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faye-websocket

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Autobahn tests: server, client

This is a robust, general-purpose WebSocket implementation extracted from the Faye project. It provides classes for easily building WebSocket servers and clients in Node. It does not provide a server itself, but rather makes it easy to handle WebSocket connections within an existing Node application. It does not provide any abstraction other than the standard WebSocket API.

It also provides an abstraction for handling EventSource connections, which are one-way connections that allow the server to push data to the client. They are based on streaming HTTP responses and can be easier to access via proxies than WebSockets.

The server-side socket can process draft-75, draft-76, hybi-07 and later versions of the protocol. It selects protocol versions automatically, supports both text and binary messages, and transparently handles ping, pong, close and fragmented messages.

Handling WebSocket connections in Node

You can handle WebSockets on the server side by listening for HTTP Upgrade requests, and creating a new socket for the request. This socket object exposes the usual WebSocket methods for receiving and sending messages. For example this is how you’d implement an echo server:

var WebSocket = require('faye-websocket'),
    http      = require('http');

var server = http.createServer();

server.addListener('upgrade', function(request, socket, head) {
  var ws = new WebSocket(request, socket, head);
  
  ws.onmessage = function(event) {
    ws.send(event.data);
  };
  
  ws.onclose = function(event) {
    console.log('close', event.code, event.reason);
    ws = null;
  };
});

server.listen(8000);

Note that under certain circumstances (notably a draft-76 client connecting through an HTTP proxy), the WebSocket handshake will not be complete after you call new WebSocket() because the server will not have received the entire handshake from the client yet. In this case, calls to ws.send() will buffer the message in memory until the handshake is complete, at which point any buffered messages will be sent to the client.

If you need to detect when the WebSocket handshake is complete, you can use the onopen event.

If the connection’s protocol version supports it, you can call ws.ping() to send a ping message and wait for the client’s response. This method takes a message string, and an optional callback that fires when a matching pong message is received. It returns true iff a ping message was sent. If the client does not support ping/pong, this method sends no data and returns false.

ws.ping('Mic check, one, two', function() {
  // fires when pong is received
});

Using the WebSocket client

The client supports both the plain-text ws protocol and the encrypted wss protocol, and has exactly the same interface as a socket you would use in a web browser. On the wire it identifies itself as hybi-13.

var WebSocket = require('faye-websocket'),
    ws        = new WebSocket.Client('ws://www.example.com/');

ws.onopen = function(event) {
  console.log('open');
  ws.send('Hello, world!');
};

ws.onmessage = function(event) {
  console.log('message', event.data);
};

ws.onclose = function(event) {
  console.log('close', event.code, event.reason);
  ws = null;
};

Subprotocol negotiation

The WebSocket protocol allows peers to select and identify the application protocol to use over the connection. On the client side, you can set which protocols the client accepts by passing a list of protocol names when you construct the socket:

var ws = new WebSocket.Client('ws://www.example.com/', ['irc', 'amqp']);

On the server side, you can likewise pass in the list of protocols the server supports after the other constructor arguments:

var ws = new WebSocket(request, socket, head, ['irc', 'amqp']);

If the client and server agree on a protocol, both the client- and server-side socket objects expose the selected protocol through the ws.protocol property. If they cannot agree on a protocol to use, the client closes the connection.

WebSocket API

The WebSocket API consists of several event handlers and a method for sending messages.

onopen fires when the socket connection is established. Event has no attributes.
onerror fires when the connection attempt fails. Event has no attributes.
onmessage fires when the socket receives a message. Event has one attribute, data, which is either a String (for text frames) or a Buffer (for binary frames).
onclose fires when either the client or the server closes the connection. Event has two optional attributes, code and reason, that expose the status code and message sent by the peer that closed the connection.
send(message) accepts either a String or a Buffer and sends a text or binary message over the connection to the other peer.
close(code, reason) closes the connection, sending the given status code and reason text, both of which are optional.
protocol is a string (which may be empty) identifying the subprotocol the socket is using.

Handling EventSource connections in Node

EventSource connections provide a very similar interface, although because they only allow the server to send data to the client, there is no onmessage API. EventSource allows the server to push text messages to the client, where each message has an optional event-type and ID.

var WebSocket   = require('faye-websocket'),
    EventSource = WebSocket.EventSource,
    http        = require('http');

var server = http.createServer();

server.addListener('request', function(request, response) {
  if (EventSource.isEventSource(request)) {
    var es = new EventSource(request, response);
    console.log('open', es.url, es.lastEventId);
    
    // Periodically send messages
    var loop = setInterval(function() { es.send('Hello') }, 1000);
    
    es.onclose = function() {
      clearInterval(loop);
      es = null;
    };
  
  } else {
    // Normal HTTP request
    response.writeHead(200, {'Content-Type': 'text/plain'});
    response.write('Hello');
    response.end();
  }
});

server.listen(8000);

The send method takes two optional parameters, event and id. The default event-type is 'message' with no ID. For example, to send a notification event with ID 99:

es.send('Breaking News!', {event: 'notification', id: '99'});

The EventSource object exposes the following properties:

url is a string containing the URL the client used to create the EventSource.
lastEventId is a string containing the last event ID received by the client. You can use this when the client reconnects after a dropped connection to determine which messages need resending.

When you initialize an EventSource with new EventSource(), you can pass configuration options after the response parameter. Available options are:

retry is a number that tells the client how long (in seconds) it should wait after a dropped connection before attempting to reconnect.
ping is a number that tells the server how often (in seconds) to send ‘ping’ packets to the client to keep the connection open, to defeat timeouts set by proxies. The client will ignore these messages.

For example, this creates a connection that pings every 15 seconds and is retryable every 10 seconds if the connection is broken:

var es = new EventSource(request, response, {ping: 15, retry: 10});

You can send a ping message at any time by calling es.ping(). Unlike WebSocket, the client does not send a response to this; it is merely to send some data over the wire to keep the connection alive.

License

(The MIT License)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the ‘Software’), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED ‘AS IS’, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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