feat(exporters/autoexport): add support of OTEL_EXPORTER_OTLP_{TRACES…

…,METRICS,LOGS}_PROTOCOL env var (open-telemetry#5807)

This commit adds support for signal-specific environment variables to configure the OTLP protocol used with the exporter.
As stated in the [specification](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.34.0/specification/protocol/exporter.md#configuration-options), you
can now use the following environment variables to configure signal-specific protocols:

- `OTEL_EXPORTER_OTLP_TRACES_PROTOCOL`
- `OTEL_EXPORTER_OTLP_LOGS_PROTOCOL`
- `OTEL_EXPORTER_OTLP_METRICS_PROTOCOL`

The package will first attempt to load the protocol for a signal from the corresponding environment variable. If it is not set or is empty, it will try to determine the protocol from `OTEL_EXPORTER_OTLP_PROTOCOL`. If this is also not defined or is empty, it will fall back to `http/protobuf`.

Signed-off-by: thomasgouveia <gouveia.thomas@outlook.fr>

exporters/autoexport/go.mod

@@ -7,6 +7,7 @@ toolchain go1.22.4
 require (
 	github.com/prometheus/client_golang v1.19.1
 	github.com/stretchr/testify v1.9.0
+	github.com/thomasgouveia/goutils/env v1.0.1
 	go.opentelemetry.io/contrib/bridges/prometheus v0.52.0
 	go.opentelemetry.io/otel v1.27.0
 	go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp v0.3.0

exporters/autoexport/go.sum

@@ -35,6 +35,8 @@ github.com/rogpeppe/go-internal v1.12.0 h1:exVL4IDcn6na9z1rAb56Vxr+CgyK3nn3O+epU
 github.com/rogpeppe/go-internal v1.12.0/go.mod h1:E+RYuTGaKKdloAfM02xzb0FW3Paa99yedzYV+kq4uf4=
 github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
 github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+github.com/thomasgouveia/goutils/env v1.0.1 h1:cn1RGQ+uuOJ8xY2ZKiVVA/WzEhziXy2meCevzRKKw+E=
+github.com/thomasgouveia/goutils/env v1.0.1/go.mod h1:GJrLBNv7WGXGZhVvr6w6BQTiT3UJk4iYludCCwxNdOY=
 go.opentelemetry.io/otel v1.27.0 h1:9BZoF3yMK/O1AafMiQTVu0YDj5Ea4hPhxCs7sGva+cg=
 go.opentelemetry.io/otel v1.27.0/go.mod h1:DMpAK8fzYRzs+bi3rS5REupisuqTheUlSZJ1WnZaPAQ=
 go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp v0.3.0 h1:ccBrA8nCY5mM0y5uO7FT0ze4S0TuFcWdDB2FxGMTjkI=

exporters/autoexport/logs.go

@@ -5,13 +5,16 @@ package autoexport // import "go.opentelemetry.io/contrib/exporters/autoexport"
 
 import (
 	"context"
-	"os"
+
+	"github.com/thomasgouveia/goutils/env"
 
 	"go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp"
 	"go.opentelemetry.io/otel/exporters/stdout/stdoutlog"
 	"go.opentelemetry.io/otel/sdk/log"
 )
 
+const otelExporterOTLPLogsProtoEnvKey = "OTEL_EXPORTER_OTLP_LOGS_PROTOCOL"
+
 // LogOption applies an autoexport configuration option.
 type LogOption = option[log.Exporter]
 
@@ -30,6 +33,9 @@ var logsSignal = newSignal[log.Exporter]("OTEL_LOGS_EXPORTER")
 //   - "http/protobuf" (default) -  protobuf-encoded data over HTTP connection;
 //     see: [go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp]
 //
+// OTEL_EXPORTER_OTLP_LOGS_PROTOCOL defines OTLP exporter's transport protocol for the logs signal;
+// supported values are the same as OTEL_EXPORTER_OTLP_PROTOCOL.
+//
 // An error is returned if an environment value is set to an unhandled value.
 //
 // Use [RegisterLogExporter] to handle more values of OTEL_LOGS_EXPORTER.
@@ -51,10 +57,10 @@ func RegisterLogExporter(name string, factory func(context.Context) (log.Exporte
 
 func init() {
 	RegisterLogExporter("otlp", func(ctx context.Context) (log.Exporter, error) {
-		proto := os.Getenv(otelExporterOTLPProtoEnvKey)
-		if proto == "" {
-			proto = "http/protobuf"
-		}
+		proto := env.WithDefaultString(
+			otelExporterOTLPLogsProtoEnvKey,
+			env.WithDefaultString(otelExporterOTLPProtoEnvKey, "http/protobuf"),
+		)
 
 		switch proto {
 		// grpc is not supported yet, should comment out when it is supported

exporters/autoexport/logs_test.go

@@ -60,6 +60,32 @@ func TestLogExporterOTLP(t *testing.T) {
 	}
 }
 
+func TestLogExporterOTLPWithDedicatedProtocol(t *testing.T) {
+	t.Setenv("OTEL_LOGS_EXPORTER", "otlp")
+
+	for _, tc := range []struct {
+		protocol, clientType string
+	}{
+		{"http/protobuf", "atomic.Pointer[go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp.client]"},
+		{"", "atomic.Pointer[go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp.client]"},
+	} {
+		t.Run(fmt.Sprintf("protocol=%q", tc.protocol), func(t *testing.T) {
+			t.Setenv("OTEL_EXPORTER_OTLP_LOGS_PROTOCOL", tc.protocol)
+
+			got, err := NewLogExporter(context.Background())
+			assert.NoError(t, err)
+			t.Cleanup(func() {
+				assert.NoError(t, got.Shutdown(context.Background()))
+			})
+			assert.Implements(t, new(log.Exporter), got)
+
+			// Implementation detail hack. This may break when bumping OTLP exporter modules as it uses unexported API.
+			clientType := reflect.Indirect(reflect.ValueOf(got)).FieldByName("client").Type()
+			assert.Equal(t, tc.clientType, clientType.String())
+		})
+	}
+}
+
 func TestLogExporterOTLPOverInvalidProtocol(t *testing.T) {
 	t.Setenv("OTEL_LOGS_EXPORTER", "otlp")
 	t.Setenv("OTEL_EXPORTER_OTLP_PROTOCOL", "invalid-protocol")

exporters/autoexport/metrics.go

@@ -13,6 +13,8 @@ import (
 	"strings"
 	"time"
 
+	"github.com/thomasgouveia/goutils/env"
+
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 
@@ -25,6 +27,8 @@ import (
 	"go.opentelemetry.io/otel/sdk/metric"
 )
 
+const otelExporterOTLPMetricsProtoEnvKey = "OTEL_EXPORTER_OTLP_METRICS_PROTOCOL"
+
 // MetricOption applies an autoexport configuration option.
 type MetricOption = option[metric.Reader]
 
@@ -50,6 +54,9 @@ func WithFallbackMetricReader(metricReaderFactory func(ctx context.Context) (met
 //   - "http/protobuf" (default) -  protobuf-encoded data over HTTP connection;
 //     see: [go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp]
 //
+// OTEL_EXPORTER_OTLP_METRICS_PROTOCOL defines OTLP exporter's transport protocol for the metrics signal;
+// supported values are the same as OTEL_EXPORTER_OTLP_PROTOCOL.
+//
 // OTEL_EXPORTER_PROMETHEUS_HOST (defaulting to "localhost") and
 // OTEL_EXPORTER_PROMETHEUS_PORT (defaulting to 9464) define the host and port for the
 // Prometheus exporter's HTTP server.
@@ -106,10 +113,10 @@ func init() {
 			readerOpts = append(readerOpts, metric.WithProducer(producer))
 		}
 
-		proto := os.Getenv(otelExporterOTLPProtoEnvKey)
-		if proto == "" {
-			proto = "http/protobuf"
-		}
+		proto := env.WithDefaultString(
+			otelExporterOTLPMetricsProtoEnvKey,
+			env.WithDefaultString(otelExporterOTLPProtoEnvKey, "http/protobuf"),
+		)
 
 		switch proto {
 		case "grpc":

exporters/autoexport/metrics_test.go

@@ -74,6 +74,33 @@ func TestMetricExporterOTLP(t *testing.T) {
 	}
 }
 
+func TestMetricExporterOTLPWithDedicatedProtocol(t *testing.T) {
+	t.Setenv("OTEL_METRICS_EXPORTER", "otlp")
+
+	for _, tc := range []struct {
+		protocol, exporterType string
+	}{
+		{"http/protobuf", "*otlpmetrichttp.Exporter"},
+		{"", "*otlpmetrichttp.Exporter"},
+		{"grpc", "*otlpmetricgrpc.Exporter"},
+	} {
+		t.Run(fmt.Sprintf("protocol=%q", tc.protocol), func(t *testing.T) {
+			t.Setenv("OTEL_EXPORTER_OTLP_METRICS_PROTOCOL", tc.protocol)
+
+			got, err := NewMetricReader(context.Background())
+			assert.NoError(t, err)
+			t.Cleanup(func() {
+				assert.NoError(t, got.Shutdown(context.Background()))
+			})
+			assert.IsType(t, &metric.PeriodicReader{}, got)
+
+			// Implementation detail hack. This may break when bumping OTLP exporter modules as it uses unexported API.
+			exporterType := reflect.Indirect(reflect.ValueOf(got)).FieldByName("exporter").Elem().Type()
+			assert.Equal(t, tc.exporterType, exporterType.String())
+		})
+	}
+}
+
 func TestMetricExporterOTLPOverInvalidProtocol(t *testing.T) {
 	t.Setenv("OTEL_METRICS_EXPORTER", "otlp")
 	t.Setenv("OTEL_EXPORTER_OTLP_PROTOCOL", "invalid-protocol")

exporters/autoexport/spans.go

@@ -5,14 +5,17 @@ package autoexport // import "go.opentelemetry.io/contrib/exporters/autoexport"
 
 import (
 	"context"
-	"os"
+
+	"github.com/thomasgouveia/goutils/env"
 
 	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
 	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp"
 	"go.opentelemetry.io/otel/exporters/stdout/stdouttrace"
 	"go.opentelemetry.io/otel/sdk/trace"
 )
 
+const otelExporterOTLPTracesProtoEnvKey = "OTEL_EXPORTER_OTLP_TRACES_PROTOCOL"
+
 // SpanOption applies an autoexport configuration option.
 type SpanOption = option[trace.SpanExporter]
 
@@ -42,6 +45,9 @@ func WithFallbackSpanExporter(spanExporterFactory func(ctx context.Context) (tra
 //   - "http/protobuf" (default) -  protobuf-encoded data over HTTP connection;
 //     see: [go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp]
 //
+// OTEL_EXPORTER_OTLP_TRACES_PROTOCOL defines OTLP exporter's transport protocol for the traces signal;
+// supported values are the same as OTEL_EXPORTER_OTLP_PROTOCOL.
+//
 // An error is returned if an environment value is set to an unhandled value.
 //
 // Use [RegisterSpanExporter] to handle more values of OTEL_TRACES_EXPORTER.
@@ -65,10 +71,10 @@ var tracesSignal = newSignal[trace.SpanExporter]("OTEL_TRACES_EXPORTER")
 
 func init() {
 	RegisterSpanExporter("otlp", func(ctx context.Context) (trace.SpanExporter, error) {
-		proto := os.Getenv(otelExporterOTLPProtoEnvKey)
-		if proto == "" {
-			proto = "http/protobuf"
-		}
+		proto := env.WithDefaultString(
+			otelExporterOTLPTracesProtoEnvKey,
+			env.WithDefaultString(otelExporterOTLPProtoEnvKey, "http/protobuf"),
+		)
 
 		switch proto {
 		case "grpc":

exporters/autoexport/spans_test.go

@@ -59,6 +59,33 @@ func TestSpanExporterOTLP(t *testing.T) {
 	}
 }
 
+func TestSpanExporterOTLPWithDedicatedProtocol(t *testing.T) {
+	t.Setenv("OTEL_TRACES_EXPORTER", "otlp")
+
+	for _, tc := range []struct {
+		protocol, clientType string
+	}{
+		{"http/protobuf", "*otlptracehttp.client"},
+		{"", "*otlptracehttp.client"},
+		{"grpc", "*otlptracegrpc.client"},
+	} {
+		t.Run(fmt.Sprintf("protocol=%q", tc.protocol), func(t *testing.T) {
+			t.Setenv("OTEL_EXPORTER_OTLP_TRACES_PROTOCOL", tc.protocol)
+
+			got, err := NewSpanExporter(context.Background())
+			assert.NoError(t, err)
+			t.Cleanup(func() {
+				assert.NoError(t, got.Shutdown(context.Background()))
+			})
+			assert.IsType(t, &otlptrace.Exporter{}, got)
+
+			// 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()
+			assert.Equal(t, tc.clientType, clientType.String())
+		})
+	}
+}
+
 func TestSpanExporterOTLPOverInvalidProtocol(t *testing.T) {
 	t.Setenv("OTEL_TRACES_EXPORTER", "otlp")
 	t.Setenv("OTEL_EXPORTER_OTLP_PROTOCOL", "invalid-protocol")