[proposal] adding configurable status resolver on prometheus middleware

echoprometheus/prometheus.go

@@ -78,6 +78,9 @@ type MiddlewareConfig struct {
 	// If DoNotUseRequestPathFor404 is true, all 404 responses (due to non-matching route) will have the same `url` label and
 	// thus won't generate new metrics.
 	DoNotUseRequestPathFor404 bool
+
+	// StatusCodeResolver resolves err & context into http status code. Default is to use context.Response().Status
+	StatusCodeResolver func(c echo.Context, err error) int
 }
 
 type LabelValueFunc func(c echo.Context, err error) string
@@ -167,6 +170,9 @@ func (conf MiddlewareConfig) ToMiddleware() (echo.MiddlewareFunc, error) {
 			return opts
 		}
 	}
+	if conf.StatusCodeResolver == nil {
+		conf.StatusCodeResolver = defaultStatusResolver
+	}
 
 	labelNames, customValuers := createLabels(conf.LabelFuncs)
 
@@ -257,16 +263,7 @@ func (conf MiddlewareConfig) ToMiddleware() (echo.MiddlewareFunc, error) {
 				url = c.Request().URL.Path
 			}
 
-			status := c.Response().Status
-			if err != nil {
-				var httpError *echo.HTTPError
-				if errors.As(err, &httpError) {
-					status = httpError.Code
-				}
-				if status == 0 || status == http.StatusOK {
-					status = http.StatusInternalServerError
-				}
-			}
+			status := conf.StatusCodeResolver(c, err)
 
 			values := make([]string, len(labelNames))
 			values[0] = strconv.Itoa(status)
@@ -458,3 +455,18 @@ func WriteGatheredMetrics(writer io.Writer, gatherer prometheus.Gatherer) error
 	}
 	return nil
 }
+
+// defaultStatusResolver resolves http status code by referencing echo.HTTPError.
+func defaultStatusResolver(c echo.Context, err error) int {
+	status := c.Response().Status
+	if err != nil {
+		var httpError *echo.HTTPError
+		if errors.As(err, &httpError) {
+			status = httpError.Code
+		}
+		if status == 0 || status == http.StatusOK {
+			status = http.StatusInternalServerError
+		}
+	}
+	return status
+}

echoprometheus/prometheus_test.go

@@ -161,6 +161,64 @@ func TestMiddlewareConfig_LabelFuncs(t *testing.T) {
 	assert.Contains(t, body, `echo_request_duration_seconds_count{code="200",host="example.com",method="overridden_GET",scheme="http",url="/ok"} 1`)
 }
 
+func TestMiddlewareConfig_StatusCodeResolver(t *testing.T) {
+	e := echo.New()
+	customRegistry := prometheus.NewRegistry()
+	customResolver := func(c echo.Context, err error) int {
+		if err == nil {
+			return c.Response().Status
+		}
+		msg := err.Error()
+		if strings.Contains(msg, "NOT FOUND") {
+			return http.StatusNotFound
+		}
+		if strings.Contains(msg, "NOT Authorized") {
+			return http.StatusUnauthorized
+		}
+		return http.StatusInternalServerError
+	}
+	e.Use(NewMiddlewareWithConfig(MiddlewareConfig{
+		Skipper: func(c echo.Context) bool {
+			return strings.HasSuffix(c.Path(), "ignore")
+		},
+		Subsystem:          "myapp",
+		Registerer:         customRegistry,
+		StatusCodeResolver: customResolver,
+	}))
+	e.GET("/metrics", NewHandlerWithConfig(HandlerConfig{Gatherer: customRegistry}))
+
+	e.GET("/handler_for_ok", func(c echo.Context) error {
+		return c.JSON(http.StatusOK, "OK")
+	})
+	e.GET("/handler_for_nok", func(c echo.Context) error {
+		return c.JSON(http.StatusConflict, "NOK")
+	})
+	e.GET("/handler_for_not_found", func(c echo.Context) error {
+		return errors.New("NOT FOUND")
+	})
+	e.GET("/handler_for_not_authorized", func(c echo.Context) error {
+		return errors.New("NOT Authorized")
+	})
+	e.GET("/handler_for_unknown_error", func(c echo.Context) error {
+		return errors.New("i do not know")
+	})
+
+	assert.Equal(t, http.StatusOK, request(e, "/handler_for_ok"))
+	assert.Equal(t, http.StatusConflict, request(e, "/handler_for_nok"))
+	assert.Equal(t, http.StatusInternalServerError, request(e, "/handler_for_not_found"))
+	assert.Equal(t, http.StatusInternalServerError, request(e, "/handler_for_not_authorized"))
+	assert.Equal(t, http.StatusInternalServerError, request(e, "/handler_for_unknown_error"))
+
+	body, code := requestBody(e, "/metrics")
+	assert.Equal(t, http.StatusOK, code)
+	assert.Contains(t, body, fmt.Sprintf("%s_requests_total", "myapp"))
+	assert.Contains(t, body, `myapp_requests_total{code="200",host="example.com",method="GET",url="/handler_for_ok"} 1`)
+	assert.Contains(t, body, `myapp_requests_total{code="409",host="example.com",method="GET",url="/handler_for_nok"} 1`)
+	assert.Contains(t, body, `myapp_requests_total{code="404",host="example.com",method="GET",url="/handler_for_not_found"} 1`)
+	assert.Contains(t, body, `myapp_requests_total{code="401",host="example.com",method="GET",url="/handler_for_not_authorized"} 1`)
+	assert.Contains(t, body, `myapp_requests_total{code="500",host="example.com",method="GET",url="/handler_for_unknown_error"} 1`)
+}
+
 func TestMiddlewareConfig_HistogramOptsFunc(t *testing.T) {
 	e := echo.New()
 	customRegistry := prometheus.NewRegistry()