listeners: improve logging

listeners.go

@@ -130,23 +130,31 @@ func updateListeners(port string) error {
 		if _, ok := listeners[host]; ok {
 			// confirm found
 			delete(vanished, host)
-		} else {
+			continue
+		}
+		addr := net.JoinHostPort(host, port)
+		ln, err := net.Listen("tcp", addr)
+		if err != nil {
+			log.Println(err) // err includes enough context
+			continue
+		}
+		log.Printf("now listening on %s", addr)
 		// add a new listener
 		srv := &http.Server{
-				Addr:    net.JoinHostPort(host, port),
 			Handler: http.HandlerFunc(authenticated),
 		}
 		listeners[host] = srv
 		go func(host string, srv *http.Server) {
-				err := srv.ListenAndServe()
+			err := srv.Serve(ln)
-				log.Printf("listener for %q died: %v", host, err)
+			log.Printf("serving on %s: %v", addr, err)
 			listenersMu.Lock()
 			defer listenersMu.Unlock()
 			delete(listeners, host)
 		}(host, srv)
-		}
+
 	}
 	for host := range vanished {
+		log.Printf("no longer listening on %s", net.JoinHostPort(host, port))
 		listeners[host].Close()
 		delete(listeners, host)
 	}