Unix: fix UDP ReuseAddress with non .NET Core UDP clients

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

@@ -1812,14 +1812,12 @@ SystemNative_SetSockOpt(intptr_t socket, int32_t socketOptionLevel, int32_t sock
     //
     if (socketOptionLevel == SocketOptionLevel_SOL_SOCKET)
     {
-        // Windows supports 3 address sharing modes:
-        // - not sharing      (SO_EXCLUSIVEADDRUSE=1, SO_REUSEADDR=0)
-        // - explicit sharing (SO_EXCLUSIVEADDRUSE=0, SO_REUSEADDR=1)
-        // - implicit sharing (SO_EXCLUSIVEADDRUSE=0, SO_REUSEADDR=0)
-        // On Unix we have two address sharing modes:
-        // - not sharing      (SO_REUSEPORT=0)
-        // - explicit sharing (SO_REUSEPORT=1)
-        // We make both SocketOptionName_SO_REUSEADDR and SocketOptionName_SO_EXCLUSIVEADDRUSE control SO_REUSEPORT.
+        // Windows supports 3 address reuse modes:
+        // - reuse not allowed        (SO_EXCLUSIVEADDRUSE=1, SO_REUSEADDR=0)
+        // - reuse explicily allowed  (SO_EXCLUSIVEADDRUSE=0, SO_REUSEADDR=1)
+        // - reuse implicitly allowed (SO_EXCLUSIVEADDRUSE=0, SO_REUSEADDR=0)
+        // On Unix we can reuse or not, there is no implicit reuse.
+        // We make both SocketOptionName_SO_REUSEADDR and SocketOptionName_SO_EXCLUSIVEADDRUSE control SO_REUSEPORT/SO_REUSEADDR.
         if (socketOptionName == SocketOptionName_SO_EXCLUSIVEADDRUSE || socketOptionName == SocketOptionName_SO_REUSEADDR)
         {
             if (optionLen != sizeof(int32_t))
@@ -1842,7 +1840,15 @@ SystemNative_SetSockOpt(intptr_t socket, int32_t socketOptionLevel, int32_t sock
                 }
             }
 
+            // An application that sets SO_REUSEPORT/SO_REUSEADDR can reuse the endpoint with another
+            // application that sets the same option. If one application sets SO_REUSEPORT and another
+            // sets SO_REUSEADDR the second application will fail to bind. We set both options, this
+            // enables reuse with applications that set one or both options.
             int err = setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &value, (socklen_t)optionLen);
+            if (err == 0)
+            {
+                err = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &value, (socklen_t)optionLen);
+            }
             return err == 0 ? Error_SUCCESS : SystemNative_ConvertErrorPlatformToPal(errno);
         }
     }

src/System.Net.Sockets/tests/FunctionalTests/Configurations.props

@@ -2,8 +2,10 @@
 <Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup>
     <BuildConfigurations>
-      netstandard;
-      netcoreapp;
+      netstandard-Windows_NT;
+      netstandard-Unix;
+      netcoreapp-Windows_NT;
+      netcoreapp-Unix;
     </BuildConfigurations>
   </PropertyGroup>
 </Project>

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

@@ -0,0 +1,14 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Runtime.InteropServices;
+
+namespace System.Net.Sockets.Tests
+{
+    public partial class SocketOptionNameTest
+    {
+        [DllImport("libc", SetLastError = true)]
+        private unsafe static extern int setsockopt(int socket, int level, int option_name, void* option_value, uint option_len);
+    }
+}

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

@@ -0,0 +1,14 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace System.Net.Sockets.Tests
+{
+    public partial class SocketOptionNameTest
+    {
+        private unsafe static int setsockopt(int socket, int level, int option_name, void* option_value, uint option_len)
+        {
+            throw new PlatformNotSupportedException();
+        }
+    }
+}

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

@@ -13,7 +13,7 @@
 
 namespace System.Net.Sockets.Tests
 {
-    public class SocketOptionNameTest
+    public partial class SocketOptionNameTest
     {
         private static bool SocketsReuseUnicastPortSupport => Capability.SocketsReuseUnicastPortSupport().HasValue;
 
@@ -490,6 +490,42 @@ public void ExclusiveAddressUseTcp()
             }
         }
 
+        [Fact]
+        [PlatformSpecific(TestPlatforms.Linux | TestPlatforms.OSX)]
+        public unsafe void ReuseAddressUdp()
+        {
+            // Verify that .NET Core Sockets can bind to the UDP address from applications
+            // that allow binding the same address.
+            int SOL_SOCKET = -1;
+            int option = -1;
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+            {
+                // Linux: use SO_REUSEADDR to allow binding the same address.
+                SOL_SOCKET = 1;
+                const int SO_REUSEADDR = 2;
+                option = SO_REUSEADDR;
+            }
+            else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+            {
+                // BSD: use SO_REUSEPORT to allow binding the same address.
+                SOL_SOCKET = 0xffff;
+                const int SO_REUSEPORT = 0x200;
+                option = SO_REUSEPORT;
+            }
+            using (Socket s1 = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp))
+            {
+                int value = 1;
+                int rv = setsockopt(s1.Handle.ToInt32(), SOL_SOCKET, option, &value, sizeof(int));
+                Assert.Equal(0, rv);
+                s1.Bind(new IPEndPoint(IPAddress.Any, 0));
+                using (Socket s2 = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp))
+                {
+                    s2.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
+                    s2.Bind(s1.LocalEndPoint);
+                }
+            }
+        }
+
         [OuterLoop] // TODO: Issue #11345
         [Theory]
         [PlatformSpecific(TestPlatforms.Windows)]  // SetIPProtectionLevel not supported on Unix

src/System.Net.Sockets/tests/FunctionalTests/System.Net.Sockets.Tests.csproj

@@ -2,7 +2,7 @@
   <PropertyGroup>
     <ProjectGuid>{8CBA022C-635F-4C8D-9D29-CD8AAC68C8E6}</ProjectGuid>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <Configurations>netcoreapp-Debug;netcoreapp-Release;netstandard-Debug;netstandard-Release</Configurations>
+    <Configurations>netcoreapp-Unix-Debug;netcoreapp-Unix-Release;netcoreapp-Windows_NT-Debug;netcoreapp-Windows_NT-Release;netstandard-Unix-Debug;netstandard-Unix-Release;netstandard-Windows_NT-Debug;netstandard-Windows_NT-Release</Configurations>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Accept.cs" />
@@ -44,6 +44,8 @@
     <Compile Include="SocketAsyncEventArgsTest.cs" />
     <Compile Include="SocketAsyncEventArgsTest.netcoreapp.cs" Condition="'$(TargetGroup)' != 'netstandard'" />
     <Compile Include="SocketOptionNameTest.cs" />
+    <Compile Include="SocketOptionNameTest.Unix.cs" Condition="'$(TargetsUnix)' == 'true'" />
+    <Compile Include="SocketOptionNameTest.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="MulticastOptionTest.cs" />
     <Compile Include="UdpClientTest.cs" />
     <Compile Include="UnixDomainSocketTest.netcoreapp.cs" Condition="'$(TargetGroup)' != 'netstandard'" />