fix(prometheus): report subsonic error code (#4282)

* fix(prometheus): report subsonic error code

* address feedback

server/subsonic/middlewares.go

@@ -226,21 +226,35 @@ func playerIDCookieName(userName string) string {
 	return cookieName
 }
 
+const subsonicErrorPointer = "subsonicErrorPointer"
+
 func recordStats(metrics metrics.Metrics) func(next http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		fn := func(w http.ResponseWriter, r *http.Request) {
 			ww := middleware.NewWrapResponseWriter(w, r.ProtoMajor)
 
+			status := int32(-1)
+			contextWithStatus := context.WithValue(r.Context(), subsonicErrorPointer, &status)
+
 			start := time.Now()
 			defer func() {
+				elapsed := time.Since(start).Milliseconds()
+
 				// We want to get the client name (even if not present for certain endpoints)
 				p := req.Params(r)
 				client, _ := p.String("c")
 
-				metrics.RecordRequest(r.Context(), strings.Replace(r.URL.Path, ".view", "", 1), r.Method, client, ww.Status(), time.Since(start).Milliseconds())
+				// If there is no Subsonic status (e.g., HTTP 501 not implemented), fallback to HTTP
+				if status == -1 {
+					status = int32(ww.Status())
+				}
+
+				shortPath := strings.Replace(r.URL.Path, ".view", "", 1)
+
+				metrics.RecordRequest(r.Context(), shortPath, r.Method, client, status, elapsed)
 			}()
 
-			next.ServeHTTP(ww, r)
+			next.ServeHTTP(ww, r.WithContext(contextWithStatus))
 		}
 		return http.HandlerFunc(fn)
 	}