instead of restarting the whole DHT when changing external IP, just rebuild the routing table and change the node IDs

ChangeLog

@@ -1,3 +1,5 @@
+	* improve DHT performance when changing external IP (primarily affects
+	  bootstrapping).
 	* add feature to stop torrents immediately after checking files is done
 	* make all non-auto managed torrents exempt from queuing logic, including
 	  checking torrents.

include/libtorrent/kademlia/dht_tracker.hpp

@@ -81,6 +81,10 @@ namespace libtorrent { namespace dht
 			, find_data::nodes_callback const& f);
 		void stop();
 
+		// tell the node to recalculate its node id based on the current
+		// understanding of its external address (which may have changed)
+		void update_node_id();
+
 		void add_node(udp::endpoint node);
 		void add_router_node(udp::endpoint const& node);
 

include/libtorrent/kademlia/node.hpp

@@ -104,7 +104,9 @@ public:
 		, dht_observer* observer, counters& cnt
 		, dht_storage_constructor_type storage_constructor = dht_default_storage_constructor);
 
-	virtual ~node();
+	~node();
+
+	void update_node_id();
 
 	void tick();
 	void bootstrap(std::vector<udp::endpoint> const& nodes

include/libtorrent/kademlia/routing_table.hpp

@@ -132,6 +132,10 @@ public:
 	// the node will be ignored.
 	void heard_about(node_id const& id, udp::endpoint const& ep);
 
+	// change our node ID. This can be expensive since nodes must be moved around
+	// and potentially dropped
+	void update_node_id(node_id id);
+
 	node_entry const* next_refresh();
 
 	enum

simulation/test_dht.cpp

@@ -113,8 +113,8 @@ TORRENT_TEST(dht_bootstrap)
 			if (ticks > 2)
 			{
 				printf("depth: %d nodes: %d\n", routing_table_depth, num_nodes);
-				TEST_CHECK(routing_table_depth >= 8);
-				TEST_CHECK(num_nodes >= 74);
+				TEST_CHECK(routing_table_depth >= 9);
+				TEST_CHECK(num_nodes >= 115);
 				dht.stop();
 				return true;
 			}

src/kademlia/dht_tracker.cpp

@@ -113,8 +113,13 @@ namespace libtorrent { namespace dht
 
 	dht_tracker::~dht_tracker() {}
 
+	void dht_tracker::update_node_id()
+	{
+		m_dht.update_node_id();
+	}
+
 	// defined in node.cpp
-	extern void nop();
+	void nop();
 
 	void dht_tracker::start(entry const& bootstrap
 		, find_data::nodes_callback const& f)

src/kademlia/node.cpp

@@ -115,8 +115,28 @@ node::node(udp_socket_interface* sock
 	TORRENT_ASSERT(m_storage.get() != NULL);
 }
 
-node::~node()
+node::~node() {}
+
+void node::update_node_id()
 {
+	// if we don't have an observer, we can't ask for the external IP (and our
+	// current node ID is likely not generated from an external address), so we
+	// can just stop here in that case.
+	if (!m_observer) return;
+
+	// it's possible that our external address hasn't actually changed. If our
+	// current ID is still valid, don't do anything.
+	if (verify_id(m_id, m_observer->external_address()))
+		return;
+
+#ifndef TORRENT_DISABLE_LOGGING
+	if (m_observer) m_observer->log(dht_logger::node
+		, "updating node ID (because external IP address changed)");
+#endif
+
+	m_id = generate_id(m_observer->external_address());
+
+	m_table.update_node_id(m_id);
 }
 
 bool node::verify_token(std::string const& token, char const* info_hash

src/kademlia/refresh.cpp

@@ -58,10 +58,15 @@ bool bootstrap::invoke(observer_ptr o)
 	entry& a = e["a"];
 
 	e["q"] = "get_peers";
-	a["info_hash"] = target().to_string();
+	// in case our node id changes during the bootstrap, make sure to always use
+	// the current node id (rather than the target stored in the traversal
+	// algorithm)
+	node_id target = get_node().nid();
+	make_id_secret(target);
+	a["info_hash"] = target.to_string();
 
 //	e["q"] = "find_node";
-//	a["target"] = target().to_string();
+//	a["target"] = target.to_string();
 	m_node.stats_counters().inc_stats_counter(counters::dht_get_peers_out);
 	return m_node.m_rpc.invoke(e, o->target_ep(), o);
 }

src/kademlia/routing_table.cpp

@@ -1024,6 +1024,38 @@ void routing_table::split_bucket()
 	}
 }
 
+void routing_table::update_node_id(node_id id)
+{
+	m_id = id;
+
+	m_ips.clear();
+
+	// pull all nodes out of the routing table, effectively emptying it
+	table_t old_buckets;
+	old_buckets.swap(m_buckets);
+
+	// then add them all back. First add the main nodes, then the replacement
+	// nodes
+	for (int i = 0; i < old_buckets.size(); ++i)
+	{
+		bucket_t const& bucket = old_buckets[i].live_nodes;
+		for (int j = 0; j < bucket.size(); ++j)
+		{
+			add_node(bucket[j]);
+		}
+	}
+
+	// now add back the replacement nodes
+	for (int i = 0; i < old_buckets.size(); ++i)
+	{
+		bucket_t const& bucket = old_buckets[i].replacements;
+		for (int j = 0; j < bucket.size(); ++j)
+		{
+			add_node(bucket[j]);
+		}
+	}
+}
+
 void routing_table::for_each_node(
 	void (*fun1)(void*, node_entry const&)
 	, void (*fun2)(void*, node_entry const&)

src/kademlia/traversal_algorithm.cpp

@@ -180,7 +180,7 @@ void traversal_algorithm::add_entry(node_id const& id, udp::endpoint addr, unsig
 					char hex_id[41];
 					to_hex(reinterpret_cast<char const*>(&o->id()[0]), 20, hex_id);
 					get_node().observer()->log(dht_logger::traversal
-						, "[%p] IGNORING result id: %s addr: %s type: %s"
+						, "[%p] traversal DUPLICATE node. id: %s addr: %s type: %s"
 						, static_cast<void*>(this), hex_id, print_address(o->target_addr()).c_str(), name());
 				}
 #endif

src/session_impl.cpp

@@ -6736,25 +6736,7 @@ retry:
 		// restart the DHT with a new node ID
 
 #ifndef TORRENT_DISABLE_DHT
-		// TODO: 1 we only need to do this if our global IPv4 address has changed
-		// since the DHT (currently) only supports IPv4. Since restarting the DHT
-		// is kind of expensive, it would be nice to not do it unnecessarily
-		if (m_dht)
-		{
-			// TODO: 3 instead of restarting the whole DHT, change the external IP,
-			// node ID and re-jiggle the routing table in-place. A complete restart
-			// throws away all outstanding requests, which may be significant
-			// during bootstrap
-			entry s = m_dht->state();
-			int cur_state = 0;
-			int prev_state = 0;
-			entry* nodes1 = s.find_key("nodes");
-			if (nodes1 && nodes1->type() == entry::list_t) cur_state = nodes1->list().size();
-			entry* nodes2 = m_dht_state.find_key("nodes");
-			if (nodes2 && nodes2->type() == entry::list_t) prev_state = nodes2->list().size();
-			if (cur_state > prev_state) m_dht_state = s;
-			start_dht(m_dht_state);
-		}
+		if (m_dht) m_dht->update_node_id();
 #endif
 	}