[opentracing] back reference from SpanContext to Span

opentracing/context.go

@@ -7,6 +7,7 @@ type SpanContext struct {
 	spanID   uint64
 	parentID uint64
 	sampled  bool
+	span     *Span
 	baggage  map[string]string
 }
 
@@ -34,5 +35,12 @@ func (c SpanContext) WithBaggageItem(key, val string) SpanContext {
 		newBaggage[key] = val
 	}
 	// Use positional parameters so the compiler will help catch new fields.
-	return SpanContext{c.traceID, c.spanID, c.parentID, c.sampled, newBaggage}
+	return SpanContext{
+		traceID:  c.traceID,
+		spanID:   c.spanID,
+		parentID: c.parentID,
+		sampled:  c.sampled,
+		span:     c.span,
+		baggage:  newBaggage,
+	}
 }

opentracing/span.go

@@ -100,9 +100,21 @@ func (s *Span) Log(data ot.LogData) {
 
 // NewSpan is the OpenTracing Span constructor
 func NewSpan(operationName string) *Span {
-	return &Span{
-		Span: &datadog.Span{
-			Name: operationName,
+	span := &datadog.Span{
+		Name: operationName,
+	}
+
+	otSpan := &Span{
+		Span: span,
+		context: SpanContext{
+			traceID:  span.TraceID,
+			spanID:   span.SpanID,
+			parentID: span.ParentID,
+			sampled:  span.Sampled,
 		},
 	}
+
+	// SpanContext is propagated and used to create children
+	otSpan.context.span = otSpan
+	return otSpan
 }