[mobile] Skip localhost subdomain with trailing dot test on Android

[github-actions]

Reasoning

The test DnsGetHostEntry_LocalhostSubdomainWithTrailingDot_ReturnsLoopback expects DNS queries for *.localhost. (with trailing dot) to resolve to loopback addresses, following RFC 6761. However, on Android devices, these queries resolve to actual network addresses (both IPv4 and IPv6) instead of loopback.

This is the same root cause as DnsGetHostEntry_LocalhostSubdomain_ReturnsLoopback (without trailing dot), which is already disabled on Android via ActiveIssue #126456. Android's DNS resolver does not treat .localhost subdomains as reserved names that must resolve to loopback, regardless of whether a trailing dot is present.

Adding the same [ActiveIssue] attribute to this test variant ensures consistent behavior across all localhost subdomain test cases on Android.

Impact on platforms

Failing on Android in build 1406427 (2026-05-03):

• android-arm64 / Windows.11.Amd64.Android.Open / exit code 1
• android-arm / Windows.11.Amd64.Android.Open / exit code 1
• android-x64 / Windows.11.Amd64.Android.Open / exit code 1
• android-x86 / Windows.11.Amd64.Android.Open / exit code 1

Errors log

From android-arm64 Helix work item System.Net.NameResolution.Functional.Tests (console log):

[FAIL] System.Net.NameResolution.Tests.GetHostEntryTest.DnsGetHostEntry_LocalhostSubdomainWithTrailingDot_ReturnsLoopback(hostName: "foo.localhost.")
Assert.All() Failure: 11 out of 12 items in the collection did not pass.
[1]:  Item:  fe80::e0ef:4bff:feb4:bb16%47
      Error: Expected loopback address but got: fe80::e0ef:4bff:feb4:bb16%47
[2]:  Item:  2001:4898:502:3:e0ef:4bff:feb4:bb16
      Error: Expected loopback address but got: 2001:4898:502:3:e0ef:4bff:feb4:bb16
[11]: Item:  10.64.36.83
      Error: Expected loopback address but got: 10.64.36.83

First build it occurred

First observed (within the scanned window) in build 1406427, finished on 2026-05-03T09:02:27Z.

Note: This test failure has the same root cause as existing issue #126456, which has been present since April 2026. The "first occurrence" reflects only the scanned window, not the true origin.

Note

This change was generated by the Mobile Platform Failure Scanner workflow.

Generated by Mobile Platform Failure Scanner · ● 6.8M · ◷

[dotnet-policy-service]

Tagging subscribers to this area: @karelz, @dotnet/ncl
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR addresses a platform-specific test failure in System.Net.NameResolution functional tests by skipping an RFC 6761 localhost-subdomain test case on Android, where the platform DNS resolver does not consistently return loopback addresses for *.localhost. names.

Changes:

• Mark DnsGetHostEntry_LocalhostSubdomainWithTrailingDot_ReturnsLoopback as an active issue on Android using existing issue #126456.

Show a summary per file

File	Description
src/libraries/System.Net.NameResolution/tests/FunctionalTests/GetHostEntryTest.cs	Adds an [ActiveIssue] skip on Android for the trailing-dot localhost subdomain loopback assertion test.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 0

[rzikm]

LGTM