Prevent dual-mode accept tests from hanging

[wfurt]

The negative dual-mode accept tests start an accept operation and then expect a mismatched-address-family connection to fail immediately. On macOS, DualModeAcceptSync.AcceptV6BoundToAnyV4_CantConnect can instead leave both operations pending indefinitely: the worker remains blocked in native accept, while the connect never completes.

This is the same class of problem historically discussed in #16265. These tests were later re-enabled as part of #1481 / #80715, but the shared negative helper still has unbounded operations.

This change:

• extends PortBlocker to accept an explicit shadow address, since the socket address family does not identify the bound endpoint family for dual-mode sockets;
• bounds the expected failed connection with the existing TryConnect helper;
• queues a valid same-family connection before invoking the accept implementation, so synchronous accept completes normally rather than relying on socket disposal for cancellation; and
• verifies that accept returned the valid client, normalizing IPv4 and IPv4-mapped IPv6 addresses.

The change is test-only and covers the shared Sync, APM, EAP, and Task implementations.

Validation:

System.Net.Sockets.Tests  Total: 32, Errors: 0, Failed: 0, Skipped: 0

A full libraries baseline was not run; the focused System.Net.Sockets test project built successfully while running the affected classes.

Note

This pull request description was generated with GitHub Copilot.

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🔵 Needs a closer look

Dispose both sockets when bind retries fail to avoid resource leaks.

Pull request overview

Hardens dual-mode socket accept tests against platform-specific hangs by bounding failed connections and validating successful same-family accepts.

Changes:

• Adds explicit shadow-address support to PortBlocker.
• Bounds mismatched-family connection attempts.
• Verifies accepted endpoints across Sync, APM, EAP, and Task implementations.

File summaries

File	Summary
src/libraries/System.Net.Sockets/tests/FunctionalTests/DualModeSocketTest.cs	Updates negative accept tests to avoid hangs and validate accepted endpoints.
src/libraries/Common/tests/System/Net/Sockets/SocketTestExtensions.cs	Supports explicit shadow addresses in PortBlocker.

Review details

Suppressed comments (1)

src/libraries/Common/tests/System/Net/Sockets/SocketTestExtensions.cs:129

• When TryBindWithoutReuseAddress returns false (the normal bind-conflict path on both Windows and Unix), this loop retries without disposing either MainSocket or _shadowSocket; the next iteration overwrites both references, and exhausting retries also leaks the final pair. The new explicit shadow-address call relies on these retries, so dispose both sockets before continuing whenever success is false.

                    success = TryBindWithoutReuseAddress(_shadowSocket, shadowEndPoint, out _);

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite