for modern libraries to manage frontend parts. In kyoto each component is a context receiver, which returns it's state. Each component becomes a part of the page or top-level component, which executes component asynchronously and gets a state future object. In that way your components are executing in a non-blocking way. Pages are just top-level components, where you can configure rendering and page related stuff. Example: As an option, you can wrap component with another function to accept additional paramenters from top-level page/component. Example: Kyoto provides a context, which holds common objects like http.ResponseWriter, *http.Request, etc. See kyoto.Context for details. Example: Kyoto provides a set of parameters and functions to provide a comfortable template building process. You can configure template building parameters with kyoto.TemplateConf configuration. See template.go for available functions and kyoto.TemplateConfiguration for configuration details. Example: Kyoto provides a way to simplify building dynamic UIs. For this purpose it has a feature named actions. Logic is pretty simple. Client calls an action (sends a request to the server). Action is executing on server side and server is sending updated component markup to the client which will be morphed into DOM. That's it. To use actions, you need to go through a few steps. You'll need to include a client into page (JS functions for communication) and register an actions handler for a needed component. Let's start from including a client. Then, let's register an actions handler for a needed component. That's all! Now we ready to use actions to provide a dynamic UI. Example: In this example you can see provided modifications to the quick start example. First, we've added a state and name into our components' markup. In this way we are saving our components' state between actions and find a component root. Unfortunately, we have to manually provide a component name for now, we haven't found a way to provide it dynamically. Second, we've added a reload button with onclick function call. We're using a function Action provided by a client. Action triggering will be described in details later. Third, we've added an action handler inside of our component. This handler will be executed when a client calls an action with a corresponding name. It's highly recommended to keep components' state as small as possible. It will be transmitted on each action call. Kyoto have multiple ways to trigger actions. Now we will check them one by one. This is the simplest way to trigger an action. It's just a function call with a referer (usually 'this', f.e. button) as a first argument (used to determine root), action name as a second argument and arguments as a rest. Arguments must to be JSON serializable. It's possible to trigger an action of another component. If you want to call an action of parent component, use $ prefix in action name. If you want to call an action of component by id, use <id:action> as an action name. This is a specific action which is triggered when a form is submitted. Usually called in onsubmit="..." attribute of a form. You'll need to implement 'Submit' action to handle this trigger. This is a special HTML attribute which will trigger an action on page load. This may be useful for components' lazy loading. With this special HTML attributes you can trigger an action with interval. Useful for components that must to be updated over time (f.e. charts, stats, etc). You can use this trigger with ssa:poll and ssa:poll.interval HTML attributes. This one attribute allows you to trigger an action when an element is visible on the screen. May be useful for lazy loading. Kyoto provides a way to control action flow. For now, it's possible to control display style on component call and push multiple UI updates to the client during a single action. Because kyoto makes a roundtrip to the server every time an action is triggered on the page, there are cases where the page may not react immediately to a user event (like a click). That's why the library provides a way to easily control display attributes on action call. You can use this HTML attribute to control display during action call. At the end of an action the layout will be restored. A small note. Don't forget to set a default display for loading elements like spinners and loaders. You can push multiple component UI updates during a single action call. Just call kyoto.ActionFlush(ctx, state) to initiate an update. Kyoto provides a way to control action rendering. Now there is at least 2 rendering options after an action call: morph (default) and replace. Morph will try to morph received markup to the current one with morphdom library. In case of an error, or explicit "replace" mode, markup will be replaced with x.outerHTML = '...'.

Extensible Go library for creating fast, SSR-first frontend avoiding vanilla templating downsides. Creating asynchronous and dynamic layout parts is a complex problem for larger projects using `html/template`. Library tries to simplify this process. Let's go straight into a simple example. Then, we will dig into details, step by step, how it works. Kyoto provides a simple net/http handlers and function wrappers to handle pages rendering and serving. See functions inside of nethttp.go file for details and advanced usage. Example: Kyoto provides a way to define components. It's a very common approach for modern libraries to manage frontend parts. In kyoto each component is a context receiver, which returns it's state. Each component becomes a part of the page or top-level component, which executes component asynchronously and gets a state future object. In that way your components are executing in a non-blocking way. Pages are just top-level components, where you can configure rendering and page related stuff. Example: As an option, you can wrap component with another function to accept additional paramenters from top-level page/component. Example: Kyoto provides a context, which holds common objects like http.ResponseWriter, *http.Request, etc. See kyoto.Context for details. Example: Kyoto provides a set of parameters and functions to provide a comfortable template building process. You can configure template building parameters with kyoto.TemplateConf configuration. See template.go for available functions and kyoto.TemplateConfiguration for configuration details. Example: Kyoto provides a way to simplify building dynamic UIs. For this purpose it has a feature named actions. Logic is pretty simple. Client calls an action (sends a request to the server). Action is executing on server side and server is sending updated component markup to the client which will be morphed into DOM. That's it. To use actions, you need to go through a few steps. You'll need to include a client into page (JS functions for communication) and register an actions handler for a needed component. Let's start from including a client. Then, let's register an actions handler for a needed component. That's all! Now we ready to use actions to provide a dynamic UI. Example: In this example you can see provided modifications to the quick start example. First, we've added a state and name into our components' markup. In this way we are saving our components' state between actions and find a component root. Unfortunately, we have to manually provide a component name for now, we haven't found a way to provide it dynamically. Second, we've added a reload button with onclick function call. We're using a function Action provided by a client. Action triggering will be described in details later. Third, we've added an action handler inside of our component. This handler will be executed when a client calls an action with a corresponding name. It's highly recommended to keep components' state as small as possible. It will be transmitted on each action call. Kyoto have multiple ways to trigger actions. Now we will check them one by one. This is the simplest way to trigger an action. It's just a function call with a referer (usually 'this', f.e. button) as a first argument (used to determine root), action name as a second argument and arguments as a rest. Arguments must to be JSON serializable. It's possible to trigger an action of another component. If you want to call an action of parent component, use $ prefix in action name. If you want to call an action of component by id, use <id:action> as an action name. This is a specific action which is triggered when a form is submitted. Usually called in onsubmit="..." attribute of a form. You'll need to implement 'Submit' action to handle this trigger. This is a special HTML attribute which will trigger an action on page load. This may be useful for components' lazy loading. With this special HTML attributes you can trigger an action with interval. Useful for components that must to be updated over time (f.e. charts, stats, etc). You can use this trigger with ssa:poll and ssa:poll.interval HTML attributes. This one attribute allows you to trigger an action when an element is visible on the screen. May be useful for lazy loading. Kyoto provides a way to control action flow. For now, it's possible to control display style on component call and push multiple UI updates to the client during a single action. Because kyoto makes a roundtrip to the server every time an action is triggered on the page, there are cases where the page may not react immediately to a user event (like a click). That's why the library provides a way to easily control display attributes on action call. You can use this HTML attribute to control display during action call. At the end of an action the layout will be restored. A small note. Don't forget to set a default display for loading elements like spinners and loaders. You can push multiple component UI updates during a single action call. Just call kyoto.ActionFlush(ctx, state) to initiate an update. Kyoto provides a way to control action rendering. Now there is at least 2 rendering options after an action call: morph (default) and replace. Morph will try to morph received markup to the current one with morphdom library. In case of an error, or explicit "replace" mode, markup will be replaced with x.outerHTML = '...'.

Extensible Go library for creating fast, SSR-first frontend avoiding vanilla templating downsides. Creating asynchronous and dynamic layout parts is a complex problem for larger projects using `html/template`. This library tries to simplify overall setup and process. Let's go straight into a simple example. Then, we will dig into details, step by step, how it works. Kyoto provides a set of simple net/http handlers, handler builders and function wrappers to provide serving, pages rendering, component actions, etc. Anyway, this is not an ultimative solution for any case. If you ever need to wrap/extend existing functionality, library encourages this. See functions inside of nethttp.go file for details and advanced usage. Example: Kyoto provides a way to define components. It's a very common approach for modern libraries to manage frontend parts. In kyoto each component is a context receiver, which returns it's state. Each component becomes a part of the page or top-level component, which executes component asynchronously and gets a state future object. In that way your components are executing in a non-blocking way. Pages are just top-level components, where you can configure rendering and page related stuff. Example: As an option, you can wrap component with another function to accept additional paramenters from top-level page/component. Example: Kyoto provides a context, which holds common objects like http.ResponseWriter, *http.Request, etc. See kyoto.Context for details. Example: Kyoto provides a set of parameters and functions to provide a comfortable template building process. You can configure template building parameters with kyoto.TemplateConf configuration. See template.go for available functions and kyoto.TemplateConfiguration for configuration details. Example: Kyoto provides a way to simplify building dynamic UIs. For this purpose it has a feature named actions. Logic is pretty simple. Client calls an action (sends a request to the server). Action is executing on server side and server is sending updated component markup to the client which will be morphed into DOM. That's it. To use actions, you need to go through a few steps. You'll need to include a client into page (JS functions for communication) and register an actions handler for a needed component. Let's start from including a client. Then, let's register an actions handler for a needed component. That's all! Now we ready to use actions to provide a dynamic UI. Example: In this example you can see provided modifications to the quick start example. First, we've added a state and name into our components' markup. In this way we are saving our components' state between actions and find a component root. Unfortunately, we have to manually provide a component name for now, we haven't found a way to provide it dynamically. Second, we've added a reload button with onclick function call. We're using a function Action provided by a client. Action triggering will be described in details later. Third, we've added an action handler inside of our component. This handler will be executed when a client calls an action with a corresponding name. It's highly recommended to keep components' state as small as possible. It will be transmitted on each action call. Kyoto have multiple ways to trigger actions. Now we will check them one by one. This is the simplest way to trigger an action. It's just a function call with a referer (usually 'this', f.e. button) as a first argument (used to determine root), action name as a second argument and arguments as a rest. Arguments must to be JSON serializable. It's possible to trigger an action of another component. If you want to call an action of parent component, use $ prefix in action name. If you want to call an action of component by id, use <id:action> as an action name. This is a specific action which is triggered when a form is submitted. Usually called in onsubmit="..." attribute of a form. You'll need to implement 'Submit' action to handle this trigger. This is a special HTML attribute which will trigger an action on page load. This may be useful for components' lazy loading. With this special HTML attributes you can trigger an action with interval. Useful for components that must to be updated over time (f.e. charts, stats, etc). You can use this trigger with ssa:poll and ssa:poll.interval HTML attributes. This one attribute allows you to trigger an action when an element is visible on the screen. May be useful for lazy loading. Kyoto provides a way to control action flow. For now, it's possible to control display style on component call and push multiple UI updates to the client during a single action. Because kyoto makes a roundtrip to the server every time an action is triggered on the page, there are cases where the page may not react immediately to a user event (like a click). That's why the library provides a way to easily control display attributes on action call. You can use this HTML attribute to control display during action call. At the end of an action the layout will be restored. A small note. Don't forget to set a default display for loading elements like spinners and loaders. You can push multiple component UI updates during a single action call. Just call kyoto.ActionFlush(ctx, state) to initiate an update. Kyoto provides a way to control action rendering. Now there is at least 2 rendering options after an action call: morph (default) and replace. Morph will try to morph received markup to the current one with morphdom library. In case of an error, or explicit "replace" mode, markup will be replaced with x.outerHTML = '...'.

Package gopacket provides packet decoding for the Go language. gopacket contains many sub-packages with additional functionality you may find useful, including: Also, if you're looking to dive right into code, see the examples subdirectory for numerous simple binaries built using gopacket libraries. Minimum go version required is 1.5. gopacket takes in packet data as a []byte and decodes it into a packet with a non-zero number of "layers". Each layer corresponds to a protocol within the bytes. Once a packet has been decoded, the layers of the packet can be requested from the packet. Packets can be decoded from a number of starting points. Many of our base types implement Decoder, which allow us to decode packets for which we don't have full data. Most of the time, you won't just have a []byte of packet data lying around. Instead, you'll want to read packets in from somewhere (file, interface, etc) and process them. To do that, you'll want to build a PacketSource. First, you'll need to construct an object that implements the PacketDataSource interface. There are implementations of this interface bundled with gopacket in the gopacket/pcap and gopacket/pfring subpackages... see their documentation for more information on their usage. Once you have a PacketDataSource, you can pass it into NewPacketSource, along with a Decoder of your choice, to create a PacketSource. Once you have a PacketSource, you can read packets from it in multiple ways. See the docs for PacketSource for more details. The easiest method is the Packets function, which returns a channel, then asynchronously writes new packets into that channel, closing the channel if the packetSource hits an end-of-file. You can change the decoding options of the packetSource by setting fields in packetSource.DecodeOptions... see the following sections for more details. gopacket optionally decodes packet data lazily, meaning it only decodes a packet layer when it needs to handle a function call. Lazily-decoded packets are not concurrency-safe. Since layers have not all been decoded, each call to Layer() or Layers() has the potential to mutate the packet in order to decode the next layer. If a packet is used in multiple goroutines concurrently, don't use gopacket.Lazy. Then gopacket will decode the packet fully, and all future function calls won't mutate the object. By default, gopacket will copy the slice passed to NewPacket and store the copy within the packet, so future mutations to the bytes underlying the slice don't affect the packet and its layers. If you can guarantee that the underlying slice bytes won't be changed, you can use NoCopy to tell gopacket.NewPacket, and it'll use the passed-in slice itself. The fastest method of decoding is to use both Lazy and NoCopy, but note from the many caveats above that for some implementations either or both may be dangerous. During decoding, certain layers are stored in the packet as well-known layer types. For example, IPv4 and IPv6 are both considered NetworkLayer layers, while TCP and UDP are both TransportLayer layers. We support 4 layers, corresponding to the 4 layers of the TCP/IP layering scheme (roughly anagalous to layers 2, 3, 4, and 7 of the OSI model). To access these, you can use the packet.LinkLayer, packet.NetworkLayer, packet.TransportLayer, and packet.ApplicationLayer functions. Each of these functions returns a corresponding interface (gopacket.{Link,Network,Transport,Application}Layer). The first three provide methods for getting src/dst addresses for that particular layer, while the final layer provides a Payload function to get payload data. This is helpful, for example, to get payloads for all packets regardless of their underlying data type: A particularly useful layer is ErrorLayer, which is set whenever there's an error parsing part of the packet. Note that we don't return an error from NewPacket because we may have decoded a number of layers successfully before running into our erroneous layer. You may still be able to get your Ethernet and IPv4 layers correctly, even if your TCP layer is malformed. gopacket has two useful objects, Flow and Endpoint, for communicating in a protocol independent manner the fact that a packet is coming from A and going to B. The general layer types LinkLayer, NetworkLayer, and TransportLayer all provide methods for extracting their flow information, without worrying about the type of the underlying Layer. A Flow is a simple object made up of a set of two Endpoints, one source and one destination. It details the sender and receiver of the Layer of the Packet. An Endpoint is a hashable representation of a source or destination. For example, for LayerTypeIPv4, an Endpoint contains the IP address bytes for a v4 IP packet. A Flow can be broken into Endpoints, and Endpoints can be combined into Flows: Both Endpoint and Flow objects can be used as map keys, and the equality operator can compare them, so you can easily group together all packets based on endpoint criteria: For load-balancing purposes, both Flow and Endpoint have FastHash() functions, which provide quick, non-cryptographic hashes of their contents. Of particular importance is the fact that Flow FastHash() is symmetric: A->B will have the same hash as B->A. An example usage could be: This allows us to split up a packet stream while still making sure that each stream sees all packets for a flow (and its bidirectional opposite). If your network has some strange encapsulation, you can implement your own decoder. In this example, we handle Ethernet packets which are encapsulated in a 4-byte header. See the docs for Decoder and PacketBuilder for more details on how coding decoders works, or look at RegisterLayerType and RegisterEndpointType to see how to add layer/endpoint types to gopacket. TLDR: DecodingLayerParser takes about 10% of the time as NewPacket to decode packet data, but only for known packet stacks. Basic decoding using gopacket.NewPacket or PacketSource.Packets is somewhat slow due to its need to allocate a new packet and every respective layer. It's very versatile and can handle all known layer types, but sometimes you really only care about a specific set of layers regardless, so that versatility is wasted. DecodingLayerParser avoids memory allocation altogether by decoding packet layers directly into preallocated objects, which you can then reference to get the packet's information. A quick example: The important thing to note here is that the parser is modifying the passed in layers (eth, ip4, ip6, tcp) instead of allocating new ones, thus greatly speeding up the decoding process. It's even branching based on layer type... it'll handle an (eth, ip4, tcp) or (eth, ip6, tcp) stack. However, it won't handle any other type... since no other decoders were passed in, an (eth, ip4, udp) stack will stop decoding after ip4, and only pass back [LayerTypeEthernet, LayerTypeIPv4] through the 'decoded' slice (along with an error saying it can't decode a UDP packet). Unfortunately, not all layers can be used by DecodingLayerParser... only those implementing the DecodingLayer interface are usable. Also, it's possible to create DecodingLayers that are not themselves Layers... see layers.IPv6ExtensionSkipper for an example of this. As well as offering the ability to decode packet data, gopacket will allow you to create packets from scratch, as well. A number of gopacket layers implement the SerializableLayer interface; these layers can be serialized to a []byte in the following manner: SerializeTo PREPENDS the given layer onto the SerializeBuffer, and they treat the current buffer's Bytes() slice as the payload of the serializing layer. Therefore, you can serialize an entire packet by serializing a set of layers in reverse order (Payload, then TCP, then IP, then Ethernet, for example). The SerializeBuffer's SerializeLayers function is a helper that does exactly that. To generate a (empty and useless, because no fields are set) Ethernet(IPv4(TCP(Payload))) packet, for example, you can run: If you use gopacket, you'll almost definitely want to make sure gopacket/layers is imported, since when imported it sets all the LayerType variables and fills in a lot of interesting variables/maps (DecodersByLayerName, etc). Therefore, it's recommended that even if you don't use any layers functions directly, you still import with:

Package gopacket provides packet decoding for the Go language. gopacket contains many sub-packages with additional functionality you may find useful, including: Also, if you're looking to dive right into code, see the examples subdirectory for numerous simple binaries built using gopacket libraries. Minimum go version required is 1.5. gopacket takes in packet data as a []byte and decodes it into a packet with a non-zero number of "layers". Each layer corresponds to a protocol within the bytes. Once a packet has been decoded, the layers of the packet can be requested from the packet. Packets can be decoded from a number of starting points. Many of our base types implement Decoder, which allow us to decode packets for which we don't have full data. Most of the time, you won't just have a []byte of packet data lying around. Instead, you'll want to read packets in from somewhere (file, interface, etc) and process them. To do that, you'll want to build a PacketSource. First, you'll need to construct an object that implements the PacketDataSource interface. There are implementations of this interface bundled with gopacket in the gopacket/pcap and gopacket/pfring subpackages... see their documentation for more information on their usage. Once you have a PacketDataSource, you can pass it into NewPacketSource, along with a Decoder of your choice, to create a PacketSource. Once you have a PacketSource, you can read packets from it in multiple ways. See the docs for PacketSource for more details. The easiest method is the Packets function, which returns a channel, then asynchronously writes new packets into that channel, closing the channel if the packetSource hits an end-of-file. You can change the decoding options of the packetSource by setting fields in packetSource.DecodeOptions... see the following sections for more details. gopacket optionally decodes packet data lazily, meaning it only decodes a packet layer when it needs to handle a function call. Lazily-decoded packets are not concurrency-safe. Since layers have not all been decoded, each call to Layer() or Layers() has the potential to mutate the packet in order to decode the next layer. If a packet is used in multiple goroutines concurrently, don't use gopacket.Lazy. Then gopacket will decode the packet fully, and all future function calls won't mutate the object. By default, gopacket will copy the slice passed to NewPacket and store the copy within the packet, so future mutations to the bytes underlying the slice don't affect the packet and its layers. If you can guarantee that the underlying slice bytes won't be changed, you can use NoCopy to tell gopacket.NewPacket, and it'll use the passed-in slice itself. The fastest method of decoding is to use both Lazy and NoCopy, but note from the many caveats above that for some implementations either or both may be dangerous. During decoding, certain layers are stored in the packet as well-known layer types. For example, IPv4 and IPv6 are both considered NetworkLayer layers, while TCP and UDP are both TransportLayer layers. We support 4 layers, corresponding to the 4 layers of the TCP/IP layering scheme (roughly anagalous to layers 2, 3, 4, and 7 of the OSI model). To access these, you can use the packet.LinkLayer, packet.NetworkLayer, packet.TransportLayer, and packet.ApplicationLayer functions. Each of these functions returns a corresponding interface (gopacket.{Link,Network,Transport,Application}Layer). The first three provide methods for getting src/dst addresses for that particular layer, while the final layer provides a Payload function to get payload data. This is helpful, for example, to get payloads for all packets regardless of their underlying data type: A particularly useful layer is ErrorLayer, which is set whenever there's an error parsing part of the packet. Note that we don't return an error from NewPacket because we may have decoded a number of layers successfully before running into our erroneous layer. You may still be able to get your Ethernet and IPv4 layers correctly, even if your TCP layer is malformed. gopacket has two useful objects, Flow and Endpoint, for communicating in a protocol independent manner the fact that a packet is coming from A and going to B. The general layer types LinkLayer, NetworkLayer, and TransportLayer all provide methods for extracting their flow information, without worrying about the type of the underlying Layer. A Flow is a simple object made up of a set of two Endpoints, one source and one destination. It details the sender and receiver of the Layer of the Packet. An Endpoint is a hashable representation of a source or destination. For example, for LayerTypeIPv4, an Endpoint contains the IP address bytes for a v4 IP packet. A Flow can be broken into Endpoints, and Endpoints can be combined into Flows: Both Endpoint and Flow objects can be used as map keys, and the equality operator can compare them, so you can easily group together all packets based on endpoint criteria: For load-balancing purposes, both Flow and Endpoint have FastHash() functions, which provide quick, non-cryptographic hashes of their contents. Of particular importance is the fact that Flow FastHash() is symmetric: A->B will have the same hash as B->A. An example usage could be: This allows us to split up a packet stream while still making sure that each stream sees all packets for a flow (and its bidirectional opposite). If your network has some strange encapsulation, you can implement your own decoder. In this example, we handle Ethernet packets which are encapsulated in a 4-byte header. See the docs for Decoder and PacketBuilder for more details on how coding decoders works, or look at RegisterLayerType and RegisterEndpointType to see how to add layer/endpoint types to gopacket. TLDR: DecodingLayerParser takes about 10% of the time as NewPacket to decode packet data, but only for known packet stacks. Basic decoding using gopacket.NewPacket or PacketSource.Packets is somewhat slow due to its need to allocate a new packet and every respective layer. It's very versatile and can handle all known layer types, but sometimes you really only care about a specific set of layers regardless, so that versatility is wasted. DecodingLayerParser avoids memory allocation altogether by decoding packet layers directly into preallocated objects, which you can then reference to get the packet's information. A quick example: The important thing to note here is that the parser is modifying the passed in layers (eth, ip4, ip6, tcp) instead of allocating new ones, thus greatly speeding up the decoding process. It's even branching based on layer type... it'll handle an (eth, ip4, tcp) or (eth, ip6, tcp) stack. However, it won't handle any other type... since no other decoders were passed in, an (eth, ip4, udp) stack will stop decoding after ip4, and only pass back [LayerTypeEthernet, LayerTypeIPv4] through the 'decoded' slice (along with an error saying it can't decode a UDP packet). Unfortunately, not all layers can be used by DecodingLayerParser... only those implementing the DecodingLayer interface are usable. Also, it's possible to create DecodingLayers that are not themselves Layers... see layers.IPv6ExtensionSkipper for an example of this. As well as offering the ability to decode packet data, gopacket will allow you to create packets from scratch, as well. A number of gopacket layers implement the SerializableLayer interface; these layers can be serialized to a []byte in the following manner: SerializeTo PREPENDS the given layer onto the SerializeBuffer, and they treat the current buffer's Bytes() slice as the payload of the serializing layer. Therefore, you can serialize an entire packet by serializing a set of layers in reverse order (Payload, then TCP, then IP, then Ethernet, for example). The SerializeBuffer's SerializeLayers function is a helper that does exactly that. To generate a (empty and useless, because no fields are set) Ethernet(IPv4(TCP(Payload))) packet, for example, you can run: If you use gopacket, you'll almost definitely want to make sure gopacket/layers is imported, since when imported it sets all the LayerType variables and fills in a lot of interesting variables/maps (DecodersByLayerName, etc). Therefore, it's recommended that even if you don't use any layers functions directly, you still import with:

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package gopacket provides packet decoding for the Go language. gopacket contains many sub-packages with additional functionality you may find useful, including: Also, if you're looking to dive right into code, see the examples subdirectory for numerous simple binaries built using gopacket libraries. Minimum go version required is 1.5 except for pcapgo/EthernetHandle, afpacket, and bsdbpf which need at least 1.7 due to x/sys/unix dependencies. gopacket takes in packet data as a []byte and decodes it into a packet with a non-zero number of "layers". Each layer corresponds to a protocol within the bytes. Once a packet has been decoded, the layers of the packet can be requested from the packet. Packets can be decoded from a number of starting points. Many of our base types implement Decoder, which allow us to decode packets for which we don't have full data. Most of the time, you won't just have a []byte of packet data lying around. Instead, you'll want to read packets in from somewhere (file, interface, etc) and process them. To do that, you'll want to build a PacketSource. First, you'll need to construct an object that implements the PacketDataSource interface. There are implementations of this interface bundled with gopacket in the gopacket/pcap and gopacket/pfring subpackages... see their documentation for more information on their usage. Once you have a PacketDataSource, you can pass it into NewPacketSource, along with a Decoder of your choice, to create a PacketSource. Once you have a PacketSource, you can read packets from it in multiple ways. See the docs for PacketSource for more details. The easiest method is the Packets function, which returns a channel, then asynchronously writes new packets into that channel, closing the channel if the packetSource hits an end-of-file. You can change the decoding options of the packetSource by setting fields in packetSource.DecodeOptions... see the following sections for more details. gopacket optionally decodes packet data lazily, meaning it only decodes a packet layer when it needs to handle a function call. Lazily-decoded packets are not concurrency-safe. Since layers have not all been decoded, each call to Layer() or Layers() has the potential to mutate the packet in order to decode the next layer. If a packet is used in multiple goroutines concurrently, don't use gopacket.Lazy. Then gopacket will decode the packet fully, and all future function calls won't mutate the object. By default, gopacket will copy the slice passed to NewPacket and store the copy within the packet, so future mutations to the bytes underlying the slice don't affect the packet and its layers. If you can guarantee that the underlying slice bytes won't be changed, you can use NoCopy to tell gopacket.NewPacket, and it'll use the passed-in slice itself. The fastest method of decoding is to use both Lazy and NoCopy, but note from the many caveats above that for some implementations either or both may be dangerous. During decoding, certain layers are stored in the packet as well-known layer types. For example, IPv4 and IPv6 are both considered NetworkLayer layers, while TCP and UDP are both TransportLayer layers. We support 4 layers, corresponding to the 4 layers of the TCP/IP layering scheme (roughly anagalous to layers 2, 3, 4, and 7 of the OSI model). To access these, you can use the packet.LinkLayer, packet.NetworkLayer, packet.TransportLayer, and packet.ApplicationLayer functions. Each of these functions returns a corresponding interface (gopacket.{Link,Network,Transport,Application}Layer). The first three provide methods for getting src/dst addresses for that particular layer, while the final layer provides a Payload function to get payload data. This is helpful, for example, to get payloads for all packets regardless of their underlying data type: A particularly useful layer is ErrorLayer, which is set whenever there's an error parsing part of the packet. Note that we don't return an error from NewPacket because we may have decoded a number of layers successfully before running into our erroneous layer. You may still be able to get your Ethernet and IPv4 layers correctly, even if your TCP layer is malformed. gopacket has two useful objects, Flow and Endpoint, for communicating in a protocol independent manner the fact that a packet is coming from A and going to B. The general layer types LinkLayer, NetworkLayer, and TransportLayer all provide methods for extracting their flow information, without worrying about the type of the underlying Layer. A Flow is a simple object made up of a set of two Endpoints, one source and one destination. It details the sender and receiver of the Layer of the Packet. An Endpoint is a hashable representation of a source or destination. For example, for LayerTypeIPv4, an Endpoint contains the IP address bytes for a v4 IP packet. A Flow can be broken into Endpoints, and Endpoints can be combined into Flows: Both Endpoint and Flow objects can be used as map keys, and the equality operator can compare them, so you can easily group together all packets based on endpoint criteria: For load-balancing purposes, both Flow and Endpoint have FastHash() functions, which provide quick, non-cryptographic hashes of their contents. Of particular importance is the fact that Flow FastHash() is symmetric: A->B will have the same hash as B->A. An example usage could be: This allows us to split up a packet stream while still making sure that each stream sees all packets for a flow (and its bidirectional opposite). If your network has some strange encapsulation, you can implement your own decoder. In this example, we handle Ethernet packets which are encapsulated in a 4-byte header. See the docs for Decoder and PacketBuilder for more details on how coding decoders works, or look at RegisterLayerType and RegisterEndpointType to see how to add layer/endpoint types to gopacket. TLDR: DecodingLayerParser takes about 10% of the time as NewPacket to decode packet data, but only for known packet stacks. Basic decoding using gopacket.NewPacket or PacketSource.Packets is somewhat slow due to its need to allocate a new packet and every respective layer. It's very versatile and can handle all known layer types, but sometimes you really only care about a specific set of layers regardless, so that versatility is wasted. DecodingLayerParser avoids memory allocation altogether by decoding packet layers directly into preallocated objects, which you can then reference to get the packet's information. A quick example: The important thing to note here is that the parser is modifying the passed in layers (eth, ip4, ip6, tcp) instead of allocating new ones, thus greatly speeding up the decoding process. It's even branching based on layer type... it'll handle an (eth, ip4, tcp) or (eth, ip6, tcp) stack. However, it won't handle any other type... since no other decoders were passed in, an (eth, ip4, udp) stack will stop decoding after ip4, and only pass back [LayerTypeEthernet, LayerTypeIPv4] through the 'decoded' slice (along with an error saying it can't decode a UDP packet). Unfortunately, not all layers can be used by DecodingLayerParser... only those implementing the DecodingLayer interface are usable. Also, it's possible to create DecodingLayers that are not themselves Layers... see layers.IPv6ExtensionSkipper for an example of this. By default, DecodingLayerParser uses native map to store and search for a layer to decode. Though being versatile, in some cases this solution may be not so optimal. For example, if you have only few layers faster operations may be provided by sparse array indexing or linear array scan. To accomodate these scenarios, DecodingLayerContainer interface is introduced along with its implementations: DecodingLayerSparse, DecodingLayerArray and DecodingLayerMap. You can specify a container implementation to DecodingLayerParser with SetDecodingLayerContainer method. Example: To skip one level of indirection (though sacrificing some capabilities) you may also use DecodingLayerContainer as a decoding tool as it is. In this case you have to handle unknown layer types and layer panics by yourself. Example: DecodingLayerSparse is the fastest but most effective when LayerType values that layers in use can decode are not large because otherwise that would lead to bigger memory footprint. DecodingLayerArray is very compact and primarily usable if the number of decoding layers is not big (up to ~10-15, but please do your own benchmarks). DecodingLayerMap is the most versatile one and used by DecodingLayerParser by default. Please refer to tests and benchmarks in layers subpackage to further examine usage examples and performance measurements. You may also choose to implement your own DecodingLayerContainer if you want to make use of your own internal packet decoding logic. As well as offering the ability to decode packet data, gopacket will allow you to create packets from scratch, as well. A number of gopacket layers implement the SerializableLayer interface; these layers can be serialized to a []byte in the following manner: SerializeTo PREPENDS the given layer onto the SerializeBuffer, and they treat the current buffer's Bytes() slice as the payload of the serializing layer. Therefore, you can serialize an entire packet by serializing a set of layers in reverse order (Payload, then TCP, then IP, then Ethernet, for example). The SerializeBuffer's SerializeLayers function is a helper that does exactly that. To generate a (empty and useless, because no fields are set) Ethernet(IPv4(TCP(Payload))) packet, for example, you can run: If you use gopacket, you'll almost definitely want to make sure gopacket/layers is imported, since when imported it sets all the LayerType variables and fills in a lot of interesting variables/maps (DecodersByLayerName, etc). Therefore, it's recommended that even if you don't use any layers functions directly, you still import with:

Package congomap provides a concurrency-safe Go Map. This repository serves as a set of examples for making maps that are accessible in concurrent Go software. The types can be used as a library, each with their own performance characteristics, but I wrote it to determine which method produced the most readable code, and the most performant code. This library exposes the Congomap interface, and a few concrete types that adhere to that interface. All provided concrete types are available here because they have individual performance characteristics, where one concrete type may be more appropriate for a desired use case than one of the other types. WARNING: To prevent resource leakage, always call the Congomap's Close method after it is no longer needed. - Lazy Loading with Lookup callback All Congomaps support providing a custom Lookup callback function that the Congomap invokes to lookup the value of a key not yet present in the data store when the LoadStore method is invoked. This is useful when you want to load a value for a key from the Congomap, but perhaps the value has yet to be stored. Congomap then invokes the Lookup function with the key string as its argument, then stores the return value of the Lookup function in the Congomap for future requests. If the Lookup instead returns an error, no value is stored in the Congomap. See the example provided in godoc for more information on taking advantage of this feature. - Expiration Notification with Reaper callback All Congomaps support providing a custom Reaper callback function that the Congomap invokes when a value is expired from the data store, either by exceeding its TTL or by being replaced with another value during a Store operation. This is useful when your program needs to perform some sort of cleanup on the feature that was in the Congomap. Note that when the Congomap is closed, if a Reaper callback function is provided, it will be called repeatedly with each value that was stored in the Congomap. See the example provided in godoc for more information on taking advantage of this feature. - Default entry Time-to-Live (TTL) All Congomaps support providing a default time-to-live for values stored in the Congomap. If *not* provided, items stored in the Congomap will remain there until expired by being superceded by the Store operation. If a default TTL *is* provided, then items will expire and must be refetched. Note that whether or not a custom TTL is provided when creating a Congomap, if the Store method or customized Lookup callback function ever return a pointer to an ExpringValue object, the default TTL is ignored and the item will expire when the ExpiringValue's Expiry passes. If the ExpiringValue's Expiry is the zero time, then this data item will not auto-expire from the data store. See the example provided in godoc for more information on taking advantage of this feature. - NewChannelMap A channel map is modeled after the Go way of sharing memory: by communicating over channels. Reads and writes are serialized by a Go routine processing anonymous functions. While not as fast as the other methods for low-concurrency loads, this particular map outpaces the competition in high-concurrency tests. - NewSyncAtomicMap A sync atomic map uses the algorithm suggested in the documentation for `sync/atomic`. It is designed for when a map is read many, many more times than it is written. Performance also depends on the number of the keys in the map. The more keys in the map, the more expensive Store and LoadStore will be. - NewSyncMutexMap A sync mutex map uses simple read/write mutex primitives from the `sync` package. This results in a highly performant way of synchronizing reads and writes to the map. This map is one of the fastest for low-concurrency tests, but takes second or even third place for high-concurrency benchmarks. - NewTwoLevelMap A two-level map implements the map using a top-level lock that guarantees mutual exclusion on adding or removing keys to the map, and individual locks for each key, guaranteeing mutual exclusion of tasks attempting to mutate or read the value associated with a given key. The initial motivation of creating this library was to calculate the relative performance of these approaches to access to a concurrent map. Here's a sample run on my Mac using Go 1.6.3. For these benchmarks, each Congomap is pre-loaded with 2500 key-value pairs, and each competing go routine must make 1000 mutations to the data store. High concurrency benchmarks just over 1000 competing go routines all making changes to a single Congomap object, whereas low concurrency refers to just over 10 go routines all making 1000 changes to a single Congomap object. Fast lookups means the Lookup function immediately responds. Slow lookups means the Lookup function slept 100 ± 50 ms before returning.

Extensible Go library for creating fast, SSR-first frontend avoiding vanilla templating downsides. Creating asynchronous and dynamic layout parts is a complex problem for larger projects using `html/template`. Library tries to simplify this process. Let's go straight into a simple example. Then, we will dig into details, step by step, how it works. Kyoto provides a simple net/http handlers and function wrappers to handle pages rendering and serving. See functions inside of nethttp.go file for details and advanced usage. Example: Kyoto provides a way to define components. It's a very common approach for modern libraries to manage frontend parts. In kyoto each component is a context receiver, which returns it's state. Each component becomes a part of the page or top-level component, which executes component asynchronously and gets a state future object. In that way your components are executing in a non-blocking way. Pages are just top-level components, where you can configure rendering and page related stuff. Example: As an option, you can wrap component with another function to accept additional paramenters from top-level page/component. Example: Kyoto provides a context, which holds common objects like http.ResponseWriter, *http.Request, etc. See kyoto.Context for details. Example: Kyoto provides a set of parameters and functions to provide a comfortable template building process. You can configure template building parameters with kyoto.TemplateConf configuration. See template.go for available functions and kyoto.TemplateConfiguration for configuration details. Example: Kyoto provides a way to simplify building dynamic UIs. For this purpose it has a feature named actions. Logic is pretty simple. Client calls an action (sends a request to the server). Action is executing on server side and server is sending updated component markup to the client which will be morphed into DOM. That's it. To use actions, you need to go through a few steps. You'll need to include a client into page (JS functions for communication) and register an actions handler for a needed component. Let's start from including a client. Then, let's register an actions handler for a needed component. That's all! Now we ready to use actions to provide a dynamic UI. Example: In this example you can see provided modifications to the quick start example. First, we've added a state and name into our components' markup. In this way we are saving our components' state between actions and find a component root. Unfortunately, we have to manually provide a component name for now, we haven't found a way to provide it dynamically. Second, we've added a reload button with onclick function call. We're using a function Action provided by a client. Action triggering will be described in details later. Third, we've added an action handler inside of our component. This handler will be executed when a client calls an action with a corresponding name. It's highly recommended to keep components' state as small as possible. It will be transmitted on each action call. Kyoto have multiple ways to trigger actions. Now we will check them one by one. This is the simplest way to trigger an action. It's just a function call with a referer (usually 'this', f.e. button) as a first argument (used to determine root), action name as a second argument and arguments as a rest. Arguments must to be JSON serializable. It's possible to trigger an action of another component. If you want to call an action of parent component, use $ prefix in action name. If you want to call an action of component by id, use <id:action> as an action name. This is a specific action which is triggered when a form is submitted. Usually called in onsubmit="..." attribute of a form. You'll need to implement 'Submit' action to handle this trigger. This is a special HTML attribute which will trigger an action on page load. This may be useful for components' lazy loading. With this special HTML attributes you can trigger an action with interval. Useful for components that must to be updated over time (f.e. charts, stats, etc). You can use this trigger with ssa:poll and ssa:poll.interval HTML attributes. This one attribute allows you to trigger an action when an element is visible on the screen. May be useful for lazy loading. Kyoto provides a way to control action flow. For now, it's possible to control display style on component call and push multiple UI updates to the client during a single action. Because kyoto makes a roundtrip to the server every time an action is triggered on the page, there are cases where the page may not react immediately to a user event (like a click). That's why the library provides a way to easily control display attributes on action call. You can use this HTML attribute to control display during action call. At the end of an action the layout will be restored. A small note. Don't forget to set a default display for loading elements like spinners and loaders. You can push multiple component UI updates during a single action call. Just call kyoto.ActionFlush(ctx, state) to initiate an update. Kyoto provides a way to control action rendering. Now there is at least 2 rendering options after an action call: morph (default) and replace. Morph will try to morph received markup to the current one with morphdom library. In case of an error, or explicit "replace" mode, markup will be replaced with x.outerHTML = '...'.

Package gopacket provides packet decoding for the Go language. gopacket contains many sub-packages with additional functionality you may find useful, including: Also, if you're looking to dive right into code, see the examples subdirectory for numerous simple binaries built using gopacket libraries. Minimum go version required is 1.5 except for pcapgo/EthernetHandle, afpacket, and bsdbpf which need at least 1.7 due to x/sys/unix dependencies. gopacket takes in packet data as a []byte and decodes it into a packet with a non-zero number of "layers". Each layer corresponds to a protocol within the bytes. Once a packet has been decoded, the layers of the packet can be requested from the packet. Packets can be decoded from a number of starting points. Many of our base types implement Decoder, which allow us to decode packets for which we don't have full data. Most of the time, you won't just have a []byte of packet data lying around. Instead, you'll want to read packets in from somewhere (file, interface, etc) and process them. To do that, you'll want to build a PacketSource. First, you'll need to construct an object that implements the PacketDataSource interface. There are implementations of this interface bundled with gopacket in the gopacket/pcap and gopacket/pfring subpackages... see their documentation for more information on their usage. Once you have a PacketDataSource, you can pass it into NewPacketSource, along with a Decoder of your choice, to create a PacketSource. Once you have a PacketSource, you can read packets from it in multiple ways. See the docs for PacketSource for more details. The easiest method is the Packets function, which returns a channel, then asynchronously writes new packets into that channel, closing the channel if the packetSource hits an end-of-file. You can change the decoding options of the packetSource by setting fields in packetSource.DecodeOptions... see the following sections for more details. gopacket optionally decodes packet data lazily, meaning it only decodes a packet layer when it needs to handle a function call. Lazily-decoded packets are not concurrency-safe. Since layers have not all been decoded, each call to Layer() or Layers() has the potential to mutate the packet in order to decode the next layer. If a packet is used in multiple goroutines concurrently, don't use gopacket.Lazy. Then gopacket will decode the packet fully, and all future function calls won't mutate the object. By default, gopacket will copy the slice passed to NewPacket and store the copy within the packet, so future mutations to the bytes underlying the slice don't affect the packet and its layers. If you can guarantee that the underlying slice bytes won't be changed, you can use NoCopy to tell gopacket.NewPacket, and it'll use the passed-in slice itself. The fastest method of decoding is to use both Lazy and NoCopy, but note from the many caveats above that for some implementations either or both may be dangerous. During decoding, certain layers are stored in the packet as well-known layer types. For example, IPv4 and IPv6 are both considered NetworkLayer layers, while TCP and UDP are both TransportLayer layers. We support 4 layers, corresponding to the 4 layers of the TCP/IP layering scheme (roughly anagalous to layers 2, 3, 4, and 7 of the OSI model). To access these, you can use the packet.LinkLayer, packet.NetworkLayer, packet.TransportLayer, and packet.ApplicationLayer functions. Each of these functions returns a corresponding interface (gopacket.{Link,Network,Transport,Application}Layer). The first three provide methods for getting src/dst addresses for that particular layer, while the final layer provides a Payload function to get payload data. This is helpful, for example, to get payloads for all packets regardless of their underlying data type: A particularly useful layer is ErrorLayer, which is set whenever there's an error parsing part of the packet. Note that we don't return an error from NewPacket because we may have decoded a number of layers successfully before running into our erroneous layer. You may still be able to get your Ethernet and IPv4 layers correctly, even if your TCP layer is malformed. gopacket has two useful objects, Flow and Endpoint, for communicating in a protocol independent manner the fact that a packet is coming from A and going to B. The general layer types LinkLayer, NetworkLayer, and TransportLayer all provide methods for extracting their flow information, without worrying about the type of the underlying Layer. A Flow is a simple object made up of a set of two Endpoints, one source and one destination. It details the sender and receiver of the Layer of the Packet. An Endpoint is a hashable representation of a source or destination. For example, for LayerTypeIPv4, an Endpoint contains the IP address bytes for a v4 IP packet. A Flow can be broken into Endpoints, and Endpoints can be combined into Flows: Both Endpoint and Flow objects can be used as map keys, and the equality operator can compare them, so you can easily group together all packets based on endpoint criteria: For load-balancing purposes, both Flow and Endpoint have FastHash() functions, which provide quick, non-cryptographic hashes of their contents. Of particular importance is the fact that Flow FastHash() is symmetric: A->B will have the same hash as B->A. An example usage could be: This allows us to split up a packet stream while still making sure that each stream sees all packets for a flow (and its bidirectional opposite). If your network has some strange encapsulation, you can implement your own decoder. In this example, we handle Ethernet packets which are encapsulated in a 4-byte header. See the docs for Decoder and PacketBuilder for more details on how coding decoders works, or look at RegisterLayerType and RegisterEndpointType to see how to add layer/endpoint types to gopacket. TLDR: DecodingLayerParser takes about 10% of the time as NewPacket to decode packet data, but only for known packet stacks. Basic decoding using gopacket.NewPacket or PacketSource.Packets is somewhat slow due to its need to allocate a new packet and every respective layer. It's very versatile and can handle all known layer types, but sometimes you really only care about a specific set of layers regardless, so that versatility is wasted. DecodingLayerParser avoids memory allocation altogether by decoding packet layers directly into preallocated objects, which you can then reference to get the packet's information. A quick example: The important thing to note here is that the parser is modifying the passed in layers (eth, ip4, ip6, tcp) instead of allocating new ones, thus greatly speeding up the decoding process. It's even branching based on layer type... it'll handle an (eth, ip4, tcp) or (eth, ip6, tcp) stack. However, it won't handle any other type... since no other decoders were passed in, an (eth, ip4, udp) stack will stop decoding after ip4, and only pass back [LayerTypeEthernet, LayerTypeIPv4] through the 'decoded' slice (along with an error saying it can't decode a UDP packet). Unfortunately, not all layers can be used by DecodingLayerParser... only those implementing the DecodingLayer interface are usable. Also, it's possible to create DecodingLayers that are not themselves Layers... see layers.IPv6ExtensionSkipper for an example of this. By default, DecodingLayerParser uses native map to store and search for a layer to decode. Though being versatile, in some cases this solution may be not so optimal. For example, if you have only few layers faster operations may be provided by sparse array indexing or linear array scan. To accomodate these scenarios, DecodingLayerContainer interface is introduced along with its implementations: DecodingLayerSparse, DecodingLayerArray and DecodingLayerMap. You can specify a container implementation to DecodingLayerParser with SetDecodingLayerContainer method. Example: To skip one level of indirection (though sacrificing some capabilities) you may also use DecodingLayerContainer as a decoding tool as it is. In this case you have to handle unknown layer types and layer panics by yourself. Example: DecodingLayerSparse is the fastest but most effective when LayerType values that layers in use can decode are not large because otherwise that would lead to bigger memory footprint. DecodingLayerArray is very compact and primarily usable if the number of decoding layers is not big (up to ~10-15, but please do your own benchmarks). DecodingLayerMap is the most versatile one and used by DecodingLayerParser by default. Please refer to tests and benchmarks in layers subpackage to further examine usage examples and performance measurements. You may also choose to implement your own DecodingLayerContainer if you want to make use of your own internal packet decoding logic. As well as offering the ability to decode packet data, gopacket will allow you to create packets from scratch, as well. A number of gopacket layers implement the SerializableLayer interface; these layers can be serialized to a []byte in the following manner: SerializeTo PREPENDS the given layer onto the SerializeBuffer, and they treat the current buffer's Bytes() slice as the payload of the serializing layer. Therefore, you can serialize an entire packet by serializing a set of layers in reverse order (Payload, then TCP, then IP, then Ethernet, for example). The SerializeBuffer's SerializeLayers function is a helper that does exactly that. To generate a (empty and useless, because no fields are set) Ethernet(IPv4(TCP(Payload))) packet, for example, you can run: If you use gopacket, you'll almost definitely want to make sure gopacket/layers is imported, since when imported it sets all the LayerType variables and fills in a lot of interesting variables/maps (DecodersByLayerName, etc). Therefore, it's recommended that even if you don't use any layers functions directly, you still import with:

Package lingua accurately detects the natural language of written text, be it long or short. Its task is simple: It tells you which language some text is written in. This is very useful as a preprocessing step for linguistic data in natural language processing applications such as text classification and spell checking. Other use cases, for instance, might include routing e-mails to the right geographically located customer service department, based on the e-mails' languages. Language detection is often done as part of large machine learning frameworks or natural language processing applications. In cases where you don't need the full-fledged functionality of those systems or don't want to learn the ropes of those, a small flexible library comes in handy. So far, the only other comprehensive open source library in the Go ecosystem for this task is Whatlanggo (https://github.com/abadojack/whatlanggo). Unfortunately, it has two major drawbacks: 1. Detection only works with quite lengthy text fragments. For very short text snippets such as Twitter messages, it does not provide adequate results. 2. The more languages take part in the decision process, the less accurate are the detection results. Lingua aims at eliminating these problems. It nearly does not need any configuration and yields pretty accurate results on both long and short text, even on single words and phrases. It draws on both rule-based and statistical methods but does not use any dictionaries of words. It does not need a connection to any external API or service either. Once the library has been downloaded, it can be used completely offline. Compared to other language detection libraries, Lingua's focus is on quality over quantity, that is, getting detection right for a small set of languages first before adding new ones. Currently, 75 languages are supported. They are listed as variants of type Language. Lingua is able to report accuracy statistics for some bundled test data available for each supported language. The test data for each language is split into three parts: 1. a list of single words with a minimum length of 5 characters 2. a list of word pairs with a minimum length of 10 characters 3. a list of complete grammatical sentences of various lengths Both the language models and the test data have been created from separate documents of the Wortschatz corpora (https://wortschatz.uni-leipzig.de) offered by Leipzig University, Germany. Data crawled from various news websites have been used for training, each corpus comprising one million sentences. For testing, corpora made of arbitrarily chosen websites have been used, each comprising ten thousand sentences. From each test corpus, a random unsorted subset of 1000 single words, 1000 word pairs and 1000 sentences has been extracted, respectively. Given the generated test data, I have compared the detection results of Lingua, and Whatlanggo running over the data of Lingua's supported 75 languages. Additionally, I have added Google's CLD3 (https://github.com/google/cld3/) to the comparison with the help of the gocld3 bindings (https://github.com/jmhodges/gocld3). Languages that are not supported by CLD3 or Whatlanggo are simply ignored during the detection process. Lingua clearly outperforms its contenders. Every language detector uses a probabilistic n-gram (https://en.wikipedia.org/wiki/N-gram) model trained on the character distribution in some training corpus. Most libraries only use n-grams of size 3 (trigrams) which is satisfactory for detecting the language of longer text fragments consisting of multiple sentences. For short phrases or single words, however, trigrams are not enough. The shorter the input text is, the less n-grams are available. The probabilities estimated from such few n-grams are not reliable. This is why Lingua makes use of n-grams of sizes 1 up to 5 which results in much more accurate prediction of the correct language. A second important difference is that Lingua does not only use such a statistical model, but also a rule-based engine. This engine first determines the alphabet of the input text and searches for characters which are unique in one or more languages. If exactly one language can be reliably chosen this way, the statistical model is not necessary anymore. In any case, the rule-based engine filters out languages that do not satisfy the conditions of the input text. Only then, in a second step, the probabilistic n-gram model is taken into consideration. This makes sense because loading less language models means less memory consumption and better runtime performance. In general, it is always a good idea to restrict the set of languages to be considered in the classification process using the respective api methods. If you know beforehand that certain languages are never to occur in an input text, do not let those take part in the classifcation process. The filtering mechanism of the rule-based engine is quite good, however, filtering based on your own knowledge of the input text is always preferable. There might be classification tasks where you know beforehand that your language data is definitely not written in Latin, for instance. The detection accuracy can become better in such cases if you exclude certain languages from the decision process or just explicitly include relevant languages. Knowing about the most likely language is nice but how reliable is the computed likelihood? And how less likely are the other examined languages in comparison to the most likely one? In the example below, a slice of ConfidenceValue is returned containing those languages which the calling instance of LanguageDetector has been built from. The entries are sorted by their confidence value in descending order. Each value is a probability between 0.0 and 1.0. The probabilities of all languages will sum to 1.0. If the language is unambiguously identified by the rule engine, the value 1.0 will always be returned for this language. The other languages will receive a value of 0.0. By default, Lingua uses lazy-loading to load only those language models on demand which are considered relevant by the rule-based filter engine. For web services, for instance, it is rather beneficial to preload all language models into memory to avoid unexpected latency while waiting for the service response. If you want to enable the eager-loading mode, you can do it as seen below. Multiple instances of LanguageDetector share the same language models in memory which are accessed asynchronously by the instances. By default, Lingua returns the most likely language for a given input text. However, there are certain words that are spelled the same in more than one language. The word `prologue`, for instance, is both a valid English and French word. Lingua would output either English or French which might be wrong in the given context. For cases like that, it is possible to specify a minimum relative distance that the logarithmized and summed up probabilities for each possible language have to satisfy. It can be stated as seen below. Be aware that the distance between the language probabilities is dependent on the length of the input text. The longer the input text, the larger the distance between the languages. So if you want to classify very short text phrases, do not set the minimum relative distance too high. Otherwise Unknown will be returned most of the time as in the example below. This is the return value for cases where language detection is not reliably possible.

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package log15 provides an opinionated, simple toolkit for best-practice logging that is both human and machine readable. It is modeled after the standard library's io and net/http packages. This package enforces you to only log key/value pairs. Keys must be strings. Values may be any type that you like. The default output format is logfmt, but you may also choose to use JSON instead if that suits you. Here's how you log: This will output a line that looks like: To get started, you'll want to import the library: Now you're ready to start logging: Because recording a human-meaningful message is common and good practice, the first argument to every logging method is the value to the *implicit* key 'msg'. Additionally, the level you choose for a message will be automatically added with the key 'lvl', and so will the current timestamp with key 't'. You may supply any additional context as a set of key/value pairs to the logging function. log15 allows you to favor terseness, ordering, and speed over safety. This is a reasonable tradeoff for logging functions. You don't need to explicitly state keys/values, log15 understands that they alternate in the variadic argument list: If you really do favor your type-safety, you may choose to pass a log.Ctx instead: Frequently, you want to add context to a logger so that you can track actions associated with it. An http request is a good example. You can easily create new loggers that have context that is automatically included with each log line: This will output a log line that includes the path context that is attached to the logger: The Handler interface defines where log lines are printed to and how they are formated. Handler is a single interface that is inspired by net/http's handler interface: Handlers can filter records, format them, or dispatch to multiple other Handlers. This package implements a number of Handlers for common logging patterns that are easily composed to create flexible, custom logging structures. Here's an example handler that prints logfmt output to Stdout: Here's an example handler that defers to two other handlers. One handler only prints records from the rpc package in logfmt to standard out. The other prints records at Error level or above in JSON formatted output to the file /var/log/service.json This package implements three Handlers that add debugging information to the context, CallerFileHandler, CallerFuncHandler and CallerStackHandler. Here's an example that adds the source file and line number of each logging call to the context. This will output a line that looks like: Here's an example that logs the call stack rather than just the call site. This will output a line that looks like: The "%+v" format instructs the handler to include the path of the source file relative to the compile time GOPATH. The github.com/go-stack/stack package documents the full list of formatting verbs and modifiers available. The Handler interface is so simple that it's also trivial to write your own. Let's create an example handler which tries to write to one handler, but if that fails it falls back to writing to another handler and includes the error that it encountered when trying to write to the primary. This might be useful when trying to log over a network socket, but if that fails you want to log those records to a file on disk. This pattern is so useful that a generic version that handles an arbitrary number of Handlers is included as part of this library called FailoverHandler. Sometimes, you want to log values that are extremely expensive to compute, but you don't want to pay the price of computing them if you haven't turned up your logging level to a high level of detail. This package provides a simple type to annotate a logging operation that you want to be evaluated lazily, just when it is about to be logged, so that it would not be evaluated if an upstream Handler filters it out. Just wrap any function which takes no arguments with the log.Lazy type. For example: If this message is not logged for any reason (like logging at the Error level), then factorRSAKey is never evaluated. The same log.Lazy mechanism can be used to attach context to a logger which you want to be evaluated when the message is logged, but not when the logger is created. For example, let's imagine a game where you have Player objects: You always want to log a player's name and whether they're alive or dead, so when you create the player object, you might do: Only now, even after a player has died, the logger will still report they are alive because the logging context is evaluated when the logger was created. By using the Lazy wrapper, we can defer the evaluation of whether the player is alive or not to each log message, so that the log records will reflect the player's current state no matter when the log message is written: If log15 detects that stdout is a terminal, it will configure the default handler for it (which is log.StdoutHandler) to use TerminalFormat. This format logs records nicely for your terminal, including color-coded output based on log level. Becasuse log15 allows you to step around the type system, there are a few ways you can specify invalid arguments to the logging functions. You could, for example, wrap something that is not a zero-argument function with log.Lazy or pass a context key that is not a string. Since logging libraries are typically the mechanism by which errors are reported, it would be onerous for the logging functions to return errors. Instead, log15 handles errors by making these guarantees to you: - Any log record containing an error will still be printed with the error explained to you as part of the log record. - Any log record containing an error will include the context key LOG15_ERROR, enabling you to easily (and if you like, automatically) detect if any of your logging calls are passing bad values. Understanding this, you might wonder why the Handler interface can return an error value in its Log method. Handlers are encouraged to return errors only if they fail to write their log records out to an external source like if the syslog daemon is not responding. This allows the construction of useful handlers which cope with those failures like the FailoverHandler. log15 is intended to be useful for library authors as a way to provide configurable logging to users of their library. Best practice for use in a library is to always disable all output for your logger by default and to provide a public Logger instance that consumers of your library can configure. Like so: Users of your library may then enable it if they like: The ability to attach context to a logger is a powerful one. Where should you do it and why? I favor embedding a Logger directly into any persistent object in my application and adding unique, tracing context keys to it. For instance, imagine I am writing a web browser: When a new tab is created, I assign a logger to it with the url of the tab as context so it can easily be traced through the logs. Now, whenever we perform any operation with the tab, we'll log with its embedded logger and it will include the tab title automatically: There's only one problem. What if the tab url changes? We could use log.Lazy to make sure the current url is always written, but that would mean that we couldn't trace a tab's full lifetime through our logs after the user navigate to a new URL. Instead, think about what values to attach to your loggers the same way you think about what to use as a key in a SQL database schema. If it's possible to use a natural key that is unique for the lifetime of the object, do so. But otherwise, log15's ext package has a handy RandId function to let you generate what you might call "surrogate keys" They're just random hex identifiers to use for tracing. Back to our Tab example, we would prefer to set up our Logger like so: Now we'll have a unique traceable identifier even across loading new urls, but we'll still be able to see the tab's current url in the log messages. For all Handler functions which can return an error, there is a version of that function which will return no error but panics on failure. They are all available on the Must object. For example: All of the following excellent projects inspired the design of this library: code.google.com/p/log4go github.com/op/go-logging github.com/technoweenie/grohl github.com/Sirupsen/logrus github.com/kr/logfmt github.com/spacemonkeygo/spacelog golang's stdlib, notably io and net/http https://xkcd.com/927/

Package gopacket provides packet decoding for the Go language. gopacket contains many sub-packages with additional functionality you may find useful, including: Also, if you're looking to dive right into code, see the examples subdirectory for numerous simple binaries built using gopacket libraries. Minimum go version required is 1.5 except for pcapgo/EthernetHandle, afpacket, and bsdbpf which need at least 1.7 due to x/sys/unix dependencies. gopacket takes in packet data as a []byte and decodes it into a packet with a non-zero number of "layers". Each layer corresponds to a protocol within the bytes. Once a packet has been decoded, the layers of the packet can be requested from the packet. Packets can be decoded from a number of starting points. Many of our base types implement Decoder, which allow us to decode packets for which we don't have full data. Most of the time, you won't just have a []byte of packet data lying around. Instead, you'll want to read packets in from somewhere (file, interface, etc) and process them. To do that, you'll want to build a PacketSource. First, you'll need to construct an object that implements the PacketDataSource interface. There are implementations of this interface bundled with gopacket in the gopacket/pcap and gopacket/pfring subpackages... see their documentation for more information on their usage. Once you have a PacketDataSource, you can pass it into NewPacketSource, along with a Decoder of your choice, to create a PacketSource. Once you have a PacketSource, you can read packets from it in multiple ways. See the docs for PacketSource for more details. The easiest method is the Packets function, which returns a channel, then asynchronously writes new packets into that channel, closing the channel if the packetSource hits an end-of-file. You can change the decoding options of the packetSource by setting fields in packetSource.DecodeOptions... see the following sections for more details. gopacket optionally decodes packet data lazily, meaning it only decodes a packet layer when it needs to handle a function call. Lazily-decoded packets are not concurrency-safe. Since layers have not all been decoded, each call to Layer() or Layers() has the potential to mutate the packet in order to decode the next layer. If a packet is used in multiple goroutines concurrently, don't use gopacket.Lazy. Then gopacket will decode the packet fully, and all future function calls won't mutate the object. By default, gopacket will copy the slice passed to NewPacket and store the copy within the packet, so future mutations to the bytes underlying the slice don't affect the packet and its layers. If you can guarantee that the underlying slice bytes won't be changed, you can use NoCopy to tell gopacket.NewPacket, and it'll use the passed-in slice itself. The fastest method of decoding is to use both Lazy and NoCopy, but note from the many caveats above that for some implementations either or both may be dangerous. During decoding, certain layers are stored in the packet as well-known layer types. For example, IPv4 and IPv6 are both considered NetworkLayer layers, while TCP and UDP are both TransportLayer layers. We support 4 layers, corresponding to the 4 layers of the TCP/IP layering scheme (roughly anagalous to layers 2, 3, 4, and 7 of the OSI model). To access these, you can use the packet.LinkLayer, packet.NetworkLayer, packet.TransportLayer, and packet.ApplicationLayer functions. Each of these functions returns a corresponding interface (gopacket.{Link,Network,Transport,Application}Layer). The first three provide methods for getting src/dst addresses for that particular layer, while the final layer provides a Payload function to get payload data. This is helpful, for example, to get payloads for all packets regardless of their underlying data type: A particularly useful layer is ErrorLayer, which is set whenever there's an error parsing part of the packet. Note that we don't return an error from NewPacket because we may have decoded a number of layers successfully before running into our erroneous layer. You may still be able to get your Ethernet and IPv4 layers correctly, even if your TCP layer is malformed. gopacket has two useful objects, Flow and Endpoint, for communicating in a protocol independent manner the fact that a packet is coming from A and going to B. The general layer types LinkLayer, NetworkLayer, and TransportLayer all provide methods for extracting their flow information, without worrying about the type of the underlying Layer. A Flow is a simple object made up of a set of two Endpoints, one source and one destination. It details the sender and receiver of the Layer of the Packet. An Endpoint is a hashable representation of a source or destination. For example, for LayerTypeIPv4, an Endpoint contains the IP address bytes for a v4 IP packet. A Flow can be broken into Endpoints, and Endpoints can be combined into Flows: Both Endpoint and Flow objects can be used as map keys, and the equality operator can compare them, so you can easily group together all packets based on endpoint criteria: For load-balancing purposes, both Flow and Endpoint have FastHash() functions, which provide quick, non-cryptographic hashes of their contents. Of particular importance is the fact that Flow FastHash() is symmetric: A->B will have the same hash as B->A. An example usage could be: This allows us to split up a packet stream while still making sure that each stream sees all packets for a flow (and its bidirectional opposite). If your network has some strange encapsulation, you can implement your own decoder. In this example, we handle Ethernet packets which are encapsulated in a 4-byte header. See the docs for Decoder and PacketBuilder for more details on how coding decoders works, or look at RegisterLayerType and RegisterEndpointType to see how to add layer/endpoint types to gopacket. TLDR: DecodingLayerParser takes about 10% of the time as NewPacket to decode packet data, but only for known packet stacks. Basic decoding using gopacket.NewPacket or PacketSource.Packets is somewhat slow due to its need to allocate a new packet and every respective layer. It's very versatile and can handle all known layer types, but sometimes you really only care about a specific set of layers regardless, so that versatility is wasted. DecodingLayerParser avoids memory allocation altogether by decoding packet layers directly into preallocated objects, which you can then reference to get the packet's information. A quick example: The important thing to note here is that the parser is modifying the passed in layers (eth, ip4, ip6, tcp) instead of allocating new ones, thus greatly speeding up the decoding process. It's even branching based on layer type... it'll handle an (eth, ip4, tcp) or (eth, ip6, tcp) stack. However, it won't handle any other type... since no other decoders were passed in, an (eth, ip4, udp) stack will stop decoding after ip4, and only pass back [LayerTypeEthernet, LayerTypeIPv4] through the 'decoded' slice (along with an error saying it can't decode a UDP packet). Unfortunately, not all layers can be used by DecodingLayerParser... only those implementing the DecodingLayer interface are usable. Also, it's possible to create DecodingLayers that are not themselves Layers... see layers.IPv6ExtensionSkipper for an example of this. By default, DecodingLayerParser uses native map to store and search for a layer to decode. Though being versatile, in some cases this solution may be not so optimal. For example, if you have only few layers faster operations may be provided by sparse array indexing or linear array scan. To accomodate these scenarios, DecodingLayerContainer interface is introduced along with its implementations: DecodingLayerSparse, DecodingLayerArray and DecodingLayerMap. You can specify a container implementation to DecodingLayerParser with SetDecodingLayerContainer method. Example: To skip one level of indirection (though sacrificing some capabilities) you may also use DecodingLayerContainer as a decoding tool as it is. In this case you have to handle unknown layer types and layer panics by yourself. Example: DecodingLayerSparse is the fastest but most effective when LayerType values that layers in use can decode are not large because otherwise that would lead to bigger memory footprint. DecodingLayerArray is very compact and primarily usable if the number of decoding layers is not big (up to ~10-15, but please do your own benchmarks). DecodingLayerMap is the most versatile one and used by DecodingLayerParser by default. Please refer to tests and benchmarks in layers subpackage to further examine usage examples and performance measurements. You may also choose to implement your own DecodingLayerContainer if you want to make use of your own internal packet decoding logic. As well as offering the ability to decode packet data, gopacket will allow you to create packets from scratch, as well. A number of gopacket layers implement the SerializableLayer interface; these layers can be serialized to a []byte in the following manner: SerializeTo PREPENDS the given layer onto the SerializeBuffer, and they treat the current buffer's Bytes() slice as the payload of the serializing layer. Therefore, you can serialize an entire packet by serializing a set of layers in reverse order (Payload, then TCP, then IP, then Ethernet, for example). The SerializeBuffer's SerializeLayers function is a helper that does exactly that. To generate a (empty and useless, because no fields are set) Ethernet(IPv4(TCP(Payload))) packet, for example, you can run: If you use gopacket, you'll almost definitely want to make sure gopacket/layers is imported, since when imported it sets all the LayerType variables and fills in a lot of interesting variables/maps (DecodersByLayerName, etc). Therefore, it's recommended that even if you don't use any layers functions directly, you still import with: