backport from v3

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

tracer/memory/memory_test.go

@@ -27,12 +27,12 @@ func TestLoggerWithTracer(t *testing.T) {
 	logger.Error(ctx, "my test error", fmt.Errorf("error"))
 
 	if !strings.Contains(buf.String(), span.TraceID()) {
-		t.Fatalf("log does not contains tracer id: %s", buf.Bytes())
+		t.Fatalf("log does not contains trace id: %s", buf.Bytes())
 	}
 
 	_, _ = tr.Start(ctx, "test2")
 
 	for _, s := range tr.Spans() {
-		t.Logf("span %#+v\n", s)
+		_ = s
 	}
 }

tracer/tracer.go

@@ -13,6 +13,26 @@ import (
 // DefaultTracer is the global default tracer
 var DefaultTracer = NewTracer()
 
+var (
+	// TraceIDKey is the key used for the trace id in the log call
+	TraceIDKey = "trace-id"
+	// SpanIDKey is the key used for the span id in the log call
+	SpanIDKey = "span-id"
+)
+
+func init() {
+	logger.DefaultContextAttrFuncs = append(logger.DefaultContextAttrFuncs,
+		func(ctx context.Context) []interface{} {
+			if span, ok := SpanFromContext(ctx); ok {
+				return []interface{}{
+					TraceIDKey, span.TraceID(),
+					SpanIDKey, span.SpanID(),
+				}
+			}
+			return nil
+		})
+}
+
 // Tracer is an interface for distributed tracing
 type Tracer interface {
 	// Name return tracer name
@@ -52,16 +72,6 @@ type Span interface {
 	SpanID() string
 }
 
-func init() {
-	logger.DefaultContextAttrFuncs = append(logger.DefaultContextAttrFuncs, func(ctx context.Context) []interface{} {
-		span, ok := SpanFromContext(ctx)
-		if !ok || span == nil {
-			return nil
-		}
-		return []interface{}{"trace", span.TraceID(), "span", span.SpanID()}
-	})
-}
-
 // sort labels alphabeticaly by label name
 type byKey []interface{}
 
@@ -76,6 +86,7 @@ func UniqLabels(labels []interface{}) []interface{} {
 	if len(labels)%2 == 1 {
 		labels = labels[:len(labels)-1]
 	}
+
 	if len(labels) > 2 {
 		sort.Sort(byKey(labels))