Made public traceparent/tracestate marshal/unmarshal

plugin/ochttp/propagation/tracecontext/propagation.go

@@ -47,11 +47,17 @@ type HTTPFormat struct{}
 
 // SpanContextFromRequest extracts a span context from incoming requests.
 func (f *HTTPFormat) SpanContextFromRequest(req *http.Request) (sc trace.SpanContext, ok bool) {
-	h, ok := getRequestHeader(req, traceparentHeader, false)
-	if !ok {
+	tp, _ := getRequestHeader(req, traceparentHeader, false)
+	ts, _ := getRequestHeader(req, tracestateHeader, true)
+	return f.SpanContextFromHeaders(tp, ts)
+}
+
+// SpanContextFromHeaders extracts a span context from provided header values.
+func (f *HTTPFormat) SpanContextFromHeaders(tp string, ts string) (sc trace.SpanContext, ok bool) {
+	if tp == "" {
 		return trace.SpanContext{}, false
 	}
-	sections := strings.Split(h, "-")
+	sections := strings.Split(tp, "-")
 	if len(sections) < 4 {
 		return trace.SpanContext{}, false
 	}
@@ -101,7 +107,7 @@ func (f *HTTPFormat) SpanContextFromRequest(req *http.Request) (sc trace.SpanCon
 		return trace.SpanContext{}, false
 	}
 
-	sc.Tracestate = tracestateFromRequest(req)
+	sc.Tracestate = tracestateFromRequest(ts)
 	return sc, true
 }
 
@@ -128,14 +134,13 @@ func getRequestHeader(req *http.Request, name string, commaSeparated bool) (hdr
 // are resolved.
 // https://github.com/w3c/distributed-tracing/issues/172
 // https://github.com/w3c/distributed-tracing/issues/175
-func tracestateFromRequest(req *http.Request) *tracestate.Tracestate {
-	h, _ := getRequestHeader(req, tracestateHeader, true)
-	if h == "" {
+func tracestateFromRequest(ts string) *tracestate.Tracestate {
+	if ts == "" {
 		return nil
 	}
 
 	var entries []tracestate.Entry
-	pairs := strings.Split(h, ",")
+	pairs := strings.Split(ts, ",")
 	hdrLenWithoutOWS := len(pairs) - 1 // Number of commas
 	for _, pair := range pairs {
 		matches := trimOWSRegExp.FindStringSubmatch(pair)
@@ -153,15 +158,15 @@ func tracestateFromRequest(req *http.Request) *tracestate.Tracestate {
 		}
 		entries = append(entries, tracestate.Entry{Key: kv[0], Value: kv[1]})
 	}
-	ts, err := tracestate.New(nil, entries...)
+	tsParsed, err := tracestate.New(nil, entries...)
 	if err != nil {
 		return nil
 	}
 
-	return ts
+	return tsParsed
 }
 
-func tracestateToRequest(sc trace.SpanContext, req *http.Request) {
+func tracestateToRequest(sc trace.SpanContext) string {
 	var pairs = make([]string, 0, len(sc.Tracestate.Entries()))
 	if sc.Tracestate != nil {
 		for _, entry := range sc.Tracestate.Entries() {
@@ -170,18 +175,28 @@ func tracestateToRequest(sc trace.SpanContext, req *http.Request) {
 		h := strings.Join(pairs, ",")
 
 		if h != "" && len(h) <= maxTracestateLen {
-			req.Header.Set(tracestateHeader, h)
+			return h
 		}
 	}
+	return ""
 }
 
-// SpanContextToRequest modifies the given request to include traceparent and tracestate headers.
-func (f *HTTPFormat) SpanContextToRequest(sc trace.SpanContext, req *http.Request) {
-	h := fmt.Sprintf("%x-%x-%x-%x",
+// SpanContextToHeaders serialize the SpanContext to traceparent and tracestate headers.
+func (f *HTTPFormat) SpanContextToHeaders(sc trace.SpanContext) (tp string, ts string) {
+	tp = fmt.Sprintf("%x-%x-%x-%x",
 		[]byte{supportedVersion},
 		sc.TraceID[:],
 		sc.SpanID[:],
 		[]byte{byte(sc.TraceOptions)})
-	req.Header.Set(traceparentHeader, h)
-	tracestateToRequest(sc, req)
+	ts = tracestateToRequest(sc)
+	return
+}
+
+// SpanContextToRequest modifies the given request to include traceparent and tracestate headers.
+func (f *HTTPFormat) SpanContextToRequest(sc trace.SpanContext, req *http.Request) {
+	tp, ts := f.SpanContextToHeaders(sc)
+	req.Header.Set(traceparentHeader, tp)
+	if ts != "" {
+		req.Header.Set(tracestateHeader, ts)
+	}
 }