don't attempt to make uTP connections if we don't have any outgoing UDP sockets

include/libtorrent/aux_/session_impl.hpp

@@ -691,6 +691,7 @@ namespace aux {
 			mutable std::condition_variable cond;
 
 			// implements session_interface
+			bool has_udp_outgoing_sockets() const override;
 			tcp::endpoint bind_outgoing_socket(socket_type& s, address
 				const& remote_address, error_code& ec) const override;
 			bool verify_incoming_interface(address const& addr);

include/libtorrent/aux_/session_interface.hpp

@@ -211,6 +211,7 @@ namespace aux {
 		virtual void for_each_listen_socket(std::function<void(aux::listen_socket_handle const&)> f) = 0;
 
 		// ask for which interface and port to bind outgoing peer connections on
+		virtual bool has_udp_outgoing_sockets() const = 0;
 		virtual tcp::endpoint bind_outgoing_socket(socket_type& s, address const&
 			remote_address, error_code& ec) const = 0;
 		virtual bool verify_bound_address(address const& addr, bool utp

src/session_impl.cpp

@@ -4964,6 +4964,11 @@ namespace aux {
 #endif
 	}
 
+	bool session_impl::has_udp_outgoing_sockets() const
+	{
+		return !m_outgoing_sockets.sockets.empty();
+	}
+
 	tcp::endpoint session_impl::bind_outgoing_socket(socket_type& s, address
 		const& remote_address, error_code& ec) const
 	{

src/torrent.cpp

@@ -6563,8 +6563,11 @@ bool is_downloading_state(int const st)
 			if (settings().get_bool(settings_pack::enable_outgoing_utp)
 				&& (!settings().get_bool(settings_pack::enable_outgoing_tcp)
 					|| peerinfo->supports_utp
-					|| peerinfo->confirmed_supports_utp))
+					|| peerinfo->confirmed_supports_utp)
+				&& m_ses.has_udp_outgoing_sockets())
+			{
 				sm = m_ses.utp_socket_manager();
+			}
 
 			// don't make a TCP connection if it's disabled
 			if (sm == nullptr && !settings().get_bool(settings_pack::enable_outgoing_tcp))