WebSocket protocol handler with pluggable I/O

Usage no npm install needed!

<script type="module">
  import adamvrWebsocketDriver from 'https://cdn.skypack.dev/@adamvr/websocket-driver';


websocket-driver Build Status

This module provides a complete implementation of the WebSocket protocols that can be hooked up to any I/O stream. It aims to simplify things by decoupling the protocol details from the I/O layer, such that users only need to implement code to stream data in and out of it without needing to know anything about how the protocol actually works. Think of it as a complete WebSocket system with pluggable I/O.

Due to this design, you get a lot of things for free. In particular, if you hook this module up to some I/O object, it will do all of this for you:

  • Select the correct server-side driver to talk to the client
  • Generate and send both server- and client-side handshakes
  • Recognize when the handshake phase completes and the WS protocol begins
  • Negotiate subprotocol selection based on Sec-WebSocket-Protocol
  • Negotiate and use extensions via the websocket-extensions module
  • Buffer sent messages until the handshake process is finished
  • Deal with proxies that defer delivery of the draft-76 handshake body
  • Notify you when the socket is open and closed and when messages arrive
  • Recombine fragmented messages
  • Dispatch text, binary, ping, pong and close frames
  • Manage the socket-closing handshake process
  • Automatically reply to ping frames with a matching pong
  • Apply masking to messages sent by the client

This library was originally extracted from the Faye project but now aims to provide simple WebSocket support for any Node-based project.


$ npm install websocket-driver


This module provides protocol drivers that have the same interface on the server and on the client. A WebSocket driver is an object with two duplex streams attached; one for incoming/outgoing messages and one for managing the wire protocol over an I/O stream. The full API is described below.

Server-side with HTTP

A Node webserver emits a special event for 'upgrade' requests, and this is where you should handle WebSockets. You first check whether the request is a WebSocket, and if so you can create a driver and attach the request's I/O stream to it.

var http = require('http'),
    websocket = require('websocket-driver');

var server = http.createServer();

server.on('upgrade', function(request, socket, body) {
  if (!websocket.isWebSocket(request)) return;

  var driver = websocket.http(request);


  driver.messages.on('data', function(message) {
    console.log('Got a message', message);


Note the line driver.io.write(body) - you must pass the body buffer to the socket driver in order to make certain versions of the protocol work.

Server-side with TCP

You can also handle WebSocket connections in a bare TCP server, if you're not using an HTTP server and don't want to implement HTTP parsing yourself.

The driver will emit a connect event when a request is received, and at this point you can detect whether it's a WebSocket and handle it as such. Here's an example using the Node net module:

var net = require('net'),
    websocket = require('websocket-driver');

var server = net.createServer(function(connection) {
  var driver = websocket.server();

  driver.on('connect', function() {
    if (websocket.isWebSocket(driver)) {
    } else {
      // handle other HTTP requests

  driver.on('close', function() { connection.end() });
  connection.on('error', function() {});




In the connect event, the driver gains several properties to describe the request, similar to a Node request object, such as method, url and headers. However you should remember it's not a real request object; you cannot write data to it, it only tells you what request data we parsed from the input.

If the request has a body, it will be in the driver.body buffer, but only as much of the body as has been piped into the driver when the connect event fires.


Similarly, to implement a WebSocket client you just need to make a driver by passing in a URL. After this you use the driver API as described below to process incoming data and send outgoing data.

var net = require('net'),
    websocket = require('websocket-driver');

var driver = websocket.client('ws://www.example.com/socket'),
    tcp = net.connect(80, 'www.example.com');


tcp.on('connect', function() {

driver.messages.on('data', function(message) {
  console.log('Got a message', message);

Client drivers have two additional properties for reading the HTTP data that was sent back by the server:

  • driver.statusCode - the integer value of the HTTP status code
  • driver.headers - an object containing the response headers

HTTP Proxies

The client driver supports connections via HTTP proxies using the CONNECT method. Instead of sending the WebSocket handshake immediately, it will send a CONNECT request, wait for a 200 response, and then proceed as normal.

To use this feature, call driver.proxy(url) where url is the origin of the proxy, including a username and password if required. This produces a duplex stream that you should pipe in and out of your TCP connection to the proxy server. When the proxy emits connect, you can then pipe driver.io to your TCP stream and call driver.start().

var net = require('net'),
    websocket = require('websocket-driver');

var driver = websocket.client('ws://www.example.com/socket'),
    proxy  = driver.proxy('http://username:password@proxy.example.com'),
    tcp    = net.connect(80, 'proxy.example.com');

tcp.pipe(proxy).pipe(tcp, {end: false});

tcp.on('connect', function() {

proxy.on('connect', function() {

driver.messages.on('data', function(message) {
  console.log('Got a message', message);

The proxy's connect event is also where you should perform a TLS handshake on your TCP stream, if you are connecting to a wss: endpoint.

In the event that proxy connection fails, proxy will emit an error. You can inspect the proxy's response via proxy.statusCode and proxy.headers.

proxy.on('error', function(error) {

Before calling proxy.start() you can set custom headers using proxy.setHeader():

proxy.setHeader('User-Agent', 'node');

Driver API

Drivers are created using one of the following methods:

driver = websocket.http(request, options)
driver = websocket.server(options)
driver = websocket.client(url, options)

The http method returns a driver chosen using the headers from a Node HTTP request object. The server method returns a driver that will parse an HTTP request and then decide which driver to use for it using the http method. The client method always returns a driver for the RFC version of the protocol with masking enabled on outgoing frames.

The options argument is optional, and is an object. It may contain the following fields:

  • maxLength - the maximum allowed size of incoming message frames, in bytes. The default value is 2^26 - 1, or 1 byte short of 64 MiB.
  • protocols - an array of strings representing acceptable subprotocols for use over the socket. The driver will negotiate one of these to use via the Sec-WebSocket-Protocol header if supported by the other peer.

A driver has two duplex streams attached to it:

  • driver.io - this stream should be attached to an I/O socket like a TCP stream. Pipe incoming TCP chunks to this stream for them to be parsed, and pipe this stream back into TCP to send outgoing frames.
  • driver.messages - this stream emits messages received over the WebSocket. Writing to it sends messages to the other peer by emitting frames via the driver.io stream.

All drivers respond to the following API methods, but some of them are no-ops depending on whether the client supports the behaviour.

Note that most of these methods are commands: if they produce data that should be sent over the socket, they will give this to you by emitting data events on the driver.io stream.

driver.on('open', function(event) {})

Adds a callback to execute when the socket becomes open.

driver.on('message', function(event) {})

Adds a callback to execute when a message is received. event will have a data attribute containing either a string in the case of a text message or a Buffer in the case of a binary message.

You can also listen for messages using the driver.messages.on('data') event, which emits strings for text messages and buffers for binary messages.

driver.on('error', function(event) {})

Adds a callback to execute when a protocol error occurs due to the other peer sending an invalid byte sequence. event will have a message attribute describing the error.

driver.on('close', function(event) {})

Adds a callback to execute when the socket becomes closed. The event object has code and reason attributes.

driver.on('ping', function(event) {})

Adds a callback block to execute when a ping is received. You do not need to handle this by sending a pong frame yourself; the driver handles this for you.

driver.on('pong', function(event) {})

Adds a callback block to execute when a pong is received. If this was in response to a ping you sent, you can also handle this event via the driver.ping(message, function() { ... }) callback.


Registers a protocol extension whose operation will be negotiated via the Sec-WebSocket-Extensions header. extension is any extension compatible with the websocket-extensions framework.

driver.setHeader(name, value)

Sets a custom header to be sent as part of the handshake response, either from the server or from the client. Must be called before start(), since this is when the headers are serialized and sent.


Initiates the protocol by sending the handshake - either the response for a server-side driver or the request for a client-side one. This should be the first method you invoke. Returns true if and only if a handshake was sent.


Takes a string and parses it, potentially resulting in message events being emitted (see on('message') above) or in data being sent to driver.io. You should send all data you receive via I/O to this method by piping a stream into driver.io.


Sends a text message over the socket. If the socket handshake is not yet complete, the message will be queued until it is. Returns true if the message was sent or queued, and false if the socket can no longer send messages.

This method is equivalent to driver.messages.write(string).


Takes a Buffer and sends it as a binary message. Will queue and return true or false the same way as the text method. It will also return false if the driver does not support binary messages.

This method is equivalent to driver.messages.write(buffer).

driver.ping(string = '', function() {})

Sends a ping frame over the socket, queueing it if necessary. string and the callback are both optional. If a callback is given, it will be invoked when the socket receives a pong frame whose content matches string. Returns false if frames can no longer be sent, or if the driver does not support ping/pong.

driver.pong(string = '')

Sends a pong frame over the socket, queueing it if necessary. string is optional. Returns false if frames can no longer be sent, or if the driver does not support ping/pong.

You don't need to call this when a ping frame is received; pings are replied to automatically by the driver. This method is for sending unsolicited pongs.


Initiates the closing handshake if the socket is still open. For drivers with no closing handshake, this will result in the immediate execution of the on('close') driver. For drivers with a closing handshake, this sends a closing frame and emit('close') will execute when a response is received or a protocol error occurs.


Returns the WebSocket version in use as a string. Will either be hixie-75, hixie-76 or hybi-$version.


Returns a string containing the selected subprotocol, if any was agreed upon using the Sec-WebSocket-Protocol mechanism. This value becomes available after emit('open') has fired.