Improve lost connection detection

[marci4]

E.g. using this lib on a smartphone, you may lose the connection.

Related issues:
#471
#180

[marci4]

Looking for some input here!

I implemented a check with a timer.
It sends pings in a definied interval (default: 30s)
If there was an error sending this ping, the websocket gets closed
You can deactivate this check setting the interval below 1.

Check out the code here

Did I miss something?
Should I add anything?

Greetings
marci4

[zhoulifu]

Hello @marci4
In my opinion, it's not enough to detecting the disconnection just sending ping.
For example, one client was shut down suddenly, without sending closeframe or closing the connection, the server could still send message to this disconnected connection without any errors due to the tcp retransmission. Drop all outgoing packages from client side using iptables can simulate this scenario:

iptables -A OUTPUT -p tcp --sport {CLIENT_PORT} -j DROP

So it's necessary to check whether the corresponding pong was received within a certain amount of time. But this would bring more pressure to server when there are plenty of clients.

[marci4]

Thx for your input @zhoulifu :)

This will add a bit more pressure but I think it is fine, especially since you have the possibility to turn it off.

Greetings
marci4

[marci4]

Ok I added a check for the pong response.

Default check interval is 30 seconds, is this to often?

Could you please check if for you this is working as well?

Greetings
marci4

[zhoulifu]

Hey @marci4, i've tested it and it works 👍
30s is okay i think since pong arrived within hundreds of milliseconds in general.