tcpconnection.java

SMC takes a state machine stored in a .sm file and generates a State pattern in twelve programming l

    /* package */ void transmitFailed(String reason)
    {
        if (_listener != null)
        {
            _listener.transmitFailed(reason, this);
        }

        return;
    }

    /* package */ void receive(TcpSegment segment)
    {
        // Send the TCP segment's data to the socket listener.
        if (_listener != null)
        {
            _listener.receive(segment.getData(), this);
        }

        return;
    }

    // Create a client socket to handle a new connection.
    /* package */ void accept(TcpSegment segment)
    {
        TcpClient accept_client;
        DatagramSocket dgram_socket;

        try
        {
            _address = segment.getSourceAddress();
            _port = segment.getSourcePort();

            // Create a new client socket to handle this side of
            // the socket pair.
            dgram_socket = new DatagramSocket();
            accept_client = new TcpClient(_address,
                                          _port,
                                          dgram_socket,
                                          _sequence_number,
                                          (TcpServer) this,
                                          _listener);


            ((TcpConnection) accept_client).acceptOpen(segment);
        }
        catch (Exception jex)
        {
            // If the open fails, send a reset to the peer.
            send(TcpSegment.RST,
                 null,
                 0,
                 0,
                 segment);
        }

        return;
    }

    /* package */ void accepted()
    {
        TcpServer server = _server;
        TcpConnectionListener listener = _listener;

        // Tell the server listener that a new connection has
        // been accepted. Then clear the server listener because
        // this socket is now truly a client socket. Clear the
        // listener member data now because the callback method
        // will be resetting it and the reset will fail if we
        // don't do it.
        _server = null;
        _listener = null;
        listener.accepted((TcpClient) this, server);

        return;
    }

    // Send the SYN/ACK reply to the client's SYN.
    /* package */ void sendAcceptSynAck(TcpSegment segment)
    {
        int client_port;
        byte[] port_bytes = new byte[2];

        // Tell the far-side client with what port it should now
        // communicate.
        client_port =
            _async_socket.getDatagramSocket().getLocalPort();

        port_bytes[0] = (byte) ((client_port & 0x0000ff00) >> 8);
        port_bytes[1] = (byte)  (client_port & 0x000000ff);
        send(TcpSegment.SYN_ACK,
             port_bytes,
             0,
             2,
             null,
             -1,
             segment);

        return;
    }

    /* package */ void send(int flags,
                            byte[] data,
                            int offset,
                            int size,
                            TcpSegment recv_segment)
    {
        send(flags,
             data,
             offset,
             size,
             recv_segment.getSourceAddress(),
             recv_segment.getSourcePort(),
             recv_segment);
        return;
    }

    /* package */ void send(int flags,
                            byte[] data,
                            int offset,
                            int size,
                            InetAddress address,
                            int port,
                            TcpSegment recv_segment)
    {
        int local_port;
        int ack_number;
        TcpSegment send_segment;
        DatagramSocket socket;

        // Quietly quit if there is not socket.
        if (_async_socket == null ||
            (socket = _async_socket.getDatagramSocket()) == null)
        {
            return;
        }

        // If the address and port were not specified, then send
        // this segment to whatever client socket we are
        // currently speaking.
        if (address == null)
        {
            address = _address;
            port = _port;
        }

        // If there is a recv_segment, then use its destination
        // port as the local port. Otherwise, use the local
        // datagram socket's local port.
        if (recv_segment != null)
        {
            local_port = recv_segment.getDestinationPort();
        }
        else
        {
            local_port =
                _async_socket.getDatagramSocket().getLocalPort();
        }

        // Send the ack number only if the ack flag is set.
        if ((flags & TcpSegment.ACK) == 0)
        {
            ack_number = 0;
        }
        else
        {
            // Figure out the ack number based on the received
            // segment's sequence number and data size.
            ack_number = getAck(recv_segment);
        }

        send_segment =
            new TcpSegment(local_port,
                           address,
                           port,
                           _sequence_number,
                           ack_number,
                           flags,
                           data,
                           offset,
                           size);

        // Advance the sequence number depending on the message
        // sent. Don't do this if message came from an
        // interloper.
        if (address.equals(_address) && port == _port)
        {
            _sequence_number = getAck(send_segment);
        }

        // Now send the data.
        try
        {
            DatagramPacket packet;

            packet = send_segment.packetize();

            // DEBUG
//                System.out.println("Sending packet to " +
//                                   packet.getAddress() +
//                                   ":" +
//                                   Integer.toString(packet.getPort()) +
//                                   ":\n" +
//                                   send_segment);

            _async_socket.getDatagramSocket().send(packet);
            // _fsm.Transmitted();
        }
        catch (IOException io_exception)
        {
            // _fsm.TransmitFailed(io_exception.getMessage());
        }

        return;
    }

    /* package */ void startTimer(String name, long time)
    {
        AsyncTimer.startTimer(name, time, this);
        return;
    }

    /* package */ void stopTimer(String name)
    {
        AsyncTimer.stopTimer(name);
        return;
    }

    /* package */ void setDestinationPort(TcpSegment segment)
    {
        byte[] data;

        // The server socket is telling us the accepted client's
        // port number. Reset the destination port to that.
        data = segment.getData();
        _port = ((((int) data[0]) & 0x000000ff) << 8) |
                 (((int) data[1]) & 0x000000ff);

        // Modify the segment's source port so that the ack will
        // go to the correct destination.
        segment.setSourcePort(_port);

        return;
    }

    private int getAck(TcpSegment segment)
    {
        int retval;

        // The ack # depends on the segment's flags.
        switch (segment.getFlags())
        {
            case TcpSegment.FIN:
            case TcpSegment.SYN:
            case TcpSegment.FIN_ACK:
            case TcpSegment.SYN_ACK:
                retval = segment.getSequenceNumber() + 1;
                break;

            case TcpSegment.PSH:
            case TcpSegment.PSH_ACK:
                retval = segment.getSequenceNumber() +
                         segment.getDataSize();
                break;

            case TcpSegment.ACK:
            default:
                retval = segment.getSequenceNumber();
                break;
        }

        return(retval);
    }

// Member data.

    protected TcpConnectionListener _listener;
    private TcpConnectionContext  _fsm;
    protected AsyncDatagramSocket   _async_socket;
    private int                   _sequence_number;

    // The port to which a client socket is connected.
    protected InetAddress _address;
    protected int         _port;

    // The server which accepted this connection.
    protected TcpServer _server;

    private String _errorMessage;

    // The Initial Sequence Number.
    private static final int ISN = 1415531521;

    // Wait only so long for an ACK (in milliseconds).
    /* package */ static final long ACK_TIMEOUT = 2000;

    // Wait a while before reusing this port (in milliseconds).
    /* package */ static final long CLOSE_TIMEOUT = 10000;

    /* package */ static final long MIN_TIMEOUT = 1;

    // Use this table to translate received segment flags into
    // state map transitions.
    private static Method[] _transition_table;

    static
    {
        try
        {
            Class context = TcpConnectionContext.class;
            Class[] parameters = new Class[1];
            Method undefined;
            int i;

            // All "TCP flag" transitions take a DatagramPacket as
            // a parameter.
            parameters[0] = TcpSegment.class;

            _transition_table = new Method[TcpSegment.FLAG_MASK + 1];

            // First, set all transitions to undefined.
            undefined = context.getDeclaredMethod("UNDEF",
                                                  parameters);
            for (i = 0; i < _transition_table.length; ++i)
            {
                _transition_table[i] = undefined;                    
            }

            // Now go back and set the known transitions.
            _transition_table[TcpSegment.FIN] =
                context.getDeclaredMethod("FIN", parameters);
            _transition_table[TcpSegment.SYN] =
                context.getDeclaredMethod("SYN", parameters);
            _transition_table[TcpSegment.RST] =
                context.getDeclaredMethod("RST", parameters);
            _transition_table[TcpSegment.PSH] =
                context.getDeclaredMethod("PSH", parameters);
            _transition_table[TcpSegment.ACK] =
                context.getDeclaredMethod("ACK", parameters);
            _transition_table[TcpSegment.URG] =
                context.getDeclaredMethod("URG", parameters);
            _transition_table[TcpSegment.FIN_ACK] =
                context.getDeclaredMethod("FIN_ACK", parameters);
            _transition_table[TcpSegment.SYN_ACK] =
                context.getDeclaredMethod("SYN_ACK", parameters);
            _transition_table[TcpSegment.PSH_ACK] =
                context.getDeclaredMethod("PSH_ACK", parameters);
        }
        catch (Exception jex) {}
    }
}