peer-emitter/read-stream.js

acknowledgeable events

var streams = require('stream');
var Readable = streams.Readable;
var PassThrough = streams.PassThrough;

module.exports = ReadStream;

function ReadStream(emitter, name) {
  var stream = new Readable({
    objectMode: true
  });

  var ackStream;
  var handler;
  var queue = [];

  stream._read = listen;

  var started;
  function listen(n) {
    if (started)
      return;

    started = true;

    if (handler)
      return;

    handler = ackStream ? handlerWithAck : simpleHandler;

    emitter.on(name, handler);
  }

  function simpleHandler(d) {
    stream.push(d);
  }

  function handlerWithAck(d, ack) {6
    queue.push({data:d, ack:ack});
    stream.push(d);
  }

  stream.AckStream = createAckStream;
  function createAckStream() {
    if (ackStream)
      throw Error('already created');

    ackStream = new PassThrough({ objectMode: true });

    ackStream.on('data', function(d) {
      var pair = queue.shift();
      pair.ack();
    });

    if (handler === simpleHandler) {
      emitter.removeListener(name, simpleHandler);
      handler = undefined;
    }

    if (! handler)
      emitter.on(name, handlerWithAck);

    return ackStream;
  }

  return stream;
}