fix(routing/dht) _always_ close chan on exit of FindProvidersAsync

the important change here is that within FindProvidersAsync, the channel
is closed using a `defer`. This ensures the channel is always closed,
regardless of the path taken to exit.

+ misc cleanup

cc @whyrusleeping @jbenet

License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>

routing/dht/dht.go

@@ -194,24 +194,21 @@ func (dht *IpfsDHT) sendRequest(ctx context.Context, p peer.Peer, pmes *pb.Messa
 
 	start := time.Now()
 
-	log.Event(ctx, "sentMessage", dht.self, p, pmes)
-
-	rmes, err := dht.sender.SendRequest(ctx, mes)
+	rmes, err := dht.sender.SendRequest(ctx, mes) // respect?
 	if err != nil {
 		return nil, err
 	}
 	if rmes == nil {
 		return nil, errors.New("no response to request")
 	}
+	log.Event(ctx, "sentMessage", dht.self, p, pmes)
 
-	rtt := time.Since(start)
-	rmes.Peer().SetLatency(rtt)
+	rmes.Peer().SetLatency(time.Since(start))
 
 	rpmes := new(pb.Message)
 	if err := proto.Unmarshal(rmes.Data(), rpmes); err != nil {
 		return nil, err
 	}
-
 	return rpmes, nil
 }
 

routing/dht/routing.go

@@ -129,21 +129,27 @@ func (dht *IpfsDHT) FindProvidersAsync(ctx context.Context, key u.Key, count int
 	log.Event(ctx, "findProviders", &key)
 	peerOut := make(chan peer.Peer, count)
 	go func() {
+		defer close(peerOut)
+
 		ps := newPeerSet()
+		// TODO may want to make this function async to hide latency
 		provs := dht.providers.GetProviders(key)
 		for _, p := range provs {
 			count--
 			// NOTE: assuming that this list of peers is unique
 			ps.Add(p)
-			peerOut <- p
+			select {
+			case peerOut <- p:
+			case <-ctx.Done():
+				return
+			}
 			if count <= 0 {
 				return
 			}
 		}
 
-		wg := new(sync.WaitGroup)
-		peers := dht.routingTables[0].NearestPeers(kb.ConvertKey(key), AlphaValue)
-		for _, pp := range peers {
+		var wg sync.WaitGroup
+		for _, pp := range dht.routingTables[0].NearestPeers(kb.ConvertKey(key), AlphaValue) {
 			wg.Add(1)
 			go func(p peer.Peer) {
 				defer wg.Done()
@@ -156,16 +162,16 @@ func (dht *IpfsDHT) FindProvidersAsync(ctx context.Context, key u.Key, count int
 			}(pp)
 		}
 		wg.Wait()
-		close(peerOut)
 	}()
 	return peerOut
 }
 
 func (dht *IpfsDHT) addPeerListAsync(ctx context.Context, k u.Key, peers []*pb.Message_Peer, ps *peerSet, count int, out chan peer.Peer) {
-	done := make(chan struct{})
+	var wg sync.WaitGroup
 	for _, pbp := range peers {
+		wg.Add(1)
 		go func(mp *pb.Message_Peer) {
-			defer func() { done <- struct{}{} }()
+			defer wg.Done()
 			// construct new peer
 			p, err := dht.ensureConnectedToPeer(ctx, mp)
 			if err != nil {
@@ -179,15 +185,17 @@ func (dht *IpfsDHT) addPeerListAsync(ctx context.Context, k u.Key, peers []*pb.M
 
 			dht.providers.AddProvider(k, p)
 			if ps.AddIfSmallerThan(p, count) {
-				out <- p
+				select {
+				case out <- p:
+				case <-ctx.Done():
+					return
+				}
 			} else if ps.Size() >= count {
 				return
 			}
 		}(pbp)
 	}
-	for _ = range peers {
-		<-done
-	}
+	wg.Wait()
 }
 
 // Find specific Peer