split-to-streams

StreamSplit

A Node.JS stream.Transform interface that splits input into streams.

• How it works
• Features
• Install and usage
  • Example
• Documentation
  • class StreamSplit
    • constructor()
    • Extending
  • class SimpleSplit
  • class LineSplit
    • Example
• Partial Matching
• License

How it works

Given input, the StreamSplit class will split input in real-time, and provide a stream.Readable object for each segment delimited by delimiter. Each stream.Readable provided, will in turn provide one or more data chunks, within the matched segment.

The utility of StreamSplit is to provide consumer interfaces the ability to process incoming chunks as they become available, without having to wait for a delimiter to be matched first.

Traditional string splitters:

_________________________________
| chunk | chunk | chunk | chunk |  => { [chunk, chunk, chunk, chunk].join() }
----------- delimiter -----------
| chunk | chunk | chunk | chunk |  => { [chunk, chunk, chunk, chunk].join() }
----------- delimiter -----------

StreamSplit default:

_________________________________
| chunk | chunk | chunk | chunk |  => { [Readable Stream] } => [ {chunk} | {chunk} | {chunk} | {chunk} ]
----------- delimiter -----------
| chunk | chunk | chunk | chunk |  => { [Readable Stream] } => [ {chunk} | {chunk} | {chunk} | {chunk} ]
----------- delimiter -----------

Features

• Allows splitting input based on a custom delimiter
• Buffer-safe; does not convert to strings for searching and splitting
• Support partial matching

Install and usage

npm install split-to-streams

Testing

npm test or node test/

Example

const StreamSplit = require('split-to-streams');

const input = getReadableStream();
const spliter = new StreamSplit('\n'); // Split by LF
splitter.on('data', function (stream) {
    // `stream` is a `stream.Readable` instance that will push data chunks within each line.
    stream.on('data', function (chunk) {
        // Handle chunks in a line.
    });
});

input.pipe(splitter);

Documentation

class StreamSplit

The class extends on stream.Transform and transforms input by splitting it based on a delimiter parameter.

constructor(delimiter = '' [, options = {}])

Creates a new StreamSplit instance.

• delimiter, the delimiter to split input by
• options (optional) Object with options to pass to the stream.Transform super.

  • ignorePrevious - default: false If set to true, disables partial matching.

  • createStream - (optional) - A custom function to create a stream.Readable-like object, every time the delimiter is matched.

Note: Emit at creation (fixed)

This behavior has been corrected in v1.1.0 The first stream object will not be emitted at creation anymore, but on first write. Overwriting createStream() method, before the first write, will not yield different objects anymore.

StreamSplit instances will always emit a new stream object on creation, in order to capture initial chunks until and if first delimiter is found.

As such, overwriting the createStream() method after creation, will result in different objects being emitted (first will always be the default). Please use options.createStream or by extending the StreamSplit class, instead of replacing the createStream() method.

Extending

const StreamSplit = require('split-to-streams');

class MyCustomStreamSplit extends StreamSplit {
    constructor( ... ) {
        super( ... );
    }

    createStream() {
        // Overwrite creating `stream.Readable` instances, and create custom objects.
        // Note: object must have a `push()` method.
        return new CustomObject();
    }

    _transform(chunk, encoding, callback) {
        // Do something before passing the chunk to `StreamSplit`
        super._transform(chunk, encoding, callback);
    }
}

class SimpleSplit

The class extends on StreamSplit, but does not provide stream.Readable objects. Instead consumers can read chunks delimited by delimiter, just like with traditional string splitters.

constructor(delimiter = '' [, options = {}])

Creates a new SimpleSplit instance.

• delimiter, the delimiter to split input by
• options (optional) Object with options to pass to the stream.Transform super.

class LineSplit

The class extends on SimpleSplit, and splits input by \n (LF) delimiters, providing lines as chunks.

Example

const {LineSplit} = require('split-to-stream');
const lineSplitter = new LineSplit();
const input = getReadableStream(); // e.g. fs.createReadStream(filename);

lineSplitter.on('data', function(lineChunk) {
    // handle lineChunk.
});

input.pipe(lineSplitter);

Partial Matching

• Enabled by default. Set options.ignorePrevious to false, in contructor, to disable.
• Works only with delimiter.length greater than 1.

Partial matching allows the StreamSplit class to quickly check incoming chunks for delimiter parts. Sometimes, a delimiter matchs comes in via two or more separate chunks.

Example:

Full string: "Hello <delimiter>World"
Incoming chunks: ["Hello <del", "imit", "er>World"]

Partial matching, will inspect the end of each chunk, and if it finds a partial match of the delimiter, it will store that part. Differently from traditional splitters, it will release the unused part of the chunk, only keeping the partial match.

Flow example:

chunk "Hello <del":
 - save( Buffer.from("<del") ); // partial match
 - push( Buffer.from("Hello ") ); // send chunk to consumer streams.
chunk "imit":
 - save( Buffer.from("imit") ); // partial match. entire stored buffer now "<delimit"
chunk "er>World":
 - save( Buffer.from("er>") ); // partial match. entire stored buffer now "<delimiter>"
 - emitDelimiterMatch(); // A delimiter matched
 - push( Buffer.from("World") ); // send chunk to consumer streams.

Note: At the end of the input stream (input stream emits end), StreamSplit will push any remaining stored chunk, to the consumers; as expected in such scenarios.

License

MIT