Fix cancelability of DNS queries

[rokonec]

Fixes: #92054

Context

ConnectAsync(EndPoint, CancellationToken) had not configured downstream code to propagate cancelation to DNS queries.

Changes made

Instruct related AwaitableSocketAsyncEventArgs to be cancelable - authored by @antonfirsov in #92862

• ConnectAsync(this, userSocket: true, saeaCancelable: false) was called with saeaCancelable: false which makes it uncancelable. Configuring it by abilities of used CT maked it work as intended.
• These changes are related to only ConnectAsync, and based on manual code analysis shall not have faulty side effects. However, it could break someone, if they relay of faulty behavior of ignoring passed CT. For example if they set previously timeout to unreasonablyt short time, f.e 100ms, if will now break them as DNS query will now timeout for them.

Propagate cancelation during connect by name (5e25367)

• this is relatively safe change, this could, currently, only happen when connect by name (DNS) is canceled, and since it was not working previously, this code can only be hit with changes from this PR.

[antonfirsov]

@rokonec just to make 100% sure this actually works, I wonder what is the output of this program (or equivalent test case) before/after the change on Windows?

using Socket socket = new(SocketType.Stream, ProtocolType.Tcp);
Stopwatch sw = Stopwatch.StartNew();
try
{
    await socket.ConnectAsync(new DnsEndPoint("does-not-exist", 80), new CancellationTokenSource(500).Token);
}
catch (OperationCanceledException)
{
    Console.WriteLine(sw.ElapsedMilliseconds);
}

I wish we could turn this into a test-case, but unfortunately it would flake in CI.

[rokonec]

just to make 100% sure this actually works

@antonfirsov Good hunch .. it was indeed NOT working properly. It was throwing wrong exception. After the fix in 5e25367 it all seems to be working fine. Please check those changes.

Before

Exception after 2816 ms ex: System.Net.Sockets.SocketException (11001): No such host is known.

After

Exception after 577 ms ex: System.OperationCanceledException: The operation was canceled.

[rokonec]

/azp run runtime

[rokonec]

/azp run runtime-libraries-coreclr outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[antonfirsov]

LGTM for 5e25367. Would be still good to have a third pair of eyes taking a look on the whole thing.

[antonfirsov]

@rokonec since the change is not immediately trivial from the first look, can you update the PR description with an explanation (1) why do these two changes fix the thing (2) why don't they impact other code paths negatively?

[liveans]

Changes LGTM, is it possible to add a test case for this?
Do we have any way to slow down the DNS resolving?

/cc @antonfirsov

[antonfirsov]

Do we have any way to slow down the DNS resolving?

This but I doubt this approach is reliable on CI. To make things robust, we would need to dockerize a custom environment config.

[rokonec]

/ba-g Known issues or unrelated tests