canvasing/node_modules/faye-websocket/README.md

faye-websocket

This is a 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.

Installation

$ npm install faye-websocket

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.on('upgrade', function(request, socket, body) {
  if (WebSocket.isWebSocket(request)) {
    var ws = new WebSocket(request, socket, body);

    ws.on('message', function(event) {
      ws.send(event.data);
    });

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

server.listen(8000);

WebSocket objects are also duplex streams, so you could replace the ws.on('message', ...) line with:

    ws.pipe(ws);

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 if and only if 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.on('open', function(event) {
  console.log('open');
  ws.send('Hello, world!');
});

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

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

The WebSocket client also lets you inspect the status and headers of the handshake response via its statusCode and headers properties.

To connect via a proxy, set the proxy option to the HTTP origin of the proxy, including any authorization information, custom headers and TLS config you require. Only the origin setting is required.

var ws = new WebSocket.Client('ws://www.example.com/', [], {
  proxy: {
    origin:  'http://username:password@proxy.example.com',
    headers: { 'User-Agent': 'node' },
    tls:     { cert: fs.readFileSync('client.crt') }
  }
});

The tls value is an object that will be passed to tls.connect().

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, body, ['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.

Protocol extensions

faye-websocket is based on the websocket-extensions framework that allows extensions to be negotiated via the Sec-WebSocket-Extensions header. To add extensions to a connection, pass an array of extensions to the :extensions option. For example, to add permessage-deflate:

var deflate = require('permessage-deflate');

var ws = new WebSocket(request, socket, body, [], { extensions: [deflate] });

Initialization options

Both the server- and client-side classes allow an options object to be passed in at initialization time, for example:

var ws = new WebSocket(request, socket, body, protocols, options);
var ws = new WebSocket.Client(url, protocols, options);

protocols is an array of subprotocols as described above, or null. options is an optional object containing any of these fields:

• extensions - an array of websocket-extensions compatible extensions, as described above
• headers - an object containing key-value pairs representing HTTP headers to be sent during the handshake process
• 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.
• ping - an integer that sets how often the WebSocket should send ping frames, measured in seconds

The client accepts some additional options:

• proxy - settings for a proxy as described above
• net - an object containing settings for the origin server that will be passed to net.connect()
• tls - an object containing TLS settings for the origin server, this will be passed to tls.connect()
• ca - (legacy) a shorthand for passing { tls: { ca: value } }

WebSocket API

Both server- and client-side WebSocket objects support the following API.

• on('open', function(event) {}) fires when the socket connection is established. Event has no attributes.
• on('message', function(event) {}) 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).
• on('error', function(event) {}) fires when there is a protocol error due to bad data sent by the other peer. This event is purely informational, you do not need to implement error recover.
• on('close', function(event) {}) 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.
• ping(message, function() {}) sends a ping frame with an optional message and fires the callback when a matching pong is received.
• close(code, reason) closes the connection, sending the given status code and reason text, both of which are optional.
• version is a string containing the version of the WebSocket protocol the connection is using.
• 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.on('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.on('close', function() {
      clearInterval(loop);
      es = null;
    });

  } else {
    // Normal HTTP request
    response.writeHead(200, { 'Content-Type': 'text/plain' });
    response.end('Hello');
  }
});

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:

• headers is an object containing custom headers to be set on the EventSource response.
• 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 allows access from any origin, pings every 15 seconds and is retryable every 10 seconds if the connection is broken:

var es = new EventSource(request, response, {
  headers: { 'Access-Control-Allow-Origin': '*' },
  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.