From a3827099c40d4931255358b918aa1a55720b1505 Mon Sep 17 00:00:00 2001
From: Matt Joiner <anacrolix@gmail.com>
Date: Thu, 1 Oct 2020 10:43:10 +1000
Subject: [PATCH] Limit simultaneous announces to the same URL

---
 client.go          |  1 +
 torrent.go         | 23 +++++++++++++++++++++++
 tracker_scraper.go |  3 +++
 3 files changed, 27 insertions(+)

diff --git a/client.go b/client.go
index 6292d778..7ae72295 100644
--- a/client.go
+++ b/client.go
@@ -78,6 +78,7 @@ type Client struct {
 	numHalfOpen     int
 
 	websocketTrackers websocketTrackers
+	activeAnnounces   map[string]struct{}
 }
 
 type ipStr string
diff --git a/torrent.go b/torrent.go
index 21069ec5..3c0bcb09 100644
--- a/torrent.go
+++ b/torrent.go
@@ -1411,9 +1411,32 @@ func (t *Torrent) startScrapingTracker(_url string) {
 				return nil
 			}
 		}
+		urlString := (*u).String()
+		cl := t.cl
 		newAnnouncer := &trackerScraper{
 			u: *u,
 			t: t,
+			allow: func() {
+				cl.lock()
+				defer cl.unlock()
+				if cl.activeAnnounces == nil {
+					cl.activeAnnounces = make(map[string]struct{})
+				}
+				for {
+					if _, ok := cl.activeAnnounces[urlString]; ok {
+						cl.event.Wait()
+					} else {
+						break
+					}
+				}
+				cl.activeAnnounces[urlString] = struct{}{}
+			},
+			done: func() {
+				cl.lock()
+				defer cl.unlock()
+				delete(cl.activeAnnounces, urlString)
+				cl.event.Broadcast()
+			},
 		}
 		go newAnnouncer.Run()
 		return newAnnouncer
diff --git a/tracker_scraper.go b/tracker_scraper.go
index 13237953..b7d38c5a 100644
--- a/tracker_scraper.go
+++ b/tracker_scraper.go
@@ -20,6 +20,7 @@ type trackerScraper struct {
 	u            url.URL
 	t            *Torrent
 	lastAnnounce trackerAnnounceResult
+	allow, done  func()
 }
 
 type torrentTrackerAnnouncer interface {
@@ -108,6 +109,8 @@ func (me *trackerScraper) announce(event tracker.AnnounceEvent) (ret trackerAnno
 		ret.Completed = time.Now()
 	}()
 	ret.Interval = time.Minute
+	me.allow()
+	defer me.done()
 	ip, err := me.getIp()
 	if err != nil {
 		ret.Err = fmt.Errorf("error getting ip: %s", err)
-- 
2.48.1