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Relax address-family check in DnsGetHostEntry_LocalhostSubdomain_RespectsAddressFamily on Android/AppleMobile #128404

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Relax address-family check in DnsGetHostEntry_LocalhostSubdomain_RespectsAddressFamily on Android/AppleMobile #128404

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Copilot May 20, 2026
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Relax DnsGetHostEntry_LocalhostSubdomain_RespectsAddressFamily on And…
Copilot May 20, 2026
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22 changes: 14 additions & 8 deletions src/libraries/System.Net.NameResolution/tests/FunctionalTests/GetHostEntryTest.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -434,21 +434,27 @@ public async Task DnsGetHostEntry_LocalhostSubdomain_RespectsAddressFamily(Addre

string hostName = "test.localhost";

// On Android and Apple mobile the OS resolver may return addresses of a different
// family than requested (e.g. link-local IPv6 results for an IPv4 query), so we
// only require the requested family to be represented in the results there.
bool strictAddressFamily = !PlatformDetection.IsAppleMobile && !PlatformDetection.IsAndroid;

// The subdomain goes to OS resolver first. If it fails, it falls back to
// resolving plain "localhost" with the same address family filter.
IPHostEntry entry = Dns.GetHostEntry(hostName, addressFamily);
if (addressFamily == AddressFamily.InterNetwork)
{
Assert.True(entry.AddressList.Length >= 1, "Expected at least one IPv4 address");
}
Assert.All(entry.AddressList, addr => Assert.Equal(addressFamily, addr.AddressFamily));
VerifyAddressFamily(entry, addressFamily, strictAddressFamily);

entry = await Dns.GetHostEntryAsync(hostName, addressFamily);
if (addressFamily == AddressFamily.InterNetwork)
VerifyAddressFamily(entry, addressFamily, strictAddressFamily);

static void VerifyAddressFamily(IPHostEntry entry, AddressFamily addressFamily, bool strictAddressFamily)
{
Assert.True(entry.AddressList.Length >= 1, "Expected at least one IPv4 address");
Assert.Contains(entry.AddressList, addr => addr.AddressFamily == addressFamily);
if (strictAddressFamily)
{
Assert.All(entry.AddressList, addr => Assert.Equal(addressFamily, addr.AddressFamily));
}
Comment on lines +452 to +456
}
Assert.All(entry.AddressList, addr => Assert.Equal(addressFamily, addr.AddressFamily));
}

// RFC 6761: Verify that localhost subdomains return loopback addresses.
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