Refactor InstrumentHandlerCounter definition

mediaapi/routing/routing.go

@@ -85,33 +85,33 @@ func makeDownloadAPI(
 	activeRemoteRequests *types.ActiveRemoteRequests,
 	activeThumbnailGeneration *types.ActiveThumbnailGeneration,
 ) http.HandlerFunc {
-	return promhttp.InstrumentHandlerCounter(
-		promauto.NewCounterVec(
-			prometheus.CounterOpts{
-				Name: name,
-				Help: "Total number of media_api requests for either thumbnails or full downloads",
-			},
-			[]string{"code"},
-		), http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
-			req = util.RequestWithLogging(req)
-
-			// Set common headers returned regardless of the outcome of the request
-			util.SetCORSHeaders(w)
-			// Content-Type will be overridden in case of returning file data, else we respond with JSON-formatted errors
-			w.Header().Set("Content-Type", "application/json")
-			vars := mux.Vars(req)
-			Download(
-				w,
-				req,
-				gomatrixserverlib.ServerName(vars["serverName"]),
-				types.MediaID(vars["mediaId"]),
-				cfg,
-				db,
-				client,
-				activeRemoteRequests,
-				activeThumbnailGeneration,
-				name == "thumbnail",
-			)
+	counterVec := promauto.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: name,
+			Help: "Total number of media_api requests for either thumbnails or full downloads",
 		},
-		))
+		[]string{"code"},
+	)
+	httpHandler := func(w http.ResponseWriter, req *http.Request) {
+		req = util.RequestWithLogging(req)
+
+		// Set common headers returned regardless of the outcome of the request
+		util.SetCORSHeaders(w)
+		// Content-Type will be overridden in case of returning file data, else we respond with JSON-formatted errors
+		w.Header().Set("Content-Type", "application/json")
+		vars := mux.Vars(req)
+		Download(
+			w,
+			req,
+			gomatrixserverlib.ServerName(vars["serverName"]),
+			types.MediaID(vars["mediaId"]),
+			cfg,
+			db,
+			client,
+			activeRemoteRequests,
+			activeThumbnailGeneration,
+			name == "thumbnail",
+		)
+	}
+	return promhttp.InstrumentHandlerCounter(counterVec, http.HandlerFunc(httpHandler))
 }