Routed host searches for new addrs issue libp2p#351

If there were addresses available for a given peer,
and they did not work, an err would be returned.
This doesn't make sense as there should be an attempt
to find new addresses through the router before determining
that a connection cannot be made.

Now the router is searched if a connection with the current
addresses cannot be made. If the router had already been
searched(This happens if no addresses were present in the peerinfo)
then we do not search repeat the search as it doesn't to
search the router twice within such a short timespan.

p2p/host/routed/routed.go

@@ -58,8 +58,11 @@ func (rh *RoutedHost) Connect(ctx context.Context, pi pstore.PeerInfo) error {
 
 	// Check if we have some addresses in our recent memory.
 	addrs := rh.Peerstore().Addrs(pi.ID)
+	hasSearched := false // Used to determine if we have used to router to search for addresses.
+
 	if len(addrs) < 1 {
 		// no addrs? find some with the routing system.
+		hasSearched = true
 		var err error
 		addrs, err = rh.findPeerAddrs(ctx, pi.ID)
 		if err != nil {
@@ -69,7 +72,48 @@ func (rh *RoutedHost) Connect(ctx context.Context, pi pstore.PeerInfo) error {
 
 	// if we're here, we got some addrs. let's use our wrapped host to connect.
 	pi.Addrs = addrs
-	return rh.host.Connect(ctx, pi)
+	connErr := rh.host.Connect(ctx, pi)
+
+	// If we could not connect with the addresses that we already had, we use
+	// the router to search for new addresses. Unless we have already searched for
+	// new addresses, then there is no reason to search again.
+	if connErr != nil && hasSearched {
+		return connErr
+	} else if connErr != nil {
+		newAddrs, findErr := rh.findPeerAddrs(ctx, pi.ID)
+
+		if findErr != nil {
+			return findErr // We could not find any addresses.
+		}
+
+		// If we have found new addresses we attempt to connect.
+		if hasNewAddr(pi.Addrs, newAddrs) {
+			pi.Addrs = addrs
+			return rh.host.Connect(ctx, pi)
+		}
+	}
+
+	return nil
+}
+
+func hasNewAddr(oldAddrs, newAddrs []ma.Multiaddr) bool {
+	for _, addr := range newAddrs {
+		if !hasAddr(addr, oldAddrs) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func hasAddr(addr ma.Multiaddr, addrs []ma.Multiaddr) bool {
+	for _, addr2 := range addrs {
+		if addr2 == addr {
+			return true
+		}
+	}
+
+	return false
 }
 
 func (rh *RoutedHost) findPeerAddrs(ctx context.Context, id peer.ID) ([]ma.Multiaddr, error) {