Set SO_REUSEADDR on managed listen sockets on Unix (#2111)

- https://github.com/dotnet/corefx/issues/24562

src/Kestrel.Transport.Sockets/SocketTransport.cs

@@ -6,10 +6,12 @@ using System.Diagnostics;
 using System.IO.Pipelines;
 using System.Net;
 using System.Net.Sockets;
+using System.Runtime.InteropServices;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Protocols;
 using Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions.Internal;
 using Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.Internal;
+using Microsoft.Extensions.Logging;
 
 namespace Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets
 {
@@ -51,6 +53,8 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets
 
             var listenSocket = new Socket(endPoint.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
 
+            EnableRebinding(listenSocket);
+
             // Kestrel expects IPv6Any to bind to both IPv6 and IPv4
             if (endPoint.Address == IPAddress.IPv6Any)
             {
@@ -128,5 +132,37 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets
                 }
             }
         }
+
+        [DllImport("libc", SetLastError = true)]
+        private static extern int setsockopt(IntPtr socket, int level, int option_name, IntPtr option_value, uint option_len);
+
+        private const int SOL_SOCKET_OSX = 0xffff;
+        private const int SO_REUSEADDR_OSX = 0x0004;
+        private const int SOL_SOCKET_LINUX = 0x0001;
+        private const int SO_REUSEADDR_LINUX = 0x0002;
+
+        // Without setting SO_REUSEADDR on macOS and Linux, binding to a recently used endpoint can fail.
+        // https://github.com/dotnet/corefx/issues/24562
+        private unsafe void EnableRebinding(Socket listenSocket)
+        {
+            var optionValue = 1;
+            var setsockoptStatus = 0;
+
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+            {
+                setsockoptStatus = setsockopt(listenSocket.Handle, SOL_SOCKET_LINUX, SO_REUSEADDR_LINUX,
+                                              (IntPtr)(&optionValue), sizeof(int));
+            }
+            else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+            {
+                setsockoptStatus = setsockopt(listenSocket.Handle, SOL_SOCKET_OSX, SO_REUSEADDR_OSX,
+                                              (IntPtr)(&optionValue), sizeof(int));
+            }
+
+            if (setsockoptStatus != 0)
+            {
+                _trace.LogInformation("Setting SO_REUSEADDR failed with errno '{errno}'.", Marshal.GetLastWin32Error());
+            }
+        }
     }
 }

test/Kestrel.FunctionalTests/AddressRegistrationTests.cs

@@ -526,10 +526,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.FunctionalTests
             }
         }
 
-        // https://github.com/dotnet/corefx/issues/24562
+        [Fact]
-        [ConditionalFact]
-        [OSSkipCondition(OperatingSystems.MacOSX, SkipReason = "Sockets transport fails to rebind on macOS.")]
-        [OSSkipCondition(OperatingSystems.Linux, SkipReason = "Sockets transport fails to rebind on Linux.")]
         public async Task CanRebindToEndPoint()
         {
             var port = GetNextPort();
@@ -566,10 +563,8 @@ namespace Microsoft.AspNetCore.Server.Kestrel.FunctionalTests
             }
         }
 
-        // https://github.com/dotnet/corefx/issues/24562
         [ConditionalFact]
-        [OSSkipCondition(OperatingSystems.MacOSX, SkipReason = "Sockets transport fails to rebind on macOS.")]
+        [IPv6SupportedCondition]
-        [OSSkipCondition(OperatingSystems.Linux, SkipReason = "Sockets transport fails to rebind on Linux.")]
         public async Task CanRebindToMultipleEndPoints()
         {
             var port = GetNextPort();
@@ -892,12 +887,6 @@ namespace Microsoft.AspNetCore.Server.Kestrel.FunctionalTests
 
             private bool CanBindToPort()
             {
-#if MACOS && SOCKETS
-                // Binding to a port with a Socket, disposing the Socket, and rebinding often fails with
-                // SocketError.AddressAlreadyInUse on macOS. This isn't an issue if binding with libuv second.
-                // https://github.com/dotnet/corefx/issues/24562
-                return false;
-#else
                 try
                 {
                     using (var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
@@ -910,7 +899,6 @@ namespace Microsoft.AspNetCore.Server.Kestrel.FunctionalTests
                 {
                     return false;
                 }
-#endif
             }
         }
     }