/**
   * Process an incoming datagram
   *
   * @param packet is the incoming datagram packet.
   */
  private void processIncomingDataPacket(DatagramPacket packet) throws Exception {
    this.peerAddress = packet.getAddress();
    int packetLength = packet.getLength();
    // Read bytes and put it in a eueue.
    byte[] bytes = packet.getData();
    byte[] msgBytes = new byte[packetLength];
    System.arraycopy(bytes, 0, msgBytes, 0, packetLength);

    // Do debug logging.
    if (sipStack.isLoggingEnabled()) {
      this.sipStack.logWriter.logDebug(
          "UDPMessageChannel: processIncomingDataPacket : peerAddress = "
              + peerAddress.getHostAddress()
              + "/"
              + packet.getPort()
              + " Length = "
              + packetLength);
    }

    SIPMessage sipMessage = null;
    try {
      this.receptionTime = System.currentTimeMillis();
      sipMessage = myParser.parseSIPMessage(msgBytes);
      myParser = null;
    } catch (ParseException ex) {
      myParser = null; // let go of the parser reference.
      if (sipStack.isLoggingEnabled()) {
        this.sipStack.logWriter.logDebug("Rejecting message !  " + new String(msgBytes));
        this.sipStack.logWriter.logDebug("error message " + ex.getMessage());
        this.sipStack.logWriter.logException(ex);
      }

      // JvB: send a 400 response for requests (except ACK)
      // Currently only UDP, @todo also other transports
      String msgString = new String(msgBytes, 0, packetLength);
      if (!msgString.startsWith("SIP/") && !msgString.startsWith("ACK ")) {

        String badReqRes = createBadReqRes(msgString, ex);
        if (badReqRes != null) {
          if (sipStack.isLoggingEnabled()) {
            sipStack.getLogWriter().logDebug("Sending automatic 400 Bad Request:");
            sipStack.getLogWriter().logDebug(badReqRes);
          }
          try {
            this.sendMessage(badReqRes.getBytes(), peerAddress, packet.getPort(), "UDP", false);
          } catch (IOException e) {
            this.sipStack.logWriter.logException(e);
          }
        } else {
          if (sipStack.isLoggingEnabled()) {
            sipStack.getLogWriter().logDebug("Could not formulate automatic 400 Bad Request");
          }
        }
      }

      return;
    }
    // No parse exception but null message - reject it and
    // march on (or return).
    // exit this message processor if the message did not parse.

    if (sipMessage == null) {
      if (sipStack.isLoggingEnabled()) {
        this.sipStack.logWriter.logDebug("Rejecting message !  + Null message parsed.");
      }
      return;
    }
    ViaList viaList = sipMessage.getViaHeaders();
    // Check for the required headers.
    if (sipMessage.getFrom() == null
        || sipMessage.getTo() == null
        || sipMessage.getCallId() == null
        || sipMessage.getCSeq() == null
        || sipMessage.getViaHeaders() == null) {
      String badmsg = new String(msgBytes);
      if (sipStack.isLoggingEnabled()) {
        this.sipStack.logWriter.logError("bad message " + badmsg);
        this.sipStack.logWriter.logError(
            ">>> Dropped Bad Msg "
                + "From = "
                + sipMessage.getFrom()
                + "To = "
                + sipMessage.getTo()
                + "CallId = "
                + sipMessage.getCallId()
                + "CSeq = "
                + sipMessage.getCSeq()
                + "Via = "
                + sipMessage.getViaHeaders());
      }

      sipStack.logWriter.logError("BAD MESSAGE!");

      return;
    }
    // For a request first via header tells where the message
    // is coming from.
    // For response, just get the port from the packet.
    if (sipMessage instanceof SIPRequest) {
      Via v = (Via) viaList.getFirst();
      Hop hop = sipStack.addressResolver.resolveAddress(v.getHop());
      this.peerPort = hop.getPort();
      this.peerProtocol = v.getTransport();

      this.peerPacketSourceAddress = packet.getAddress();
      this.peerPacketSourcePort = packet.getPort();
      try {
        this.peerAddress = packet.getAddress();
        // Check to see if the received parameter matches
        // the peer address and tag it appropriately.

        boolean hasRPort = v.hasParameter(Via.RPORT);
        if (hasRPort || !hop.getHost().equals(this.peerAddress.getHostAddress())) {
          v.setParameter(Via.RECEIVED, this.peerAddress.getHostAddress());
        }

        if (hasRPort) {
          v.setParameter(Via.RPORT, Integer.toString(this.peerPacketSourcePort));
        }
      } catch (java.text.ParseException ex1) {
        InternalErrorHandler.handleException(ex1);
      }

    } else {

      this.peerPacketSourceAddress = packet.getAddress();
      this.peerPacketSourcePort = packet.getPort();
      this.peerAddress = packet.getAddress();
      this.peerPort = packet.getPort();
      this.peerProtocol = ((Via) viaList.getFirst()).getTransport();
    }

    this.processMessage(sipMessage);
  }