support optional LSD IP broadcast

docs/manual.rst

@@ -3856,6 +3856,7 @@ session_settings
 
 		int default_peer_upload_rate;
 		int default_peer_download_rate;
+		bool broadcast_lsd;
 	};
 
 ``user_agent`` this is the client identification to the tracker.
@@ -4467,6 +4468,11 @@ set on new peer connections (not existing ones). The peer rate limits can
 be changed individually later using
 `set_peer_upload_limit() set_peer_download_limit()`_.
 
+if ``broadcast_lsd`` is set to true, the local peer discovery
+(or Local Service Discovery) will not only use IP multicast, but also
+broadcast its messages. This can be useful when running on networks
+that don't support multicast. It's off by default since it's inefficient.
+
 pe_settings
 ===========
 

include/libtorrent/broadcast_socket.hpp

@@ -72,26 +72,37 @@ namespace libtorrent
 		void send(char const* buffer, int size, error_code& ec);
 		void close();
 		int num_send_sockets() const { return m_unicast_sockets.size(); }
+		void enable_ip_broadcast(bool e);
 
 	private:
 
 		struct socket_entry
 		{
-			socket_entry(boost::shared_ptr<datagram_socket> const& s): socket(s) {}
+			socket_entry(boost::shared_ptr<datagram_socket> const& s)
+				: socket(s) {}
+			socket_entry(boost::shared_ptr<datagram_socket> const& s
+				, address_v4 const& mask): socket(s), netmask(mask) {}
 			boost::shared_ptr<datagram_socket> socket;
 			char buffer[1024];
 			udp::endpoint remote;
+			address_v4 netmask;
 			void close()
 			{
 				if (!socket) return;
 				error_code ec;
 				socket->close(ec);
 			}
+			address_v4 broadcast_address() const
+			{
+				error_code ec;
+				return address_v4::broadcast(socket->local_endpoint(ec).address().to_v4(), netmask);
+			}
 		};
 	
 		void on_receive(socket_entry* s, error_code const& ec
 			, std::size_t bytes_transferred);
-		void open_unicast_socket(io_service& ios, address const& addr);
+		void open_unicast_socket(io_service& ios, address const& addr
+			, address_v4 const& mask);
 		void open_multicast_socket(io_service& ios, address const& addr
 			, bool loopback, error_code& ec);
 
@@ -107,6 +118,11 @@ namespace libtorrent
 		udp::endpoint m_multicast_endpoint;
 		receive_handler_t m_on_receive;
 
+		// if set, use IP broadcast as well as IP multicast
+		// this is off by default because it's expensive in
+		// terms of bandwidth usage
+		bool m_ip_broadcast;
+		
 	};
 }
 	

include/libtorrent/lsd.hpp

@@ -64,6 +64,8 @@ public:
 	void announce(sha1_hash const& ih, int listen_port);
 	void close();
 
+	void use_broadcast(bool b);
+
 private:
 
 	void resend_announce(error_code const& e, std::string msg);

include/libtorrent/session_settings.hpp

@@ -207,6 +207,7 @@ namespace libtorrent
 			, strict_end_game_mode(true)
 			, default_peer_upload_rate(0)
 			, default_peer_download_rate(0)
+			, broadcast_lsd(false)
 		{}
 
 		// this is the user agent that will be sent to the tracker
@@ -791,6 +792,12 @@ namespace libtorrent
 		// each peer will have these limits set on it
 		int default_peer_upload_rate;
 		int default_peer_download_rate;
+
+		// if this is true, the broadcast socket will not only use IP multicast
+		// but also send the messages on the broadcast address. This is false by
+		// default in order to avoid flooding networks for no good reason. If
+		// a network is known not to support multicast, this can be enabled
+		bool broadcast_lsd;
 	};
 
 #ifndef TORRENT_DISABLE_DHT

src/broadcast_socket.cpp

@@ -187,6 +187,7 @@ namespace libtorrent
 		, bool loopback)
 		: m_multicast_endpoint(multicast_endpoint)
 		, m_on_receive(handler)
+		, m_ip_broadcast(false)
 	{
 		TORRENT_ASSERT(is_multicast(m_multicast_endpoint.address()));
 
@@ -218,7 +219,22 @@ namespace libtorrent
 //				, print_address(multicast_endpoint.address()).c_str()
 //				, ec.message().c_str());
 #endif
-			open_unicast_socket(ios, i->interface_address);
+			open_unicast_socket(ios, i->interface_address
+				, i->netmask.is_v4() ? i->netmask.to_v4() : address_v4());
+		}
+	}
+
+	void broadcast_socket::enable_ip_broadcast(bool e)
+	{
+		if (e == m_ip_broadcast) return;
+		m_ip_broadcast = e;
+
+		asio::socket_base::broadcast option(m_ip_broadcast);
+		for (std::list<socket_entry>::iterator i = m_unicast_sockets.begin()
+			, end(m_unicast_sockets.end()); i != end; ++i)
+		{
+			if (i->socket) continue;
+			i->socket->set_option(option);
 		}
 	}
 
@@ -246,7 +262,8 @@ namespace libtorrent
 			, se.remote, bind(&broadcast_socket::on_receive, this, &se, _1, _2));
 	}
 
-	void broadcast_socket::open_unicast_socket(io_service& ios, address const& addr)
+	void broadcast_socket::open_unicast_socket(io_service& ios, address const& addr
+		, address_v4 const& mask)
 	{
 		using namespace asio::ip::multicast;
 		error_code ec;
@@ -255,7 +272,7 @@ namespace libtorrent
 		if (ec) return;
 		s->bind(udp::endpoint(addr, 0), ec);
 		if (ec) return;
-		m_unicast_sockets.push_back(socket_entry(s));
+		m_unicast_sockets.push_back(socket_entry(s, mask));
 		socket_entry& se = m_unicast_sockets.back();
 		s->async_receive_from(asio::buffer(se.buffer, sizeof(se.buffer))
 			, se.remote, bind(&broadcast_socket::on_receive, this, &se, _1, _2));
@@ -289,6 +306,9 @@ namespace libtorrent
 			if (!i->socket) continue;
 			error_code e;
 			i->socket->send_to(asio::buffer(buffer, size), m_multicast_endpoint, 0, e);
+			if (m_ip_broadcast && i->socket->local_endpoint(e).address().is_v4())
+				i->socket->send_to(asio::buffer(buffer, size)
+					, udp::endpoint(i->broadcast_address(), m_multicast_endpoint.port()), 0, e);
 #ifndef NDEBUG
 //			extern std::string print_address(address const& addr);
 //			extern std::string print_endpoint(udp::endpoint const& ep);

src/lsd.cpp

@@ -213,3 +213,8 @@ void lsd::close()
 	m_callback.clear();
 }
 
+void lsd::use_broadcast(bool b)
+{
+	m_socket.enable_ip_broadcast(b);
+}
+

src/session_impl.cpp

@@ -806,6 +806,12 @@ namespace aux {
 			}
 		}
 #endif
+
+ 		if (m_settings.connection_speed < 0) m_settings.connection_speed = 200;
+
+		if (m_settings.broadcast_lsd && m_lsd)
+			m_lsd->use_broadcast(true);
+
 		update_disk_thread_settings();
 	}
 
@@ -1164,6 +1170,8 @@ namespace aux {
 			m_auto_manage_time_scaler = 2;
 		m_settings = s;
  		if (m_settings.connection_speed < 0) m_settings.connection_speed = 200;
+		if (m_settings.broadcast_lsd && m_lsd)
+			m_lsd->use_broadcast(true);
  
 		if (update_disk_io_thread)
 			update_disk_thread_settings();
@@ -3630,6 +3638,8 @@ namespace aux {
 		m_lsd = new lsd(m_io_service
 			, m_listen_interface.address()
 			, bind(&session_impl::on_lsd_peer, this, _1, _2));
+		if (m_settings.broadcast_lsd)
+			m_lsd->use_broadcast(true);
 	}
 	
 	void session_impl::start_natpmp(natpmp* n)