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I am making an app that checks for certain connections (looking for a list of SSIDs) and creates an hotspot for said connection if it doesn't find any. Basically it should act as a local area network. I am successful in creating the hotspot, and after that it listens on a server socket for incoming connections:

Thread socketThread = new Thread(new Runnable() {
        @Override
        public void run() {
            int port = Constants.PORT + socketList.size()-1;
            try {
                ServerSocket serverSocket = null;
                serverSocket = new ServerSocket(port);
                Log.d(TAG, "Socket listening for connections: " + port);
                Socket client = serverSocket.accept();
                Log.d(TAG, "Server: connection done");
                InputStream inputstream = client.getInputStream();
                DataInputStream commStream = new DataInputStream(inputstream);
                byte[] b = new byte[16];
                while (commStream.read(b,0, 16) != -1)
                    Log.d(TAG, new String(b, "ASCII"));
                serverSocket.close();
                Log.d(TAG, "Server socket done");
            } catch (Exception e) {
                Log.e(TAG, e.toString());
            }
        }

    });
    socketList.add(socketThread);
    socketThread.start();

If I create the hotspot and connect to it with my pc I am able to use netcat and connect with said socket:

netcat 192.168.43.1 8988

Where 192.168.43.1 is the default Android IP address for the hotspot and 8988 is the port I'm using. However, when I try to do the same through another device running the app and connecting to the hotspot, it doesn't work. Here's the client code:

clientThread = new Thread(new Runnable() {
        @Override
        public void run() {
            int port = Constants.PORT ;
            try {
                Socket socket =new Socket();
                socket.bind(null);
                socket.connect((new InetSocketAddress("192.168.43.1", port)), 20000);
                OutputStream stream = socket.getOutputStream();
                DataOutputStream commStream = new DataOutputStream(stream);
                commStream.write("1234567890123456".getBytes());
                socket.close();
                Log.d(TAG, "Client socket done");
            } catch (Exception e) {
                Log.e(TAG, e.toString());
            }
        }

    });
    clientThread.start();

It doesn't even connect to the server socket, it just waits until timeout. Is there anything I'm doing wrong here?

Thanks in advance.

Maldus
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  • 192.168.43.1 is a local IP address, are you trying this on your local network? – earthw0rmjim Jun 17 '16 at 07:44
  • It should be the IP address of the provider of the hotspot (my device); I want it to create a LAN and to communicate with the devices connected to it. – Maldus Jun 17 '16 at 07:45
  • Not really, I just adapted to opening the server socket on the clients and making the access point start the connection. Still haven't figured out what was wrong. It served its purpose already, but maybe I'll look it up again in the future. – Maldus Jun 28 '16 at 07:43

1 Answers1

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You cannot create a server socket with IP(192.168.43.1) on the device which has created the hotspot. So just reverse the server socket on another device that has been connected to the hotspot.

e.g. Let's say you have created hotspot on Device A and Device B has been connected to A so create the server socket on Device B with assigned local IP and create Socket instance in A by finding the IP of Device B.

Yogeshwar Sharma
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