Use timers for duplicate requests

Nothing was triggering request updates when timeouts expired. This is the simplest fix, no performance considered.

connection.go

@@ -512,7 +512,17 @@ func (cn *connection) request(r request, mw messageWriter) bool {
 	}
 	cn.validReceiveChunks[r] = struct{}{}
 	cn.t.pendingRequests[r]++
-	cn.t.lastRequested[r] = time.Now()
+	cn.t.lastRequested[r] = time.AfterFunc(cn.t.duplicateRequestTimeout, func() {
+		torrent.Add("duplicate request timeouts", 1)
+		cn.mu().Lock()
+		defer cn.mu().Unlock()
+		delete(cn.t.lastRequested, r)
+		for cn := range cn.t.conns {
+			if cn.PeerHasPiece(pieceIndex(r.Index)) {
+				cn.updateRequests()
+			}
+		}
+	})
 	cn.updateExpectingChunks()
 	return mw(pp.Message{
 		Type:   pp.Request,
@@ -761,13 +771,10 @@ func (cn *connection) iterPendingRequests(piece int, f func(request) bool) bool
 	return iterUndirtiedChunks(piece, cn.t, func(cs chunkSpec) bool {
 		r := request{pp.Integer(piece), cs}
 		if cn.t.requestStrategy == 3 {
-			lr := cn.t.lastRequested[r]
-			if !lr.IsZero() {
-				if time.Since(lr) < cn.t.duplicateRequestTimeout {
-					return true
-				} else {
-					torrent.Add("requests duplicated due to timeout", 1)
-				}
+			if _, ok := cn.t.lastRequested[r]; ok {
+				// This piece has been requested on another connection, and
+				// the duplicate request timer is still running.
+				return true
 			}
 		}
 		return f(r)
@@ -1470,7 +1477,10 @@ func (c *connection) deleteRequest(r request) bool {
 	}
 	delete(c.requests, r)
 	c.updateExpectingChunks()
-	delete(c.t.lastRequested, r)
+	if t, ok := c.t.lastRequested[r]; ok {
+		t.Stop()
+		delete(c.t.lastRequested, r)
+	}
 	pr := c.t.pendingRequests
 	pr[r]--
 	n := pr[r]

torrent.go

@@ -147,7 +147,7 @@ type Torrent struct {
 	pendingRequests map[request]int
 	// The last time we requested a chunk. Deleting the request from any
 	// connection will clear this value.
-	lastRequested map[request]time.Time
+	lastRequested map[request]*time.Timer
 }
 
 func (t *Torrent) tickleReaders() {
@@ -407,7 +407,7 @@ func (t *Torrent) onSetInfo() {
 	t.gotMetainfo.Set()
 	t.updateWantPeersEvent()
 	t.pendingRequests = make(map[request]int)
-	t.lastRequested = make(map[request]time.Time)
+	t.lastRequested = make(map[request]*time.Timer)
 }
 
 // Called when metadata for a torrent becomes available.
@@ -1240,6 +1240,9 @@ func (t *Torrent) assertNoPendingRequests() {
 	if len(t.pendingRequests) != 0 {
 		panic(t.pendingRequests)
 	}
+	if len(t.lastRequested) != 0 {
+		panic(t.lastRequested)
+	}
 }
 
 func (t *Torrent) dropConnection(c *connection) {