Do not add invalid context to references (#521)

* Do not add invalid context to references

Signed-off-by: Yuri Shkuro <ys@uber.com>

* Rename helper

Signed-off-by: Yuri Shkuro <ys@uber.com>

span_context.go

@@ -212,10 +212,14 @@ func (c SpanContext) SetFirehose() {
 }
 
 func (c SpanContext) String() string {
+	var flags int32
+	if c.samplingState != nil {
+		flags = c.samplingState.stateFlags.Load()
+	}
 	if c.traceID.High == 0 {
-		return fmt.Sprintf("%016x:%016x:%016x:%x", c.traceID.Low, uint64(c.spanID), uint64(c.parentID), c.samplingState.stateFlags.Load())
+		return fmt.Sprintf("%016x:%016x:%016x:%x", c.traceID.Low, uint64(c.spanID), uint64(c.parentID), flags)
 	}
-	return fmt.Sprintf("%016x%016x:%016x:%016x:%x", c.traceID.High, c.traceID.Low, uint64(c.spanID), uint64(c.parentID), c.samplingState.stateFlags.Load())
+	return fmt.Sprintf("%016x%016x:%016x:%016x:%x", c.traceID.High, c.traceID.Low, uint64(c.spanID), uint64(c.parentID), flags)
 }
 
 // ContextFromString reconstructs the Context encoded in a string

tracer.go

@@ -216,10 +216,10 @@ func (t *Tracer) startSpanWithOptions(
 		options.StartTime = t.timeNow()
 	}
 
-	// Predicate whether the given span context is a valid reference
-	// which may be used as parent / debug ID / baggage items source
-	isValidReference := func(ctx SpanContext) bool {
-		return ctx.IsValid() || ctx.isDebugIDContainerOnly() || len(ctx.baggage) != 0
+	// Predicate whether the given span context is an empty reference
+	// or may be used as parent / debug ID / baggage items source
+	isEmptyReference := func(ctx SpanContext) bool {
+		return !ctx.IsValid() && !ctx.isDebugIDContainerOnly() && len(ctx.baggage) == 0
 	}
 
 	var references []Reference
@@ -235,7 +235,7 @@ func (t *Tracer) startSpanWithOptions(
 				reflect.ValueOf(ref.ReferencedContext)))
 			continue
 		}
-		if !isValidReference(ctxRef) {
+		if isEmptyReference(ctxRef) {
 			continue
 		}
 
@@ -245,14 +245,17 @@ func (t *Tracer) startSpanWithOptions(
 			continue
 		}
 
-		references = append(references, Reference{Type: ref.Type, Context: ctxRef})
+		if ctxRef.IsValid() {
+			// we don't want empty context that contains only debug-id or baggage
+			references = append(references, Reference{Type: ref.Type, Context: ctxRef})
+		}
 
 		if !hasParent {
 			parent = ctxRef
 			hasParent = ref.Type == opentracing.ChildOfRef
 		}
 	}
-	if !hasParent && isValidReference(parent) {
+	if !hasParent && !isEmptyReference(parent) {
 		// If ChildOfRef wasn't found but a FollowFromRef exists, use the context from
 		// the FollowFromRef as the parent
 		hasParent = true

tracer_test.go

@@ -414,6 +414,7 @@ func TestThrottling_DebugHeader(t *testing.T) {
 
 	sp := tracer.StartSpan("root", opentracing.ChildOf(ctx)).(*Span)
 	assert.True(t, sp.context.IsDebug())
+	assert.Len(t, sp.References(), 0)
 	closer.Close()
 
 	tracer, closer = NewTracer("DOOP", NewConstSampler(true), NewNullReporter(),