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Re-enable localhost loopback assertions on Apple mobile and Android #128480

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Re-enable localhost loopback assertions on Apple mobile and Android #128480

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Copilot May 22, 2026
29932fb
Enable localhost loopback assertions on Apple mobile and Android
Copilot May 22, 2026
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45 changes: 8 additions & 37 deletions src/libraries/System.Net.NameResolution/tests/FunctionalTests/GetHostAddressesTest.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -235,23 +235,13 @@ public async Task DnsGetHostAddresses_LocalhostSubdomain_ReturnsLoopback(string
{
// The subdomain goes to OS resolver first. If it fails (likely on most systems),
// it falls back to resolving plain "localhost", which should return loopback addresses.
// On Android/Apple mobile platforms the OS resolver may return non-loopback addresses
// for *.localhost.
bool requireLoopback = !PlatformDetection.IsAppleMobile && !PlatformDetection.IsAndroid;

IPAddress[] addresses = Dns.GetHostAddresses(hostName);
Assert.True(addresses.Length >= 1, "Expected at least one address");
if (requireLoopback)
{
Assert.All(addresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}
Assert.All(addresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));

addresses = await Dns.GetHostAddressesAsync(hostName);
Assert.True(addresses.Length >= 1, "Expected at least one address");
if (requireLoopback)
{
Assert.All(addresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}
Assert.All(addresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}

// RFC 6761: "*.localhost" subdomains should respect AddressFamily parameter.
Expand Down Expand Up @@ -291,35 +281,24 @@ public async Task DnsGetHostAddresses_LocalhostSubdomain_RespectsAddressFamily(A
// 1. The OS resolver is tried first for subdomains
// 2. The OS may return different results (e.g., both IPv4+IPv6 vs IPv4 only)
// 3. Different systems configure localhost differently
// On Android and Apple mobile the OS resolver may return non-loopback addresses
// for both plain "localhost" and "*.localhost" (e.g. link-local IPv6 or
// multicast DNS results), so we only require any address to be returned there.
[Fact]
public async Task DnsGetHostAddresses_LocalhostAndSubdomain_BothReturnLoopback()
{
bool requireLoopback = !PlatformDetection.IsAppleMobile && !PlatformDetection.IsAndroid;

IPAddress[] localhostAddresses = Dns.GetHostAddresses("localhost");
IPAddress[] subdomainAddresses = Dns.GetHostAddresses("foo.localhost");

Assert.True(localhostAddresses.Length >= 1);
Assert.True(subdomainAddresses.Length >= 1);
if (requireLoopback)
{
Assert.All(localhostAddresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
Assert.All(subdomainAddresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}
Assert.All(localhostAddresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
Assert.All(subdomainAddresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));

localhostAddresses = await Dns.GetHostAddressesAsync("localhost");
subdomainAddresses = await Dns.GetHostAddressesAsync("bar.localhost");

Assert.True(localhostAddresses.Length >= 1);
Assert.True(subdomainAddresses.Length >= 1);
if (requireLoopback)
{
Assert.All(localhostAddresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
Assert.All(subdomainAddresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}
Assert.All(localhostAddresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
Assert.All(subdomainAddresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}

// RFC 6761: Localhost subdomains with trailing dot should work (e.g., "foo.localhost.")
Expand All @@ -328,21 +307,13 @@ public async Task DnsGetHostAddresses_LocalhostAndSubdomain_BothReturnLoopback()
[InlineData("bar.test.localhost.")]
public async Task DnsGetHostAddresses_LocalhostSubdomainWithTrailingDot_ReturnsLoopback(string hostName)
{
bool requireLoopback = !PlatformDetection.IsAppleMobile && !PlatformDetection.IsAndroid;

IPAddress[] addresses = Dns.GetHostAddresses(hostName);
Assert.True(addresses.Length >= 1, "Expected at least one address");
if (requireLoopback)
{
Assert.All(addresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}
Assert.All(addresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));

addresses = await Dns.GetHostAddressesAsync(hostName);
Assert.True(addresses.Length >= 1, "Expected at least one address");
if (requireLoopback)
{
Assert.All(addresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}
Assert.All(addresses, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}

// RFC 6761: Ensure names that look similar but are not reserved are still resolved via OS.
Expand Down
45 changes: 8 additions & 37 deletions src/libraries/System.Net.NameResolution/tests/FunctionalTests/GetHostEntryTest.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -357,23 +357,13 @@ public async Task DnsGetHostEntry_LocalhostSubdomain_ReturnsLoopback(string host
{
// The subdomain goes to OS resolver first. If it fails (likely on most systems),
// it falls back to resolving plain "localhost", which should return loopback addresses.
// On Android/Apple mobile platforms the OS resolver may return non-loopback addresses
// for *.localhost.
bool requireLoopback = !PlatformDetection.IsAppleMobile && !PlatformDetection.IsAndroid;

IPHostEntry entry = Dns.GetHostEntry(hostName);
Assert.True(entry.AddressList.Length >= 1, "Expected at least one address");
if (requireLoopback)
{
Assert.All(entry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}
Assert.All(entry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));

entry = await Dns.GetHostEntryAsync(hostName);
Assert.True(entry.AddressList.Length >= 1, "Expected at least one address");
if (requireLoopback)
{
Assert.All(entry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}
Assert.All(entry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}

// RFC 6761: Ensure names that look similar but are not reserved are still resolved via OS.
Expand Down Expand Up @@ -456,35 +446,24 @@ public async Task DnsGetHostEntry_LocalhostSubdomain_RespectsAddressFamily(Addre
// 1. The OS resolver is tried first for subdomains
// 2. The OS may return different results (e.g., both IPv4+IPv6 vs IPv4 only)
// 3. Different systems configure localhost differently
// On Android and Apple mobile the OS resolver may return non-loopback addresses
// for both plain "localhost" and "*.localhost" (e.g. link-local IPv6 or
// multicast DNS results), so we only require any address to be returned there.
[Fact]
public async Task DnsGetHostEntry_LocalhostAndSubdomain_BothReturnLoopback()
{
bool requireLoopback = !PlatformDetection.IsAppleMobile && !PlatformDetection.IsAndroid;

IPHostEntry localhostEntry = Dns.GetHostEntry("localhost");
IPHostEntry subdomainEntry = Dns.GetHostEntry("foo.localhost");

Assert.True(localhostEntry.AddressList.Length >= 1);
Assert.True(subdomainEntry.AddressList.Length >= 1);
if (requireLoopback)
{
Assert.All(localhostEntry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
Assert.All(subdomainEntry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}
Assert.All(localhostEntry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
Assert.All(subdomainEntry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));

localhostEntry = await Dns.GetHostEntryAsync("localhost");
subdomainEntry = await Dns.GetHostEntryAsync("bar.localhost");

Assert.True(localhostEntry.AddressList.Length >= 1);
Assert.True(subdomainEntry.AddressList.Length >= 1);
if (requireLoopback)
{
Assert.All(localhostEntry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
Assert.All(subdomainEntry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}
Assert.All(localhostEntry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
Assert.All(subdomainEntry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}

// RFC 6761: Localhost subdomains with trailing dot should work (e.g., "foo.localhost.")
Expand All @@ -494,21 +473,13 @@ public async Task DnsGetHostEntry_LocalhostAndSubdomain_BothReturnLoopback()
[InlineData("bar.test.localhost.")]
public async Task DnsGetHostEntry_LocalhostSubdomainWithTrailingDot_ReturnsLoopback(string hostName)
{
bool requireLoopback = !PlatformDetection.IsAppleMobile && !PlatformDetection.IsAndroid;

IPHostEntry entry = Dns.GetHostEntry(hostName);
Assert.True(entry.AddressList.Length >= 1, "Expected at least one address");
if (requireLoopback)
{
Assert.All(entry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}
Assert.All(entry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));

entry = await Dns.GetHostEntryAsync(hostName);
Assert.True(entry.AddressList.Length >= 1, "Expected at least one address");
if (requireLoopback)
{
Assert.All(entry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}
Assert.All(entry.AddressList, addr => Assert.True(IPAddress.IsLoopback(addr), $"Expected loopback address but got: {addr}"));
}

[Fact]
Expand Down
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