httpserver: Ignore ErrServerClosed when closing server

caddy.go

@@ -798,7 +798,7 @@ func startServers(serverList []Server, inst *Instance, restartFds map[string]res
 				continue
 			}
 			if strings.Contains(err.Error(), "use of closed network connection") {
-				// this error is normal when closing the listener
+				// this error is normal when closing the listener; see https://github.com/golang/go/issues/4373
 				continue
 			}
 			log.Println(err)

caddyhttp/httpserver/server.go

@@ -319,6 +319,9 @@ func (s *Server) Serve(ln net.Listener) error {
 	}
 
 	err := s.Server.Serve(ln)
+	if err == http.ErrServerClosed {
+		err = nil // not an error worth reporting since closing a server is intentional
+	}
 	if s.quicServer != nil {
 		s.quicServer.Close()
 	}