[client, relay] Expose relay transport and connection errors in status and metrics (#6342)

shared/relay/client/dialer/quic/conn.go

@@ -57,6 +57,11 @@ func (c *Conn) Write(b []byte) (int, error) {
 	return len(b), nil
 }
 
+// Protocol returns the transport name for this connection.
+func (c *Conn) Protocol() string {
+	return Network
+}
+
 func (c *Conn) RemoteAddr() net.Addr {
 	return c.session.RemoteAddr()
 }

shared/relay/client/dialer/quic/quic.go

@@ -59,14 +59,12 @@ func (d Dialer) Dial(ctx context.Context, address, serverName string) (net.Conn,
 
 	udpConn, err := nbnet.ListenUDP("udp", &net.UDPAddr{Port: 0})
 	if err != nil {
-		log.Errorf("failed to listen on UDP: %s", err)
-		return nil, err
+		return nil, fmt.Errorf("listen udp: %w", err)
 	}
 
 	udpAddr, err := net.ResolveUDPAddr("udp", quicURL)
 	if err != nil {
-		log.Errorf("failed to resolve UDP address: %s", err)
-		return nil, err
+		return nil, fmt.Errorf("resolve %s: %w", quicURL, err)
 	}
 
 	session, err := quic.Dial(ctx, udpConn, udpAddr, tlsClientConfig, quicConfig)
@@ -74,7 +72,7 @@ func (d Dialer) Dial(ctx context.Context, address, serverName string) (net.Conn,
 		if errors.Is(err, context.Canceled) {
 			return nil, err
 		}
-		log.Errorf("failed to dial to Relay server via QUIC '%s': %s", quicURL, err)
+		log.Debugf("failed to dial to Relay server via QUIC '%s': %s", quicURL, err)
 		return nil, err
 	}