Question

Im trying to send a command through telnet to my computer which then sends the command to a serial port, when using telnet using

adb shell
$telnet 172.20.104.203 5334
$h

it returns the data from the command h, how ever when I try to do this using android it connects to the socket, I can see this on the computer, it sends the command but then as soon as it logs that it has sent it hangs and comes up with “Application not responding” and it has wait or force close and if I wait it just stays the same.

This is my code for the telnet part

    private static final int TCP_SERVER_PORT = 5334;

    private void runTcpClient() {
        try {
            Socket s = new Socket("172.20.104.203", TCP_SERVER_PORT);
            BufferedReader in = new BufferedReader(new InputStreamReader(s.getInputStream()));
            BufferedWriter out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
            //send output msg
            String outMsg = "$getPos"; 
            out.write(outMsg);
            out.flush();
            Log.i("TcpClient", "sent: " + outMsg);
            //accept server response
            String inMsg = in.readLine() + System.getProperty("line.separator");
            Log.i("TcpClient", "received: " + inMsg);
            //close connection
            s.close();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } 
    }

It logs the send, but it never logs the receive, I thought it might be something to do with the amount of data being received so I just sent

$getPos 

instead but it still hangs.

Any one know what could be happening?

Answer 1

I’m not familiar with the particulars of the platform, but its unlikely that a readline will work on a socket/tcp stream, or if it works, it will work unreliably. Data coming in from a socket is not necessarily organized into ‘lines’, but instead packets of a particular size. A ‘read’ performed on a socket will return some number of bytes.

The client doing such reads needs to read each packet, buffer them until it receives an agreed-upon ‘end of data’ marker. The marker agreed-upon is determined by protocol.

You’ve shown us the client side of your code. Do you have a corresponding server side?

From what you have here, my guess is that your client code is waiting patiently for an ‘end of line’ that for some reason, will never come. OR there’s something wrong at the server end and the server isn’t sending any data to the client.