feat(interceptor.go): add logging of span context trace ID and span ID

refactor(connect_service.go): rename GetBalance method to Call to improve semantics
feat(utils.go): add utility functions to convert span context to and from binary format for tracing purposes

connect/interceptor.go

@@ -17,7 +17,10 @@ func InjectTraceContext() connect.UnaryInterceptorFunc {
 		) (connect.AnyResponse, error) {
 			if !req.Spec().IsClient {
 				log.Println(req.Header())
-				log.Println(req.Header().Get(trace.TraceparentHeader))
+				log.Println(req.Header().Get(trace.GrpcTraceBinHeader))
+				t := req.Header().Get(trace.GrpcTraceBinHeader)
+				sc, ok := trace.SpanContextFromBinary([]byte(t))
+				log.Println(sc.TraceID(), sc.SpanID(), ok)
 			}
 			return next(ctx, req)
 		})

connect_service.go

@@ -34,7 +34,7 @@ func NewConnectService(cfg Config, caller Callee) error {
 	)
 }
 
-func (s *connectService) GetBalance(
+func (s *connectService) Call(
 	ctx context.Context,
 	req *connect.Request[example.CallRequest],
 ) (*connect.Response[example.CallResponse], error) {

trace/utils.go

@@ -0,0 +1,50 @@
+package trace
+
+import "go.opentelemetry.io/otel/trace"
+
+var emptySpanContext trace.SpanContext
+
+// BinaryFromSpanContext returns the binary format representation of a SpanContext.
+//
+// If sc is the zero value, Binary returns nil.
+func BinaryFromSpanContext(sc trace.SpanContext) []byte {
+	traceID := sc.TraceID()
+	spanID := sc.SpanID()
+	traceFlags := sc.TraceFlags()
+	if sc.Equal(emptySpanContext) {
+		return nil
+	}
+	var b [29]byte
+	copy(b[2:18], traceID[:])
+	b[18] = 1
+	copy(b[19:27], spanID[:])
+	b[27] = 2
+	b[28] = uint8(traceFlags)
+	return b[:]
+}
+
+// SpanContextFromBinary returns the SpanContext represented by b.
+//
+// If b has an unsupported version ID or contains no TraceID, SpanContextFromBinary returns with ok==false.
+func SpanContextFromBinary(b []byte) (sc trace.SpanContext, ok bool) {
+	var scConfig trace.SpanContextConfig
+	if len(b) == 0 || b[0] != 0 {
+		return trace.SpanContext{}, false
+	}
+	b = b[1:]
+	if len(b) >= 17 && b[0] == 0 {
+		copy(scConfig.TraceID[:], b[1:17])
+		b = b[17:]
+	} else {
+		return trace.SpanContext{}, false
+	}
+	if len(b) >= 9 && b[0] == 1 {
+		copy(scConfig.SpanID[:], b[1:9])
+		b = b[9:]
+	}
+	if len(b) >= 2 && b[0] == 2 {
+		scConfig.TraceFlags = trace.TraceFlags(b[1])
+	}
+	sc = trace.NewSpanContext(scConfig)
+	return sc, true
+}