enable all disabled trackers when listen sockets are re-opened

include/libtorrent/torrent.hpp

@@ -1011,6 +1011,10 @@ namespace libtorrent {
 		std::vector<announce_entry> const& trackers() const
 		{ return m_trackers; }
 
+		// this sets all the "enabled" states on all trackers, giving them
+		// all one more chance of being tried
+		void enable_all_trackers();
+
 		void replace_trackers(std::vector<announce_entry> const& urls);
 
 		// returns true if the tracker was added, and false if it was already

src/session_impl.cpp

@@ -2027,6 +2027,16 @@ namespace aux {
 #if TORRENT_USE_I2P
 		open_new_incoming_i2p_connection();
 #endif
+
+		// trackers that were not reachable, may have become reachable now.
+		// so clear the "disabled" flags to let them be tried one more time
+		// TODO: it would probably be better to do this by having a
+		// listen-socket "version" number that gets bumped. And instead of
+		// setting a bool to disable a tracker, we set the version number that
+		// it was disabled at. This change would affect the ABI in 1.2, so
+		// should be done in 2.0 or later
+		for (auto& t : m_torrents)
+			t.second->enable_all_trackers();
 	}
 
 	void session_impl::reopen_network_sockets(reopen_network_flags_t const options)

src/torrent.cpp

@@ -6201,6 +6201,13 @@ bool is_downloading_state(int const st)
 		return m_torrent_file;
 	}
 
+	void torrent::enable_all_trackers()
+	{
+		for (announce_entry& ae : m_trackers)
+			for (announce_endpoint& aep : ae.endpoints)
+				aep.enabled = true;
+	}
+
 	void torrent::write_resume_data(add_torrent_params& ret) const
 	{
 		ret.version = LIBTORRENT_VERSION_NUM;