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Socket.IO stream

Build Status NPM version

This is the module for bidirectional binary data transfer with Stream API through Socket.IO.


npm install


If you are not familiar with Stream API, be sure to check out the docs. I also recommend checking out the awesome Stream Handbook.

For streaming between server and client, you will send stream instances first. To receive streams, you just wrap socket with, then listen any events as usual.


var io = require('').listen(80);
var ss = require('');
var path = require('path');

io.of('/user').on('connection', function(socket) {
  ss(socket).on('profile-image', function(stream, data) {
    var filename = path.basename(;

createStream() returns a new stream which can be sent by emit().


var io = require('');
var ss = require('');

var socket = io.connect('');
var stream = ss.createStream();
var filename = 'profile.jpg';

ss(socket).emit('profile-image', stream, {name: filename});

You can stream data from a client to server, and vice versa.

// send data
ss(socket).on('file', function(stream) {

// receive data
ss(socket).emit('file', stream);


This module can be used on the browser. To do so, just copy a file to a public directory.

$ cp node_modules/ somewhere/public/

You can also use browserify to create your own bundle.

$ npm install browserify -g
$ cd node_modules/
$ browserify index.js -s ss >
<input id="file" type="file" />

<script src="/"></script>
<script src="/js/"></script>
<script src="/js/jquery.js"></script>
$(function() {
  var socket = io.connect('/foo');

  $('#file').change(function(e) {
    var file =[0];
    var stream = ss.createStream();

    // upload a file to the server.
    ss(socket).emit('file', stream, {size: file.size});

Upload progress

You can track upload progress like the following:

var blobStream = ss.createBlobReadStream(file);
var size = 0;

blobStream.on('data', function(chunk) {
  size += chunk.length;
  console.log(Math.floor(size / file.size * 100) + '%');
  // -> e.g. '42%'


Socket.IO v0.9 support

You have to set forceBase64 option true when using the library with v0.9.x.

ss.forceBase64 = true;



  • sio Socket A socket of Socket.IO, both for client and server
  • return Socket

Look up an existing Socket instance based on sio (a socket of Socket.IO), or create one if it doesn't exist.

socket.emit(event, [arg1], [arg2], [...])

  • event String The event name

Emit an event with variable number of arguments including at least a stream.

ss(socket).emit('myevent', stream, {name: 'thefilename'}, function() { ... });

// send some streams at a time.
ss(socket).emit('multiple-streams', stream1, stream2);

// as members of array or object.
ss(socket).emit('flexible', [stream1, { foo: stream2 }]);

// get streams through the ack callback
ss(socket).emit('ack', function(stream1, stream2) { ... });

socket.on(event, listener)

  • event String The event name
  • listener Function The event handler function

Add a listener for event. listener will take stream(s) with any data as arguments.

ss(socket).on('myevent', function(stream, data, callback) { ... });

// access stream options
ss(socket).on('foo', function(stream) {
  if (stream.options && stream.options.highWaterMark > 1024) {
    console.error('Too big highWaterMark.');


  • options Object
    • highWaterMark Number
    • encoding String
    • decodeStrings Boolean
    • objectMode Boolean
    • allowHalfOpen Boolean if true, then the stream won't automatically close when the other endpoint ends. Default to false.
  • return Duplex Stream

Create a new duplex stream. See the docs for the details of stream and options.

var stream = ss.createStream();

// with options
var stream = ss.createStream({
  highWaterMark: 1024,
  objectMode: true,
  allowHalfOpen: true

ss.createBlobReadStream(blob, [options])

  • options Object
    • highWaterMark Number
    • encoding String
    • objectMode Boolean
  • return Readable Stream

Create a new readable stream for Blob and File on browser. See the docs for the details of stream and options.

var stream = ss.createBlobReadStream(new Blob([1, 2, 3]));


Node Buffer class to use on browser, which is exposed for convenience. On Node environment, you should just use normal Buffer.

var stream = ss.createStream();
stream.write(new ss.Buffer([0, 1, 2]));