contrib/gofiber/fiber.v2: capture error from fiber handler (#988)

The error returned from the fiber handler was being ignored
by the middleware. It now correctly captures the error and
sets it on the span.

Fixes #978

contrib/gofiber/fiber.v2/fiber.go

@@ -64,7 +64,9 @@ func Middleware(opts ...Option) func(c *fiber.Ctx) error {
 		}
 		span.SetTag(ext.HTTPCode, strconv.Itoa(status))
 
-		if cfg.isStatusError(status) {
+		if err != nil {
+			span.SetTag(ext.Error, err)
+		} else if cfg.isStatusError(status) {
 			// mark 5xx server error
 			span.SetTag(ext.Error, fmt.Errorf("%d: %s", status, http.StatusText(status)))
 		}

contrib/gofiber/fiber.v2/fiber_test.go

@@ -94,7 +94,7 @@ func TestTrace200(t *testing.T) {
 	})
 }
 
-func TestError(t *testing.T) {
+func TestStatusError(t *testing.T) {
 	assert := assert.New(t)
 	mt := mocktracer.Start()
 	defer mt.Stop()
@@ -128,6 +128,36 @@ func TestError(t *testing.T) {
 	assert.Equal(wantErr, span.Tag(ext.Error).(error).Error())
 }
 
+func TestCustomError(t *testing.T) {
+	assert := assert.New(t)
+	mt := mocktracer.Start()
+	defer mt.Stop()
+
+	router := fiber.New()
+	router.Use(Middleware(WithServiceName("foobar")))
+
+	router.Get("/err", func(c *fiber.Ctx) error {
+		c.SendStatus(400)
+		return fiber.ErrBadRequest
+	})
+	r := httptest.NewRequest("GET", "/err", nil)
+
+	response, err := router.Test(r, 100)
+	assert.Equal(nil, err)
+	assert.Equal(response.StatusCode, 400)
+
+	spans := mt.FinishedSpans()
+	assert.Len(spans, 1)
+	if len(spans) < 1 {
+		t.Fatalf("no spans")
+	}
+	span := spans[0]
+	assert.Equal("http.request", span.OperationName())
+	assert.Equal("foobar", span.Tag(ext.ServiceName))
+	assert.Equal("400", span.Tag(ext.HTTPCode))
+	assert.Equal(fiber.ErrBadRequest, span.Tag(ext.Error).(*fiber.Error))
+}
+
 func TestGetSpanNotInstrumented(t *testing.T) {
 	assert := assert.New(t)
 	router := fiber.New()