+package torrent
+
+import (
+ "log"
+ "time"
+
+ "github.com/anacrolix/missinggo"
+
+ "github.com/anacrolix/torrent/tracker"
+)
+
+// Announces a torrent to a tracker at regular intervals, when peers are
+// required.
+type trackerScraper struct {
+ url string
+ // Causes the trackerScraper to stop running.
+ stop missinggo.Event
+ t *Torrent
+}
+
+func trackerToTorrentPeers(ps []tracker.Peer) (ret []Peer) {
+ ret = make([]Peer, 0, len(ps))
+ for _, p := range ps {
+ ret = append(ret, Peer{
+ IP: p.IP,
+ Port: p.Port,
+ Source: peerSourceTracker,
+ })
+ }
+ return
+}
+
+// Return how long to wait before trying again.
+func (me *trackerScraper) announce() time.Duration {
+ blocked, urlToUse, host, err := me.t.cl.prepareTrackerAnnounceUnlocked(me.url)
+ if blocked {
+ // Wait for DNS to potentially change. Very few people do it faster
+ // than 5 minutes.
+ return 5 * time.Minute
+ }
+ me.t.cl.mu.Lock()
+ req := me.t.announceRequest()
+ me.t.cl.mu.Unlock()
+ res, err := tracker.AnnounceHost(urlToUse, &req, host)
+ if err != nil {
+ log.Printf("error announcing %s %q to %q: %s", me.t.InfoHash().HexString(), me.t.Name(), me.url, err)
+ return 5 * time.Minute
+ }
+ me.t.AddPeers(trackerToTorrentPeers(res.Peers))
+ return time.Duration(res.Interval) * time.Second
+}
+
+func (me *trackerScraper) Run() {
+ for {
+ select {
+ case <-me.t.closed.LockedChan(&me.t.cl.mu):
+ return
+ case <-me.stop.LockedChan(&me.t.cl.mu):
+ return
+ case <-me.t.wantPeersEvent.LockedChan(&me.t.cl.mu):
+ }
+
+ intervalChan := time.After(me.announce())
+
+ select {
+ case <-me.t.closed.LockedChan(&me.t.cl.mu):
+ return
+ case <-me.stop.LockedChan(&me.t.cl.mu):
+ return
+ case <-intervalChan:
+ }
+ }
+}