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Android UDP Communication

I read a lot of posts on this site about how to receive UDP packets in Android. However, none of this works for me!

Some basics:

I am testing my HTC Incredible (Android 2.2) on 3G (not Wi-Fi or something else). Emulators are not involved here.

My code is simple:

  • My server (runs on my PC) listens for UDP traffic on port 8752.
  • My Android application opens a DatagramSocket on a random port and sends a packet to my server with that port.
  • Then I save this information (InetAddress forms the received packet and the port found in the packet).
  • I am trying to send a UDP packet from my server (again, on my PC) to my Android application (works on my phone), and it does NOT work.
//Server code to initialize the UDP socket (snippet)
public void init() {
    datagram_server_socket = new DatagramSocket(port,local_addr);
    datagram_server_socket.setSoTimeout(1000);
}

// Code snippet on ANDROID APP that sends the packet to the server

public void connect() {
    Random r = new Random(System.currentTimeMillis());
    int udp_port = 0;
    while(true){
        try {
            udp_port = r.nextInt(1000)+8000;
            udp_port = 8000;
            comm_skt = new DatagramSocket(udp_port);
            Log.i("ServerWrapper", "UDP Listening on port: " + udp_port);
            break;
        } catch(SocketException e) {
            Log.e("ServerWrapper", "Could not bind to port " + udp_port);
        }
    }
    byte[] sdata = new byte[4+tid.length];
    i = 0;
    sdata[i++] = (byte)(0XFF&(udp_port>>24));
    sdata[i++] = (byte)(0XFF&(udp_port>>16));
    sdata[i++] = (byte)(0XFF&(udp_port>>8));
    sdata[i++] = (byte)(0XFF&(udp_port));
    for(byte b: tid){
        sdata[i++] = b;
    }
    DatagramPacket pkt = new DatagramPacket(sdata, sdata.length, 
                                InetAddress.getByName(hostname), port);
    comm_skt.send(pkt);
}

//Server UDP socket listening code
public void serverUDPListener() {
    try {
        datagram_server_socket.receive(rpkt);
        int port = 0;
        byte[] rdata = rpkt.getData();
        port += rdata[0]<<24;
        port += rdata[1]<<16;
        port += rdata[2]<<8;
        port += (0XFF)&rdata[3];
        byte[] tid = new byte[rdata.length];
        for(int i = 4; i < rdata.length && rdata[i] > 0; i++) {
            tid[i-4] = rdata[i];
        }
        String thread_id = new String(tid).trim();
        for(int i = 0; i < threads.size(); i++) {
        ClientThread t = threads.get(i);
        if(t.getThreadId().compareTo(thread_id) == 0) {
            t.setCommSocket(rpkt, port);
        } else {
            System.err.println("THREAD ID " + thread_id + " COULD NOT BE FOUND");
        }
        }
    } catch (IOException e) {
        if(!(e instanceof SocketException) && !(e instanceof SocketTimeoutException))
        log.warning("Error while listening for an UDP Packet.");
    }
}

//Corresponds to the setCommSocket call above to save the IP and Port of the incoming UDP packet on the server-end
public void setCommSocket(DatagramPacket pkt, int port) {
    comm_ip = pkt.getAddress();
    comm_port = pkt.getPort(); //Try the port from the packet?
}

//Sends an UDP packet from the SERVER to the ANDROID APP
public void sendIdle() {
    if(comm_ip != null) {
        System.err.println("Sent IDLE Packet (" + comm_ip.getHostAddress() + ":" + comm_port + ")");
        DatagramPacket spkt = new DatagramPacket(new byte[]{1, ProtocolWrapper.IDLE}, 2, comm_ip, comm_port);
        DatagramSocket skt;
        try {
            skt = new DatagramSocket();
            skt.send(spkt);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

, 8000. , , EVERYTIME ( IP-, ), , 33081. , UDP- Android-, "receive (packet)":

public void AndroidUDPListener() {
    while(true) {
        synchronized(stop) {
        if(stop) return;
        }
        byte[] recieve_data = new byte[64];
        DatagramPacket rpkt = new DatagramPacket(recieve_data, recieve_data.length);
        try {
        if(comm_skt == null) 
                continue;
        comm_skt.receive(rpkt);
        byte[] data = rpkt.getData();
        switch(data[1]) {
            case IDLE:
            if(ocl != null) ocl.onCompletion(null);
            break;
            case KEEP_ALIVE:
            break;
        }
        } catch (Exception e) {
        if(!(e instanceof SocketException) && !(e instanceof SocketTimeoutException))
                Log.w("ServerWrapper", "Error while listening for an UDP Packet.");
        }
    }
}

- ? - /, ? -.

( getPort()):

Android App - UDP 8000

Android- -

- XXXXXX: 33081

- IDLE XXXXXX: 33081

( ):

Android App - UDP 8000

Android- -

- XXXXXX: 8000

- IDLE XXXXXX: 8000

Android- UDP- .

+5
3

, . ​​ :

DatagramSocket . , . .

:

public void setCommSocket(DatagramPacket pkt, int port, DatagramSocket skt)
{
  comm_ip = pkt.getAddress();
  comm_port = pkt.getPort();
  synchronized(comm_pkt) {
    comm_pkt = pkt;
  }
  comm_skt = skt;
}

:

public void UDPListen() {
        while(true) {
            synchronized(stop) {
                if(stop)
                    break;
            }

            byte[] recieve_data = new byte[64];
            DatagramPacket rpkt = new DatagramPacket(recieve_data, recieve_data.length);
            try {
                datagram_server_socket.receive(rpkt);
                int port = 0;
                byte[] rdata = rpkt.getData();
                port += rdata[0]<<24;
                port += rdata[1]<<16;
                port += rdata[2]<<8;
                port += (0XFF)&rdata[3];
                byte[] tid = new byte[rdata.length];
                for(int i = 4; i < rdata.length && rdata[i] > 0; i++)
                {
                    tid[i-4] = rdata[i];
                }
                String thread_id = new String(tid).trim();
                for(int i = 0; i < threads.size(); i++) {
                    ClientThread t = threads.get(i);
                    if(t.getThreadId().compareTo(thread_id) == 0)
                    {
                        t.setCommSocket(rpkt, port, datagram_server_socket);
                    } else {
                        System.err.println("THREAD ID " + thread_id + " COULD NOT BE FOUND");
                    }
                }
            } catch (IOException e) {
                if(!(e instanceof SocketException) && !(e instanceof SocketTimeoutException))
                    log.warning("Error while listening for an UDP Packet.");
            } finally {
                for(int i = 0; i < threads.size(); i++) {
                    ClientThread t = threads.get(i);
                    t.sendKeepAlive();
                }
            }
        }
    }

/, . , , , . , :

public void sendIdle() {
        if(comm_ip != null) {
            synchronized(comm_pkt) {
                try {
                    comm_pkt.setData(new byte[]{1, ProtocolWrapper.IDLE});
                    comm_skt.send(comm_pkt);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }

    }

-, , :

public class PeerWrapper {

    private InetAddress ipaddress;
    private Integer port;
    private Socket client_socket;
    private InetAddress comm_ip;
    private DatagramSocket comm_skt;
    private DatagramPacket comm_pkt;
    private int comm_port;
    private byte status;
+3

. Android (/), - (/). , . , , , , .

: Android: java.net.DatagramSocket.bind: . , . , , ( IP-) , .getLocalPort() [], .

+2

Android

+1
source

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