feat: add client_idle_timeout option

[abc3]

This PR adds a configurable option to prevent zombie issues and enables keepalive in incoming connections.

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• If a client stays connected but doesn't send any messages over the connection for N milliseconds, then disconnect the client
• Disabled by default
• Put on tenant record
• Name it client_idle_timeout or idle_timeout_downstream??
• Set keepalive in ranch to true

[chasers]

Let’s call this the same thing as pgbouncer client_idle_timeout

[abc3]

the terms downstream/upstream offer more specific and clear definitions and we are already using them in the project

[chasers]

Yeah but people will be looking for equivalent configs.

[josevalim]

👍 on client_idle_timeout.

The current implementation is great as is, because it seems you only want to enable the timeout in certain scenarios. Although I believe the current implementation would not close the connection if it asks for a query and then forgets (or is too slow) to read it for some reason, right?

In any case, if you wanted to enable the timeout on most handle_event returns, then I am not the biggest fan of gen_statem/gen_server timeouts because if you forget to return timeout in a single callback, then it may no longer trigger as expected.

[abc3]

Although I believe the current implementation would not close the connection if it asks for a query and then forgets (or is > too slow) to read it for some reason, right?

Yeah, that is not covered

In any case, if you wanted to enable the timeout on most handle_event returns, then I am not the biggest fan of gen_statem/gen_server timeouts because if you forget to return timeout in a single callback, then it may no longer trigger as expected.

@josevalim, what would you recommend using for timeouts? Should I use Process.send_after? I'll need to add a bunch of other timeouts soon

[josevalim]

It really depends on the nature of timeouts. Sometimes send_after. Sometimes you can store timestamps on the state and compare when messages arrive, etc. Once you have more details, let us know, and we will gladly discuss :)