How to reconnect with socket after server power failure from Android Client

Question

I have a server program in python which sends and receives data packets to and from android client. I am using TCP with sockets in android client to communicate with python program. Every thing is working fine but when the server is shutdown with an NSF power failure it disconnected from client.

My Question is how I check for the availability of the server all the time using android services or any BroadcastReceiver or inside my MainActivity when socket closed or disconnected. I don't want to restart my client application again after server power failure.

selbie · Answer 1 · 2016-11-24T11:28:13.110

In the absence of data being exchanged and without the TCP keep-alive option set on the socket, a socket will be unaware that the remote connection suddenly disappeared. This isn't anything new, it's been a well known socket design problem.

The general pattern is to have some sort of keep alive or ping protocol on the socket that sends a "I'm still here" message between client and server so both endpoints know the other side hasn't gone away. When an endpoint goes offline, the remote socket will fail on a subsequent recv\send call (or throw an exception). Thereby the application or server can handle the disconnect as it sees fit. But this presents an interesting challenge on mobile - frequent network messages may drain the battery by keeping the radio on.

Mobile devices, including Android, typically don't keep long running socket connections to services. Instead, the client will "connect on demand" and close the socket when it's done. Similarly, if the server needs to send something to the device, it typically makes use of the platform's "push" notification service. On Android, the current push notification service is FCM. The client registers with FCM and the server. When the server has something new to give to the client, it sends a push notification through FCM. The client app in turn, gets the notification message as a wakeup that something new is available, and then reconnects to the server to get the actual message. The best example of this is email on a mobile device.

score 0 · Answer 2 · edited Nov 24 '16 at 09:42

0

You can send ping packets to check if the server is alive.

edited Nov 24 '16 at 09:42

Ole V.V.

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answered Nov 24 '16 at 09:21

baliman

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But where? as I am on the MainActivity of the application. – Husnain Aslam Nov 24 '16 at 09:24
I don't know android but maybe you can fire some thread which checks your server every xxx seconds or something like that. – baliman Nov 24 '16 at 09:45
see also http://stackoverflow.com/questions/1443166/android-how-to-check-if-the-server-is-available – baliman Nov 24 '16 at 09:47

score 0 · Accepted Answer · answered Nov 24 '16 at 12:59

For those with the same issue.

I have created AsyncTask to ping or heartbeat the server and call this task every second using Timer in my MainActivity.

new Timer().schedule(new TimerTask(){
  @Override
  public void run(){
      new connectTaskMain().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
  }
}, 1000);

How to reconnect with socket after server power failure from Android Client

3 Answers3