autoexport: Handle OTEL_TRACES_EXPORTER=none (#4130)

CHANGELOG.md

@@ -12,7 +12,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Add `NewMiddleware` function in `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp`. (#2964)
 - Add the new `go.opentelemetry.io/contrib/instrgen` package to provide auto-generated source code instrumentation. (#3068, #3108)
-- The `go.opentelemetry.io/contrib/exporters/autoexport` package to provide configuration of trace exporters with useful defaults and envar support. (#2753, #4100)
+- The `go.opentelemetry.io/contrib/exporters/autoexport` package to provide configuration of trace exporters with useful defaults and envar support. (#2753, #4100, #4129)
 - `WithRouteTag` in `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp` adds HTTP route attribute to metrics. (#615)
 
 ### Fixed

exporters/autoexport/exporter_test.go

@@ -28,8 +28,7 @@ import (
 func TestOTLPExporterReturnedWhenNoEnvOrFallbackExporterConfigured(t *testing.T) {
 	exporter, err := NewSpanExporter(context.Background())
 	assert.NoError(t, err)
-	assert.NotNil(t, exporter)
-	assert.IsType(t, &otlptrace.Exporter{}, exporter)
+	assertOTLPHTTPExporter(t, exporter)
 }
 
 func TestFallbackExporterReturnedWhenNoEnvExporterConfigured(t *testing.T) {
@@ -40,6 +39,7 @@ func TestFallbackExporterReturnedWhenNoEnvExporterConfigured(t *testing.T) {
 	)
 	assert.NoError(t, err)
 	assert.Equal(t, testExporter, exporter)
+	assert.False(t, IsNone(exporter))
 }
 
 func TestEnvExporterIsPreferredOverFallbackExporter(t *testing.T) {
@@ -81,6 +81,14 @@ func TestEnvExporterOTLPInvalidProtocol(t *testing.T) {
 	assert.Nil(t, exporter)
 }
 
+func TestEnvExporterNone(t *testing.T) {
+	t.Setenv("OTEL_TRACES_EXPORTER", "none")
+
+	exporter, err := NewSpanExporter(context.Background())
+	assert.NoError(t, err)
+	assert.True(t, IsNone(exporter))
+}
+
 func assertOTLPHTTPExporter(t *testing.T, got trace.SpanExporter) {
 	t.Helper()
 
@@ -91,6 +99,8 @@ func assertOTLPHTTPExporter(t *testing.T, got trace.SpanExporter) {
 	// Implementation detail hack. This may break when bumping OTLP exporter modules as it uses unexported API.
 	clientType := reflect.Indirect(reflect.ValueOf(got)).FieldByName("client").Elem().Type().String()
 	assert.Equal(t, "*otlptracehttp.client", clientType)
+
+	assert.False(t, IsNone(got))
 }
 
 func assertOTLPGRPCExporter(t *testing.T, got trace.SpanExporter) {
@@ -103,6 +113,8 @@ func assertOTLPGRPCExporter(t *testing.T, got trace.SpanExporter) {
 	// Implementation detail hack. This may break when bumping OTLP exporter modules as it uses unexported API.
 	clientType := reflect.Indirect(reflect.ValueOf(got)).FieldByName("client").Elem().Type().String()
 	assert.Equal(t, "*otlptracegrpc.client", clientType)
+
+	assert.False(t, IsNone(got))
 }
 
 type testExporter struct{}

exporters/autoexport/noop.go

@@ -0,0 +1,43 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package autoexport // import "go.opentelemetry.io/contrib/exporters/autoexport"
+
+import (
+	"context"
+
+	"go.opentelemetry.io/otel/sdk/trace"
+)
+
+// noop is an implementation of trace.SpanExporter that performs no operations.
+type noop struct{}
+
+var _ trace.SpanExporter = noop{}
+
+// ExportSpans is part of trace.SpanExporter interface.
+func (e noop) ExportSpans(ctx context.Context, spans []trace.ReadOnlySpan) error {
+	return nil
+}
+
+// Shutdown is part of trace.SpanExporter interface.
+func (e noop) Shutdown(ctx context.Context) error {
+	return nil
+}
+
+// IsNone returns true for the exporter returned by [NewSpanExporter]
+// when OTEL_TRACES_EXPORTER environment variable is set to "none".
+func IsNone(e trace.SpanExporter) bool {
+	_, ok := e.(noop)
+	return ok
+}

exporters/autoexport/registry.go

@@ -43,6 +43,7 @@ func newRegistry() registry {
 		names: map[string]func(context.Context) (trace.SpanExporter, error){
 			"":     buildOTLPExporter,
 			"otlp": buildOTLPExporter,
+			"none": func(ctx context.Context) (trace.SpanExporter, error) { return noop{}, nil },
 		},
 	}
 }

exporters/autoexport/registry_test.go

@@ -23,7 +23,6 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
-	"go.opentelemetry.io/otel/exporters/otlp/otlptrace"
 	"go.opentelemetry.io/otel/exporters/stdout/stdouttrace"
 	"go.opentelemetry.io/otel/sdk/trace"
 )
@@ -99,11 +98,11 @@ func TestSubsequentCallsToGetExporterReturnsNewInstances(t *testing.T) {
 func TestDefaultOTLPExporterFactoriesAreAutomaticallyRegistered(t *testing.T) {
 	exp1, err := spanExporter(context.Background(), "")
 	assert.Nil(t, err)
-	assert.IsType(t, &otlptrace.Exporter{}, exp1)
+	assertOTLPHTTPExporter(t, exp1)
 
 	exp2, err := spanExporter(context.Background(), "otlp")
 	assert.Nil(t, err)
-	assert.IsType(t, &otlptrace.Exporter{}, exp2)
+	assertOTLPHTTPExporter(t, exp2)
 }
 
 func TestEnvRegistryCanRegisterExporterFactory(t *testing.T) {