feat: adds support for isNoop check on spans. (openzipkin#181)

* feat: adds support for isNoop check on spans.

Span.IsNoop is specially usefull to avoid expensive operations when the tags or logs are not being recorded e.g. if you are about to read the body and process it to obtain certain tags, the check would save that computation as no changes will take effect.

* chore: fixes license year.

* chore: changes the IsNoop change into a package level function as per @basvanbeek's suggestion

IsNoop is more of the concern of the tracer and not necessarily of the span's concern, hence turning this method into a function.

middleware/grpc/server.go

@@ -1,4 +1,4 @@
-// Copyright 2019 The OpenZipkin Authors
+// Copyright 2020 The OpenZipkin Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -83,8 +83,10 @@ func (s *serverHandler) TagRPC(ctx context.Context, rti *stats.RPCTagInfo) conte
 
 	span := s.tracer.StartSpan(name, zipkin.Kind(model.Server), zipkin.Parent(sc), zipkin.RemoteEndpoint(remoteEndpointFromContext(ctx, "")))
 
-	for k, v := range s.defaultTags {
-		span.Tag(k, v)
+	if !zipkin.IsNoop(span) {
+		for k, v := range s.defaultTags {
+			span.Tag(k, v)
+		}
 	}
 
 	return zipkin.NewContext(ctx, span)

middleware/grpc/shared.go

@@ -1,4 +1,4 @@
-// Copyright 2019 The OpenZipkin Authors
+// Copyright 2020 The OpenZipkin Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -39,6 +39,9 @@ func spanName(rti *stats.RPCTagInfo) string {
 
 func handleRPC(ctx context.Context, rs stats.RPCStats) {
 	span := zipkin.SpanFromContext(ctx)
+	if zipkin.IsNoop(span) {
+		return
+	}
 
 	switch rs := rs.(type) {
 	case *stats.End:

middleware/http/server.go

@@ -1,4 +1,4 @@
-// Copyright 2019 The OpenZipkin Authors
+// Copyright 2020 The OpenZipkin Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -107,8 +107,6 @@ func (h handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	remoteEndpoint, _ := zipkin.NewEndpoint("", r.RemoteAddr)
-
 	if len(h.name) == 0 {
 		spanName = r.Method
 	} else {
@@ -120,16 +118,23 @@ func (h handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		spanName,
 		zipkin.Kind(model.Server),
 		zipkin.Parent(sc),
-		zipkin.RemoteEndpoint(remoteEndpoint),
 	)
+	// add our span to context
+	ctx := zipkin.NewContext(r.Context(), sp)
+
+	if zipkin.IsNoop(sp) {
+		// While the span is not being recorded, we still want to propagate the context.
+		h.next.ServeHTTP(w, r.WithContext(ctx))
+		return
+	}
+
+	remoteEndpoint, _ := zipkin.NewEndpoint("", r.RemoteAddr)
+	sp.SetRemoteEndpoint(remoteEndpoint)
 
 	for k, v := range h.defaultTags {
 		sp.Tag(k, v)
 	}
 
-	// add our span to context
-	ctx := zipkin.NewContext(r.Context(), sp)
-
 	// tag typical HTTP request items
 	zipkin.TagHTTPMethod.Set(sp, r.Method)
 	zipkin.TagHTTPPath.Set(sp, r.URL.Path)

middleware/http/transport.go

@@ -1,4 +1,4 @@
-// Copyright 2019 The OpenZipkin Authors
+// Copyright 2020 The OpenZipkin Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -154,6 +154,12 @@ func (t *transport) RoundTrip(req *http.Request) (res *http.Response, err error)
 		req.Context(), req.URL.Scheme+"/"+req.Method, zipkin.Kind(model.Client), zipkin.RemoteEndpoint(t.remoteEndpoint),
 	)
 
+	if zipkin.IsNoop(sp) {
+		// While the span is not being recorded, we still want to propagate the context.
+		_ = b3.InjectHTTP(req)(sp.Context())
+		return t.rt.RoundTrip(req)
+	}
+
 	for k, v := range t.defaultTags {
 		sp.Tag(k, v)
 	}

noop.go

@@ -1,4 +1,4 @@
-// Copyright 2019 The OpenZipkin Authors
+// Copyright 2020 The OpenZipkin Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -39,3 +39,10 @@ func (*noopSpan) Finish() {}
 func (*noopSpan) FinishedWithDuration(duration time.Duration) {}
 
 func (*noopSpan) Flush() {}
+
+// IsNoop tells whether the span is noop or not. Usually used to avoid resource misusage
+// when customizing a span as data won't be recorded
+func IsNoop(s Span) bool {
+	_, ok := s.(*noopSpan)
+	return ok
+}

span.go

@@ -1,4 +1,4 @@
-// Copyright 2019 The OpenZipkin Authors
+// Copyright 2020 The OpenZipkin Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.

span_implementation.go

@@ -1,4 +1,4 @@
-// Copyright 2019 The OpenZipkin Authors
+// Copyright 2020 The OpenZipkin Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.