fix(echo): return nil from middleware to handle error only once (#377)

CHANGELOG.md

@@ -14,6 +14,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ### Fixed
 
+- The `go.opentelemetry.io/contrib/instrumentation/github.com/labstack/echo/otelecho.Middleware` no longer sends duplicate errors to the global `ErrorHandler`. (#377, #364)
 - The import comment in `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp` is now correctly quoted. (#379)
 
 ## [0.12.0] - 2020-09-25
@@ -124,7 +125,6 @@ This release upgrades its [go.opentelemetry.io/otel](https://github.com/open-tel
 - Update dependabot configuration to correctly check all included packages. (#131)
 - Update `RELEASING.md` with correct `tag.sh` command. (#130)
 
-
 ## [0.8.0] - 2020-07-10
 
 This release upgrades its [go.opentelemetry.io/otel](https://github.com/open-telemetry/opentelemetry-go/releases/tag/v0.8.0) dependency to v0.8.0, includes minor fixes, and new instrumentation.

instrumentation/github.com/labstack/echo/otelecho/echo.go

@@ -89,7 +89,7 @@ func Middleware(service string, opts ...Option) echo.MiddlewareFunc {
 			span.SetAttributes(attrs...)
 			span.SetStatus(spanStatus, spanMessage)
 
-			return err
+			return nil
 		}
 	}
 }

instrumentation/github.com/labstack/echo/otelecho/echo_test.go

@@ -147,6 +147,23 @@ func TestError(t *testing.T) {
 	assert.Equal(t, codes.Internal, span.Status)
 }
 
+func TestErrorOnlyHandledOnce(t *testing.T) {
+	router := echo.New()
+	timesHandlingError := 0
+	router.HTTPErrorHandler = func(e error, c echo.Context) {
+		timesHandlingError++
+	}
+	router.Use(Middleware("test-service"))
+	router.GET("/", func(c echo.Context) error {
+		return errors.New("Mock Error")
+	})
+	r := httptest.NewRequest(http.MethodGet, "/", nil)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, r)
+
+	assert.Equal(t, 1, timesHandlingError)
+}
+
 func TestGetSpanNotInstrumented(t *testing.T) {
 	router := echo.New()
 	router.GET("/ping", func(c echo.Context) error {