/**
   * Opens new WebRTC data channel using specified parameters.
   *
   * @param type channel type as defined in control protocol description. Use 0 for "reliable".
   * @param prio channel priority. The higher the number, the lower the priority.
   * @param reliab Reliability Parameter<br>
   *     This field is ignored if a reliable channel is used. If a partial reliable channel with
   *     limited number of retransmissions is used, this field specifies the number of
   *     retransmissions. If a partial reliable channel with limited lifetime is used, this field
   *     specifies the maximum lifetime in milliseconds. The following table summarizes this:<br>
   *     </br>
   *     <p>+------------------------------------------------+------------------+ | Channel Type |
   *     Reliability | | | Parameter |
   *     +------------------------------------------------+------------------+ |
   *     DATA_CHANNEL_RELIABLE | Ignored | | DATA_CHANNEL_RELIABLE_UNORDERED | Ignored | |
   *     DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT | Number of RTX | |
   *     DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT_UNORDERED | Number of RTX | |
   *     DATA_CHANNEL_PARTIAL_RELIABLE_TIMED | Lifetime in ms | |
   *     DATA_CHANNEL_PARTIAL_RELIABLE_TIMED_UNORDERED | Lifetime in ms |
   *     +------------------------------------------------+------------------+
   * @param sid SCTP stream id that will be used by new channel (it must not be already used).
   * @param label text label for the channel.
   * @return new instance of <tt>WebRtcDataStream</tt> that represents opened WebRTC data channel.
   * @throws IOException if IO error occurs.
   */
  public synchronized WebRtcDataStream openChannel(
      int type, int prio, long reliab, int sid, String label) throws IOException {
    if (channels.containsKey(sid)) {
      throw new IOException("Channel on sid: " + sid + " already exists");
    }

    // Label Length & Label
    byte[] labelBytes;
    int labelByteLength;

    if (label == null) {
      labelBytes = null;
      labelByteLength = 0;
    } else {
      labelBytes = label.getBytes("UTF-8");
      labelByteLength = labelBytes.length;
      if (labelByteLength > 0xFFFF) labelByteLength = 0xFFFF;
    }

    // Protocol Length & Protocol
    String protocol = WEBRTC_DATA_CHANNEL_PROTOCOL;
    byte[] protocolBytes;
    int protocolByteLength;

    if (protocol == null) {
      protocolBytes = null;
      protocolByteLength = 0;
    } else {
      protocolBytes = protocol.getBytes("UTF-8");
      protocolByteLength = protocolBytes.length;
      if (protocolByteLength > 0xFFFF) protocolByteLength = 0xFFFF;
    }

    ByteBuffer packet = ByteBuffer.allocate(12 + labelByteLength + protocolByteLength);

    // Message open new channel on current sid
    // Message Type
    packet.put((byte) MSG_OPEN_CHANNEL);
    // Channel Type
    packet.put((byte) type);
    // Priority
    packet.putShort((short) prio);
    // Reliability Parameter
    packet.putInt((int) reliab);
    // Label Length
    packet.putShort((short) labelByteLength);
    // Protocol Length
    packet.putShort((short) protocolByteLength);
    // Label
    if (labelByteLength != 0) {
      packet.put(labelBytes, 0, labelByteLength);
    }
    // Protocol
    if (protocolByteLength != 0) {
      packet.put(protocolBytes, 0, protocolByteLength);
    }

    int sentCount = sctpSocket.send(packet.array(), true, sid, WEB_RTC_PPID_CTRL);

    if (sentCount != packet.capacity()) {
      throw new IOException("Failed to open new chanel on sid: " + sid);
    }

    WebRtcDataStream channel = new WebRtcDataStream(sctpSocket, sid, label, false);

    channels.put(sid, channel);

    return channel;
  }
  /**
   * Handles control packet.
   *
   * @param data raw packet data that arrived on control PPID.
   * @param sid SCTP stream id on which the data has arrived.
   */
  private synchronized void onCtrlPacket(byte[] data, int sid) throws IOException {
    ByteBuffer buffer = ByteBuffer.wrap(data);
    int messageType = /* 1 byte unsigned integer */ 0xFF & buffer.get();

    if (messageType == MSG_CHANNEL_ACK) {
      if (logger.isDebugEnabled()) {
        logger.debug(getEndpoint().getID() + " ACK received SID: " + sid);
      }
      // Open channel ACK
      WebRtcDataStream channel = channels.get(sid);
      if (channel != null) {
        // Ack check prevents from firing multiple notifications
        // if we get more than one ACKs (by mistake/bug).
        if (!channel.isAcknowledged()) {
          channel.ackReceived();
          notifyChannelOpened(channel);
        } else {
          logger.warn("Redundant ACK received for SID: " + sid);
        }
      } else {
        logger.error("No channel exists on sid: " + sid);
      }
    } else if (messageType == MSG_OPEN_CHANNEL) {
      int channelType = /* 1 byte unsigned integer */ 0xFF & buffer.get();
      int priority = /* 2 bytes unsigned integer */ 0xFFFF & buffer.getShort();
      long reliability = /* 4 bytes unsigned integer */ 0xFFFFFFFFL & buffer.getInt();
      int labelLength = /* 2 bytes unsigned integer */ 0xFFFF & buffer.getShort();
      int protocolLength = /* 2 bytes unsigned integer */ 0xFFFF & buffer.getShort();
      String label;
      String protocol;

      if (labelLength == 0) {
        label = "";
      } else {
        byte[] labelBytes = new byte[labelLength];

        buffer.get(labelBytes);
        label = new String(labelBytes, "UTF-8");
      }
      if (protocolLength == 0) {
        protocol = "";
      } else {
        byte[] protocolBytes = new byte[protocolLength];

        buffer.get(protocolBytes);
        protocol = new String(protocolBytes, "UTF-8");
      }

      if (logger.isDebugEnabled()) {
        logger.debug(
            "!!! "
                + getEndpoint().getID()
                + " data channel open request on SID: "
                + sid
                + " type: "
                + channelType
                + " prio: "
                + priority
                + " reliab: "
                + reliability
                + " label: "
                + label
                + " proto: "
                + protocol);
      }

      if (channels.containsKey(sid)) {
        logger.error("Channel on sid: " + sid + " already exists");
      }

      WebRtcDataStream newChannel = new WebRtcDataStream(sctpSocket, sid, label, true);
      channels.put(sid, newChannel);

      sendOpenChannelAck(sid);

      notifyChannelOpened(newChannel);
    } else {
      logger.error("Unexpected ctrl msg type: " + messageType);
    }
  }