Sending binary data multiple times using Sockets in Java/Android

Question

I need to send binary data multiple times with Java Sockets on Android devices. This is a simple object that exports run() and send() methods.

public class GpcSocket {

    private Socket socket;

    private static final int SERVERPORT = 9999;
    private static final String SERVER_IP = "10.0.1.4";

    public void run() {
        new Thread(new ClientThread()).start();
    }

    public int send(byte[] str) {
        try {
            final BufferedOutputStream outStream = new BufferedOutputStream(socket.getOutputStream());
            outStream.write(str);
            outStream.flush();
            outStream.close();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return str.length;
    }

    class ClientThread implements Runnable {
        @Override
        public void run() {
            try {
                InetAddress serverAddr = InetAddress.getByName(SERVER_IP);
                socket = new Socket(serverAddr, SERVERPORT);
            } catch (UnknownHostException e1) {
                e1.printStackTrace();
            } catch (IOException e1) {
                e1.printStackTrace();
            }
        }
    }
}

For Android Programming, I use Scaloid, and this is the code to send the binary data multiple times. count is given from a parameter. result is Byte[Array] type data, and gpc is initialized in onCreate() method as gpc = new GpcSocket().

gpc.run()
for (i <- 1 to count) {
  val length = gpc.send(result)
  toast(s"Sent: $i $length")
}

The issue is that even when I try to send data multiple times, the receiver receives only one packet. This is what is shown in the server (receiver) side when I send the information 5 times:

55:2015-03-21 03:46:51 86: <RECEIVED DATA>
10.0.1.27 wrote:
56:2015-03-21 03:46:51 0:
10.0.1.27 wrote:
57:2015-03-21 03:46:51 0:
10.0.1.27 wrote:
58:2015-03-21 03:46:51 0:
10.0.1.27 wrote:
59:2015-03-21 03:46:51 0:

My questions are

• Why is this? Why the receiver receives only one time? The sender shows that it sends the information five times.
• Do I need to use run() one time only before sending multiple times? Or, do I have to call run() whenever I use send()?

This is the server side code in Python:

import SocketServer
from time import gmtime, strftime

count = 1

class MyTCPHandler(SocketServer.BaseRequestHandler):
    """
    The RequestHandler class for our server.

    It is instantiated once per connection to the server, and must
    override the handle() method to implement communication to the
    client.
    """

    def handle(self):
        # self.request is the TCP socket connected to the client
        self.data = self.request.recv(1024).strip()
        print "{} wrote:".format(self.client_address[0])
        global count
        count += 1
        print "%d:%s %d:%s" % (count, strftime("%Y-%m-%d %H:%M:%S", gmtime()), len(self.data), self.data)
        # just send back the same data, but upper-cased
        self.request.sendall(self.data.upper())

if __name__ == "__main__":
    HOST, PORT = "10.0.1.4", 9999

    # Create the server, binding to localhost on port 9999
    server = SocketServer.TCPServer((HOST, PORT), MyTCPHandler)

    # Activate the server; this will keep running until you
    # interrupt the program with Ctrl-C
    server.serve_forever()

Answer 1

From this post: Sending ByteArray using Java Sockets (Android programming) and How to fix java.net.SocketException: Broken pipe?, it seems like that the send() method is wrong.

Close the resources when I'm done using them

I modified the send() to be simple that create the socket and close it when I'm done using it.

public int send(byte[] str) throws IOException {
    InetAddress serverAddr = InetAddress.getByName(SERVER_IP);
    socket = new Socket(serverAddr, SERVERPORT);
    out = socket.getOutputStream();
    out.write(str);
    out.flush();
    out.close();
    socket.close();
    return str.length;
}

Modification in the caller code

The scala code that calls it is modified to invoke the send() method.

// gpc.run()
for (i <- 1 to count) {
  ...
  val length = gpc.send(result)
  println(s"Sent: $i $length")
}

... in initializer
gpc = new GpcSocket()

Change policy mode in Android

Hints from this post: android.os.NetworkOnMainThreadException at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1145), this code should be added for Android device to prevent E/AndroidRuntime﹕ FATAL EXCEPTION: main Process: scaloid.example, PID: 1791 android.os.NetworkOnMainThreadException error.

val policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);