improved super seeding with strict option

docs/manual.rst

@@ -3147,6 +3147,7 @@ that will be sent to the tracker. The user-agent is a good way to identify your
 
 		bool announce_to_all_trackers;
 		bool prefer_udp_trackers;
+		bool strict_super_seeding;
 	};
 
 ``user_agent`` this is the client identification to the tracker.
@@ -3445,6 +3446,10 @@ trackers for the same hostname. Setting this to fails means that the
 trackers' tier is respected and there's no preference of one protocol
 over another.
 
+``strict_super_seeding`` when this is set to true, a piece has to
+have been forwarded to a third peer before another one is handed out.
+This is the traditional definition of super seeding.
+
 pe_settings
 ===========
 

include/libtorrent/session_settings.hpp

@@ -146,6 +146,7 @@ namespace libtorrent
 			, rate_limit_ip_overhead(true)
 			, announce_to_all_trackers(false)
 			, prefer_udp_trackers(true)
+			, strict_super_seeding(false)
 		{}
 
 		// this is the user agent that will be sent to the tracker
@@ -468,6 +469,10 @@ namespace libtorrent
 		// with udp:// protocol, it is preferred over the same
 		// tracker over http://.
 		bool prefer_udp_trackers;
+
+		// when set to true, a piece has to have been forwarded
+		// to a third peer before another one is handed out
+		bool strict_super_seeding;
 	};
 
 #ifndef TORRENT_DISABLE_DHT

src/peer_connection.cpp

@@ -1234,7 +1234,7 @@ namespace libtorrent
 			return;
 		}
 
-		if (t->super_seeding())
+		if (t->super_seeding() && !m_ses.settings().strict_super_seeding)
 		{
 			// if we're superseeding and the peer just told
 			// us that it completed the piece we're superseeding
@@ -1284,6 +1284,23 @@ namespace libtorrent
 				}
 			}
 			
+			// if we're super seeding, this might mean that somebody
+			// forwarded this piece. In which case we need to give
+			// a new piece to that peer
+			if (t->super_seeding()
+				&& m_ses.settings().strict_super_seeding
+				&& (index != m_superseed_piece || t->num_peers() == 1))
+			{
+				for (torrent::peer_iterator i = t->begin()
+					, end(t->end()); i != end; ++i)
+				{
+					peer_connection* p = *i;
+					if (p->superseed_piece() != index) continue;
+					if (!p->has_piece(index)) continue;
+					p->superseed_piece(t->get_piece_to_super_seed(p->get_bitfield()));
+				}
+			}
+
 			if (is_seed())
 			{
 				m_peer_info->seed = true;

test/test_swarm.cpp

@@ -44,7 +44,7 @@ POSSIBILITY OF SUCH DAMAGE.
 using boost::filesystem::remove_all;
 using boost::filesystem::exists;
 
-void test_swarm(bool super_seeding = false)
+void test_swarm(bool super_seeding = false, bool strict = false)
 {
 	using namespace libtorrent;
 
@@ -74,6 +74,7 @@ void test_swarm(bool super_seeding = false)
 	session_settings settings;
 	settings.allow_multiple_connections_per_ip = true;
 	settings.ignore_limits_on_local_network = false;
+	settings.strict_super_seeding = strict;
 	ses1.set_settings(settings);
 	ses2.set_settings(settings);
 	ses3.set_settings(settings);
@@ -205,6 +206,9 @@ int test_main()
 	// with super seeding
 	test_swarm(true);
 	
+	// with strict super seeding
+	test_swarm(true, true);
+
 	return 0;
 }