let ping only ping when no activity happened

[dvc94ch]

Currently it takes a long time to detect networking issues. It may even take longer to detect the networking issue than it does to resolve it. Some ways to fix this are either:

1. use if-watch to kill connections as soon as the interface going down was detected
2. ping more frequently

there are some caveats with these options:

1. seems pretty unreliable as we need to track what interface the connection comes from.
2. should work well. but to avoid spaming the network with ping messages it would be nice if there was the ability to send pings only if the connection was idle

[thomaseizinger]

Hmm, we could implement a final callback on ProtocolsHandler that gets called if we are planning to shutdown.

An alternative would be to refactor away the automatic closing of connections and instead only report to the behaviour that all handlers for a connection are idle. The behaviour could then choose to either send a message or close the connection.

[dvc94ch]

I don't think this will be required for quic as quic already has a built in keep alive mechansim. tcp kind of has something but it apparently doesn't always work as one would expect.

• https://blog.cloudflare.com/keepalives-considered-harmful/

[thomaseizinger]

Closing as stale. Some related discussion in #3353.