limit the number of DHT nodes to run

include/libtorrent/aux_/session_impl.hpp

@@ -139,9 +139,17 @@ namespace aux {
 
 	struct TORRENT_EXTRA_EXPORT listen_socket_t : utp_socket_interface
 	{
+		// we accept incoming connections on this interface
 		static constexpr listen_socket_flags_t accept_incoming = 0_bit;
+
+		// this interface has a gateway associated with it, and can
+		// route to the internet (of the same address family)
 		static constexpr listen_socket_flags_t has_gateway = 1_bit;
 
+		// this interface was expanded from the user requesting to
+		// listen on an unspecified address (either IPv4 or IPv6)
+		static constexpr listen_socket_flags_t was_expanded = 2_bit;
+
 		listen_socket_t() = default;
 
 		// listen_socket_t should not be copied or moved because

src/kademlia/dht_tracker.cpp

@@ -116,14 +116,7 @@ namespace libtorrent { namespace dht {
 
 	void dht_tracker::new_socket(aux::listen_socket_handle const& s)
 	{
-		if (s.is_ssl()) return;
-
 		address const local_address = s.get_local_endpoint().address();
-		// don't try to start dht nodes on non-global IPv6 addresses
-		// with IPv4 the interface might be behind NAT so we can't skip them based on the scope of the local address
-		// and we might not have the external address yet
-		if (local_address.is_v6() && is_local(local_address))
-			return;
 		auto stored_nid = std::find_if(m_state.nids.begin(), m_state.nids.end()
 			, [&](node_ids_t::value_type const& nid) { return nid.first == local_address; });
 		node_id const nid = stored_nid != m_state.nids.end() ? stored_nid->second : node_id();
@@ -157,13 +150,6 @@ namespace libtorrent { namespace dht {
 
 	void dht_tracker::delete_socket(aux::listen_socket_handle const& s)
 	{
-		if (s.is_ssl()) return;
-
-		address local_address = s.get_local_endpoint().address();
-		// since we don't start nodes on local IPv6 interfaces we don't need to remove them either
-		if (local_address.is_v6() && is_local(local_address))
-			return;
-		TORRENT_ASSERT(m_nodes.count(s) == 1);
 		m_nodes.erase(s);
 	}
 

src/session_impl.cpp

@@ -200,6 +200,7 @@ namespace aux {
 
 	constexpr listen_socket_flags_t listen_socket_t::accept_incoming;
 	constexpr listen_socket_flags_t listen_socket_t::has_gateway;
+	constexpr listen_socket_flags_t listen_socket_t::was_expanded;
 
 	constexpr ip_source_t session_interface::source_dht;
 	constexpr ip_source_t session_interface::source_peer;
@@ -273,7 +274,7 @@ namespace aux {
 				}
 
 				eps.emplace_back(ipface.interface_address, uep.port, uep.device
-					, uep.ssl, uep.flags);
+					, uep.ssl, uep.flags | listen_socket_t::was_expanded);
 			}
 		}
 	}
@@ -1897,8 +1898,18 @@ namespace aux {
 				m_listen_sockets.emplace_back(s);
 
 #ifndef TORRENT_DISABLE_DHT
-				if (m_dht)
+				// addresses that we expanded from an
+				// unspecified address don't get a DHT running
+				// on them, unless they have a gateway (in
+				// which case we believe they can reach the
+				// internet)
+				if (m_dht
+					&& s->ssl != transport::ssl
+					&& ((s->flags & listen_socket_t::has_gateway)
+						|| !(s->flags & listen_socket_t::was_expanded)))
+				{
 					m_dht->new_socket(m_listen_sockets.back());
+				}
 #endif
 
 				TORRENT_ASSERT(bool(s->flags & listen_socket_t::accept_incoming) == bool(s->sock));
@@ -5745,7 +5756,14 @@ namespace aux {
 			, std::move(m_dht_state));
 
 		for (auto& s : m_listen_sockets)
+		{
+			if (s->ssl != transport::ssl
+				&& ((s->flags & listen_socket_t::has_gateway)
+					|| !(s->flags & listen_socket_t::was_expanded)))
+			{
 				m_dht->new_socket(s);
+			}
+		}
 
 		for (auto const& n : m_dht_router_nodes)
 		{

test/test_session_params.cpp

@@ -121,6 +121,8 @@ TORRENT_TEST(dht_state)
 	params.dht_settings = sett;
 	params.dht_state = s;
 
+	params.settings.set_str(settings_pack::listen_interfaces, "127.0.0.1:6881");
+
 	lt::session ses1(params);
 	TEST_CHECK(ses1.is_dht_running() == true);
 	entry e;
@@ -138,11 +140,10 @@ TORRENT_TEST(dht_state)
 	TEST_EQUAL(params1.dht_settings.max_dht_items, 10000);
 	TEST_EQUAL(params1.dht_settings.max_peers, 20000);
 
+	TEST_EQUAL(params1.dht_state.nids.size(), 1);
+
 	// not a chance the nid will be the fake initial ones
 	TEST_CHECK(params1.dht_state.nids[0].second != s.nids[0].second);
-	// the host machine may not have IPv6 support in which case there will only be one entry
-	if (params1.dht_state.nids.size() > 1)
-		TEST_CHECK(params1.dht_state.nids[1].second != s.nids[1].second);
 }
 #endif