introduce new, optional, get_peers mechanism that is more privacy preserving (doesn't leak the info-hash to as many DHT nodes)

examples/client_test.cpp

@@ -1541,6 +1541,10 @@ int main(int argc, char* argv[])
 	}
 
 #ifndef TORRENT_DISABLE_DHT
+	dht_settings dht;
+	dht.privacy_lookups = true;
+	ses.set_dht_settings(dht);
+
 	if (start_dht)
 	{
 		settings.use_dht_as_fallback = false;

include/libtorrent/kademlia/find_data.hpp

@@ -74,18 +74,18 @@ public:
 		, nodes_callback const& ncallback
 		, bool noseeds);
 
-	virtual char const* name() const { return "get_peers"; }
+	virtual void start();
+
+	virtual char const* name() const;
 
 	node_id const target() const { return m_target; }
 
 protected:
 
-	void done();
+	virtual void done();
 	observer_ptr new_observer(void* ptr, udp::endpoint const& ep, node_id const& id);
 	virtual bool invoke(observer_ptr o);
 
-private:
-
 	data_callback m_data_callback;
 	nodes_callback m_nodes_callback;
 	std::map<node_id, std::string> m_write_tokens;
@@ -95,6 +95,25 @@ private:
 	bool m_noseeds:1;
 };
 
+class obfuscated_get_peers : public find_data
+{
+public:
+	typedef find_data::nodes_callback done_callback;
+
+	obfuscated_get_peers(node_impl& node, node_id target
+		, data_callback const& dcallback
+		, nodes_callback const& ncallback
+		, bool noseeds);
+
+	virtual char const* name() const;
+
+protected:
+
+	observer_ptr new_observer(void* ptr, udp::endpoint const& ep, node_id const& id);
+	virtual bool invoke(observer_ptr o);
+	virtual void done();
+};
+
 class find_data_observer : public observer
 {
 public:

include/libtorrent/kademlia/node_id.hpp

@@ -55,7 +55,10 @@ node_id TORRENT_EXTRA_EXPORT distance(node_id const& n1, node_id const& n2);
 bool TORRENT_EXTRA_EXPORT compare_ref(node_id const& n1, node_id const& n2, node_id const& ref);
 
 // returns n in: 2^n <= distance(n1, n2) < 2^(n+1)
-// usefult for finding out which bucket a node belongs to
+// useful for finding out which bucket a node belongs to
+// the value that's returned is the number of trailing bits
+// after the shared bit prefix of ``n1`` and ``n2``.
+// if the first bits are different, that's 160.
 int TORRENT_EXTRA_EXPORT distance_exp(node_id const& n1, node_id const& n2);
 
 node_id TORRENT_EXTRA_EXPORT generate_id(address const& external_ip);

include/libtorrent/kademlia/traversal_algorithm.hpp

@@ -71,7 +71,7 @@ struct traversal_algorithm : boost::noncopyable
 	void* allocate_observer();
 	void free_observer(void* ptr);
 
-	virtual char const* name() const { return "traversal_algorithm"; }
+	virtual char const* name() const;
 	virtual void start();
 
 	node_id const& target() const { return m_target; }

include/libtorrent/session_settings.hpp

@@ -1405,6 +1405,7 @@ namespace libtorrent
 			, restrict_search_ips(true)
 			, extended_routing_table(true)
 			, aggressive_lookups(true)
+			, privacy_lookups(false)
 		{}
 		
 		// the maximum number of peers to send in a
@@ -1470,6 +1471,10 @@ namespace libtorrent
 		// i.e. every time we get results back with closer nodes, we query them right away.
 		// It lowers the lookup times at the cost of more outstanding queries.
 		bool aggressive_lookups;
+
+		// when set, perform lookups in a way that is slightly more expensive, but which
+		// minimizes the amount of information leaked about you.
+		bool privacy_lookups;
 	};
 
 #ifndef TORRENT_DISABLE_ENCRYPTION

src/kademlia/find_data.cpp

@@ -183,7 +183,16 @@ find_data::find_data(
 	, m_got_peers(false)
 	, m_noseeds(noseeds)
 {
-	node.m_table.for_each_node(&add_entry_fun, 0, (traversal_algorithm*)this);
+}
+
+void find_data::start()
+{
+	// if the user didn't add seed-nodes manually, grab a bunch of nodes from the
+	// routing table
+	if (m_results.empty())
+		m_node.m_table.for_each_node(&add_entry_fun, 0, (traversal_algorithm*)this);
+
+	traversal_algorithm::start();
 }
 
 observer_ptr find_data::new_observer(void* ptr
@@ -196,6 +205,8 @@ observer_ptr find_data::new_observer(void* ptr
 	return o;
 }
 
+char const* find_data::name() const { return "get_peers"; }
+
 bool find_data::invoke(observer_ptr o)
 {
 	if (m_done)
@@ -206,17 +217,19 @@ bool find_data::invoke(observer_ptr o)
 
 	entry e;
 	e["y"] = "q";
-	e["q"] = "get_peers";
 	entry& a = e["a"];
+
+	e["q"] = "get_peers";
 	a["info_hash"] = m_target.to_string();
 	if (m_noseeds) a["noseed"] = 1;
+
 	return m_node.m_rpc.invoke(e, o->target_ep(), o);
 }
 
 void find_data::got_peers(std::vector<tcp::endpoint> const& peers)
 {
 	if (!peers.empty()) m_got_peers = true;
-	m_data_callback(peers);
+	if (m_data_callback) m_data_callback(peers);
 }
 
 void find_data::done()
@@ -242,10 +255,95 @@ void find_data::done()
 		results.push_back(std::make_pair(node_entry(o->id(), o->target_ep()), j->second));
 		--num_results;
 	}
-	m_nodes_callback(results, m_got_peers);
+	if (m_nodes_callback) m_nodes_callback(results, m_got_peers);
 
 	traversal_algorithm::done();
 }
 
+obfuscated_get_peers::obfuscated_get_peers(
+	node_impl& node
+	, node_id info_hash
+	, data_callback const& dcallback
+	, nodes_callback const& ncallback
+	, bool noseeds)
+	: find_data(node, info_hash, dcallback, ncallback, noseeds)
+{
+}
+
+char const* obfuscated_get_peers::name() const { return "get_peers [obfuscated]"; }
+
+observer_ptr obfuscated_get_peers::new_observer(void* ptr
+	, udp::endpoint const& ep, node_id const& id)
+{
+	observer_ptr o(new (ptr) find_data_observer(this, ep, id));
+#if defined TORRENT_DEBUG || TORRENT_RELEASE_ASSERTS
+	o->m_in_constructor = false;
+#endif
+	return o;
+}
+
+bool obfuscated_get_peers::invoke(observer_ptr o)
+{
+	entry e;
+	e["y"] = "q";
+	e["q"] = "find_node";
+	entry& a = e["a"];
+
+	// This logic will obfuscate the target info-hash
+	// we're looking up, in order to preserve more privacy
+	// on the DHT. This is done by only including enough
+	// bits in the info-hash for the node we're querying to
+	// give a good answer, but not more.
+
+	node_id id = o->id();
+	int shared_prefix = 160 - distance_exp(id, m_target);
+
+	// now, obfuscate the bits past shared_prefix + 5
+	node_id obfuscated_target = generate_random_id();
+	obfuscated_target >>= shared_prefix + 6;
+	obfuscated_target^= m_target;
+	a["target"] = obfuscated_target.to_string();
+
+	return m_node.m_rpc.invoke(e, o->target_ep(), o);
+}
+
+void obfuscated_get_peers::done()
+{
+	boost::intrusive_ptr<find_data> ta(new find_data(m_node, m_target
+		, m_data_callback
+		, m_nodes_callback
+		, m_noseeds));
+
+	// don't call these when the obfuscated_get_peers
+	// is done, we're passing them on to be called when
+	// ta completes.
+	m_data_callback.clear();
+	m_nodes_callback.clear();
+
+#ifdef TORRENT_DHT_VERBOSE_LOGGING
+	TORRENT_LOG(traversal) << " [" << this << "]"
+		<< " obfuscated get_peers phase 1 done, spawning get_peers [" << ta.get() << "]";
+#endif
+
+	int num_added = 0;
+	for (std::vector<observer_ptr>::iterator i = m_results.begin()
+		, end(m_results.end()); i != end && num_added < 10; ++i)
+	{
+		observer_ptr o = *i;
+
+		// only add nodes whose node ID we knoe and that
+		// we know are alive
+		if (o->flags & observer::flag_no_id) continue;
+		if ((o->flags & observer::flag_alive) == 0) continue;
+
+		ta->add_entry(o->id(), o->target_ep(), observer::flag_initial);
+		++num_added;
+	}
+
+	ta->start();
+
+	find_data::done();
+}
+
 } } // namespace libtorrent::dht
 

src/kademlia/node.cpp

@@ -332,9 +332,21 @@ void node_impl::announce(sha1_hash const& info_hash, int listen_port, bool seed
 #endif
 	// search for nodes with ids close to id or with peers
 	// for info-hash id. then send announce_peer to them.
-	boost::intrusive_ptr<find_data> ta(new find_data(*this, info_hash, f
+
+	boost::intrusive_ptr<find_data> ta;
+	if (m_settings.privacy_lookups)
+	{
+		ta.reset(new obfuscated_get_peers(*this, info_hash, f
 			, boost::bind(&announce_fun, _1, boost::ref(*this)
 			, listen_port, info_hash, seed), seed));
+	}
+	else
+	{
+		ta.reset(new find_data(*this, info_hash, f
+			, boost::bind(&announce_fun, _1, boost::ref(*this)
+			, listen_port, info_hash, seed), seed));
+	}
+
 	ta->start();
 }
 

src/kademlia/traversal_algorithm.cpp

@@ -191,6 +191,11 @@ void traversal_algorithm::free_observer(void* ptr)
 	m_node.m_rpc.free_observer(ptr);
 }
 
+char const* traversal_algorithm::name() const
+{
+	return "traversal_algorithm";
+}
+
 void traversal_algorithm::traverse(node_id const& id, udp::endpoint addr)
 {
 #ifdef TORRENT_DHT_VERBOSE_LOGGING

test/test_dht.cpp

@@ -322,6 +322,7 @@ struct print_alert : alert_dispatcher
 	}
 };
 
+// TODO: 3 test find_data, obfuscated_get_peers and bootstrap
 int test_main()
 {
 	dht_settings sett;