Expose a global switch to disable IPV6 (#55012)

antonfirsov · web-flow · commit 067aa165d973 · 2021-07-12T14:24:54.000+02:00
Fixes #47583. Resolves #52287, #54807 and similar issues, without changing customer application code. Introduces an AppContext switch `System.Net.DisableIPv6` and environment variable `DOTNET_SYSTEM_NET_DISABLEIPV6` to emulate the lack of OS-level IPv6 support. This is useful to workaround dual-stack socket issues when the OS reports support of IPv6, but some other underlying infrastructure element (typically VPN) doesn't function well with IPv6 request. For consistency, this switch also impacts NameResolution and Ping, not only Sockets.
diff --git a/src/libraries/Common/src/System/Net/SocketProtocolSupportPal.Unix.cs b/src/libraries/Common/src/System/Net/SocketProtocolSupportPal.Unix.cs
@@ -7,12 +7,8 @@
 
 namespace System.Net
 {
-    internal static class SocketProtocolSupportPal
+    internal static partial class SocketProtocolSupportPal
     {
-        public static bool OSSupportsIPv6 { get; } = IsSupported(AddressFamily.InterNetworkV6);
-        public static bool OSSupportsIPv4 { get; } = IsSupported(AddressFamily.InterNetwork);
-        public static bool OSSupportsUnixDomainSockets { get; } = IsSupported(AddressFamily.Unix);
-
         private static unsafe bool IsSupported(AddressFamily af)
         {
             IntPtr invalid = (IntPtr)(-1);
diff --git a/src/libraries/Common/src/System/Net/SocketProtocolSupportPal.Windows.cs b/src/libraries/Common/src/System/Net/SocketProtocolSupportPal.Windows.cs
@@ -9,12 +9,8 @@
 
 namespace System.Net
 {
-    internal static class SocketProtocolSupportPal
+    internal static partial class SocketProtocolSupportPal
     {
-        public static bool OSSupportsIPv6 { get; } = IsSupported(AddressFamily.InterNetworkV6);
-        public static bool OSSupportsIPv4 { get; } = IsSupported(AddressFamily.InterNetwork);
-        public static bool OSSupportsUnixDomainSockets { get; } = IsSupported(AddressFamily.Unix);
-
         private static bool IsSupported(AddressFamily af)
         {
             Interop.Winsock.EnsureInitialized();
diff --git a/src/libraries/Common/src/System/Net/SocketProtocolSupportPal.cs b/src/libraries/Common/src/System/Net/SocketProtocolSupportPal.cs
@@ -0,0 +1,36 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Net.Sockets;
+
+namespace System.Net
+{
+    internal static partial class SocketProtocolSupportPal
+    {
+        private const string DisableIPv6AppCtxSwitch = "System.Net.DisableIPv6";
+        private const string DisableIPv6EnvironmentVariable = "DOTNET_SYSTEM_NET_DISABLEIPV6";
+
+        public static bool OSSupportsIPv6 { get; } = IsSupported(AddressFamily.InterNetworkV6) && !IsIPv6Disabled();
+        public static bool OSSupportsIPv4 { get; } = IsSupported(AddressFamily.InterNetwork);
+        public static bool OSSupportsUnixDomainSockets { get; } = IsSupported(AddressFamily.Unix);
+
+        private static bool IsIPv6Disabled()
+        {
+            // First check for the AppContext switch, giving it priority over the environment variable.
+            if (AppContext.TryGetSwitch(DisableIPv6AppCtxSwitch, out bool disabled))
+            {
+                return disabled;
+            }
+
+            // AppContext switch wasn't used. Check the environment variable.
+            string? envVar = Environment.GetEnvironmentVariable(DisableIPv6EnvironmentVariable);
+
+            if (envVar is not null)
+            {
+                return envVar == "1" || envVar.Equals("true", StringComparison.OrdinalIgnoreCase);
+            }
+
+            return false;
+        }
+    }
+}
diff --git a/src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csproj b/src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csproj
@@ -31,6 +31,8 @@
              Link="Common\System\Net\IPAddressParserStatics.cs" />
     <Compile Include="$(CommonPath)System\Net\IPEndPointStatics.cs"
              Link="Common\System\Net\IPEndPointStatics.cs" />
+    <Compile Include="$(CommonPath)System\Net\SocketProtocolSupportPal.cs"
+             Link="Common\System\Net\SocketProtocolSupportPal.cs" />
   </ItemGroup>
   <ItemGroup Condition=" '$(TargetsWindows)' == 'true'">
     <Compile Include="System\Net\NameResolutionPal.Windows.cs" />
diff --git a/src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionPal.Unix.cs b/src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionPal.Unix.cs
@@ -76,9 +76,11 @@ private static unsafe void ParseHostEntry(Interop.Sys.HostEntry hostEntry, bool
                     Interop.Sys.IPAddress* addressHandle = hostEntry.IPAddressList;
                     for (int i = 0; i < hostEntry.IPAddressCount; i++)
                     {
-                        if (Array.IndexOf(nativeAddresses, addressHandle[i], 0, nativeAddressCount) == -1)
+                        Interop.Sys.IPAddress nativeAddr = addressHandle[i];
+                        if (Array.IndexOf(nativeAddresses, nativeAddr, 0, nativeAddressCount) == -1 &&
+                            (!nativeAddr.IsIPv6 || SocketProtocolSupportPal.OSSupportsIPv6)) // Do not include IPv6 addresses if IPV6 support is force-disabled
                         {
-                            nativeAddresses[nativeAddressCount++] = addressHandle[i];
+                            nativeAddresses[nativeAddressCount++] = nativeAddr;
                         }
                     }
 
diff --git a/src/libraries/System.Net.NameResolution/tests/FunctionalTests/GetHostEntryTest.cs b/src/libraries/System.Net.NameResolution/tests/FunctionalTests/GetHostEntryTest.cs
@@ -6,7 +6,7 @@
 using System.Net.Sockets;
 using System.Threading;
 using System.Threading.Tasks;
-
+using Microsoft.DotNet.RemoteExecutor;
 using Microsoft.DotNet.XUnitExtensions;
 using Xunit;
 
@@ -21,9 +21,16 @@ public async Task Dns_GetHostEntryAsync_IPAddress_Ok()
             await TestGetHostEntryAsync(() => Dns.GetHostEntryAsync(localIPAddress));
         }
 
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/1488", TestPlatforms.OSX)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/51377", TestPlatforms.iOS | TestPlatforms.tvOS | TestPlatforms.MacCatalyst)]
-        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsNotArm64Process))] // [ActiveIssue("https://github.com/dotnet/runtime/issues/27622")]
+
+        public static bool GetHostEntryWorks =
+            // [ActiveIssue("https://github.com/dotnet/runtime/issues/27622")]
+            PlatformDetection.IsNotArmNorArm64Process &&
+            // [ActiveIssue("https://github.com/dotnet/runtime/issues/1488", TestPlatforms.OSX)]
+            PlatformDetection.IsNotOSX &&
+            // [ActiveIssue("https://github.com/dotnet/runtime/issues/51377", TestPlatforms.iOS | TestPlatforms.tvOS | TestPlatforms.MacCatalyst)]
+            !PlatformDetection.IsiOS && !PlatformDetection.IstvOS && !PlatformDetection.IsMacCatalyst;
+
+        [ConditionalTheory(nameof(GetHostEntryWorks))]
         [InlineData("")]
         [InlineData(TestSettings.LocalHost)]
         public async Task Dns_GetHostEntry_HostString_Ok(string hostName)
@@ -77,12 +84,10 @@ public async Task Dns_GetHostEntry_HostString_Ok(string hostName)
             }
         }
 
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/1488", TestPlatforms.OSX)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/51377", TestPlatforms.iOS | TestPlatforms.tvOS | TestPlatforms.MacCatalyst)]
-        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsNotArm64Process))] // [ActiveIssue("https://github.com/dotnet/runtime/issues/27622")]
+        [ConditionalTheory(nameof(GetHostEntryWorks))]
         [InlineData("")]
         [InlineData(TestSettings.LocalHost)]
-        public async Task Dns_GetHostEntryAsync_HostString_Ok(string hostName)
+        public async Task Dns_GetHostEntryAsync_HostString_Ok(string hostName)    
         {
             if (PlatformDetection.IsSLES)
             {
@@ -112,6 +117,44 @@ private static async Task TestGetHostEntryAsync(Func<Task<IPHostEntry>> getHostE
             Assert.Equal<IPAddress>(list1, list2);
         }
 
+        public static bool GetHostEntry_DisableIPv6_Condition = GetHostEntryWorks && RemoteExecutor.IsSupported;
+
+        [ConditionalTheory(nameof(GetHostEntry_DisableIPv6_Condition))]
+        [InlineData("")]
+        [InlineData(TestSettings.LocalHost)]
+        public void Dns_GetHostEntry_DisableIPv6_ExcludesIPv6Addresses(string hostnameOuter)
+        {
+            RemoteExecutor.Invoke(RunTest, hostnameOuter).Dispose();
+
+            static void RunTest(string hostnameInner)
+            {
+                AppContext.SetSwitch("System.Net.DisableIPv6", true);
+                IPHostEntry entry = Dns.GetHostEntry(hostnameInner);
+                foreach (IPAddress address in entry.AddressList)
+                {
+                    Assert.NotEqual(AddressFamily.InterNetworkV6, address.AddressFamily);
+                }
+            }   
+        }
+
+        [ConditionalTheory(nameof(GetHostEntry_DisableIPv6_Condition))]
+        [InlineData("")]
+        [InlineData(TestSettings.LocalHost)]
+        public void Dns_GetHostEntryAsync_DisableIPv6_ExcludesIPv6Addresses(string hostnameOuter)
+        {
+            RemoteExecutor.Invoke(RunTest, hostnameOuter).Dispose();
+
+            static async Task RunTest(string hostnameInner)
+            {
+                AppContext.SetSwitch("System.Net.DisableIPv6", true);
+                IPHostEntry entry = await Dns.GetHostEntryAsync(hostnameInner);
+                foreach (IPAddress address in entry.AddressList)
+                {
+                    Assert.NotEqual(AddressFamily.InterNetworkV6, address.AddressFamily);
+                }
+            }
+        }
+
         [Fact]
         public async Task Dns_GetHostEntry_NullStringHost_Fail()
         {
diff --git a/src/libraries/System.Net.NameResolution/tests/PalTests/System.Net.NameResolution.Pal.Tests.csproj b/src/libraries/System.Net.NameResolution/tests/PalTests/System.Net.NameResolution.Pal.Tests.csproj
@@ -28,6 +28,8 @@
              Link="Common\System\Net\IPEndPointStatics.cs" />
     <Compile Include="$(CommonPath)System\Net\IPAddressParserStatics.cs"
              Link="Common\System\Net\IPAddressParserStatics.cs" />
+    <Compile Include="$(CommonPath)System\Net\SocketProtocolSupportPal.cs"
+             Link="Common\System\Net\SocketProtocolSupportPal.cs" />
     <Compile Include="$(CommonTestPath)System\Net\Configuration.cs"
              Link="Common\System\Net\Configuration.cs" />
     <Compile Include="$(CommonTestPath)System\Net\Configuration.Http.cs"
diff --git a/src/libraries/System.Net.Ping/src/System.Net.Ping.csproj b/src/libraries/System.Net.Ping/src/System.Net.Ping.csproj
@@ -21,6 +21,8 @@
              Link="Common\System\Net\IPAddressParserStatics.cs" />
     <Compile Include="$(CommonPath)System\Net\SocketAddress.cs"
              Link="Common\System\Net\SocketAddress.cs" />
+    <Compile Include="$(CommonPath)System\Net\SocketProtocolSupportPal.cs"
+             Link="Common\System\Net\SocketProtocolSupportPal.cs" />
     <!-- Logging -->
     <Compile Include="$(CommonPath)System\Net\Logging\NetEventSource.Common.cs"
              Link="Common\System\Net\Logging\NetEventSource.Common.cs" />
diff --git a/src/libraries/System.Net.Sockets/src/System.Net.Sockets.csproj b/src/libraries/System.Net.Sockets/src/System.Net.Sockets.csproj
@@ -65,6 +65,8 @@
              Link="Common\System\Net\SocketAddress.cs" />
     <Compile Include="$(CommonPath)System\Net\TcpValidationHelpers.cs"
              Link="Common\System\Net\TcpValidationHelpers.cs" />
+    <Compile Include="$(CommonPath)System\Net\SocketProtocolSupportPal.cs"
+             Link="Common\System\Net\SocketProtocolSupportPal.cs" />
     <Compile Include="$(CommonPath)System\Threading\Tasks\TaskToApm.cs"
              Link="Common\System\Threading\Tasks\TaskToApm.cs" />
     <!-- System.Net.Internals -->
diff --git a/src/libraries/System.Net.Sockets/tests/FunctionalTests/OSSupport.cs b/src/libraries/System.Net.Sockets/tests/FunctionalTests/OSSupport.cs
@@ -3,6 +3,7 @@
 
 
 using System.Threading;
+using Microsoft.DotNet.RemoteExecutor;
 using Xunit;
 
 namespace System.Net.Sockets.Tests
@@ -25,6 +26,37 @@ public void SupportsIPv6_MatchesOSSupportsIPv6()
 #pragma warning restore
         }
 
+        [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+        public void DisableIPv6_OSSupportsIPv6_False()
+        {
+            RemoteInvokeOptions options = new RemoteInvokeOptions();
+            options.StartInfo.EnvironmentVariables["DOTNET_SYSTEM_NET_DISABLEIPV6"] = "1";
+            RemoteExecutor.Invoke(RunTest, options).Dispose();
+
+            static void RunTest()
+            {
+                Assert.False(Socket.OSSupportsIPv6);
+            }
+        }
+
+        [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+        public void DisableIPv6_SocketConstructor_CreatesIPv4Socket()
+        {
+            RemoteExecutor.Invoke(RunTest).Dispose();
+
+            static void RunTest()
+            {
+                AppContext.SetSwitch("System.Net.DisableIPv6", true);
+                using Socket socket1 = new Socket(SocketType.Stream, ProtocolType.Tcp);
+                using Socket socket2 = new Socket(SocketType.Dgram, ProtocolType.Udp);
+
+                Assert.Equal(AddressFamily.InterNetwork, socket1.AddressFamily);
+                Assert.Equal(AddressFamily.InterNetwork, socket2.AddressFamily);
+                Assert.False(socket1.DualMode);
+                Assert.False(socket2.DualMode);
+            }
+        }
+
         [Fact]
         public void IOControl_FIONREAD_Success()
         {

Original file line number	Diff line number	Diff line change
`@@ -7,12 +7,8 @@`
`7`	`7`
`8`	`8`	`namespace System.Net`
`9`	`9`	`{`
`10`		`- internal static class SocketProtocolSupportPal`
	`10`	`+ internal static partial class SocketProtocolSupportPal`
`11`	`11`	`{`
`12`		`- public static bool OSSupportsIPv6 { get; } = IsSupported(AddressFamily.InterNetworkV6);`
`13`		`- public static bool OSSupportsIPv4 { get; } = IsSupported(AddressFamily.InterNetwork);`
`14`		`- public static bool OSSupportsUnixDomainSockets { get; } = IsSupported(AddressFamily.Unix);`
`15`		`-`
`16`	`12`	`private static unsafe bool IsSupported(AddressFamily af)`
`17`	`13`	`{`
`18`	`14`	`IntPtr invalid = (IntPtr)(-1);`
Original file line number	Diff line number	Diff line change
`@@ -9,12 +9,8 @@`
`9`	`9`
`10`	`10`	`namespace System.Net`
`11`	`11`	`{`
`12`		`- internal static class SocketProtocolSupportPal`
	`12`	`+ internal static partial class SocketProtocolSupportPal`
`13`	`13`	`{`
`14`		`- public static bool OSSupportsIPv6 { get; } = IsSupported(AddressFamily.InterNetworkV6);`
`15`		`- public static bool OSSupportsIPv4 { get; } = IsSupported(AddressFamily.InterNetwork);`
`16`		`- public static bool OSSupportsUnixDomainSockets { get; } = IsSupported(AddressFamily.Unix);`
`17`		`-`
`18`	`14`	`private static bool IsSupported(AddressFamily af)`
`19`	`15`	`{`
`20`	`16`	`Interop.Winsock.EnsureInitialized();`
Original file line number	Diff line number	Diff line change
`@@ -76,9 +76,11 @@ private static unsafe void ParseHostEntry(Interop.Sys.HostEntry hostEntry, bool`
`76`	`76`	`Interop.Sys.IPAddress* addressHandle = hostEntry.IPAddressList;`
`77`	`77`	`for (int i = 0; i < hostEntry.IPAddressCount; i++)`
`78`	`78`	`{`
`79`		`- if (Array.IndexOf(nativeAddresses, addressHandle[i], 0, nativeAddressCount) == -1)`
	`79`	`+ Interop.Sys.IPAddress nativeAddr = addressHandle[i];`
	`80`	`+ if (Array.IndexOf(nativeAddresses, nativeAddr, 0, nativeAddressCount) == -1 &&`
	`81`	`+ (!nativeAddr.IsIPv6 \|\| SocketProtocolSupportPal.OSSupportsIPv6)) // Do not include IPv6 addresses if IPV6 support is force-disabled`
`80`	`82`	`{`
`81`		`- nativeAddresses[nativeAddressCount++] = addressHandle[i];`
	`83`	`+ nativeAddresses[nativeAddressCount++] = nativeAddr;`
`82`	`84`	`}`
`83`	`85`	`}`
`84`	`86`