Promised Lifestream

Creating promisified stream pipeline for Node.js

Feature

• Streams are pipelined and it resolves when last stream have finished.
• If an error occurred at any stream, it rejects with the error.
• If last stream is Readable or Transform, it appends auto-generated writer to streams.
• Last stream must raise finish event. process.stdout doesn't raise it.

Install

$ npm install -save promised-lifestream

How to use

PromisedLifestream(streams, [options])

• streams <Array<Stream>> streams composes pipeline. The first stream must be Readable. The second and any later stream must be Writable. The last stream can be Transform.
• options <Object>
  • needResult <Boolean> Whether the last stream result is resolved or not. Defaults to false

Example

'use strict';
 
const fs = require('fs');
const stream = require('stream');
const es = require('event-stream');
const PromisedLifestream = require('promised-lifestream');
 
var i = 0;
 
PromisedLifestream([
  new stream.Readable({
    read(size) {
      if (++i < 10) {
        this.push(String(i));
      } else {
        this.push(null);
      }
    }
  }),
  new stream.PassThrough(),
  fs.createWriteStream('out.txt')
])
.then(() => {
  const str = fs.readFileSync('out.txt', { encoding: 'ascii' });
  console.log(str);
  // 123456789
})
.catch(err => {
  console.error(err);
});

Get last result

 
PromisedLifestream([
  es.readArray([1, 2, 3]),
  es.map(function (data, callback) {
    callback(null, data * 2);
  })
], {
  needResult: true
})
.then(result => {
  console.log(result);
  // [2, 4, 6]
})
.catch(err => {
  console.error(err);
});

License

MIT