[distributed tracing] handling is-sampled header

tracer/contrib/tracegrpc/grpc.go

@@ -68,9 +68,10 @@ func serverSpan(t *tracer.Tracer, ctx context.Context, method, service string) *
 	span.SetMeta("gprc.method", method)
 	span.Type = "go"
 
-	traceID, parentID := getIDs(ctx)
+	traceID, parentID, isSampled := getIDs(ctx)
 	if traceID != 0 && parentID != 0 {
 		span.TraceID = traceID
+		t.Sample(span) // depends on trace ID so needs to be updated to maximize the chances we get complete traces
 		span.ParentID = parentID
 	}
 
@@ -94,14 +95,17 @@ func setIDs(span *tracer.Span, ctx context.Context) context.Context {
 }
 
 // getIDs will return ids embededd an ahe context.
-func getIDs(ctx context.Context) (traceID, parentID uint64) {
+func getIDs(ctx context.Context) (traceID, parentID uint64, isSampled bool) {
 	if md, ok := metadata.FromContext(ctx); ok {
 		if id := getID(md, traceIDKey); id > 0 {
 			traceID = id
 		}
 		if id := getID(md, parentIDKey); id > 0 {
 			parentID = id
 		}
+		if b, found := getBool(md, isSampledKey); found {
+			parentID = id
+		}
 	}
 	return traceID, parentID
 }
@@ -116,3 +120,17 @@ func getID(md metadata.MD, name string) uint64 {
 	}
 	return 0
 }
+
+// getBool gets a bool from the metadata (0 or 1 converted to bool).
+func getBool(md metadata.MD, name string) (bool, bool) {
+	for _, str := range md[name] {
+		if str == "0" {
+			return false, true
+		}
+		n, err := strconv.Atoi(str)
+		if err == nil && n > 0 {
+			return true, true
+		}
+	}
+	return true, false
+}

tracer/tracer.go

@@ -176,7 +176,7 @@ func (t *Tracer) NewRootSpan(name, service, resource string) *Span {
 	span := NewSpan(name, service, resource, spanID, spanID, 0, t)
 
 	span.buffer = newSpanBuffer(t.channels, 0, 0)
-	t.sampler.Sample(span)
+	t.Sample(span)
 	span.buffer.Push(span)
 
 	// Add the process id to all root spans
@@ -198,7 +198,7 @@ func (t *Tracer) NewChildSpan(name string, parent *Span) *Span {
 		span := NewSpan(name, "", name, spanID, spanID, spanID, t)
 
 		span.buffer = newSpanBuffer(t.channels, 0, 0)
-		t.sampler.Sample(span)
+		t.Sample(span)
 		span.buffer.Push(span)
 
 		return span
@@ -339,6 +339,11 @@ func (t *Tracer) ForceFlush() {
 	<-t.forceFlushOut
 }
 
+// Sample samples a span with the internal sampler.
+func (t *Tracer) Sample(span *Span) {
+	t.sampler.Sample(span)
+}
+
 // worker periodically flushes traces and services to the transport.
 func (t *Tracer) worker() {
 	defer t.exitWG.Done()