forward-port reuse address patch for windows

ChangeLog

@@ -84,6 +84,7 @@
 	* almost completely changed the storage interface (for custom storage)
 	* added support for hashing pieces in multiple threads
 
+	* improve reliability of binding listen sockets
 	* support SNI in https web seeds and trackers
 	* fix unhandled exception in DHT when receiving a DHT packet over IPv6
 

include/libtorrent/socket.hpp

@@ -120,7 +120,21 @@ namespace libtorrent
 		size_t size(Protocol const&) const { return sizeof(m_value); }
 		int m_value;
 	};
-#endif
+
+	struct exclusive_address_use
+	{
+		exclusive_address_use(int enable): m_value(enable) {}
+		template<class Protocol>
+		int level(Protocol const&) const { return SOL_SOCKET; }
+		template<class Protocol>
+		int name(Protocol const&) const { return SO_EXCLUSIVEADDRUSE; }
+		template<class Protocol>
+		int const* data(Protocol const&) const { return &m_value; }
+		template<class Protocol>
+		size_t size(Protocol const&) const { return sizeof(m_value); }
+		int m_value;
+	};
+#endif // TORRENT_WINDOWS
 
 #ifdef IPV6_TCLASS
 	struct traffic_class

src/session_impl.cpp

@@ -1708,16 +1708,14 @@ namespace aux {
 			return ret;
 		}
 
-		// SO_REUSEADDR on windows is a bit special. It actually allows
-		// two active sockets to bind to the same port. That means we
-		// may end up binding to the same socket as some other random
-		// application. Don't do it!
-#ifndef TORRENT_WINDOWS
 		{
-			error_code err; // ignore errors here
+			// this is best-effort. ignore errors
+			error_code err;
+#ifdef TORRENT_WINDOWS
+			ret.sock->set_option(exclusive_address_use(true), err);
+#endif
 			ret.sock->set_option(tcp::acceptor::reuse_address(true), err);
 		}
-#endif
 
 #if TORRENT_USE_IPV6
 		if (!ipv4)
@@ -1726,6 +1724,7 @@ namespace aux {
 #ifdef IPV6_V6ONLY
 			ret.sock->set_option(v6only(true), err);
 #endif
+
 #ifdef TORRENT_WINDOWS
 
 #ifndef PROTECTION_LEVEL_UNRESTRICTED
@@ -1733,7 +1732,7 @@ namespace aux {
 #endif
 			// enable Teredo on windows
 			ret.sock->set_option(v6_protection_level(PROTECTION_LEVEL_UNRESTRICTED), err);
-#endif
+#endif // TORRENT_WINDOWS
 		}
 #endif // TORRENT_USE_IPV6
 
@@ -4893,6 +4892,9 @@ retry:
 		tcp::endpoint bind_ep(address_v4(), 0);
 		if (m_settings.get_int(settings_pack::outgoing_port) > 0)
 		{
+#ifdef TORRENT_WINDOWS
+			s.set_option(exclusive_address_use(true), ec);
+#endif
 			s.set_option(tcp::acceptor::reuse_address(true), ec);
 			// ignore errors because the underlying socket may not
 			// be opened yet. This happens when we're routing through

src/udp_socket.cpp

@@ -789,6 +789,14 @@ void udp_socket::bind(udp::endpoint const& ep, error_code& ec)
 	{
 		m_ipv4_sock.open(udp::v4(), ec);
 		if (ec) return;
+
+		// this is best-effort. ignore errors
+		error_code err;
+#ifdef TORRENT_WINDOWS
+		m_ipv4_sock.set_option(exclusive_address_use(true), err);
+#endif
+		m_ipv4_sock.set_option(boost::asio::socket_base::reuse_address(true), err);
+
 		m_ipv4_sock.bind(ep, ec);
 		if (ec) return;
 		udp::socket::non_blocking_io ioc(true);
@@ -807,10 +815,17 @@ void udp_socket::bind(udp::endpoint const& ep, error_code& ec)
 		if (is_any(ep.address())) ep6.address(address_v6::any());
 		m_ipv6_sock.open(udp::v6(), ec);
 		if (ec) return;
-#ifdef IPV6_V6ONLY
-		m_ipv6_sock.set_option(v6only(true), ec);
-		ec.clear();
+
+		// this is best-effort. ignore errors
+		error_code err;
+#ifdef TORRENT_WINDOWS
+		m_ipv4_sock.set_option(exclusive_address_use(true), err);
 #endif
+		m_ipv4_sock.set_option(boost::asio::socket_base::reuse_address(true), err);
+#ifdef IPV6_V6ONLY
+		m_ipv6_sock.set_option(v6only(true), err);
+#endif
+
 		m_ipv6_sock.bind(ep6, ec);
 		if (ec != error_code(boost::system::errc::address_not_available
 			, boost::system::generic_category()))