Description

The issue - how to make Puma respond gracefully when a io connection can misbehave/fail at any point in its handling?

This is a difficult thing to test in CI, especially with multiple VM's running on CI runners.

The are infrequent errors in Puma CI, one example below:

Error in reactor loop escaped: mode not supported for this object: r (ArgumentError)
org/nio4r/Selector.java:124:in `register'
/Users/runner/work/puma/puma/lib/puma/reactor.rb:93:in `register'
/Users/runner/work/puma/puma/lib/puma/reactor.rb:77:in `select_loop'
/Users/runner/work/puma/puma/lib/puma/reactor.rb:34:in `block in run'

The error mode not supported for this object: r implies that the socket is no longer valid in some way.

Does it represent a CI specific issue, or is it something that could occur in real use?

At present, there is a great deal of 'rescue handling' re sockets, and where and how exceptions are raised/caught can get messy.

So, is there a way to conditionally test the socket? This PR is just a guess, using an io_ok? method in Client.

I believe @schneems has mentioned something similar somewhere.

Anyway, if people think it's valid, maybe a method needs to also be added somewhere that takes a socket as a parameter, which Client#io_ok? could call. I also haven't thought about logging, etc.

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