Retry syscalls on EINTR in internal.Connect (fixes: #141)

[MaxMaeder]

Retry connect and select syscalls if we get EINTR in Internal.Connect().

[sergiu128]

Looks good, thank you very much! Just needs to handle some edge cases.. and my mistake of not correctly testing for syscall.Errnos :)

[sergiu128]

Unlikely to happen, but there's an extreme case here where we always get EINTR. In this scenario we don't want to hot loop endlessly, so I think we should take note of the timeout here by making it a for condition. We'll then only loop for at most timeout.

[sergiu128]

Another improvement is to return an error if the timeout is zero.

[sergiu128]

Another improvement is to test for Errnos correctly, according to the spec https://pkg.go.dev/syscall#Errno. This means using errors.Is pretty much everywhere in this function.

[sergiu128]

We should also not hot-loop endlessly here if select gets EINTR. Because this syscall takes a timeout already, what we can do here is retry on EINTR for at most say 5 * timeout.

[MaxMaeder]

Should be fixed! I now test for errno correctly.

For the timeouts, I added a specific case in the connect() loop so we can return a sonicerrors.ErrTimeout:

// Prevent an infinite connect() loop, time out eventually
if time.Since(startTime) > 5 * timeout {
	return sonicerrors.ErrTimeout
}

For the select() loop, I just updated the timeout we pass to the syscall.

Linux will update t with the time not slept after each call to select() (man page), so we don't need an separate check like the other loop. This works because we already check if an individual select() call times out.

This was not a very readable solution, and had dubious compatibility with BSD etc. I've replaced the select() loop logic with:

for {
	// Prevent an infinite select() loop, time out eventually
	remainingTime := 5 * timeout - time.Since(startTime)
	if remainingTime < 0 { 
		return sonicerrors.ErrTimeout
	}

	t := unix.NsecToTimeval(remainingTime.Nanoseconds())

	n, err := unix.Select(fd+1, nil, &fds, nil, &t)

	...

[sergiu128]

Excellent solution! Thanks a lot, changes are good! Sorry for the late review, had a lot going on at work the past week.