#co-stream Streams are node's best and most misunderstood idea, and co-stream is a toolkit to make creating and working with streams easy.

This package is very similar to event-stream, the difference is this package is in co style, so we can write async stream processing code in a nice way.

Installation

npm install co-stream

wait(stream)

Wait for stream 'end'/'finish' event;

co(function *() {
  // blabla
  yield* cs.wait(your_stream);
});

through (write?, end?)

Re-emits data synchronously. Easy way to create synchronous through streams. Pass in optional write and end methods. They will be called in the context of the stream. Use this.pause() and this.resume() to manage flow. Check this.paused to see current flow state. (write always returns !this.paused)

this function is the basis for most of the synchronous streams in event-stream.

cs.through(function write(data) {
    this.emit('data', data)
    //this.pause() 
  },
  function end () { //optional
    this.emit('end')
  })

fromEmitter(eventEmitter, opt)

Create a stream from an event emitter.

var cs = require('co-stream');

var es = cs.fromEmitter(evt, {
            objectMode: true,
            data: 'message',     // event name for data, default 'data'
            end: 'finish',       // event name for end, default 'end'
            pause: evt.stop,     // method to pause event emitter, default evt.pause || function () {}
            resume: evt.start });// method to resume event emiiter, default evt.resume || function () {}

es.pipe(process.stdout);

// cs.object.fromEmitter (cs.fromEmitter with default opt { objectMode: true })
// cs.string.fromEmitter (cs.fromEmitter with default opt { encoding: 'utf8' })

fromIterable(iterable)

Create a stream from an iterable object.

var cs = require('co-stream');

cs.fromIterable([1, 2, 3, 4, 5, 6, 7, 8]).pipe(cs.object.each(console.log));

// Promise is also supported.
const promise = new Promise(resolve => setTimeout(() => resolve(['a', 'b', 'c']), 1000));
cs.fromIterable(promise).pipe(cs.object.each(console.log));

map

Create a map stream from a function(can be generator / async function).

var cs = require('co-stream')

var ms = cs.map(function *(data) {
  //transform data
  return transformed_data;
}, { objectMode: true, parallel: 3 });

your_source_stream.pipe(ms).pipe(your_dest_stream);

// parallel param will allow you to process data parallelly, but the sequence of data may be changed if you have async call in the processor.
// cs.object.map (cs.map with default opt { objectMode: true })
// cs.string.map (cs.map with default opt { encoding: 'utf8' })

filter

Create a filter stream from a function(can be generator / async function).

var cs = require('co-stream')

var fs = cs.filter(async (data) => {
  // async data processing.
  return processingResult;
}, { objectMode: true, parallel: 3 });

your_source_stream.pipe(fs).pipe(your_dest_stream);

// parallel param will allow you to process data parallelly, but the sequence of data may be changed if you have async call in the processor.
// cs.object.filter (cs.filter with default opt { objectMode: true })
// cs.string.filter (cs.filter with default opt { encoding: 'utf8' })

each

If you just want to process data without any data to output, use this.

var cs = require('co-stream')

var ms = cs.each(function *(data) {
  // process data
}, { objectMode: true, parallel: 3 });

your_source_stream.pipe(ms);
// NOTE: ms.pipe is invalid.

// parallel param will allow you to process data parallelly.
// cs.object.each (cs.each with default opt { objectMode: true })
// cs.string.each (cs.each with default opt { encoding: 'utf8' })

split (matcher)

Break up a stream and reassemble it so that each line is a chunk. matcher may be a String, or a RegExp

Example, read every line in a file ...

fs.createReadStream(file, {flags: 'r'})
  .pipe(cs.split())
  .pipe(cs.object.each(function *(line) {
    //do something with the line 
    console.log('line: ', line);
  }))

duplex (writeStream, readStream)

Takes a writable stream and a readable stream and makes them appear as a readable writable stream.

It is assumed that the two streams are connected to each other in some way.

(This is used by pipeline and child.)

  var grep = cp.exec('grep Stream')

  cs.duplex(grep.stdin, grep.stdout)

Legacy API

var cs = require('co-stream'),
    co = require('co'),
    fs = require('fs');

co(function *() {
  var input = fs.createReadStream('test.in'),
      output = fs.createWriteStream('test.out');
      
  var cin = new (cs.Reader)(input), // new (cs.LineReader)(input) will create a line reader.
      cout = new (cs.Writer)(output);
      
  var txt;
  while (txt = yield cin.read('utf8')) {
    yield cout.write(txt); // or: yield cout.writeLine(txt)
  }
})();

// Object mode can process object streams such as mongodb stream.
co(function *() {
    var objstream = collection.find({ age: { $gte: 10, $lt: 15 } }).stream(),
        reader = new (cs.Reader)(objstream, { objectMode: true });

    var obj;
    while (obj = (yield  reader.read())) {
        // blabla....
    }
})();