How can I connect two Android device by socket without server

Question

I am trying to develop an android application that can exchange data on peer to peer connection with other devices without server. So please suggest how can I do this. Thank you

Answer 1

If you're looking for such P2P over a local network, there are two parts to it:

1. Discovering peers
2. Communicating with peers

Among Android APIs, you can either use Network Service Discovery APIs for this or Wifi P2P Service Discovery APIs.

There's a wrapper library which which uses these internally and has comparatively better documentation - Salut, which can also be used.

I also created a library for P2P - Near, which uses sockets directly. The problem I was facing with Android APIs was that discovery wasn't happening with certainty every time and the underlying issue was unknown.

If you're looking for P2P across the internet, socket IO is a prevalent solution. Even Near should be able to facilitate the transfers if you provide the IP addresses and they're not behind NAT firewalls.

Answer 2

Java provides ServerSocket and Socket to communicate b/w devices. One of the device you can make as server and other device you can make as client and communicate b/w 'em without introducing server hosted on some machine.

The Other and better option is Using Wi-Fi Peer-to-Peer. WifiP2pManager help you to achieve your purpose.Here is an example.

Answer 3

Your design has a big problem : ...

If there is no central server some android devices should act as client and others as server but this will not work in some situations:

• When the mobile telephony provider assigns private and non-public IP

• When the device is connected to a Wi-Fi network but no NAT rule is defined on the router.

In both cases the problem is that the listening port of the device that must act as server is unreachable.

Answer 4

This is a complete code for chat by SocketProgramming without server.

In my Application, first you are a client and you search for a server. When you do not find any server, you become a server and wait for a client.

public class MainActivity extends ActionBarActivity {

private Handler handler = new Handler();
private TextView text;
private EditText input;
private Button send;
private Socket socket;
private DataOutputStream outputStream;
private BufferedReader inputStream;
private String DeviceName = "Device";

private boolean searchNetwork() {
    log("Connecting");
    String range = "192.168.56.";
    for (int i = 1; i <= 255; i++) {
        String ip = range + i;
        try {
            socket = new Socket();
            socket.connect(new InetSocketAddress(ip, 9000), 50);
            outputStream = new DataOutputStream(socket.getOutputStream());
            inputStream = new BufferedReader(new InputStreamReader(
                    socket.getInputStream()));
            DeviceName += "1";
            Log.i("Server", DeviceName);
            log("Connected");
            return true;
        } catch (Exception e) {
        }
    }
    return false;

}

private void runNewChatServer() {
    ServerSocket serverSocket;
    try {
        serverSocket = new ServerSocket(9000);
        log("Waiting for client...");
        socket = serverSocket.accept();
        DeviceName += "2";
        log("a new client Connected");
    } catch (IOException e) {
    }

}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    text = (TextView) findViewById(R.id.text);
    input = (EditText) findViewById(R.id.input);
    send = (Button) findViewById(R.id.send);
    Thread thread = new Thread(new Runnable() {

        @Override
        public void run() {
            try {
                if (!searchNetwork()) {
                    runNewChatServer();

                }

                outputStream = new DataOutputStream(
                        socket.getOutputStream());
                inputStream = new BufferedReader(new InputStreamReader(
                        socket.getInputStream()));
                while (true) {

                    String Message = inputStream.readLine();
                    if (Message != null) {
                        log(Message);
                    }
                }
            } catch (IOException e) {
                log("Error: IO Exception");
                e.printStackTrace();
            }
        }
    });
    send.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {
            if (outputStream == null) {
                return;
            }
            try {
                String Message = input.getText().toString() + "\n";
                outputStream.write(Message.getBytes());
                log2(input.getText().toString());
            } catch (IOException e) {
                e.printStackTrace();
            }
            input.setText("");
        }
    });
    thread.start();

}

private void log(final String message) {
    handler.post(new Runnable() {
        String DeviceName2="";
        @Override
        public void run() {
            if (DeviceName.equals("Device1")) {
                DeviceName2 = "Device2";
            }else if(DeviceName.equals("Device2")) {
                DeviceName2 = "Device1";
            }else{
                DeviceName2 = "UnknowDevice";
            }

            text.setText(text.getText() + "\n" + DeviceName2 + " :"
                    + message);

        }
    });
}
private void log2(final String message) {
    handler.post(new Runnable() {

        @Override
        public void run() {


            text.setText(text.getText() + "\n" + "you" + " :"
                    + message);

        }
    });
}

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_BACK) {
        if (socket != null) {
            try {
                socket.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        System.exit(0);
        return true;
    }
    return super.onKeyDown(keyCode, event);
}

}