Check connection activity

[zerodivisi0n]

Added sending pings if no activity on connection. If no response is received, connection is likely lost.

I found that the writing to SocketChannel succeeds even if the connection is broken. Even there is a bug in Android. It exists everywhere, including 4.1.

So the only way to determine the loss of connection is sending WebSocket pings. My solution is based on similar in Pusher Protocol.

[william-ferguson-au]

Is there any plans to merge this change?
I think it might resolve #36

[Berglund]

Looks good to me.

[ghost]

I am using pingpong mechanism in my project but the connection stable if the pingpong interval is less than 5 min, I tested with 6 min and more time interval but in that case after 2 or 3 pingpong there is no connection, i'am using 2.3.3 device for testing.

[ingcaratozzolo]

Are there news about this problem? The call to onClose is successful with a device with Android 4.4.2 kitkat; instead of a device with Android 5.0.1 lollipop the problem persists.

[oberstet]

We have started basically a complete rewrite of AutobahnAndroid (incubated on branch https://github.com/crossbario/autobahn-java/tree/abjv2), so this PR/issue does not apply anymore.

The rewrite will add full support for both TLS and WAMPv2. It will run on both Android and plain Java 8 (client). The user API for WAMP will be based on CompletableFuture (no callback hell anymore).