Concatenate two (or n) streams

Question

• 2 streams:

  Given readable streams stream1 and stream2, what's an idiomatic (concise) way to get a stream containing stream1 and stream2 concatenated?

  I cannot do stream1.pipe(outStream); stream2.pipe(outStream), because then the stream contents are jumbled together.

• n streams:

  Given an EventEmitter that emits an indeterminate number of streams, e.g.

  eventEmitter.emit('stream', stream1) eventEmitter.emit('stream', stream2) eventEmitter.emit('stream', stream3) ... eventEmitter.emit('end') 

  what's an idiomatic (concise) way to get a stream with all streams concatenated together?

Answer 1

The combined-stream package concatenates streams. Example from the README:

var CombinedStream = require('combined-stream'); var fs = require('fs');  var combinedStream = CombinedStream.create(); combinedStream.append(fs.createReadStream('file1.txt')); combinedStream.append(fs.createReadStream('file2.txt'));  combinedStream.pipe(fs.createWriteStream('combined.txt')); 

I believe you have to append all streams at once. If the queue runs empty, the combinedStream automatically ends. See issue #5.

The stream-stream library is an alternative that has an explicit .end, but it's much less popular and presumably not as well-tested. It uses the streams2 API of Node 0.10 (see this discussion).

Answer 2

this can be done with vanilla nodejs

import { PassThrough } from 'stream' const merge = (...streams) => {     let pass = new PassThrough()     let waiting = streams.length     for (let stream of streams) {         pass = stream.pipe(pass, {end: false})         stream.once('end', () => --waiting === 0 && pass.emit('end'))     }     return pass }