Fix server open connection leaks

[tengattack]

Hi,

I think we should close connection & sig in the server after io.ReadFull errors.

Some healthcheck method (K8s, AWS ELB Target Groups, etc.) will close connection and trigger the EOF error here.

[cla-checker-service]

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[andresrc]

@elastic/agent

[urso]

Nice catch. We should always close sig. How about changing the go function to always close sig via defer? In that case the second go-routine will do the client.Close always.

e.g.

go func() {
  defer close(sig)
  
  var buf [1]byte
  // keep rest as is
}()

Actually we might consider to remove the client.Close at the end, as the second go-routine in handle waits for a) the server shutting down or b) the handling go-routine having finished. If sig is closed properly we will always close the client.

[tengattack]

Sure, defer would be better here. Actually, the second go-routine will not do the client.Close after sig closed as it placed in a difference case and the client connection will be used in the channel. So I kept the client.Close here.

[urso]

Change looks good. Thanks.