Eval

Packages in the Plugin directory contain plugins for [goa v2](https://godoc.org/goa.design/goa). Plugins can extend the goa DSL, generate new artifacts and modify the output of existing generators. There are currently two plugins in the directory: The [goakit](https://godoc.org/goa.design/plugins/goakit) plugin generates code that integrates with the [go-kit](https://github.com/go-kit/kit) library. The [cors](https://godoc.org/goa.design/plugins/cors) plugin adds new DSL to define CORS policies. The plugin generates HTTP server code that respond to CORS requests in compliance with the policies defined in the design. Writing a plugin consists of two steps: 1. Writing the functions that gets called by the goa tool during code generation. 2. Registering the functions with the goa tool. A plugin may implement the "gen" goa command, the "example" goa command or both. In each case a plugin may register one or two functions: the first function called "Prepare" gets called prior to any code generation actually happening. The function can modify the design data structures before goa uses them to generate code. The second function called "Generate" does the actual code generation. The signature of the Generate function is: where: The function must return the entire set of generated files (even the files that the plugin does not modify). The functions must then be registered with the goa code generator tool using the "RegisterPlugin" function of the "codegen" package. This is typically done in a package "init" function, for example: The first argument of RegisterPlugin must be one of "gen" or "example" and specifies the "goa" command that triggers the call to the plugin functions. The second argument is the Prepare function if any, nil otherwise. The last argument is the code generator function if any, nil otherwise. A plugin may introduce new DSL "keywords" (typically Go package functions). The DSL functions initialize the content of a design root object (an object that implements the "eval.Root" interface), for example: The [eval](https://godoc.org/goa.design/goa/codegen/eval) package contains a number of functions that can be leveraged to implement the DSL such as error reporting functions. The plugin design root object is then given to the plugin Generate function (if there's one) which may take advantage of it to generate the code.

Package rod is a high-level driver directly based on DevTools Protocol. This example opens https://github.com/, searches for "git", and then gets the header element which gives the description for Git. Rod use https://golang.org/pkg/context to handle cancellations for IO blocking operations, most times it's timeout. Context will be recursively passed to all sub-methods. For example, methods like Page.Context(ctx) will return a clone of the page with the ctx, all the methods of the returned page will use the ctx if they have IO blocking operations. Page.Timeout or Page.WithCancel is just a shortcut for Page.Context. Of course, Browser or Element works the same way. Shows how we can further customize the browser with the launcher library. Usually you use launcher lib to set the browser's command line flags (switches). Doc for flags: https://peter.sh/experiments/chromium-command-line-switches Shows how to change the retry/polling options that is used to query elements. This is useful when you want to customize the element query retry logic. When rod doesn't have a feature that you need. You can easily call the cdp to achieve it. List of cdp API: https://github.com/go-rod/rod/tree/main/lib/proto Shows how to disable headless mode and debug. Rod provides a lot of debug options, you can set them with setter methods or use environment variables. Doc for environment variables: https://pkg.go.dev/github.com/go-rod/rod/lib/defaults We use "Must" prefixed functions to write example code. But in production you may want to use the no-prefix version of them. About why we use "Must" as the prefix, it's similar to https://golang.org/pkg/regexp/#MustCompile Shows how to share a remote object reference between two Eval. Shows how to listen for events. Shows how to intercept requests and modify both the request and the response. The entire process of hijacking one request: The --req-> and --res-> are the parts that can be modified. Show how to handle multiple results of an action. Such as when you login a page, the result can be success or wrong password. Example_search shows how to use Search to get element inside nested iframes or shadow DOMs. It works the same as https://developers.google.com/web/tools/chrome-devtools/dom#search Shows how to update the state of the current page. In this example we enable the network domain. Rod uses mouse cursor to simulate clicks, so if a button is moving because of animation, the click may not work as expected. We usually use WaitStable to make sure the target isn't changing anymore. When you want to wait for an ajax request to complete, this example will be useful.

Package radix implements all functionality needed to work with redis and all things related to it, including redis cluster, pubsub, sentinel, scanning, lua scripting, and more. For a single node redis instance use NewPool to create a connection pool. The connection pool is thread-safe and will automatically create, reuse, and recreate connections as needed: If you're using sentinel or cluster you should use NewSentinel or NewCluster (respectively) to create your client instead. Any redis command can be performed by passing a Cmd into a Client's Do method. Each Cmd should only be used once. The return from the Cmd can be captured into any appopriate go primitive type, or a slice, map, or struct, if the command returns an array. FlatCmd can also be used if you wish to use non-string arguments like integers, slices, maps, or structs, and have them automatically be flattened into a single string slice. Cmd and FlatCmd can unmarshal results into a struct. The results must be a key/value array, such as that returned by HGETALL. Exported field names will be used as keys, unless the fields have the "redis" tag: Embedded structs will inline that struct's fields into the parent's: The same rules for field naming apply when a struct is passed into FlatCmd as an argument. Cmd and FlatCmd both implement the Action interface. Other Actions include Pipeline, WithConn, and EvalScript.Cmd. Any of these may be passed into any Client's Do method. There are two ways to perform transactions in redis. The first is with the MULTI/EXEC commands, which can be done using the WithConn Action (see its example). The second is using EVAL with lua scripting, which can be done using the EvalScript Action (again, see its example). EVAL with lua scripting is recommended in almost all cases. It only requires a single round-trip, it's infinitely more flexible than MULTI/EXEC, it's simpler to code, and for complex transactions, which would otherwise need a WATCH statement with MULTI/EXEC, it's significantly faster. All the client creation functions (e.g. NewPool) take in either a ConnFunc or a ClientFunc via their options. These can be used in order to set up timeouts on connections, perform authentication commands, or even implement custom pools. All interfaces in this package were designed such that they could have custom implementations. There is no dependency within radix that demands any interface be implemented by a particular underlying type, so feel free to create your own Pools or Conns or Actions or whatever makes your life easier. Errors returned from redis can be explicitly checked for using the the resp2.Error type. Note that the errors.As function, introduced in go 1.13, should be used. Use the golang.org/x/xerrors package if you're using an older version of go. Implicit pipelining is an optimization implemented and enabled in the default Pool implementation (and therefore also used by Cluster and Sentinel) which involves delaying concurrent Cmds and FlatCmds a small amount of time and sending them to redis in a single batch, similar to manually using a Pipeline. By doing this radix significantly reduces the I/O and CPU overhead for concurrent requests. Note that only commands which do not block are eligible for implicit pipelining. See the documentation on Pool for more information about the current implementation of implicit pipelining and for how to configure or disable the feature. For a performance comparisons between Clients with and without implicit pipelining see the benchmark results in the README.md.

Package reflow implements the core data structures and (abstract) runtime for Reflow. Reflow is a system for distributed program execution. The programs are described by Flows, which are an abstract specification of the program's execution. Each Flow node can take any number of other Flows as dependent inputs and perform some (local) execution over these inputs in order to compute some output value. Reflow supports a limited form of dynamic dependencies: a Flow may evaluate to a list of values, each of which may be executed independently. This mechanism also provides parallelism. The system orchestrates Flow execution by evaluating the flow in the manner of an abstract syntax tree; see Eval for more details.