/lib/socket.js

/**
 * An abstraction on top of WebSockets and XHR streaming to provide fastest
 * possible connection for peers.
 */
function Socket(secure, host, port, path, key) {
  if (!(this instanceof Socket)) return new Socket(secure, host, port, path, key);

  EventEmitter.call(this);

  // Disconnected manually.
  this.disconnected = false;
  this._queue = [];

  var httpProtocol = secure ? 'https://' : 'http://';
  var wsProtocol = secure ? 'wss://' : 'ws://';
  this._httpUrl = httpProtocol + host + ':' + port + path + key;
  this._wsUrl = wsProtocol + host + ':' + port + path + 'peerjs?key=' + key;
}

util.inherits(Socket, EventEmitter);


/** Check in with ID or get one from server. */
Socket.prototype.start = function(id, token) {
  this.id = id;

  this._httpUrl += '/' + id + '/' + token;
  this._wsUrl += '&id='+id+'&token='+token;

  this._startXhrStream();
  this._startWebSocket();
}


/** Start up websocket communications. */
Socket.prototype._startWebSocket = function(id) {
  var self = this;

  if (this._socket) {
    return;
  }

  this._socket = new WebSocket(this._wsUrl);

  this._socket.onmessage = function(event) {
    var data;
    try {
      data = JSON.parse(event.data);
    } catch(e) {
      util.log('Invalid server message', event.data);
      return;
    }
    self.emit('message', data);
  };

  // Take care of the queue of connections if necessary and make sure Peer knows
  // socket is open.
  this._socket.onopen = function() {
    if (self._timeout) {
      clearTimeout(self._timeout);
      setTimeout(function(){
        self._http.abort();
        self._http = null;
      }, 5000);
    }
    self._sendQueuedMessages();
    util.log('Socket open');
  };
}

/** Start XHR streaming. */
Socket.prototype._startXhrStream = function(n) {
  try {
    var self = this;
    this._http = new XMLHttpRequest();
    this._http._index = 1;
    this._http._streamIndex = n || 0;
    this._http.open('post', this._httpUrl + '/id?i=' + this._http._streamIndex, true);
    this._http.onreadystatechange = function() {
      if (this.readyState == 2 && this.old) {
        this.old.abort();
        delete this.old;
      }
      if (this.readyState > 2 && this.status == 200 && this.responseText) {
        self._handleStream(this);
      }
    };
    this._http.send(null);
    this._setHTTPTimeout();
  } catch(e) {
    util.log('XMLHttpRequest not available; defaulting to WebSockets');
  }
}


/** Handles onreadystatechange response as a stream. */
Socket.prototype._handleStream = function(http) {
  // 3 and 4 are loading/done state. All others are not relevant.
  var messages = http.responseText.split('\n');

  // Check to see if anything needs to be processed on buffer.
  if (http._buffer) {
    while (http._buffer.length > 0) {
      var index = http._buffer.shift();
      var bufferedMessage = messages[index];
      try {
        bufferedMessage = JSON.parse(bufferedMessage);
      } catch(e) {
        http._buffer.shift(index);
        break;
      }
      this.emit('message', bufferedMessage);
    }
  }

  var message = messages[http._index];
  if (message) {
    http._index += 1;
    // Buffering--this message is incomplete and we'll get to it next time.
    // This checks if the httpResponse ended in a `\n`, in which case the last
    // element of messages should be the empty string.
    if (http._index === messages.length) {
      if (!http._buffer) {
        http._buffer = [];
      }
      http._buffer.push(http._index - 1);
    } else {
      try {
        message = JSON.parse(message);
      } catch(e) {
        util.log('Invalid server message', message);
        return;
      }
      this.emit('message', message);
    }
  }
}

Socket.prototype._setHTTPTimeout = function() {
  var self = this;
  this._timeout = setTimeout(function() {
    var old = self._http;
    if (!self._wsOpen()) {
      self._startXhrStream(old._streamIndex + 1);
      self._http.old = old;
    } else {
      old.abort();
    }
  }, 25000);
}

/** Is the websocket currently open? */
Socket.prototype._wsOpen = function() {
  return this._socket && this._socket.readyState == 1;
}

/** Send queued messages. */
Socket.prototype._sendQueuedMessages = function() {
  for (var i = 0, ii = this._queue.length; i < ii; i += 1) {
    this.send(this._queue[i]);
  }
}

/** Exposed send for DC & Peer. */
Socket.prototype.send = function(data) {
  if (this.disconnected) {
    return;
  }

  // If we didn't get an ID yet, we can't yet send anything so we should queue
  // up these messages.
  if (!this.id) {
    this._queue.push(data);
    return;
  }

  if (!data.type) {
    this.emit('error', 'Invalid message');
    return;
  }

  var message = JSON.stringify(data);
  if (this._wsOpen()) {
    this._socket.send(message);
  } else {
    var http = new XMLHttpRequest();
    var url = this._httpUrl + '/' + data.type.toLowerCase();
    http.open('post', url, true);
    http.setRequestHeader('Content-Type', 'application/json');
    http.send(message);
  }
}

Socket.prototype.close = function() {
  if (!this.disconnected && this._wsOpen()) {
    this._socket.close();
    this.disconnected = true;
  }
}