Question

I am learning android but I can’t get past the InputStream.read().
This is just a socket test – the server sends back two bytes when it receives a connection and I know that this working fine. All I want to do is read these values. The b = data.read reads both values in turn but then hangs, it never returns the -1 value which is what expect it to. Also it does not throw an exception.

Any ideas?
Thanks.

protected void startLongRunningOperation() {

    // Fire off a thread to do some work that we shouldn't do directly in the UI thread
    Thread t = new Thread() {
        public void run() {
            try {
                Log.d("Socket", "try connect ");
                Socket sock = new Socket("192.168.0.12", 5001);
                Log.d("socket", "connected");
                InputStream data = sock.getInputStream();

                int b = 0;
                while (b != -1) {
                    b = data.read();

                }


                data.close();
            } catch (Exception e) {
                Log.d("Socket", e.toString());
            }
        }
    };
    t.start();
}

Answer 1

Reaching the end of the stream is a special state. It doesn’t happen just because there is nothing left to read. If the stream is still open, but there’s nothing to be read, it will “hang” (or block) as you’ve noticed until a byte comes across.

To do what you want, the server either needs to close/end the stream, or you need to use:

while (data.available() > 0) {
  ..

When the number of available bytes is zero, there’s nothing sitting in the stream buffer to be read.

On the other hand, if you know that there should only ever be two bytes to read, and that’s the end of your data, then just read the two bytes and move on (i.e. don’t use a while loop). The reason to use a while loop here would only be if you weren’t sure how many total bytes to expect.