diff --git a/ChangeLog b/ChangeLog
index ede928591..b3324423e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,4 @@
+	* added share-mode feature for improving share ratios
 	* merged all proxy settings into a single one
 	* improved SOCKS5 support by proxying hostname lookups
 	* improved support for multi-homed clients
diff --git a/docs/features.rst b/docs/features.rst
index dfd8fde82..55288709d 100644
--- a/docs/features.rst
+++ b/docs/features.rst
@@ -48,6 +48,8 @@ extensions
 * support for IPv6, including `BEP 7`_ and `BEP 24`_.
 * support for merkle hash tree torrents. This makes the size of torrent files
   scale well with the size of the content.
+* share-mode. This is a special mode torrents can be put in to optimize share
+  ratio rather than downloading the torrent.
 
 .. _extensions: manual.html#extensions
 .. _`http seeding`: manual.html#http-seeding
@@ -252,6 +254,17 @@ and hence decreasing the likelihood of slow peers blocking the completion of pie
 
 The piece picker can also be set to download pieces in sequential order.
 
+share mode
+----------
+
+The share mode feature in libtorrent is intended for users who are only interested in
+helping out swarms, not downloading the torrents.
+
+It works by predicting the demand for pieces, and only download pieces if there is enough
+demand. New pieces will only be downloaded once the share ratio has hit a certain target.
+
+This feature is especially useful when combined with RSS, so that a client can be set up
+to provide additional bandwidth to an entire feed.
 
 merkle hash tree torrents
 -------------------------
diff --git a/docs/manual.rst b/docs/manual.rst
index 92eb13d38..80b84a903 100644
--- a/docs/manual.rst
+++ b/docs/manual.rst
@@ -393,6 +393,7 @@ add_torrent()
 			bool override_resume_data;
 			bool upload_mode;
 			std::vector<boost::uint8_t> const* file_priorities;
+			bool share_mode;
 		};
 
 		torrent_handle add_torrent(add_torrent_params const& params);
@@ -503,6 +504,22 @@ on disk I/O errors, and if the torrent is also auto managed, it will be taken ou
 of this state periodically. This mode can be used to avoid race conditions when
 adjusting priorities of pieces before allowing the torrent to start downloading.
 
+``share_mode`` determines if the torrent should be added in *share mode* or not.
+Share mode indicates that we are not interested in downloading the torrent, but
+merlely want to improve our share ratio (i.e. increase it). A torrent started in
+share mode will do its best to never download more than it uploads to the swarm.
+If the swarm does not have enough demand for upload capacity, the torrent will
+not download anything. This mode is intended to be safe to add any number of torrents
+to, without manual screening, without the risk of downloading more than is uploaded.
+
+A torrent in share mode sets the priority to all pieces to 0, except for the pieces
+that are downloaded, when pieces are decided to be downloaded. This affects the progress
+bar, which might be set to "100% finished" most of the time. Do not change file or piece
+priorities for torrents in share mode, it will make it not work.
+
+The share mode has one setting, the share ratio target, see ``session_settings::share_mode_target``
+for more info.
+
 ``file_priorities`` can be set to control the initial file priorities when adding
 a torrent. The semantics are the same as for ``torrent_handle::prioritize_files()``.
 
@@ -2058,6 +2075,7 @@ Its declaration looks like this::
 		void force_recheck() const;
 		void clear_error() const;
 		void set_upload_mode(bool m) const;
+		void set_share_mode(bool m) const;
 
 		void flush_cache() const;
 
@@ -2559,6 +2577,18 @@ are automatically put in upload mode whenever they encounter a disk write error.
 To test if a torrent is in upload mode, call ``torrent_handle::status()`` and inspect
 ``torrent_status::upload_mode``.
 
+set_share_mode()
+----------------
+
+	::
+
+		void set_share_mode(bool m) const;
+
+Enable or disable share mode for this torrent. When in share mode, the torrent will
+not necessarily be downloaded, especially not the whole of it. Only parts that are likely
+to be distributed to more than 2 other peers are downloaded, and only if the previous
+prediction was correct.
+
 resolve_countries()
 -------------------
 
@@ -3129,8 +3159,8 @@ It contains the following fields::
 		int sparse_regions;
 
 		bool seed_mode;
-
 		bool upload_mode;
+		bool share_mode;
 
 		int priority;
 
@@ -3363,6 +3393,9 @@ been resolved. If the torrent is not auto-managed, you have to explicitly
 take it out of the upload mode by calling `set_upload_mode()`_ on the
 torrent_handle_.
 
+``share_mode`` is true if the torrent is currently in share-mode, i.e.
+not downloading the torrent, but just helping the swarm out.
+
 ``added_time`` is the posix-time when this torrent was added. i.e. what
 ``time(NULL)`` returned at the time.
 
@@ -3929,6 +3962,7 @@ session_settings
 		bool ignore_resume_timestamps;
 		bool anonymous_mode;
 		int tick_interval;
+		int share_mode_target;
 	};
 
 ``version`` is automatically set to the libtorrent version you're using
@@ -4590,6 +4624,15 @@ peers. It should not be more than one second (i.e. 1000 ms). Setting this
 to a low value (around 100) means higher resolution bandwidth quota distribution,
 setting it to a higher value saves CPU cycles.
 
+``share_mode_target`` specifies the target share ratio for share mode torrents.
+This defaults to 3, meaning we'll try to upload 3 times as much as we download.
+Setting this very high, will make it very conservative and you might end up
+not downloading anything ever (and not affecting your share ratio). It does
+not make any sense to set this any lower than 2. For instance, if only 3 peers
+need to download the rarest piece, it's impossible to download a single piece
+and upload it more than 3 times. If the share_mode_target is set to more than 3,
+nothing is downloaded.
+
 pe_settings
 ===========
 
diff --git a/examples/client_test.cpp b/examples/client_test.cpp
index bade7c6ef..1a0e5e8c3 100644
--- a/examples/client_test.cpp
+++ b/examples/client_test.cpp
@@ -530,6 +530,8 @@ std::string outgoing_interface = "";
 int poll_interval = 5;
 int max_connections_per_torrent = 50;
 
+bool share_mode = false;
+
 using boost::bind;
 
 // monitored_dir is true if this torrent is added because
@@ -560,6 +562,7 @@ void add_torrent(libtorrent::session& ses
 	printf("%s\n", t->name().c_str());
 
 	add_torrent_params p;
+	p.share_mode = share_mode;
 	lazy_entry resume_data;
 
 	std::string filename = combine_path(save_path, t->name() + ".resume");
@@ -810,7 +813,7 @@ int main(int argc, char* argv[])
 	//settings.announce_to_all_trackers = true;
 	settings.optimize_hashing_for_speed = false;
 	settings.disk_cache_algorithm = session_settings::largest_contiguous;
-	settings.volatile_read_cache = true;
+	settings.volatile_read_cache = false;
 
 	proxy_settings ps;
 
@@ -868,6 +871,7 @@ int main(int argc, char* argv[])
 				from_hex(argv[i], 40, (char*)&info_hash[0]);
 
 				add_torrent_params p;
+				p.share_mode = share_mode;
 				p.tracker_url = argv[i] + 41;
 				p.info_hash = info_hash;
 				p.save_path = save_path;
@@ -908,6 +912,7 @@ int main(int argc, char* argv[])
 			case 'U': torrent_upload_limit = atoi(arg) * 1000; break;
 			case 'D': torrent_download_limit = atoi(arg) * 1000; break;
 			case 'm': monitor_dir = arg; break;
+			case 'M': share_mode = true; --i; break;
 			case 'b': bind_to_interface = arg; break;
 			case 'w': settings.urlseed_wait_retry = atoi(arg); break;
 			case 't': poll_interval = atoi(arg); break;
@@ -1053,6 +1058,7 @@ int main(int argc, char* argv[])
 		if (std::strstr(i->c_str(), "magnet:") == i->c_str())
 		{
 			add_torrent_params p;
+			p.share_mode = share_mode;
 			p.save_path = save_path;
 			p.storage_mode = (storage_mode_t)allocation_mode;
 			printf("adding MANGET link: %s\n", i->c_str());
@@ -1404,7 +1410,7 @@ int main(int argc, char* argv[])
 				out += str;
 			}
 
-			if (print_piece_bar && s.progress_ppm < 1000000 && s.progress > 0)
+			if (print_piece_bar && s.state != torrent_status::seeding)
 			{
 				out += "     ";
 				out += piece_bar(s.pieces, terminal_width - 7);
diff --git a/include/libtorrent/add_torrent_params.hpp b/include/libtorrent/add_torrent_params.hpp
index add438104..2e46314a1 100644
--- a/include/libtorrent/add_torrent_params.hpp
+++ b/include/libtorrent/add_torrent_params.hpp
@@ -62,6 +62,7 @@ namespace libtorrent
 			, override_resume_data(false)
 			, upload_mode(false)
 			, file_priorities(0)
+			, share_mode(false)
 		{}
 
 		// libtorrent version. Used for forward binary compatibility
@@ -82,6 +83,7 @@ namespace libtorrent
 		bool override_resume_data;
 		bool upload_mode;
 		std::vector<boost::uint8_t> const* file_priorities;
+		bool share_mode;
 	};
 }
 
diff --git a/include/libtorrent/bt_peer_connection.hpp b/include/libtorrent/bt_peer_connection.hpp
index 3240d8706..f5a3f0f85 100644
--- a/include/libtorrent/bt_peer_connection.hpp
+++ b/include/libtorrent/bt_peer_connection.hpp
@@ -102,7 +102,7 @@ namespace libtorrent
 
 		void start();
 
-		enum { upload_only_msg = 2 };
+		enum { upload_only_msg = 2, share_mode_msg = 3 };
 
 		~bt_peer_connection();
 		
@@ -205,6 +205,7 @@ namespace libtorrent
 #ifndef TORRENT_DISABLE_EXTENSIONS
 		void write_extensions();
 		void write_upload_only();
+		void write_share_mode();
 #endif
 		void write_metadata(std::pair<int, int> req);
 		void write_metadata_request(std::pair<int, int> req);
@@ -365,6 +366,10 @@ private:
 		// 0 if not supported
 		int m_upload_only_id;
 
+		// the message ID for share mode message
+		// 0 if not supported
+		int m_share_mode_id;
+
 		char m_reserved_bits[8];
 		// this is set to true if the handshake from
 		// the peer indicated that it supports the
diff --git a/include/libtorrent/peer_connection.hpp b/include/libtorrent/peer_connection.hpp
index a947f4a26..0d25cc3e0 100644
--- a/include/libtorrent/peer_connection.hpp
+++ b/include/libtorrent/peer_connection.hpp
@@ -274,6 +274,10 @@ namespace libtorrent
 		bool can_read(char* state = 0) const;
 
 		bool is_seed() const;
+		int num_have_pieces() const { return m_num_pieces; }
+
+		void set_share_mode(bool m);
+		bool share_mode() const { return m_share_mode; }
 
 		void set_upload_only(bool u);
 		bool upload_only() const { return m_upload_only; }
@@ -1043,7 +1047,10 @@ namespace libtorrent
 		// the http-downloader, to request whole pieces
 		// at a time.
 		bool m_request_large_blocks:1;
-		
+
+		// set to true if this peer is in share mode		
+		bool m_share_mode:1;
+
 		// set to true when this peer is only uploading
 		bool m_upload_only:1;
 
diff --git a/include/libtorrent/piece_picker.hpp b/include/libtorrent/piece_picker.hpp
index b32b01bd9..1e9c0115e 100644
--- a/include/libtorrent/piece_picker.hpp
+++ b/include/libtorrent/piece_picker.hpp
@@ -95,6 +95,8 @@ namespace libtorrent
 	{
 	public:
 
+		struct piece_pos;
+
 		enum
 		{
 			// the number of priority levels
@@ -162,7 +164,7 @@ namespace libtorrent
 			// the number of blocks in the requested state
 			boost::int16_t requested;
 		};
-
+		
 		piece_picker();
 
 		void get_availability(std::vector<int>& avail) const;
@@ -292,7 +294,13 @@ namespace libtorrent
 
 		// returns information about the given piece
 		void piece_info(int index, piece_picker::downloading_piece& st) const;
-		
+
+		piece_pos const& piece_stats(int index) const
+		{
+			TORRENT_ASSERT(index >= 0 && index < int(m_piece_map.size()));
+			return m_piece_map[index];
+		}
+
 		// if a piece had a hash-failure, it must be restored and
 		// made available for redownloading
 		void restore_piece(int index);
@@ -359,6 +367,8 @@ namespace libtorrent
 		std::pair<int, int> expand_piece(int piece, int whole_pieces
 			, bitfield const& have) const;
 
+	public:
+
 		struct piece_pos
 		{
 			piece_pos() {}
@@ -452,6 +462,8 @@ namespace libtorrent
 
 		};
 
+	private:
+
 		BOOST_STATIC_ASSERT(sizeof(piece_pos) == sizeof(char) * 4);
 
 		void update_pieces() const;
diff --git a/include/libtorrent/session_settings.hpp b/include/libtorrent/session_settings.hpp
index c71337004..f0ac941e3 100644
--- a/include/libtorrent/session_settings.hpp
+++ b/include/libtorrent/session_settings.hpp
@@ -221,6 +221,7 @@ namespace libtorrent
 			, anonymous_mode(false)
 			, tick_interval(100)
 			, report_web_seed_downloads(true)
+			, share_mode_target(3)
 		{}
 
 		// libtorrent version. Used for forward binary compatibility
@@ -843,6 +844,9 @@ namespace libtorrent
 		// specifies whether downloads from web seeds is reported to the
 		// tracker or not. Defaults to on
 		bool report_web_seed_downloads;
+
+		// this is the target share ratio for share-mode torrents
+		int share_mode_target;
 	};
 
 #ifndef TORRENT_DISABLE_DHT
diff --git a/include/libtorrent/torrent.hpp b/include/libtorrent/torrent.hpp
index 8c7eefab9..8f9aee70e 100644
--- a/include/libtorrent/torrent.hpp
+++ b/include/libtorrent/torrent.hpp
@@ -178,8 +178,12 @@ namespace libtorrent
 		void start_announcing();
 		void stop_announcing();
 
+		void send_share_mode();
 		void send_upload_only();
 
+		void set_share_mode(bool s);
+		bool share_mode() const { return m_share_mode; }
+
 		void set_upload_mode(bool b);
 		bool upload_mode() const { return m_upload_mode; }
 		bool is_upload_only() const
@@ -502,6 +506,8 @@ namespace libtorrent
 // --------------------------------------------
 		// PIECE MANAGEMENT
 
+		void recalc_share_mode();
+
 		void update_sparse_piece_prio(int piece, int cursor, int reverse_cursor);
 
 		void get_suggested_pieces(std::vector<int>& s) const;
@@ -525,8 +531,8 @@ namespace libtorrent
 		int num_have() const
 		{
 			return has_picker()
-				?m_picker->num_have()
-				:m_torrent_file->num_pieces();
+				? m_picker->num_have()
+				: m_torrent_file->num_pieces();
 		}
 
 		// when we get a have message, this is called for that piece
@@ -1210,6 +1216,9 @@ namespace libtorrent
 		// slots.
 		bool m_auto_managed:1;
 
+		// this is set when the torrent is in share-mode
+		bool m_share_mode:1;
+
 		// m_num_verified = m_verified.count()
 		boost::uint16_t m_num_verified;
 
diff --git a/include/libtorrent/torrent_handle.hpp b/include/libtorrent/torrent_handle.hpp
index 62d0801f7..2c152a59a 100644
--- a/include/libtorrent/torrent_handle.hpp
+++ b/include/libtorrent/torrent_handle.hpp
@@ -123,6 +123,7 @@ namespace libtorrent
 			, sparse_regions(0)
 			, seed_mode(false)
 			, upload_mode(false)
+			, share_mode(false)
 			, priority(0)
 			, added_time(0)
 			, completed_time(0)
@@ -306,6 +307,9 @@ namespace libtorrent
 		// write operation failing
 		bool upload_mode;
 
+		// this is true if the torrent is in share-mode
+		bool share_mode;
+
 		// the priority of this torrent
 		int priority;
 
@@ -468,6 +472,7 @@ namespace libtorrent
 		void pause() const;
 		void resume() const;
 		void set_upload_mode(bool b) const;
+		void set_share_mode(bool b) const;
 		void flush_cache() const;
 
 		void force_recheck() const;
diff --git a/src/bt_peer_connection.cpp b/src/bt_peer_connection.cpp
index 4cd80cbf9..f14038133 100644
--- a/src/bt_peer_connection.cpp
+++ b/src/bt_peer_connection.cpp
@@ -98,6 +98,7 @@ namespace libtorrent
 		, m_state(read_protocol_identifier)
 #ifndef TORRENT_DISABLE_EXTENSIONS
 		, m_upload_only_id(0)
+		, m_share_mode_id(0)
 		, m_supports_extensions(false)
 #endif
 		, m_supports_dht_port(false)
@@ -1496,6 +1497,13 @@ namespace libtorrent
 			return;
 		}
 
+		if (extended_id == share_mode_msg)
+		{
+			if (!packet_finished()) return;
+			set_share_mode(detail::read_uint8(recv_buffer.begin));
+			return;
+		}
+
 		disconnect(errors::invalid_message, 2);
 		return;
 	}
@@ -1564,6 +1572,9 @@ namespace libtorrent
 		if (root.dict_find_int_value("upload_only", 0))
 			set_upload_only(true);
 
+		if (root.dict_find_int_value("share_mode", 0))
+			set_share_mode(true);
+
 		std::string myip = root.dict_find_string_value("yourip");
 		if (!myip.empty())
 		{
@@ -1591,7 +1602,8 @@ namespace libtorrent
 		// if we're finished and this peer is uploading only
 		// disconnect it
 		if (t->is_finished() && upload_only()
-			&& t->settings().close_redundant_connections)
+			&& t->settings().close_redundant_connections
+			&& !t->share_mode())
 			disconnect(errors::upload_upload_connection);
 	}
 
@@ -1662,6 +1674,7 @@ namespace libtorrent
 		
 		boost::shared_ptr<torrent> t = associated_torrent().lock();
 		if (m_upload_only_id == 0) return;
+		if (t->share_mode()) return;
 
 		char msg[7] = {0, 0, 0, 3, msg_extended};
 		char* ptr = msg + 5;
@@ -1669,6 +1682,20 @@ namespace libtorrent
 		detail::write_uint8(t->is_upload_only(), ptr);
 		send_buffer(msg, sizeof(msg));
 	}
+
+	void bt_peer_connection::write_share_mode()
+	{
+		INVARIANT_CHECK;
+		
+		boost::shared_ptr<torrent> t = associated_torrent().lock();
+		if (m_share_mode_id == 0) return;
+
+		char msg[7] = {0, 0, 0, 3, msg_extended};
+		char* ptr = msg + 5;
+		detail::write_uint8(m_share_mode_id, ptr);
+		detail::write_uint8(t->share_mode(), ptr);
+		send_buffer(msg, sizeof(msg));
+	}
 #endif
 
 	void bt_peer_connection::write_keepalive()
@@ -1900,19 +1927,25 @@ namespace libtorrent
 		TORRENT_ASSERT(t);
 
 		m["upload_only"] = upload_only_msg;
+		m["share_mode"] = share_mode_msg;
 		int complete_ago = -1;
 		if (t->last_seen_complete() > 0) complete_ago = t->time_since_complete();
 		handshake["complete_ago"] = complete_ago;
 
 		// if we're using lazy bitfields or if we're super seeding, don't say
 		// we're upload only, since it might make peers disconnect
-		if (t->is_upload_only() && (!m_ses.settings().lazy_bitfields
+		// don't tell anyone we're upload only when in share mode
+		// we want to stay connected to seeds
+		if (t->is_upload_only() && !t->share_mode() && (!m_ses.settings().lazy_bitfields
 #ifndef TORRENT_DISABLE_ENCRYPTION
 			|| m_encrypted
 #endif
 			))
 			handshake["upload_only"] = 1;
 
+		if (t->share_mode())
+			handshake["share_mode"] = 1;
+
 		if (!m_ses.m_settings.anonymous_mode)
 		{
 			tcp::endpoint ep = m_ses.get_ipv6_interface();
diff --git a/src/lt_trackers.cpp b/src/lt_trackers.cpp
index ac7aeb9a5..6bb490757 100644
--- a/src/lt_trackers.cpp
+++ b/src/lt_trackers.cpp
@@ -156,7 +156,7 @@ namespace libtorrent { namespace
 		virtual void add_handshake(entry& h)
 		{
 			entry& messages = h["m"];
-			messages["lt_tex"] = 3;
+			messages["lt_tex"] = 19;
 			h["tr"] = m_tp.list_hash().to_string();
 		}
 
@@ -186,7 +186,7 @@ namespace libtorrent { namespace
 		virtual bool on_extended(int length
 			, int extended_msg, buffer::const_interval body)
 		{
-			if (extended_msg != 3) return false;
+			if (extended_msg != 19) return false;
 			if (m_message_index == 0) return false;
 			if (!m_pc.packet_finished()) return true;
 
diff --git a/src/peer_connection.cpp b/src/peer_connection.cpp
index 7102dd39b..8ebeefba8 100644
--- a/src/peer_connection.cpp
+++ b/src/peer_connection.cpp
@@ -144,6 +144,7 @@ namespace libtorrent
 		, m_connecting(true)
 		, m_queued(true)
 		, m_request_large_blocks(false)
+		, m_share_mode(false)
 		, m_upload_only(false)
 		, m_snubbed(false)
 		, m_bitfield_received(false)
@@ -282,6 +283,7 @@ namespace libtorrent
 		, m_connecting(false)
 		, m_queued(false)
 		, m_request_large_blocks(false)
+		, m_share_mode(false)
 		, m_upload_only(false)
 		, m_snubbed(false)
 		, m_bitfield_received(false)
@@ -513,7 +515,7 @@ namespace libtorrent
 	void peer_connection::update_interest()
 	{
 		boost::shared_ptr<torrent> t = m_torrent.lock();
-		TORRENT_ASSERT(t);
+		if (!t) return;
 
 		// if m_have_piece is 0, it means the connections
 		// have not been initialized yet. The interested
@@ -1794,6 +1796,9 @@ namespace libtorrent
 		boost::shared_ptr<torrent> t = m_torrent.lock();
 		if (!t) return;
 
+		// don't close connections in share mode, we don't know if we need them
+		if (t->share_mode()) return;
+
 		if (m_upload_only && t->is_finished())
 		{
 			disconnect(errors::upload_upload_connection);
@@ -4025,6 +4030,7 @@ namespace libtorrent
 		INVARIANT_CHECK;
 #endif
 
+		bool sent_a_piece = false;
 		boost::shared_ptr<torrent> t = m_torrent.lock();
 		if (!t) return;
 
@@ -4070,7 +4076,11 @@ namespace libtorrent
 			m_reading_bytes += r.length;
 
 			m_requests.erase(m_requests.begin());
+			sent_a_piece = true;
 		}
+
+		if (t->share_mode() && sent_a_piece)
+			t->recalc_share_mode();
 	}
 
 	void peer_connection::on_disk_read_complete(int ret, disk_io_job const& j, peer_request r)
@@ -5143,7 +5153,8 @@ namespace libtorrent
 		if (t->ready_for_connections() && m_initialized)
 			TORRENT_ASSERT(t->torrent_file().num_pieces() == int(m_have_piece.size()));
 
-		if (m_ses.settings().close_redundant_connections)
+		// in share mode we don't close redundant connections
+		if (m_ses.settings().close_redundant_connections && !t->share_mode())
 		{
 			// make sure upload only peers are disconnected
 			if (t->is_finished() && m_upload_only)
@@ -5333,6 +5344,14 @@ namespace libtorrent
 		return m_num_pieces == (int)m_have_piece.size() && m_num_pieces > 0 && t && t->valid_metadata();
 	}
 
+	void peer_connection::set_share_mode(bool u)
+	{
+		// if the peer is a seed, ignore share mode messages
+		if (is_seed()) return;
+
+		m_share_mode = u;
+	}
+
 	void peer_connection::set_upload_only(bool u)
 	{
 		// if the peer is a seed, don't allow setting
diff --git a/src/torrent.cpp b/src/torrent.cpp
index 8c4576913..d9c27575c 100644
--- a/src/torrent.cpp
+++ b/src/torrent.cpp
@@ -378,6 +378,7 @@ namespace libtorrent
 		, m_allow_peers(!p.paused)
 		, m_upload_mode(p.upload_mode)
 		, m_auto_managed(p.auto_managed)
+		, m_share_mode(p.share_mode)
 		, m_num_verified(0)
 		, m_last_scrape(0)
 		, m_last_download(0)
@@ -418,7 +419,6 @@ namespace libtorrent
 			m_trackers.back().source = announce_entry::source_magnet_link;
 			m_torrent_file->add_tracker(p.tracker_url);
 		}
-
 	}
 
 	void torrent::start()
@@ -533,6 +533,19 @@ namespace libtorrent
 		}
 	}
 
+	void torrent::send_share_mode()
+	{
+#ifndef TORRENT_DISABLE_EXTENSIONS
+		for (std::set<peer_connection*>::iterator i = m_connections.begin()
+			, end(m_connections.end()); i != end; ++i)
+		{
+			if ((*i)->type() != peer_connection::bittorrent_connection) continue;
+			bt_peer_connection* p = (bt_peer_connection*)*i;
+			p->write_share_mode();
+		}
+#endif
+	}
+
 	void torrent::send_upload_only()
 	{
 #ifndef TORRENT_DISABLE_EXTENSIONS
@@ -546,6 +559,20 @@ namespace libtorrent
 #endif
 	}
 
+	void torrent::set_share_mode(bool s)
+	{
+		if (s == m_share_mode) return;
+
+		m_share_mode = s;
+
+		// in share mode, all pieces have their priorities initialized to 0
+		std::fill(m_file_priority.begin(), m_file_priority.end(), !m_share_mode);
+
+		update_piece_priorities();
+
+		if (m_share_mode) recalc_share_mode();
+	}
+
 	void torrent::set_upload_mode(bool b)
 	{
 		if (b == m_upload_mode) return;
@@ -855,6 +882,16 @@ namespace libtorrent
 			m_picker->init(blocks_per_piece, blocks_in_last_piece, m_torrent_file->num_pieces());
 		}
 
+		if (m_share_mode)
+		{
+			// in share mode, all pieces have their priorities initialized to 0
+			std::fill(m_file_priority.begin(), m_file_priority.end(), 0);
+		}
+
+		// in case file priorities were passed in via the add_torrent_params
+		// ans also in the case of share mode, we need to update the priorities
+		update_piece_priorities();
+
 		std::vector<std::string> const& url_seeds = m_torrent_file->url_seeds();
 		for (std::vector<std::string>::const_iterator i = url_seeds.begin()
 			, end(url_seeds.end()); i != end; ++i)
@@ -2335,6 +2372,9 @@ namespace libtorrent
 		}
 
 		m_last_download = 0;
+
+		if (m_share_mode)
+			recalc_share_mode();
 	}
 
 	void torrent::piece_failed(int index)
@@ -3744,6 +3784,7 @@ namespace libtorrent
 				m_file_priority[i] = file_priority->list_int_value_at(i, 1);
 			update_piece_priorities();
 		}
+
 		lazy_entry const* piece_priority = rd.dict_find_string("piece_priority");
 		if (piece_priority && piece_priority->string_length()
 			== m_torrent_file->num_pieces())
@@ -4365,6 +4406,9 @@ namespace libtorrent
 		}
 #endif
 
+		if (m_share_mode)
+			recalc_share_mode();
+
 		return peerinfo->connection;
 	}
 
@@ -4494,6 +4538,10 @@ namespace libtorrent
 #if defined TORRENT_DEBUG && !defined TORRENT_DISABLE_INVARIANT_CHECKS
 		m_policy.check_invariant();
 #endif
+
+		if (m_share_mode)
+			recalc_share_mode();
+
 		return true;
 	}
 
@@ -4961,7 +5009,7 @@ namespace libtorrent
 				if (!i->not_wanted && !i->timed_out) ++num_requests[i->block];
 			if (!p.is_choked() && !p.ignore_unchoke_slots()) ++num_uploads;
 			torrent* associated_torrent = p.associated_torrent().lock().get();
-			if (associated_torrent != this)
+			if (associated_torrent != this && associated_torrent != 0)
 				TORRENT_ASSERT(false);
 		}
 		TORRENT_ASSERT(num_uploads == m_num_uploads);
@@ -5862,6 +5910,152 @@ namespace libtorrent
 		m_stat.second_tick(tick_interval_ms);
 	}
 
+	void torrent::recalc_share_mode()
+	{
+		TORRENT_ASSERT(share_mode());
+		if (is_seed()) return;
+
+		int pieces_in_torrent = m_torrent_file->num_pieces();
+		int num_seeds = 0;
+		int num_peers = 0;
+		int num_downloaders = 0;
+		int missing_pieces = 0;
+		int num_interested = 0;
+		for (std::set<peer_connection*>::iterator i = m_connections.begin()
+			, end(m_connections.end()); i != end; ++i)
+		{
+			peer_connection* p = *i;
+			if (p->is_connecting()) continue;
+			++num_peers;
+			if (p->is_seed())
+			{
+				++num_seeds;
+				continue;
+			}
+
+			if (p->share_mode()) continue;
+
+			if ((*i)->is_peer_interested()) ++num_interested;
+			++num_downloaders;
+			missing_pieces += pieces_in_torrent - p->num_have_pieces();
+		}
+
+		if (num_peers == 0) return;
+
+		if (num_seeds * 100 / num_peers > 50
+			&& (num_peers * 100 / m_max_connections > 90
+				|| num_peers > 20))
+		{
+			// we are connected to more than 90% seeds (and we're beyond
+			// 90% of the max number of connections). That will
+			// limit our ability to upload. We need more downloaders.
+			// disconnect some seeds so that we don't have more than 50%
+			int to_disconnect = num_seeds - num_peers / 2;
+			std::vector<peer_connection*> seeds;
+			seeds.reserve(num_seeds);
+			for (std::set<peer_connection*>::iterator i = m_connections.begin()
+				, end(m_connections.end()); i != end; ++i)
+			{
+				peer_connection* p = *i;
+				if (p->is_seed()) seeds.push_back(p);
+			}
+
+			std::random_shuffle(seeds.begin(), seeds.end());
+			TORRENT_ASSERT(to_disconnect <= int(seeds.size()));
+			for (int i = 0; i < to_disconnect; ++i)
+				seeds[i]->disconnect(errors::upload_upload_connection);
+		}
+
+		if (num_downloaders == 0) return;
+
+		// assume that the seeds are about as fast as us. During the time
+		// we can download one piece, and upload one piece, each seed
+		// can upload two pieces.
+		missing_pieces -= 2 * num_seeds;
+
+		if (missing_pieces <= 0) return;
+		
+		// missing_pieces represents our opportunity to download pieces
+		// and share them more than once each
+
+		// now, download at least one piece, otherwise download one more
+		// piece if our downloaded (and downloading) pieces is less than 50%
+		// of the uploaded bytes
+		int num_downloaded_pieces = (std::max)(m_picker->num_have()
+			, pieces_in_torrent - m_picker->num_filtered());
+
+		if (num_downloaded_pieces * m_torrent_file->piece_length()
+			* settings().share_mode_target > m_total_uploaded
+			&& num_downloaded_pieces > 0)
+			return;
+
+		// don't have more pieces downloading in parallel than 5% of the total
+		// number of pieces we have downloaded
+		if (m_picker->get_download_queue().size() > num_downloaded_pieces / 20)
+			return;
+
+		// one more important property is that there are enough pieces
+		// that more than one peer wants to download
+		// make sure that there are enough downloaders for the rarest
+		// piece. Go through all pieces, figure out which one is the rarest
+		// and how many peers that has that piece
+
+		std::vector<int> rarest_pieces;
+
+		int num_pieces = m_torrent_file->num_pieces();
+		int rarest_rarity = INT_MAX;
+		bool prio_updated = false;
+		for (int i = 0; i < num_pieces; ++i)
+		{
+			piece_picker::piece_pos const& pp = m_picker->piece_stats(i);
+			if (pp.peer_count == 0) continue;
+			if (pp.filtered() && (pp.have() || pp.downloading))
+			{
+				m_picker->set_piece_priority(i, 1);
+				prio_updated = true;
+				continue;
+			}
+			// don't count pieces we already have or are downloading
+			if (!pp.filtered() || pp.have()) continue;
+			if (pp.peer_count > rarest_rarity) continue;
+			if (pp.peer_count == rarest_rarity)
+			{
+				rarest_pieces.push_back(i);
+				continue;
+			}
+
+			rarest_pieces.clear();
+			rarest_rarity = pp.peer_count;
+			rarest_pieces.push_back(i);
+		}
+
+		if (prio_updated)
+			m_policy.recalculate_connect_candidates();
+
+		// now, rarest_pieces is a list of all pieces that are the rarest ones.
+		// and rarest_rarity is the number of peers that have the rarest pieces
+
+		// if there's only a single peer that doesn't have the rarest piece
+		// it's impossible for us to download one piece and upload it
+		// twice. i.e. we cannot get a positive share ratio
+		if (num_peers - rarest_rarity < settings().share_mode_target) return;
+
+		// we might be able to do better than a share ratio of 2 if there are
+		// enough downloaders of the pieces we already have.
+		// TODO: go through the pieces we have and count the total number
+		// of downloaders we have. Only count peers that are interested in us
+		// since some peers might not send have messages for pieces we have
+		// it num_interested == 0, we need to pick a new piece
+
+		// now, pick one of the rarest pieces to download
+		int pick = rand() % rarest_pieces.size();
+		bool was_finished = is_finished();
+		m_picker->set_piece_priority(rarest_pieces[pick], 1);
+		update_peer_interest(was_finished);
+
+		m_policy.recalculate_connect_candidates();
+	}
+
 	void torrent::refresh_explicit_cache(int cache_size)
 	{
 		TORRENT_ASSERT(m_ses.is_network_thread());
@@ -6404,6 +6598,7 @@ namespace libtorrent
 		st.completed_time = m_completed_time;
 
 		st.last_scrape = m_last_scrape;
+		st.share_mode = m_share_mode;
 		st.upload_mode = m_upload_mode;
 		st.up_bandwidth_queue = 0;
 		st.down_bandwidth_queue = 0;
diff --git a/src/torrent_handle.cpp b/src/torrent_handle.cpp
index 01cb464ee..01a16c6e1 100644
--- a/src/torrent_handle.cpp
+++ b/src/torrent_handle.cpp
@@ -363,6 +363,12 @@ namespace libtorrent
 		TORRENT_ASYNC_CALL(pause);
 	}
 
+	void torrent_handle::set_share_mode(bool b) const
+	{
+		INVARIANT_CHECK;
+		TORRENT_ASYNC_CALL1(set_share_mode, b);
+	}
+
 	void torrent_handle::set_upload_mode(bool b) const
 	{
 		INVARIANT_CHECK;