retry failed trackers a little bit sooner. make the exponential back-off not quite grow as fast

ChangeLog

@@ -1,3 +1,4 @@
+	* lower the default tracker retry intervals
 	* support banning web seeds sending corrupt data
 	* don't let hung outgoing connection attempts block incoming connections
 	* improve SSL torrent support by using SNI and a single SSL listen socket

include/libtorrent/torrent_info.hpp

@@ -66,8 +66,8 @@ namespace libtorrent
 
 	enum
 	{
-		// wait 60 seconds before retrying a failed tracker
+		// wait at least 5 seconds before retrying a failed tracker
-		tracker_retry_delay_min = 10
+		tracker_retry_delay_min = 5
 		// when tracker_failed_max trackers
 		// has failed, wait 60 minutes instead
 		, tracker_retry_delay_max = 60 * 60

src/http_tracker_connection.cpp

@@ -386,8 +386,8 @@ namespace libtorrent
 		boost::shared_ptr<request_callback> cb = requester();
 		if (!cb) return;
 
-		int interval = int(e.dict_find_int_value("interval", 1800));
+		int interval = int(e.dict_find_int_value("interval", 0));
-		int min_interval = int(e.dict_find_int_value("min interval", 60));
+		int min_interval = int(e.dict_find_int_value("min interval", 30));
 
 		std::string trackerid;
 		lazy_entry const* tracker_id = e.dict_find_string("tracker id");
@@ -427,6 +427,10 @@ namespace libtorrent
 					, interval, min_interval);
 				return;
 			}
+
+			// if no interval is specified, default to 30 minutes
+			if (interval == 0) interval == 1800;
+
 			int complete = int(scrape_data->dict_find_int_value("complete", -1));
 			int incomplete = int(scrape_data->dict_find_int_value("incomplete", -1));
 			int downloaded = int(scrape_data->dict_find_int_value("downloaded", -1));

src/torrent_info.cpp

@@ -473,8 +473,10 @@ namespace libtorrent
 	void announce_entry::failed(int retry_interval)
 	{
 		++fails;
+		// the exponential back-off ends up being:
+		// 7, 15, 27, 45, 95, 127, 165, ... seconds
 		int delay = (std::min)(tracker_retry_delay_min + int(fails) * int(fails)
-			* tracker_retry_delay_min, int(tracker_retry_delay_max));
+			* tracker_retry_delay_min / 2, int(tracker_retry_delay_max));
 		delay = (std::max)(delay, retry_interval);
 		next_announce = time_now() + seconds(delay);
 		updating = false;

test/test_primitives.cpp

@@ -396,6 +396,20 @@ int test_main()
 	error_code ec;
 	int ret = 0;
 
+	// make sure the retry interval keeps growing
+	// on failing announces
+	announce_entry ae("dummy");
+	int last = 0;
+	for (int i = 0; i < 10; ++i)
+	{
+		ae.failed(5);
+		int delay = ae.next_announce_in();
+		TEST_CHECK(delay > last);
+		last = delay;
+		fprintf(stderr, "%d, ", delay);
+	}
+	fprintf(stderr, "\n");
+
 #if defined TORRENT_USE_OPENSSL
 	// test sign_rsa and verify_rsa
 	char private_key[1192];