Phone to phone/emulator comminication

[Mike Brooks]

Hello what i am doing is creating a program that will let me allow two android phones to communicate over TCP. The code that I have is

Server:

 

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.ServerSocket;
import java.net.Socket;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

public class TCPServer extends Activity {
    /** Called when the activity is first created. */
	public static TextView tv;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
//        setContentView(R.layout.main);
        
        tv = new TextView(this);
        tv.setText("Main - server");        
        setContentView(tv);
        
        Thread sThread = new Thread(new TCPServerTest());

        sThread.start();
    }
}

class TCPServerTest implements Runnable{
    
    public static final String SERVERIP = "127.0.0.1";
    public static final int SERVERPORT = 4444;
         
    public void run() {
         try {
              Log.d("TCP", "S: Connecting...");
             
              ServerSocket serverSocket = new ServerSocket(SERVERPORT);
              while (true) {
                 Socket client = serverSocket.accept();
                 Log.d("TCP", "S: Receiving...");
                 try {
                      BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
                      String str = in.readLine();
                      Log.d("TCP", "S: Received: '" + str + "'");
                      TCPServer.tv.setText(str);
                    } catch(Exception e) {
                        Log.e("TCP", "S: Error", e);
                    } finally {
                         client.close();
                         Log.d("TCP", "S: Done.");
                    }

              }
             
         } catch (Exception e) {
           Log.e("TCP", "S: Error", e);
         }
    }
} 

Client:

    

import java.io.BufferedWriter;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

public class TCPClient extends Activity {
    /** Called when the activity is first created. */
	public TextView tv;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
//        setContentView(R.layout.main);
        
        tv = new TextView(this);
        tv.setText("Main - client");        
        setContentView(tv);
        
        Thread cThread = new Thread(new TCPClientTest());
        
        cThread.start();
    }
}

class TCPClientTest implements Runnable {

    
    public void run() {
         try {
           
           InetAddress serverAddr = InetAddress.getByName("127.0.0.1");
           
           Log.d("TCP", "C: Connecting...");
           Socket socket = new Socket(serverAddr, 4444);
           String message = "Hello from Client";
               try {
                Log.d("TCP", "C: Sending: '" + message + "'");
                PrintWriter out = new PrintWriter( new BufferedWriter( new OutputStreamWriter(socket.getOutputStream())),true);
               
                out.println(message);
                Log.d("TCP", "C: Sent.");
                  Log.d("TCP", "C: Done.");
               
             } catch(Exception e) {
                 Log.e("TCP", "S: Error", e);
                } finally {
                  socket.close();
                }
         } catch (Exception e) {
              Log.e("TCP", "C: Error", e);
         }
    }
}

The problem is when I run the client on the emulator and then the server on the phone the client produces the following error. Note the server is running first and both programs have Internet permissions in the mainifest.

   

D/TCP     (  700): C: Connecting...
E/TCP     (  700): C: Error
E/TCP     (  700): java.net.ConnectException: /127.0.0.1:4444 - Connection refused
E/TCP     (  700): 	at org.apache.harmony.luni.net.PlainSocketImpl.connect(PlainSocketImpl.java:237)
E/TCP     (  700): 	at org.apache.harmony.luni.net.PlainSocketImpl.connect(PlainSocketImpl.java:199)
E/TCP     (  700): 	at java.net.Socket.startupSocket(Socket.java:734)
E/TCP     (  700): 	at java.net.Socket.<init>(Socket.java:245)
E/TCP     (  700): 	at com.budasmj.TCPClientTest.run(TCPClient.java:41)
E/TCP     (  700): 	at java.lang.Thread.run(Thread.java:1058)

My aim is to use two phone where a phone is the server and the client is also on a phone. Any help would be much appreciated.

[Tim Holloway]

Your first problem is that the "server" phone probably won't have a unique public tcp/ip address. When you're networking via the phone company's over-the-air service, they frequently use DHCP to allocate out of one or more of the private ip address pools.

Assuming, however, that you overcame that problem, you still can expect that there's a fairly serious firewall built into the phones themselves. Phones make very good targets, and there have already been incidents of exploits such as "bluejacking" phones at airports and other public places.

To reliably get 2 phones to converse, you'd need an intermediary that they both could contact. Kind of like Adobe's Acrobat conferencing tool.