scramjet-core

Scramjet core

This is the minimal, dependency free version of scramjet used as of Scramjet version 3.0.0 as a base for scramjet and scramjet plugins.

Unless you are sure, you should be better off with using the main repo and module.

It is built upon the logic behind three well known javascript array operations - namingly map, filter and reduce. This means that if you've ever performed operations on an Array in JavaScript - you already know Scramjet like the back of your hand.

Usage

Scramjet uses functional programming to run transformations on your data streams in a fashion very similar to the well known event-stream node module. Most transformations are done by passing a transform function. You can write your function in three ways:

1. Synchronous

Example: a simple stream transform that outputs a stream of objects of the same id property and the length of the value string.

   datastream.map(
       (item) => ({id: item.id, length: item.value.length})
   )

1. Asynchronous using ES2015 async await

Example: A simple stream that uses Fetch API to get all the contents of all entries in the stream

datastream.map(
    async (item) => fetch(item)
)

1. Asynchronous using Promises

Example: A simple stream that fetches an url mentioned in the incoming object

   datastream.map(
       (item) => new Promise((resolve, reject) => {
           request(item.url, (err, res, data) => {
               if (err)
                   reject(err); // will emit an "error" event on the stream
               else
                   resolve(data);
           });
       })
   )

The actual logic of this transform function is as if you passed your function to the then method of a Promise resolved with the data from the input stream.

API Docs

Here's the list of the exposed classes and methods, please review the specific documentation for details:

• scramjet.DataStream - the base class for all scramjet classes.
• scramjet.BufferStream - a DataStream of Buffers.
• scramjet.StringStream - a DataStream of Strings.
• scramjet.MultiStream - a DataStream of Strings.
• scramjet.plugin - method for adding plugins, please see the docs
• more on plugins - a description and link.

Note that:

• Most of the methods take a callback argument that operates on the stream items.
• The callback, unless it's stated otherwise, will receive an argument with the next chunk.
• If you want to perform your operations asynchronously, return a Promise, otherwise just return the right value.

The quick reference of the exposed classes:

DataStream ⇐ stream.PassThrough

DataStream is the primary stream type for Scramjet. When you parse your stream, just pipe it you can then perform calculations on the data objects streamed through your flow.

 await (DataStream.fromArray([1,2,3,4,5]) // create a DataStream
     .map(readFile)                       // read some data asynchronously
     .map(sendToApi)                      // send the data somewhere
     .whenEnd());                         // wait until end

Detailed DataStream docs here

Method	Description	Example
new DataStream(opts)	Create the DataStream.
dataStream.map(func, Clazz) ⇒ DataStream	Transforms stream objects into new ones, just like Array.prototype.map	map example
dataStream.filter(func) ⇒ DataStream	Filters object based on the function outcome, just like	filter example
dataStream.reduce(func, into) ⇒ Promise	Reduces the stream into a given accumulator	reduce example
dataStream.into(func, into) ⇒ DataStream	Pushes the data into another scramjet stream while keeping flow control and
dataStream.use(func) ⇒ *	Calls the passed method in place with the stream as first argument, returns result.	use example
dataStream.tee(func) ⇒ DataStream	Duplicate the stream	tee example
dataStream.each(func) ↩︎	Performs an operation on every chunk, without changing the stream
dataStream.while(func) ⇒ DataStream	Reads the stream while the function outcome is truthy.
dataStream.until(func) ⇒ DataStream	Reads the stream until the function outcome is truthy.
dataStream.catch(callback) ↩︎	Provides a way to catch errors in chained streams.
dataStream.raise(err) ⇒ Promise	Executes all error handlers and if none resolves, then emits an error.
dataStream.pipe(to, options) ⇒ Writable	Override of node.js Readable pipe.
dataStream.bufferify(serializer) ⇒ BufferStream	Creates a BufferStream	bufferify example
dataStream.stringify(serializer) ⇒ StringStream	Creates a StringStream	stringify example
dataStream.run() ⇒ Promise	Consumes all stream items without doing anything
dataStream.toArray(initial) ⇒ Promise	Aggregates the stream into a single Array
dataStream.toGenerator() ⇒ Iterable.<Promise.<*>>	Returns an async generator
dataStream.tap()	Stops merging transform callbacks at the current place in the command chain.	tap example
dataStream.whenRead() ⇒ Promise.<Object>	Reads a chunk from the stream and resolves the promise when read.
dataStream.whenWrote(...data) ⇒ Promise	Writes a chunk to the stream and returns a Promise resolved when more chunks can be written.
dataStream.whenEnd() ⇒ Promise	Resolves when stream ends - rejects on uncaught error
dataStream.whenDrained() ⇒ Promise	Returns a promise that resolves when the stream is drained
dataStream.whenError() ⇒ Promise	Returns a promise that resolves (!) when the stream is errors
dataStream.setOptions(options) ↩︎	Allows resetting stream options.
DataStream.fromArray(arr) ⇒ DataStream	Create a DataStream from an Array	fromArray example
DataStream.fromIterator(iter) ⇒ DataStream	Create a DataStream from an Iterator	fromIterator example

StringStream ⇐ DataStream

A stream of string objects for further transformation on top of DataStream.

Detailed StringStream docs here

Method	Description	Example
new StringStream(encoding)	Constructs the stream with the given encoding
stringStream.shift(bytes, func) ⇒ StringStream	Shifts given length of chars from the original stream	shift example
stringStream.split(splitter) ⇒ StringStream	Splits the string stream by the specified regexp or string	split example
stringStream.match(splitter) ⇒ StringStream	Finds matches in the string stream and streams the match results	match example
stringStream.toBufferStream() ⇒ StringStream	Transforms the StringStream to BufferStream	toBufferStream example
stringStream.parse(parser) ⇒ DataStream	Parses every string to object	parse example
StringStream.SPLIT_LINE	A handly split by line regex to quickly get a line-by-line stream
StringStream.fromString(str, encoding) ⇒ StringStream	Creates a StringStream and writes a specific string.

BufferStream ⇐ DataStream

A factilitation stream created for easy splitting or parsing buffers.

Useful for working on built-in Node.js streams from files, parsing binary formats etc.

A simple use case would be:

 fs.createReadStream('pixels.rgba')
     .pipe(new BufferStream)         // pipe a buffer stream into scramjet
     .breakup(4)                     // split into 4 byte fragments
     .parse(buf => [
         buf.readInt8(0),            // the output is a stream of R,G,B and Alpha
         buf.readInt8(1),            // values from 0-255 in an array.
         buf.readInt8(2),
         buf.readInt8(3)
     ]);

Detailed BufferStream docs here

Method	Description	Example
new BufferStream(opts)	Creates the BufferStream
bufferStream.shift(chars, func) ⇒ BufferStream	Shift given number of bytes from the original stream	shift example
bufferStream.split(splitter) ⇒ BufferStream	Splits the buffer stream into buffer objects	split example
bufferStream.breakup(number) ⇒ BufferStream	Breaks up a stream apart into chunks of the specified length	breakup example
bufferStream.stringify(encoding) ⇒ StringStream	Creates a string stream from the given buffer stream	stringify example
bufferStream.parse(parser) ⇒ DataStream	Parses every buffer to object	parse example

MultiStream

An object consisting of multiple streams than can be refined or muxed.

Detailed MultiStream docs here

Method	Description	Example
new MultiStream(streams, options)	Crates an instance of MultiStream with the specified stream list
multiStream.streams : Array	Array of all streams
multiStream.length ⇒ number	Returns the current stream length
multiStream.map(aFunc) ⇒ MultiStream	Returns new MultiStream with the streams returned by the tranform.	map example
multiStream.find(...args) ⇒ DataStream	Calls Array.prototype.find on the streams
multiStream.filter(func) ⇒ MultiStream	Filters the stream list and returns a new MultiStream with only the	filter example
multiStream.mux(cmp) ⇒ DataStream	Muxes the streams into a single one	mux example
multiStream.add(stream)	Adds a stream to the MultiStream	add example
multiStream.remove(stream)	Removes a stream from the MultiStream	remove example

CLI

Check out the command line interface for simplified scramjet usage with scramjet-cli

$ sjr -i http://datasource.org/file.csv ./transform-module-1 ./transform-module-1 | gzip > logs.gz

License and contributions

As of version 2.0 Scramjet is MIT Licensed.

Help wanted

The project need's your help! There's lots of work to do - transforming and muxing, joining and splitting, browserifying, modularizing, documenting and issuing those issues.

If you want to help and be part of the Scramjet team, please reach out to me, signicode on Github or email me: [e-mail].

Changelog

Scramjet Core 4.11.1

• Fix into method: forward errors and end stream correctly.
• Streams will now resume immediately, not on nextTick.
• Typo fixes and code clarity fixes.