fix(dht/routing) buffer promise response to prevent resource leak

When performing this "promise" pattern, it is important to
provide a
channel with space for one value. Otherwise the sender may
block forever
in the case of a receiver that decides to abandon the
request. A subtle
detail, but one that is important for avoiding
leaked goroutines.

cc @whyrusleeping @jbenet

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

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

routing/dht/providers.go

@@ -102,9 +102,10 @@ func (pm *ProviderManager) AddProvider(k u.Key, val peer.Peer) {
 }
 
 func (pm *ProviderManager) GetProviders(ctx context.Context, k u.Key) []peer.Peer {
-	gp := new(getProv)
-	gp.k = k
-	gp.resp = make(chan []peer.Peer)
+	gp := &getProv{
+		k:    k,
+		resp: make(chan []peer.Peer, 1), // buffered to prevent sender from blocking
+	}
 	select {
 	case pm.getprovs <- gp:
 		return <-gp.resp