AndroidAsync TCP -- proper way to detect socket is no longer available using write?

Question

I am wondering what is the proper way to check on the client side that a TCP socket opened using the AndroidAsync library is no longer available? This is in the case the (plain TCP, non-AndroidAsync) server did not initiate explicitly closing the socket (so the ClosedCallback is not invoked). For instance, when the server has been cold rebooted.

It seems that the DataCallback is available only when the server sends back data and can't be used to receive error messages.

It seems to me also that

Util.writeAll(socket, (byte[]) payload.array(), new CompletedCallback()
    {
        @Override
        public void onCompleted(Exception ex)
        {
            if (ex != null)
            {
                Log.e(TAG, "write failed with ex message= " + ex.getMessage());
                throw new RuntimeException(ex);
            }
        }
    });

does not throw an Exception either.

So at this point I'm not sure how to detect the socket is no longer available even if the client periodically writes data to it.

score 0 · Answer 1 · answered May 11 '16 at 00:24

0

It will throw an IOexception if you send enough data or call it enough times. It won't throw on the first call due to TCP buffering at both ends.

answered May 11 '16 at 00:24

user207421

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That makes sense. However, the client is a remote controller to the server which has a visual front end. By the time "enough" data/calls are sent, the two would be long out of sync causing a bad user experience. – Objectist May 11 '16 at 21:55

score 0 · Answer 2 · answered May 24 '16 at 20:13

I ended up implementing some sort of a "ping"-alike periodic check. The client opens and immediately closes a TCP connection to the very same port using a plain Java NIO socket call (not using AndroidAsync). If that one times out, it is assumed that the connection has been lost, and a recovery attempt is made once it succeeds again. This periodic check is performed only when the app has focus, or is just awakened. This is clearly a far from ideal workaround but it seems to work for my purposes.

score -1 · Answer 3 · answered May 11 '16 at 00:22

-1

You could use the closed/end callbacks

socket.setClosedCallback(new CompletedCallback()
{
            @Override
            public void onCompleted(Exception ex)
            {

            }
        });

socket.setEndCallback(new CompletedCallback()
{
            @Override
            public void onCompleted(Exception ex)
            {

            }
 });

answered May 11 '16 at 00:22

behelit

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Unfortunately the server is not an AndroidAsync server and won't close the connection so that the callbacks could be invoked. – Objectist May 11 '16 at 21:52
Sorry, what do you mean by non-AndroidAsync server? Even with a node.js, or even a custom c++ tcp server, I still get the end and closed callbacks on the client when the server dies, I don't think it has anything to do with AndroidAsync and it is more of a tcp standard – behelit May 12 '16 at 05:09
In my environment there are other use cases besides shutting down the server (gracefully) when the connection is no longer valid from the viewpoint of both the client and the server. Because the server is not an AndroidAsync server implemented/controlled by me that has to be discovered purely on the client's side. – Objectist May 24 '16 at 20:08

AndroidAsync TCP -- proper way to detect socket is no longer available using write?

3 Answers3