add a bool in payload struct

call.go

@@ -164,7 +164,11 @@ func Invoke(ctx context.Context, method string, args, reply interface{}, cc *Cli
 			return toRPCErr(err)
 		}
 		if EnableTracing {
-			c.traceInfo.tr.LazyLog(&fmtStringer{"sent: %v", []interface{}{payload{args}}}, true)
+			p := &payload{
+				sent: true,
+				msg:  args,
+			}
+			c.traceInfo.tr.LazyLog(p, true)
 		}
 		stream, err = sendRequest(ctx, cc.dopts.codec, callHdr, t, args, topts)
 		if err != nil {
@@ -183,7 +187,11 @@ func Invoke(ctx context.Context, method string, args, reply interface{}, cc *Cli
 			continue
 		}
 		if EnableTracing {
-			c.traceInfo.tr.LazyLog(&fmtStringer{"received: %v", []interface{}{payload{reply}}}, true)
+			p := &payload{
+				sent: false,
+				msg:  reply,
+			}
+			c.traceInfo.tr.LazyLog(p, true)
 		}
 		t.CloseStream(stream, lastErr)
 		if lastErr != nil {

stream.go

@@ -166,7 +166,11 @@ func (cs *clientStream) SendMsg(m interface{}) (err error) {
 	if cs.tracing {
 		cs.mu.Lock()
 		if cs.traceInfo.tr != nil {
-			cs.traceInfo.tr.LazyLog(&fmtStringer{"sent: %v", []interface{}{payload{m}}}, true)
+			p := &payload{
+				sent: true,
+				msg:  m,
+			}
+			cs.traceInfo.tr.LazyLog(p, true)
 		}
 		cs.mu.Unlock()
 	}
@@ -190,7 +194,13 @@ func (cs *clientStream) RecvMsg(m interface{}) (err error) {
 	if cs.tracing {
 		cs.mu.Lock()
 		if cs.traceInfo.tr != nil {
-			cs.traceInfo.tr.LazyLog(&fmtStringer{"received: %v", []interface{}{payload{m}}}, true)
+			if cs.traceInfo.tr != nil {
+				p := &payload{
+					sent: false,
+					msg:  m,
+				}
+				cs.traceInfo.tr.LazyLog(p, true)
+			}
 		}
 		cs.mu.Unlock()
 	}

trace.go

@@ -93,12 +93,17 @@ func (f *firstLine) String() string {
 
 // payload represents an RPC request or response payload.
 type payload struct {
-	m interface{} // e.g. a proto.Message
+	sent bool        // whether this is a request or response
+	msg  interface{} // e.g. a proto.Message
 	// TODO(dsymonds): add stringifying info to codec, and limit how much we hold here?
 }
 
 func (p payload) String() string {
-	return fmt.Sprint(p.m)
+	if p.sent {
+		return fmt.Sprintf("sent: %v", p.msg)
+	} else {
+		return fmt.Sprintf("recv: %v", p.msg)
+	}
 }
 
 type fmtStringer struct {