Zipkin Exporter: Use default resouce's serviceName as default serivce…

… name (open-telemetry#1777)

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

exporters/trace/zipkin/model.go

@@ -18,6 +18,7 @@ import (
 	"encoding/binary"
 	"encoding/json"
 	"fmt"
+	"go.opentelemetry.io/otel/sdk/resource"
 	"net"
 	"strconv"
 
@@ -54,8 +55,13 @@ func getServiceName(attrs []attribute.KeyValue) string {
 		}
 	}
 
-	// Resource holds a default value so this might not be reach.
-	return ""
+	// Fetch default service.name from default resource for backup
+	var defaultServiceName string
+	defaultResource := resource.Default()
+	if value, exists := defaultResource.Set().Value(semconv.ServiceNameKey); exists {
+		defaultServiceName = value.AsString()
+	}
+	return defaultServiceName
 }
 
 func toZipkinSpanModel(data *tracesdk.SpanSnapshot) zkmodel.SpanModel {

exporters/trace/zipkin/model_test.go

@@ -953,11 +953,12 @@ func TestRemoteEndpointTransformation(t *testing.T) {
 }
 
 func TestServiceName(t *testing.T) {
+	defaultServiceName := "unknown_service:___TestServiceName_in_go_opentelemetry_io_otel_exporters_trace_zipkin"
 	attrs := []attribute.KeyValue{}
-	assert.Empty(t, getServiceName(attrs))
+	assert.Equal(t, getServiceName(attrs), defaultServiceName)
 
 	attrs = append(attrs, attribute.String("test_key", "test_value"))
-	assert.Empty(t, getServiceName(attrs))
+	assert.Equal(t, getServiceName(attrs), defaultServiceName)
 
 	attrs = append(attrs, semconv.ServiceNameKey.String("my_service"))
 	assert.Equal(t, "my_service", getServiceName(attrs))