Zipkin Exporter: Use default resouce's serviceName as default serivce name (#1777) (#1786)

Signed-off-by: lastchiliarch <lastchiliarch@163.com>

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

CHANGELOG.md

@@ -49,6 +49,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ### Changed
 
+- Modify Zipkin Exporter default service name, use default resouce's serviceName instead of empty. (#1777)
 - Updated Jaeger Environment Variables: `JAEGER_ENDPOINT`, `JAEGER_USER`, `JAEGER_PASSWORD`
   to `OTEL_EXPORTER_JAEGER_ENDPOINT`, `OTEL_EXPORTER_JAEGER_USER`, `OTEL_EXPORTER_JAEGER_PASSWORD` 
   in compliance with OTel spec (#1752)

exporters/trace/zipkin/model.go

@@ -21,14 +21,16 @@ import (
 	"net"
 	"strconv"
 
-	zkmodel "github.com/openzipkin/zipkin-go/model"
-
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/codes"
-	sdktrace "go.opentelemetry.io/otel/sdk/trace"
-	tracesdk "go.opentelemetry.io/otel/sdk/trace"
+	"go.opentelemetry.io/otel/sdk/resource"
 	"go.opentelemetry.io/otel/semconv"
 	"go.opentelemetry.io/otel/trace"
+
+	zkmodel "github.com/openzipkin/zipkin-go/model"
+
+	sdktrace "go.opentelemetry.io/otel/sdk/trace"
+	tracesdk "go.opentelemetry.io/otel/sdk/trace"
 )
 
 const (
@@ -39,6 +41,16 @@ const (
 	keyPeerAddress  attribute.Key = "peer.address"
 )
 
+var defaultServiceName string
+
+func init() {
+	// fetch service.name from default resource for backup
+	defaultResource := resource.Default()
+	if value, exists := defaultResource.Set().Value(semconv.ServiceNameKey); exists {
+		defaultServiceName = value.AsString()
+	}
+}
+
 func toZipkinSpanModels(batch []*tracesdk.SpanSnapshot) []zkmodel.SpanModel {
 	models := make([]zkmodel.SpanModel, 0, len(batch))
 	for _, data := range batch {
@@ -54,8 +66,7 @@ func getServiceName(attrs []attribute.KeyValue) string {
 		}
 	}
 
-	// Resource holds a default value so this might not be reach.
-	return ""
+	return defaultServiceName
 }
 
 func toZipkinSpanModel(data *tracesdk.SpanSnapshot) zkmodel.SpanModel {

exporters/trace/zipkin/model_test.go

@@ -954,10 +954,10 @@ func TestRemoteEndpointTransformation(t *testing.T) {
 
 func TestServiceName(t *testing.T) {
 	attrs := []attribute.KeyValue{}
-	assert.Empty(t, getServiceName(attrs))
+	assert.Equal(t, defaultServiceName, getServiceName(attrs))
 
 	attrs = append(attrs, attribute.String("test_key", "test_value"))
-	assert.Empty(t, getServiceName(attrs))
+	assert.Equal(t, defaultServiceName, getServiceName(attrs))
 
 	attrs = append(attrs, semconv.ServiceNameKey.String("my_service"))
 	assert.Equal(t, "my_service", getServiceName(attrs))