Add read-only support in dht_settings and outgoing query messages.

include/libtorrent/kademlia/rpc_manager.hpp

@@ -83,7 +83,8 @@ public:
 	rpc_manager(node_id const& our_id
 		, routing_table& table
 		, udp_socket_interface* sock
-		, dht_logger* log);
+		, dht_logger* log
+		, bool read_only = false);
 	~rpc_manager();
 
 	void unreachable(udp::endpoint const& ep);
@@ -130,6 +131,7 @@ private:
 	node_id m_our_id;
 	boost::uint32_t m_allocated_observers:31;
 	boost::uint32_t m_destructing:1;
+	bool m_read_only;
 };
 
 } } // namespace libtorrent::dht

include/libtorrent/session_settings.hpp

@@ -1403,6 +1403,7 @@ namespace libtorrent
 			, ignore_dark_internet(true)
 			, block_timeout(5 * 60)
 			, block_ratelimit(5)
+			, read_only(false)
 		{}
 
 		// the maximum number of peers to send in a reply to ``get_peers``
@@ -1488,6 +1489,15 @@ namespace libtorrent
 		// the max number of packets per second a DHT node is allowed to send
 		// without getting banned.
 		int block_ratelimit;
+
+		// when set, the other nodes won't kept this node in their routing
+		// tables, it's meant for low-power and/or ephemeral devices that
+		// cannot support the DHT, it is also useful for mobile devices which
+		// are sensitive to network traffic and battery life.
+		// this node no longer responds to 'query' messages, and will place a
+		// 'ro' key (value = 1) in the top-level message dictionary of outgoing
+		// query messages.
+		bool read_only;
 	};
 
 

src/kademlia/node.cpp

@@ -109,7 +109,7 @@ node::node(udp_socket_interface* sock
 	: m_settings(settings)
 	, m_id(calculate_node_id(nid, observer))
 	, m_table(m_id, 8, settings, observer)
-	, m_rpc(m_id, m_table, sock, observer)
+	, m_rpc(m_id, m_table, sock, observer, settings.read_only)
 	, m_observer(observer)
 	, m_last_tracker_tick(aux::time_now())
 	, m_last_self_refresh(min_time())
@@ -280,6 +280,10 @@ void node::incoming(msg const& m)
 		case 'q':
 		{
 			TORRENT_ASSERT(m.message.dict_find_string_value("y") == "q");
+			// When a DHT node enters the read-only state, it no longer
+			// responds to 'query' messages that it receives.
+			if (m_settings.read_only) break;
+
 			entry e;
 			incoming_request(m, e);
 			m_sock->send_packet(e, m.addr, 0);

src/kademlia/rpc_manager.cpp

@@ -164,7 +164,8 @@ enum { observer_size = max3<
 
 rpc_manager::rpc_manager(node_id const& our_id
 	, routing_table& table, udp_socket_interface* sock
-	, dht_logger* log)
+	, dht_logger* log
+	, bool read_only)
 	: m_pool_allocator(observer_size, 10)
 	, m_sock(sock)
 	, m_log(log)
@@ -173,6 +174,7 @@ rpc_manager::rpc_manager(node_id const& our_id
 	, m_our_id(our_id)
 	, m_allocated_observers(0)
 	, m_destructing(false)
+	, m_read_only(read_only)
 {}
 
 rpc_manager::~rpc_manager()
@@ -439,6 +441,10 @@ bool rpc_manager::invoke(entry& e, udp::endpoint target_addr
 	io::write_uint16(tid, out);
 	e["t"] = transaction_id;
 
+	// When a DHT node enters the read-only state, in each outgoing query message,
+	// places a 'ro' key in the top-level message dictionary and sets its value to 1.
+	if (m_read_only) e["ro"] = 1;
+
 	o->set_target(target_addr);
 	o->set_transaction_id(tid);