Fix response ContentLength metrics tripperware (#37)

tripperware/metrics.go

@@ -26,7 +26,13 @@ func Metrics(recorder metrics.Recorder, options ... metrics.Option) httpware.Tri
 				contentLength := int64(0)
 				if resp != nil {
 					statusCode = resp.StatusCode
-					contentLength = resp.ContentLength
+					// ContentLength records the length of the associated content. The
+					// value -1 indicates that the length is unknown. Unless Request.Method
+					// is "HEAD", values >= 0 indicate that the given number of bytes may
+					// be read from Body.
+					if resp.ContentLength > 0 {
+						contentLength = resp.ContentLength
+					}
 				}
 				code := strconv.Itoa(statusCode)
 				if !config.SplitStatus {

tripperware/metrics_test.go

@@ -52,6 +52,42 @@ func TestMetrics(t *testing.T) {
 	_, _ = stack.DecorateRoundTripper(roundTripperMock).RoundTrip(req)
 }
 
+func TestMetricsContentLengthUnknown(t *testing.T) {
+	var recorderMock = &mocks.Recorder{}
+	var roundTripperMock = &mocks.RoundTripper{}
+	var req *http.Request
+	var requestTimeDuration = 10 * time.Millisecond
+	var resp = &http.Response{
+		Status:        "OK",
+		StatusCode:    http.StatusOK,
+		ContentLength: -1,
+	}
+	expectedContentLength := int64(0)
+	var baseTime = time.Unix(513216000, 0)
+
+	req = httptest.NewRequest(http.MethodGet, "http://fake-addr", nil)
+	// mock roundTripper calls
+	roundTripperMock.On("RoundTrip", req).Return(resp, nil)
+	// assert recorder calls
+	recorderMock.On("AddInflightRequests", req.Context(), req.URL.String(), 1).Once()
+	recorderMock.On("AddInflightRequests", req.Context(), req.URL.String(), -1).Once()
+	recorderMock.On("ObserveHTTPRequestDuration", req.Context(), req.URL.String(), requestTimeDuration, http.MethodGet, "2xx")
+	recorderMock.On("ObserveHTTPResponseSize", req.Context(), req.URL.String(), expectedContentLength, http.MethodGet, "2xx")
+	// mock time.Now method in order to return always the same time whenever the test is launched
+	monkey.Patch(time.Now, func() time.Time { return baseTime })
+	monkey.Patch(time.Since, func(since time.Time) time.Duration {
+		assert.Equal(t, baseTime, since)
+		return requestTimeDuration
+	})
+	defer monkey.UnpatchAll()
+
+	// create metrics httpClient middleware
+	stack := httpware.TripperwareStack(
+		tripperware.Metrics(recorderMock),
+	)
+	_, _ = stack.DecorateRoundTripper(roundTripperMock).RoundTrip(req)
+}
+
 // =====================================================================================================================
 // ========================================= EXAMPLES ==================================================================
 // =====================================================================================================================