Custom Node.js readable stream that accepts data from any source

any-source-readable.js

'use strict';

const Readable = require('stream').Readable;

// Easily turn anything into a readable stream.

// This is pretty much taken verbatim from the node documentation. Why re-invent
// the wheel?
// https://nodejs.org/api/stream.html#stream_readable_push_chunk_encoding

// AnySourceReadable extends the standard node readable stream to accept data
// from any source that correctly implements readStart(), readStop(),
// onData(chunk), and onEnd();

class AnySourceReadable extends Readable {

  constructor(source, options) {
    super(options);
    this._source = source;
    this._source.onData = (chunk) => {
      // this.push() is a built in Node.js stream method that returns false when
      // the downstream can't handle any more data. Once this.push() returns
      // false _read() will not be called again till the downstream is ready to
      // receive more data.
      if (!this.push(chunk))
        this._source.readStop();
    };
    this._source.onEnd = () => {
      console.log('onEnd');
      // pushing null tells the downstream we are done. there's no more data to
      // be had.
      this.push(null);
    };
  }

  // Any time the downstream wants data, _read() is called. We may or may not
  // have data to send. If not, we just do nothing. If so we send data via
  // this.push(chunk).
  _read(size) {
    this._source.readStart();
  }
}

exports = module.exports = AnySourceReadable;