report tracker errors in the tracker list

docs/manual.rst

@@ -1804,6 +1804,10 @@ ones with lower tier will always be tried before the one with higher tier number
 		int next_announce_in() const;
 		int min_announce_in() const;
 
+		error_code last_error;
+
+		std::string message;
+
 		boost::uint8_t tier;
 		boost::uint8_t fail_limit;
 		boost::uint8_t fails;
@@ -1827,6 +1831,12 @@ ones with lower tier will always be tried before the one with higher tier number
 this tracker. ``min_announce_in()`` returns the number of seconds until we are
 allowed to force another tracker update with this tracker.
 
+If the last time this tracker was contacted failed, ``last_error`` is the error
+code describing what error occurred.
+
+If the last time this tracker was contacted, the tracker returned a warning
+or error message, ``message`` contains that message.
+
 ``fail_limit`` is the max number of failures to announce to this tracker in
 a row, before this tracker is not used anymore.
 

examples/client_test.cpp

@@ -1428,11 +1428,13 @@ int main(int argc, char* argv[])
 				for (std::vector<announce_entry>::iterator i = tr.begin()
 					, end(tr.end()); i != end; ++i)
 				{
-					snprintf(str, sizeof(str), "%2d %-55s fails: %-3d %s %s\n"
+					snprintf(str, sizeof(str), "%2d %-55s fails: %-3d %s %s \"%s\" %s\n"
 						, i->tier, i->url.c_str(), i->fails, i->verified?"OK ":"-  "
 						, i->updating?"updating"
 							:!i->verified?""
-							:to_string(total_seconds(i->next_announce - now), 8).c_str());
+							:to_string(total_seconds(i->next_announce - now), 8).c_str()
+						, i->last_error ? i->last_error.message().c_str() : ""
+						, i->message.c_str());
 					out += str;
 				}
 			}

include/libtorrent/torrent_info.hpp

@@ -97,6 +97,14 @@ namespace libtorrent
 		// no announces before this time
 		ptime min_announce;
 
+		// if this tracker failed the last time it was contacted
+		// this error code specifies what error occurred
+		error_code last_error;
+
+		// if this tracker has returned an error or warning message
+		// that message is stored here
+		std::string message;
+
 		boost::uint8_t tier;
 		// the number of times this tracker can fail
 		// in a row before it's removed. 0 means unlimited

src/torrent.cpp

@@ -6459,6 +6459,8 @@ namespace libtorrent
 			if (ae)
 			{
 				ae->failed(retry_interval);
+				ae->last_error = ec;
+				ae->message = msg;
 				int tracker_index = ae - &m_trackers[0];
 				deprioritize_tracker(tracker_index);
 			}