[9.0][OSX] ip_mreqn struct is not supported for IPv4 Multicast #119481
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) * Fix IPv4 multicast on macOS by handling ip_mreqn struct compatibility * Remove Active Issue for iOS * Add support for IP_MULTICAST_IFINDEX * Refactor IPv4 multicast option handling to directly use IP_MULTICAST_IFINDEX for interface index specification * Accept 0 interface as valid --------- Co-authored-by: Tomas Weinfurt <tweinfurt@yahoo.com>
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Pull Request Overview
This PR backports a fix for IPv4 multicast socket options on macOS/OSX by adding support for IP_MULTICAST_IFINDEX when the ip_mreqn struct is not available. The fix addresses platform-specific networking issues where the standard ip_mreqn structure wasn't supported.
- Adds build-time detection for IP_MULTICAST_IFINDEX socket option availability
- Implements fallback logic to use IP_MULTICAST_IFINDEX for interface index specification on macOS
- Removes test exclusion for Apple mobile platforms that was previously needed due to this issue
Reviewed Changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| src/native/libs/configure.cmake | Adds build configuration check for IP_MULTICAST_IFINDEX availability |
| src/native/libs/System.Native/pal_networking.c | Implements IP_MULTICAST_IFINDEX fallback logic for multicast interface setting |
| src/native/libs/Common/pal_config.h.in | Defines configuration macro for IP_MULTICAST_IFINDEX feature detection |
| src/libraries/System.Net.Sockets/tests/FunctionalTests/SocketOptionNameTest.cs | Removes ActiveIssue attribute that excluded Apple mobile platforms from multicast tests |
wfurt
approved these changes
Sep 9, 2025
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Backport of #119354 to release/9.0-staging
/cc @liveans
Customer Impact
[Select one or both of the boxes. Describe how this issue impacts customers, citing the expected and actual behaviors and scope of the issue. If customer-reported, provide the issue number.]
Regression
[If yes, specify when the regression was introduced. Provide the PR or commit if known.]
Testing
For SocketOption, it has been tested through CI, manual test runs, for actual multicast behavior we made a limited manual testing.
Risk
Low, this was broken for a while.
IMPORTANT: If this backport is for a servicing release, please verify that:
release/X.0-staging, notrelease/X.0.Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.