Avoid socket telemetry errors for pending nonblocking connects

[tulior]

Fixes #129252.

Non-blocking Socket.Connect can report WouldBlock on Windows or InProgress on Unix while the OS connect attempt remains pending. Sockets telemetry treated that result as a failure even though Connect has only reported a pending state.

This keeps the connect Activity, but leaves the status unset and omits error.type for pending results. It also suppresses the corresponding ConnectFailed EventSource event for the same pending states. Other SocketError values keep the existing failure path.

The EventSource part is included because it is the same pending-result case at the event layer. It can be separated if reviewers prefer to keep this PR scoped only to the experimental Activity surface.

This does not change the existing counter limitation: a pending connect that later succeeds is still not counted in outgoing-connections-established. Before this change it was not counted either; the pending result was reported as a failure instead.

The regression test covers the real synchronous Socket.Connect path for a non-blocking loopback connect. It asserts immediately after WouldBlock or InProgress because the Activity starts and stops inside Connect, so no later network completion is needed to verify the telemetry state.

Validation run locally on Windows:

dotnet.cmd build /t:Test /p:XunitMethodName=System.Net.Sockets.Tests.TelemetryTest.Connect_NonBlockingPending_ActivityNotMarkedAsError

dotnet.cmd build /t:Test /p:XUnitClassName=System.Net.Sockets.Tests.TelemetryTest

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR updates sockets telemetry to avoid treating non-blocking Connect “pending” results (WouldBlock/InProgress) as failures, and adds a regression test ensuring the emitted connect Activity is not marked as an error in that scenario.

Changes:

• Adjust SocketsTelemetry.AfterConnect to skip error status/tagging and failure counting for non-blocking connect pending errors.
• Add a functional test covering non-blocking connects that initially return pending but ultimately succeed.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/libraries/System.Net.Sockets/tests/FunctionalTests/TelemetryTest.cs	Adds a new test validating telemetry Activity is not marked error for pending non-blocking connect.
src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketsTelemetry.cs	Avoids reporting WouldBlock/InProgress as connect failures in telemetry.

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Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

[Copilot]

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Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.