spv: delay reconnect attempts

spv/sync.go

@@ -480,7 +480,7 @@ var errBreaksMinVersionTarget = errors.New("peer uses too low version to satisif
 
 // connectAndRunPeer connects to and runs the syncing process with the specified
 // peer. It blocks until the peer disconnects and logs any errors.
-func (s *Syncer) connectAndRunPeer(ctx context.Context, raddr string, persistent bool) {
+func (s *Syncer) connectAndRunPeer(ctx context.Context, raddr string, persistent bool) error {
 	// Attempt connection to peer.
 	rp, err := s.lp.ConnectOutbound(ctx, raddr, reqSvcs)
 	if err != nil {
@@ -492,7 +492,7 @@ func (s *Syncer) connectAndRunPeer(ctx context.Context, raddr string, persistent
 		if !errors.Is(err, context.Canceled) {
 			log.Warnf("Peering attempt failed: %v", err)
 		}
-		return
+		return err
 	}
 
 	// Track peer as running as opposed to attempting connection.
@@ -502,7 +502,7 @@ func (s *Syncer) connectAndRunPeer(ctx context.Context, raddr string, persistent
 		s.remotesMu.Unlock()
 		log.Debugf("Disconnecting %v: %v", raddr, errBreaksMinVersionTarget)
 		rp.Disconnect(errBreaksMinVersionTarget)
-		return
+		return errBreaksMinVersionTarget
 	}
 	s.remotes[raddr] = rp
 	n := len(s.remotes)
@@ -535,16 +535,17 @@ func (s *Syncer) connectAndRunPeer(ctx context.Context, raddr string, persistent
 			log.Infof("Lost peer %v", raddr)
 		}
 		rp.Disconnect(err)
-		return
+		return err
 	}
 
 	// Finally, block until the peer disconnects.
 	err = rp.Err()
 	if !errors.Is(err, context.Canceled) {
 		log.Warnf("Lost peer %v: %v", raddr, err)
-	} else {
-		log.Infof("Lost peer %v", raddr)
+		return err
 	}
+	log.Infof("Lost peer %v", raddr)
+	return nil
 }
 
 func (s *Syncer) breaksMinVersionTarget(rp *p2p.RemotePeer) bool {
@@ -569,7 +570,7 @@ func (s *Syncer) breaksMinVersionTarget(rp *p2p.RemotePeer) bool {
 
 func (s *Syncer) connectToPersistent(ctx context.Context, raddr string) error {
 	for {
-		s.connectAndRunPeer(ctx, raddr, true)
+		_ = s.connectAndRunPeer(ctx, raddr, true)
 
 		// Retry persistent peer after 5 seconds.
 		select {
@@ -607,9 +608,14 @@ func (s *Syncer) connectToCandidates(ctx context.Context) error {
 
 		wg.Add(1)
 		go func() {
+			defer wg.Done()
 			raddr := na.String()
-			s.connectAndRunPeer(ctx, raddr, false)
-			wg.Done()
+			err := s.connectAndRunPeer(ctx, raddr, false)
+			if err != nil {
+				// Delay next connect attempt to save resources and not overwhelm peers,
+				// it's unlikely to succeed anyway if we do retry immediately.
+				time.Sleep(5 * time.Second)
+			}
 			<-sem
 		}()
 	}