[Android] Fix DNS localhost subdomain resolution with IPv6 on Android#125478
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simonrozsival wants to merge 2 commits intodotnet:mainfrom
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[Android] Fix DNS localhost subdomain resolution with IPv6 on Android#125478simonrozsival wants to merge 2 commits intodotnet:mainfrom
simonrozsival wants to merge 2 commits intodotnet:mainfrom
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Pull request overview
Fixes Android-specific failures in RFC 6761 *.localhost subdomain resolution when an AddressFamily filter is applied (notably InterNetworkV6), by adding an Android IPv6 localhost fallback that retries using ip6-localhost if localhost IPv6 resolution fails.
Changes:
- Add Android-only IPv6 fallback: if resolving
localhostwithInterNetworkV6fails withHostNotFound, retry withip6-localhost(sync + async paths). - Refactor async localhost-subdomain fallback to use helper local functions that include the Android retry behavior.
- Re-enable the Android variants of the
RespectsAddressFamilytests by removing[ActiveIssue]annotations.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| src/libraries/System.Net.NameResolution/src/System/Net/Dns.cs | Adds Android IPv6 retry (localhost → ip6-localhost) for InterNetworkV6 when localhost-subdomain fallback resolves plain localhost; applied to sync + async telemetry path. |
| src/libraries/System.Net.NameResolution/tests/FunctionalTests/GetHostEntryTest.cs | Removes Android [ActiveIssue] to re-enable localhost subdomain AddressFamily test coverage. |
| src/libraries/System.Net.NameResolution/tests/FunctionalTests/GetHostAddressesTest.cs | Removes Android [ActiveIssue] to re-enable localhost subdomain AddressFamily test coverage. |
On Android, getaddrinfo("localhost", AF_INET6) fails with EAI_NONAME
because the default /etc/hosts maps ::1 to "ip6-localhost" instead of
"localhost". This causes the RFC 6761 localhost subdomain fallback to
fail when InterNetworkV6 is requested.
Add an Android-specific catch in the fallback path: when IPv6 localhost
resolution fails with HostNotFound, retry with "ip6-localhost".
Fixes dotnet#124751
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Remove the OperatingSystem.IsAndroid() guard so the ip6-localhost IPv6 fallback applies on any system where /etc/hosts maps ::1 to ip6-localhost instead of localhost (e.g. Android, some Linux distros). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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This was referenced Mar 13, 2026
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Fix DNS localhost subdomain tests with AddressFamily on Android
Fixes #124751
Problem
The
DnsGetHostEntry_LocalhostSubdomain_RespectsAddressFamilyandDnsGetHostAddresses_LocalhostSubdomain_RespectsAddressFamilytests consistently fail on Android.The RFC 6761 localhost subdomain fallback (introduced in #123076) resolves
"test.localhost"by first trying the OS resolver, then falling back to resolving plain"localhost"with the sameAddressFamily. On Android, the second step fails forInterNetworkV6because Android's default/etc/hostsmaps::1toip6-localhostinstead oflocalhost:This causes
getaddrinfo("localhost", AF_INET6)to returnEAI_NONAME.Fix
When the localhost fallback fails with
InterNetworkV6on Android, retry the resolution using"ip6-localhost"— Android's default hostname for the IPv6 loopback address.The fallback chain becomes:
getaddrinfo("test.localhost", AF_INET6)→ fails → existing subdomain fallbackgetaddrinfo("localhost", AF_INET6)→ fails on Android → new: Android IPv6 fallbackgetaddrinfo("ip6-localhost", AF_INET6)→ succeedsThis is applied to both the sync (
GetHostEntryOrAddressesCore) and async (GetAddrInfoWithTelemetryAsync) code paths.Testing
RespectsAddressFamilytest cases[ActiveIssue]annotations for DNS localhost subdomain tests with AddressFamily fail on Android #124751 are removed from both test methods