peerjs/lib/dataconnection.js

/**
 * Wraps a DataChannel between two Peers.
 */
function DataConnection(peer, provider, options) {
  if (!(this instanceof DataConnection)) return new DataConnection(peer, provider, options);
  EventEmitter.call(this);

  // TODO: perhaps default serialization should be binary-utf8?
  this.options = util.extend({
    serialization: 'binary',
    reliable: false
  }, options);

  // Connection is not open yet.
  this.open = false;
  this.type = 'data';
  this.peer = peer;
  this.provider = provider;

  this.id = this.options.connectionId || DataConnection._idPrefix + util.randomToken();

  this.label = this.options.label || this.id;
  this.metadata = this.options.metadata;
  this.serialization = this.options.serialization;
  this.reliable = this.options.reliable;

  // Data channel buffering.
  this._buffer = [];
  this._buffering = false;
  this.bufferSize = 0;

  // For storing large data.
  this._chunkedData = {};

  Negotiator.startConnection(
    this,
    this.options._payload || {
      originator: true
    }
  );
}

util.inherits(DataConnection, EventEmitter);

DataConnection._idPrefix = 'dc_';

/** Called by the Negotiator when the DataChannel is ready. */
DataConnection.prototype.initialize = function(dc) {
  this._dc = this.dataChannel = dc;
  this._configureDataChannel();
}

DataConnection.prototype._configureDataChannel = function() {
  var self = this;
  if (util.supports.sctp) {
    this._dc.binaryType = 'arraybuffer';
  }
  this._dc.onopen = function() {
    util.log('Data channel connection success');
    self.open = true;
    self.emit('open');
  }

  // Use the Reliable shim for non Firefox browsers
  if (!util.supports.sctp && this.reliable) {
    this._reliable = new Reliable(this._dc, util.debug);
  }

  if (this._reliable) {
    this._reliable.onmessage = function(msg) {
      self.emit('data', msg);
    };
  } else {
    this._dc.onmessage = function(e) {
      self._handleDataMessage(e);
    };
  }
  this._dc.onclose = function(e) {
    util.log('DataChannel closed for:', self.peer);
    self.close();
  };
}

// Handles a DataChannel message.
DataConnection.prototype._handleDataMessage = function(e) {
  var self = this;
  var data = e.data;
  var datatype = data.constructor;
  if (this.serialization === 'binary' || this.serialization === 'binary-utf8') {
    if (datatype === Blob) {
      // Datatype should never be blob
      util.blobToArrayBuffer(data, function(ab) {
        data = util.unpack(ab);
        self.emit('data', data);
      });
      return;
    } else if (datatype === ArrayBuffer) {
      data = util.unpack(data);
    } else if (datatype === String) {
      // String fallback for binary data for browsers that don't support binary yet
      var ab = util.binaryStringToArrayBuffer(data);
      data = util.unpack(ab);
    }
  } else if (this.serialization === 'json') {
    data = JSON.parse(data);
  }

  // Check if we've chunked--if so, piece things back together.
  // We're guaranteed that this isn't 0.
  if (data.__peerData) {
    var id = data.__peerData;
    var chunkInfo = this._chunkedData[id] || {data: [], count: 0, total: data.total};

    chunkInfo.data[data.n] = data.data;
    chunkInfo.count += 1;

    if (chunkInfo.total === chunkInfo.count) {
      // We've received all the chunks--time to construct the complete data.
      data = new Blob(chunkInfo.data);
      this._handleDataMessage({data: data});

      // We can also just delete the chunks now.
      delete this._chunkedData[id];
    }

    this._chunkedData[id] = chunkInfo;
    return;
  }

  this.emit('data', data);
}

/**
 * Exposed functionality for users.
 */

/** Allows user to close connection. */
DataConnection.prototype.close = function() {
  if (!this.open) {
    return;
  }
  this.open = false;
  Negotiator.cleanup(this);
  this.emit('close');
}

/** Allows user to send data. */
DataConnection.prototype.send = function(data, chunked) {
  if (!this.open) {
    this.emit('error', new Error('Connection is not open. You should listen for the `open` event before sending messages.'));
    return;
  }
  if (this._reliable) {
    // Note: reliable shim sending will make it so that you cannot customize
    // serialization.
    this._reliable.send(data);
    return;
  }
  var self = this;
  if (this.serialization === 'json') {
    this._bufferedSend(JSON.stringify(data));
  } else if ('binary-utf8'.indexOf(this.serialization) !== -1) {
    var utf8 = (this.serialization === 'binary-utf8');
    var blob = util.pack(data, utf8);

    // For Chrome-Firefox interoperability, we need to make Firefox "chunking" the data it sends out. Future sophistication of this approach could make the decision on chunking dependent on the remote browser.
    if (/*util.browser !== 'Firefox' && */!chunked && blob.size > util.chunkedMTU) {
      this._sendChunks(blob);
      return;
    }

    // DataChannel currently only supports strings.
    if (!util.supports.sctp) {
      util.blobToBinaryString(blob, function(str) {
        self._bufferedSend(str);
      });
    } else if (!util.supports.binaryBlob) {
      // We only do this if we really need to (e.g. blobs are not supported),
      // because this conversion is costly.
      util.blobToArrayBuffer(blob, function(ab) {
        self._bufferedSend(ab);
      });
    } else {
      this._bufferedSend(blob);
    }
  } else {
    this._bufferedSend(data);
  }
}

DataConnection.prototype._bufferedSend = function(msg) {
  if (this._buffering || !this._trySend(msg)) {
    this._buffer.push(msg);
    this.bufferSize = this._buffer.length;
  }
}

// Returns true if the send succeeds.
DataConnection.prototype._trySend = function(msg) {
  try {
    this._dc.send(msg);
  } catch (e) {
    this._buffering = true;

    var self = this;
    setTimeout(function() {
      // Try again.
      self._buffering = false;
      self._tryBuffer();
    }, 100);
    return false;
  }
  return true;
}

// Try to send the first message in the buffer.
DataConnection.prototype._tryBuffer = function() {
  if (this._buffer.length === 0) {
    return;
  }

  var msg = this._buffer[0];

  if (this._trySend(msg)) {
    this._buffer.shift();
    this.bufferSize = this._buffer.length;
    this._tryBuffer();
  }
}

DataConnection.prototype._sendChunks = function(blob) {
  var blobs = util.chunk(blob);
  for (var i = 0, ii = blobs.length; i < ii; i += 1) {
    var blob = blobs[i];
    this.send(blob, true);
  }
}

DataConnection.prototype.handleMessage = function(message) {
  var payload = message.payload;

  switch (message.type) {
    case 'ANSWER':
      // Forward to negotiator
      Negotiator.handleSDP(message.type, this, payload.sdp);
      break;
    case 'CANDIDATE':
      Negotiator.handleCandidate(this, payload.candidate);
      break;
    default:
      util.warn('Unrecognized message type:', message.type, 'from peer:', this.peer);
      break;
  }
}