Set SocketsHttpHandler.ConnectTimeout to 15 seconds by default

[mahpate]

Fixes #1678

Setting SocketsHttpHandler.ConnectTimeout to 15 seconds as default value in .Net 7.
See dotnet/runtime#66673 (comment)

[Tratcher]

@miha, the change to SocketsHttpHandler's ConnectTimeout default was reverted, correct?

[MihaZupan]

Yes, that change was reverted. The default ConnectTimeout stayed the same (infinite).

We went a different route in runtime with dotnet/runtime#71785. A connection attempt will now be canceled 5 seconds after the request that started it is completed/canceled.
In practice, this should have a similar effect to ConnectTimeout, but without impacting the exception type surfaced to requests (a stalled connection attempt won't show up as a ConnectTimeout by default).

The issue mentioned in the linked comment about wasting connection attempts on canceled requests is also no longer a problem as we backported mitigations for that to 6.0 (dotnet/runtime#66990).

---

That said, the reason the change to 15 seconds was reverted is not that the change is bad in itself.
We reverted it because users were expecting a different kind of exception (from the Sockets layer) and started getting ConnectTimeout exceptions instead. This broke code that was doing retries based on the kind of exception.

YARP is in a different situation here given that we are the ones calling into HttpClient to make requests. While someone could have implemented retry logic in a similar way, it's much less likely.

I would be okay with changing the default to 15s in YARP, but I don't think we should be linking to that comment as justification. The reason for doing so is not to avoid "connection leaks", but to avoid potential memory leaks/higher request failure rates.

[MihaZupan]

For reference, this is the issue tracking making such changes in YARP: #1678

[MihaZupan]

@mahpate can you please also update this property in other places where we specify these defaults:

• Direct forwarding sample
• HttpClient docs
• Direct forwarding docs

[MihaZupan]

Suggested change

	ConnectTimeout = TimeSpan.FromSeconds(15), // See: https://github.com/dotnet/runtime/issues/66673#issuecomment-1073811798
	ConnectTimeout = TimeSpan.FromSeconds(15),

[MihaZupan]

@mahpate are you still interested in making this change?

[MihaZupan]

@mahpate are you able to apply the recommended fixes here?

Feel free to reopen the PR if you wish to continue working on this change.