Adding chained server info to error logs closes #2960

src/github.com/getlantern/balancer/balancer.go

@@ -94,12 +94,13 @@ func (b *Balancer) DialQOS(network, addr string, targetQOS int) (net.Conn, error
 		}
 		log.Debugf("Dialing %s://%s with %s", network, addr, d.Label)
 		conn, err := d.Dial(network, addr)
+
 		if err != nil {
-			log.Errorf("Unable to dial %s://%s: %v on pass %v...continuing", network, addr, err, i)
+			log.Errorf("Unable to dial via %v to %s://%s: %v on pass %v...continuing", d.Label, network, addr, err, i)
 			d.onError(err)
 			continue
 		}
-		log.Debugf("Successfully dialed to %v://%v on pass %v", network, addr, i)
+		log.Debugf("Successfully dialed via %v to %v://%v on pass %v", d.Label, network, addr, i)
 		return conn, nil
 	}
 }

src/github.com/getlantern/chained/dialer.go

@@ -19,6 +19,9 @@ type Config struct {
 	// the server and is allowed to modify the http.Request before it passes to
 	// the server.
 	OnRequest func(req *http.Request)
+
+	// Label: a optional label for debugging.
+	Label string
 }
 
 // dialer is an implementation of proxy.Dialer that proxies traffic via an
@@ -38,7 +41,7 @@ func NewDialer(cfg Config) proxy.Dialer {
 func (d *dialer) Dial(network, addr string) (net.Conn, error) {
 	conn, err := d.DialServer()
 	if err != nil {
-		return nil, fmt.Errorf("Unable to dial server: %s", err)
+		return nil, fmt.Errorf("Unable to dial server %v: %s", d.Label, err)
 	}
 	if err := d.sendCONNECT(network, addr, conn); err != nil {
 		// We discard this error, since we are only interested in sendCONNECT

src/github.com/getlantern/flashlight/client/chained.go

@@ -75,8 +75,16 @@ func (s *ChainedServerInfo) Dialer() (*balancer.Dialer, error) {
 		}
 	}
 
+	// Is this a trusted proxy that we could use for HTTP traffic?
+	var trusted string
+	if s.Trusted {
+		trusted = "(trusted) "
+	}
+	label := fmt.Sprintf("%schained proxy at %s", trusted, s.Addr)
+
 	ccfg := chained.Config{
 		DialServer: dial,
+		Label:      label,
 	}
 	if s.AuthToken != "" {
 		ccfg.OnRequest = func(req *http.Request) {
@@ -85,14 +93,8 @@ func (s *ChainedServerInfo) Dialer() (*balancer.Dialer, error) {
 	}
 	d := chained.NewDialer(ccfg)
 
-	// Is this a trusted proxy that we could use for HTTP traffic?
-	var trusted string
-	if s.Trusted {
-		trusted = "(trusted) "
-	}
-
 	return &balancer.Dialer{
-		Label:   fmt.Sprintf("%schained proxy at %s", trusted, s.Addr),
+		Label:   label,
 		Weight:  s.Weight,
 		QOS:     s.QOS,
 		Trusted: s.Trusted,