fix bind-to-device for UDP sockets

include/libtorrent/aux_/session_impl.hpp

@@ -579,10 +579,9 @@ namespace libtorrent
 			bool is_dht_running() const { return (m_dht.get() != nullptr); }
 			int external_udp_port() const override
 			{
-				for (std::list<listen_socket_t>::const_iterator i = m_listen_sockets.begin()
-					, end(m_listen_sockets.end()); i != end; ++i)
+				for (auto const& s : m_listen_sockets)
 				{
-					if (i->udp_sock) return i->udp_external_port;
+					if (s.udp_sock) return s.udp_external_port;
 				}
 				return -1;
 			}

include/libtorrent/udp_socket.hpp

@@ -89,6 +89,7 @@ namespace libtorrent
 
 		void send(udp::endpoint const& ep, span<char const> p
 			, error_code& ec, int flags = 0);
+		void open(udp const& protocol, error_code& ec);
 		void bind(udp::endpoint const& ep, error_code& ec);
 		void close();
 		int local_port() const { return m_bind_port; }

src/session_impl.cpp

@@ -1635,8 +1635,28 @@ namespace aux {
 			= (flags & open_ssl_socket)
 			? socket_type_t::utp_ssl
 			: socket_type_t::udp;
+		udp::endpoint const udp_bind_ep(bind_ep.address(), bind_ep.port());
 
 		ret.udp_sock = std::make_shared<udp_socket>(m_io_service);
+		ret.udp_sock->open(udp_bind_ep.protocol(), ec);
+		if (ec)
+		{
+#ifndef TORRENT_DISABLE_LOGGING
+			if (should_log())
+			{
+				session_log("failed to open UDP socket: %s: %s"
+					, device.c_str(), ec.message().c_str());
+			}
+#endif
+
+			last_op = listen_failed_alert::open;
+			if (m_alerts.should_post<listen_failed_alert>())
+				m_alerts.emplace_alert<listen_failed_alert>(device
+					, bind_ep, last_op, ec, udp_sock_type);
+
+			return ret;
+		}
+
 #if TORRENT_HAS_BINDTODEVICE
 		if (!device.empty())
 		{
@@ -1661,8 +1681,7 @@ namespace aux {
 			}
 		}
 #endif
-		ret.udp_sock->bind(udp::endpoint(bind_ep.address(), bind_ep.port())
-			, ec);
+		ret.udp_sock->bind(udp_bind_ep, ec);
 
 		last_op = listen_failed_alert::bind;
 		if (ec)
@@ -1670,7 +1689,7 @@ namespace aux {
 #ifndef TORRENT_DISABLE_LOGGING
 			if (should_log())
 			{
-				session_log("failed to open UDP socket: %s: %s"
+				session_log("failed to bind UDP socket: %s: %s"
 					, device.c_str(), ec.message().c_str());
 			}
 #endif

src/udp_socket.cpp

@@ -404,7 +404,7 @@ void udp_socket::close()
 	m_abort = true;
 }
 
-void udp_socket::bind(udp::endpoint const& ep, error_code& ec)
+void udp_socket::open(udp const& protocol, error_code& ec)
 {
 	TORRENT_ASSERT(is_single_thread());
 
@@ -413,16 +413,11 @@ void udp_socket::bind(udp::endpoint const& ep, error_code& ec)
 	if (m_socket.is_open()) m_socket.close(ec);
 	ec.clear();
 
-	if (ep.address().is_v4())
-	{
-		m_socket.open(udp::v4(), ec);
-		if (ec) return;
-	}
+	m_socket.open(protocol, ec);
+	if (ec) return;
 #if TORRENT_USE_IPV6
-	else if (ep.address().is_v6())
+	if (protocol == udp::v6())
 	{
-		m_socket.open(udp::v6(), ec);
-		if (ec) return;
 		error_code err;
 		m_socket.set_option(boost::asio::ip::v6_only(true), err);
 
@@ -439,7 +434,12 @@ void udp_socket::bind(udp::endpoint const& ep, error_code& ec)
 	m_socket.set_option(exclusive_address_use(true), err);
 #endif
 	m_socket.set_option(boost::asio::socket_base::reuse_address(true), err);
+}
 
+void udp_socket::bind(udp::endpoint const& ep, error_code& ec)
+{
+	if (!m_socket.is_open()) open(ep.protocol(), ec);
+	if (ec) return;
 	m_socket.bind(ep, ec);
 	if (ec) return;
 	udp::socket::non_blocking_io ioc(true);