[mobile] Skip failing Android localhost subdomain DNS tests

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Summary

Fixes failing System.Net.NameResolution tests on Android by adding ActiveIssue attributes to skip tests that expect localhost subdomain resolution to return loopback addresses.

Details

On Android, DNS resolution for .localhost subdomains (e.g., foo.localhost, test.localhost) returns link-local IPv6 addresses (fe80::/10) instead of loopback addresses, causing test failures.

Tests Fixed

• DnsGetHostEntry_LocalhostSubdomain_ReturnsLoopback
• DnsGetHostAddresses_LocalhostSubdomain_ReturnsLoopback

These tests are now skipped on Android with reference to existing issue #124751, which already tracks the same underlying problem for the RespectsAddressFamily variants of these tests.

Build Information

• Build: 1406427
• Date: 2026-05-03
• Job: android-arm Release AllSubsets_Mono
• Helix Job: 6255e58e-bf4f-4c25-ba48-27c957d4ea3e
• Work Item: System.Net.NameResolution.Functional.Tests

Console Log Excerpt (sanitized)

[20:56:01] info: Instrumentation finished normally with exit code 1
[FAIL] System.Net.NameResolution.Tests.GetHostAddressesTest.DnsGetHostAddresses_LocalhostSubdomain_ReturnsLoopback(hostName: "foo.localhost")
Assert.All() Failure: 2 out of 3 items in the collection did not pass.
     Error: Expected loopback address but got: fe80::cb7c:d6fd:eb1f:6f44%10
     Error: Expected loopback address but got: fe80::b4f2:efff:fea1:dbef%3
[FAIL] System.Net.NameResolution.Tests.GetHostAddressesTest.DnsGetHostAddresses_LocalhostSubdomain_ReturnsLoopback(hostName: "test.localhost")
Assert.All() Failure: 2 out of 3 items in the collection did not pass.
     Error: Expected loopback address but got: fe80::cb7c:d6fd:eb1f:6f44%10
     Error: Expected loopback address but got: fe80::b4f2:efff:fea1:dbef%3

The tests receive link-local IPv6 addresses instead of the expected loopback addresses (127.0.0.1 or ::1).

Root Cause

Android's DNS resolver behavior for RFC 6761 localhost subdomains differs from desktop platforms. When the OS resolver fallback tries to resolve plain "localhost" with or without an address family filter, Android may return the device's network interface addresses instead of loopback addresses.

Related Issue

Closes: #124751

Note

This content was generated by GitHub Copilot and may contain AI-generated content.

Note

🔒 Integrity filter blocked 2 items

The following items were blocked because they don't meet the GitHub integrity level.

• #19443 search_issues: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
• #126805 search_pull_requests: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".

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Generated by Mobile Platform Failure Scanner · ● 3.6M · ◷

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[Copilot]

Pull request overview

This PR updates System.Net.NameResolution functional tests to avoid consistent Android failures by skipping the localhost-subdomain loopback assertions on Android via ActiveIssue.

Changes:

• Skip DnsGetHostEntry_LocalhostSubdomain_ReturnsLoopback on Android with an ActiveIssue attribute.
• Skip DnsGetHostAddresses_LocalhostSubdomain_ReturnsLoopback on Android with an ActiveIssue attribute.

Show a summary per file

File	Description
src/libraries/System.Net.NameResolution/tests/FunctionalTests/GetHostEntryTest.cs	Adds an Android ActiveIssue skip for the localhost-subdomain loopback theory.
src/libraries/System.Net.NameResolution/tests/FunctionalTests/GetHostAddressesTest.cs	Adds an Android ActiveIssue skip for the localhost-subdomain loopback theory.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 2

[github-actions]

🤖 Copilot Code Review — PR #127742

Note

This review was generated by GitHub Copilot.

Holistic Assessment

Motivation: Justified. These two DNS tests (DnsGetHostAddresses_LocalhostSubdomain_ReturnsLoopback and DnsGetHostEntry_LocalhostSubdomain_ReturnsLoopback) are failing on Android because localhost subdomain resolution returns link-local IPv6 addresses instead of loopback. Skipping them with a tracking issue is the standard approach in dotnet/runtime.

Approach: Correct. Adding [ActiveIssue] with TestPlatforms.Android targeting is the established pattern in this test file and across the repository.

Summary: ✅ LGTM. The change is minimal, correctly scoped, and follows established conventions. The tracking issue (#126456) is already referenced by sibling tests in the same files, confirming it's the correct issue for this class of Android DNS failures.

---

Detailed Findings

✅ Correctness — Attribute usage is correct

The [ActiveIssue("https://github.com/dotnet/runtime/issues/126456", TestPlatforms.Android)] annotation correctly:

• References an existing tracking issue (NameResolution tests fail on tvos/Android devices - localhost resolves to non-loopback addresses #126456) already used for related localhost subdomain tests in the same files (e.g., DnsGetHostAddresses_LocalhostSubdomain_RespectsAddressFamily at line 253, and DnsGetHostEntry_LocalhostSubdomain_RespectsAddressFamily at line 453)
• Targets only TestPlatforms.Android (not overly broad)
• Is placed in the correct position relative to [Theory] and [InlineData] attributes

✅ Consistency — Follows existing patterns

The issue reference and attribute pattern matches the established convention in these test files. The consolidated issue #126456 covers all localhost subdomain failures on mobile platforms, making it the appropriate tracking reference.

✅ Scope — Appropriately focused

Only the two affected tests are skipped; no unrelated changes are included. The commit message includes the failing build link, work item, and Helix job for traceability.

💡 Observation — Related test uses different issue

The sibling test DnsGetHostAddresses_LocalhostSubdomain_RespectsAddressFamily (line 253) still references issue #124751 rather than #126456. This is a pre-existing inconsistency and out of scope for this PR, but could be consolidated in a follow-up.

Generated by Code Review for issue #127742 · ◷