Fix MulticasInterface SocketOption to work with IPv6 on Linux (#25544)

Fix MulticasInterface SocketOption to work with IPv6 on Linux

Bug#25525

Author: pepone

src/Native/Unix/System.Native/pal_networking.c

@@ -1273,7 +1273,7 @@ static int8_t GetMulticastOptionName(int32_t multicastOption, int8_t isIPv6, int
             return true;
 
         case MulticastOption_MULTICAST_IF:
-            *optionName = IP_MULTICAST_IF;
+            *optionName = isIPv6 ? IPV6_MULTICAST_IF : IP_MULTICAST_IF;
             return true;
 
         default:
@@ -1372,7 +1372,7 @@ int32_t SystemNative_GetIPv6MulticastOption(intptr_t socket, int32_t multicastOp
 
     struct ipv6_mreq opt;
     socklen_t len = sizeof(opt);
-    int err = getsockopt(fd, IPPROTO_IP, optionName, &opt, &len);
+    int err = getsockopt(fd, IPPROTO_IPV6, optionName, &opt, &len);
     if (err != 0)
     {
         return SystemNative_ConvertErrorPlatformToPal(errno);
@@ -1410,7 +1410,7 @@ int32_t SystemNative_SetIPv6MulticastOption(intptr_t socket, int32_t multicastOp
 
     ConvertByteArrayToIn6Addr(&opt.ipv6mr_multiaddr, &option->Address.Address[0], NUM_BYTES_IN_IPV6_ADDRESS);
 
-    int err = setsockopt(fd, IPPROTO_IP, optionName, &opt, sizeof(opt));
+    int err = setsockopt(fd, IPPROTO_IPV6, optionName, &opt, sizeof(opt));
     return err == 0 ? Error_SUCCESS : SystemNative_ConvertErrorPlatformToPal(errno);
 }
 
@@ -1987,6 +1987,10 @@ static bool TryGetPlatformSocketOption(int32_t socketOptionName, int32_t socketO
                     *optName = IPV6_RECVPKTINFO;
                     return true;
 
+                case SocketOptionName_SO_IP_MULTICAST_IF:
+                    *optName = IPV6_MULTICAST_IF;
+                    return true;
+
                 default:
                     return false;
             }

src/System.Net.Sockets/tests/FunctionalTests/SocketOptionNameTest.cs

@@ -150,6 +150,81 @@ public void MulticastInterface_Set_InvalidIndex_Throws()
             }
         }
 
+        [OuterLoop] // TODO: Issue #11345
+        [Fact]
+        public async Task MulticastInterface_Set_IPv6_AnyInterface_Succeeds()
+        {
+            if (PlatformDetection.IsFedora || PlatformDetection.IsRedHatFamily7 || PlatformDetection.IsOSX)
+            {
+                return; // [ActiveIssue(24008)]
+            }
+
+            // On all platforms, index 0 means "any interface"
+            await MulticastInterface_Set_IPv6_Helper(0);
+        }
+
+        [OuterLoop] // TODO: Issue #11345
+        [Fact]
+        [PlatformSpecific(TestPlatforms.Windows)]
+        [ActiveIssue(21327, TargetFrameworkMonikers.Uap)] // UWP Apps are forbidden to send network traffic to the local Computer.
+        public async void MulticastInterface_Set_IPv6_Loopback_Succeeds()
+        {
+            // On Windows, we can apparently assume interface 1 is "loopback." On other platforms, this is not a
+            // valid assumption. We could maybe use NetworkInterface.LoopbackInterfaceIndex to get the index, but
+            // this would introduce a dependency on System.Net.NetworkInformation, which depends on System.Net.Sockets,
+            // which is what we're testing here....  So for now, we'll just assume "loopback == 1" and run this on
+            // Windows only.
+            await MulticastInterface_Set_IPv6_Helper(1);
+        }
+
+        private async Task MulticastInterface_Set_IPv6_Helper(int interfaceIndex)
+        {
+            IPAddress multicastAddress = IPAddress.Parse("ff11::1:1");
+            string message = "hello";
+            int port;
+
+            using (Socket receiveSocket = CreateBoundUdpIPv6Socket(out port),
+                          sendSocket = new Socket(AddressFamily.InterNetworkV6, SocketType.Dgram, ProtocolType.Udp))
+            {
+                receiveSocket.ReceiveTimeout = 1000;
+                receiveSocket.SetSocketOption(SocketOptionLevel.IPv6, SocketOptionName.AddMembership, new IPv6MulticastOption(multicastAddress, interfaceIndex));
+
+                // https://github.com/Microsoft/BashOnWindows/issues/990
+                if (!PlatformDetection.IsWindowsSubsystemForLinux)
+                {
+                    sendSocket.SetSocketOption(SocketOptionLevel.IPv6, SocketOptionName.MulticastInterface, interfaceIndex);
+                }
+
+                var receiveBuffer = new byte[1024];
+                var receiveTask = receiveSocket.ReceiveAsync(new ArraySegment<byte>(receiveBuffer), SocketFlags.None);
+
+                for (int i = 0; i < TestSettings.UDPRedundancy; i++)
+                {
+                    sendSocket.SendTo(Encoding.UTF8.GetBytes(message), new IPEndPoint(multicastAddress, port));
+                }
+
+                var cts = new CancellationTokenSource();
+                Assert.True(await Task.WhenAny(receiveTask, Task.Delay(20_000, cts.Token)) == receiveTask, "Waiting for received data timed out");
+                cts.Cancel();
+
+                int bytesReceived = await receiveTask;
+                string receivedMessage = Encoding.UTF8.GetString(receiveBuffer, 0, bytesReceived);
+
+                Assert.Equal(receivedMessage, message);
+            }
+        }
+
+        [Fact]
+        public void MulticastInterface_Set_IPv6_InvalidIndex_Throws()
+        {
+            int interfaceIndex = 31415;
+            using (Socket s = new Socket(AddressFamily.InterNetworkV6, SocketType.Dgram, ProtocolType.Udp))
+            {
+                Assert.Throws<SocketException>(() =>
+                                               s.SetSocketOption(SocketOptionLevel.IPv6, SocketOptionName.MulticastInterface, interfaceIndex));
+            }
+        }
+
         [OuterLoop] // TODO: Issue #11345
         [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsNotWindowsSubsystemForLinux))] // In WSL, the connect() call fails immediately.
         [InlineData(false)]
@@ -215,6 +290,21 @@ private static Socket CreateBoundUdpSocket(out int localPort)
             return receiveSocket;
         }
 
+        // Create an Udp Socket and binds it to an available port
+        private static Socket CreateBoundUdpIPv6Socket(out int localPort)
+        {
+            Socket receiveSocket = new Socket(AddressFamily.InterNetworkV6, SocketType.Dgram, ProtocolType.Udp);
+
+            // sending a message will bind the socket to an available port
+            string sendMessage = "dummy message";
+            int port = 54320;
+            IPAddress multicastAddress = IPAddress.Parse("ff11::1:1");
+            receiveSocket.SendTo(Encoding.UTF8.GetBytes(sendMessage), new IPEndPoint(multicastAddress, port));
+
+            localPort = (receiveSocket.LocalEndPoint as IPEndPoint).Port;
+            return receiveSocket;
+        }
+
         [Theory]
         [InlineData(null, null, null, true)]
         [InlineData(null, null, false, true)]