[System] Fix TCP socket reuse.

mcs/class/System/Test/System.Net.Sockets/SocketTest.cs

@@ -9,8 +9,10 @@
 //
 
 using System;
+using System.Linq;
 using System.Collections;
 using System.Threading;
+using System.Text.RegularExpressions;
 using System.Net;
 using System.Net.Sockets;
 using NUnit.Framework;
@@ -3476,7 +3478,65 @@ public void UdpDoubleBind ()
 			ss.Close ();
 			s.Close ();
 		}
-
+
+		static bool supportsTcpReuse = false;
+		static bool supportsTcpReuseSet = false;
+
+		static bool SupportsTcpReuse ()
+		{
+			if (supportsTcpReuseSet)
+				return supportsTcpReuse;
+
+			if (Path.DirectorySeparatorChar == '/') {
+				/*
+				 * On UNIX OS
+				 * Multiple threads listening to the same address and port are not possible
+				 * before linux 3.9 kernel, where the socket option SO_REUSEPORT was introduced.
+				 */
+				Regex reg = new Regex(@"^#define\s*SO_REUSEPORT");
+				foreach (string directory in Directory.GetDirectories ("/usr/include")) {
+					var f = Directory.GetFiles (directory, "socket.h").SingleOrDefault ();
+					if (f != null && File.ReadLines (f).Any (l => reg.Match (l).Success)) {
+						supportsTcpReuse = true;
+						break;
+					}
+				}
+			} else {
+				supportsTcpReuse = true;
+			}
+
+			supportsTcpReuseSet = true;
+
+			return supportsTcpReuse;
+		}
+
+		// Test case for bug #31557
+		[Test]
+		public void TcpDoubleBind ()
+		{
+			using (Socket s = new Socket (AddressFamily.InterNetwork,
+						SocketType.Stream, ProtocolType.Tcp))
+			using (Socket ss = new Socket (AddressFamily.InterNetwork,
+						SocketType.Stream, ProtocolType.Tcp)) {
+				s.SetSocketOption (SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
+
+				s.Bind (new IPEndPoint (IPAddress.Any, 12345));
+				s.Listen(1);
+
+				ss.SetSocketOption (SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
+
+				Exception ex = null;
+				try {
+					ss.Bind (new IPEndPoint (IPAddress.Any, 12345));
+					ss.Listen(1);
+				} catch (SocketException e) {
+					ex = e;
+				}
+
+				Assert.AreEqual (SupportsTcpReuse (), ex == null);
+			}
+		}
+
 		[Test]
 		[Category ("NotOnMac")]
                 public void ConnectedProperty ()

mono/io-layer/sockets.c

@@ -733,7 +733,7 @@ int _wapi_setsockopt(guint32 fd, int level, int optname,
 		socklen_t type_len = sizeof (type);
 
 		if (!getsockopt (fd, level, SO_TYPE, &type, &type_len)) {
-			if (type == SOCK_DGRAM)
+			if (type == SOCK_DGRAM || type == SOCK_STREAM)
 				setsockopt (fd, level, SO_REUSEPORT, tmp_val, optlen);
 		}
 	}