Fix logging of received response messages

As documented: OnRecv causes all requests received on conn to invoke
f(req, nil) and all responses to invoke f(req, resp).

Since OnRecv is called with both *Request and *Response being non-nil
when we're handling a response, we need to check that *Response is
non-nil before we check *Request is non-nil. This change just swaps the
two cases in the switch statement to fix the issue. For consistency,
I've swapped the cases for OnSend also, even when it's not needed.

conn_opt.go

@@ -43,18 +43,6 @@ func LogMessages(logger Logger) ConnOpt {
 
 		OnRecv(func(req *Request, resp *Response) {
 			switch {
-			case req != nil:
-				mu.Lock()
-				reqMethods[req.ID] = req.Method
-				mu.Unlock()
-
-				params, _ := json.Marshal(req.Params)
-				if req.Notif {
-					logger.Printf("jsonrpc2: --> notif: %s: %s\n", req.Method, params)
-				} else {
-					logger.Printf("jsonrpc2: --> request #%s: %s: %s\n", req.ID, req.Method, params)
-				}
-
 			case resp != nil:
 				var method string
 				if req != nil {
@@ -70,18 +58,22 @@ func LogMessages(logger Logger) ConnOpt {
 					err, _ := json.Marshal(resp.Error)
 					logger.Printf("jsonrpc2: --> error #%s: %s: %s\n", resp.ID, method, err)
 				}
+
+			case req != nil:
+				mu.Lock()
+				reqMethods[req.ID] = req.Method
+				mu.Unlock()
+
+				params, _ := json.Marshal(req.Params)
+				if req.Notif {
+					logger.Printf("jsonrpc2: --> notif: %s: %s\n", req.Method, params)
+				} else {
+					logger.Printf("jsonrpc2: --> request #%s: %s: %s\n", req.ID, req.Method, params)
+				}
 			}
 		})(c)
 		OnSend(func(req *Request, resp *Response) {
 			switch {
-			case req != nil:
-				params, _ := json.Marshal(req.Params)
-				if req.Notif {
-					logger.Printf("jsonrpc2: <-- notif: %s: %s\n", req.Method, params)
-				} else {
-					logger.Printf("jsonrpc2: <-- request #%s: %s: %s\n", req.ID, req.Method, params)
-				}
-
 			case resp != nil:
 				mu.Lock()
 				method := reqMethods[resp.ID]
@@ -98,6 +90,14 @@ func LogMessages(logger Logger) ConnOpt {
 					err, _ := json.Marshal(resp.Error)
 					logger.Printf("jsonrpc2: <-- error #%s: %s: %s\n", resp.ID, method, err)
 				}
+
+			case req != nil:
+				params, _ := json.Marshal(req.Params)
+				if req.Notif {
+					logger.Printf("jsonrpc2: <-- notif: %s: %s\n", req.Method, params)
+				} else {
+					logger.Printf("jsonrpc2: <-- request #%s: %s: %s\n", req.ID, req.Method, params)
+				}
 			}
 		})(c)
 	}

conn_opt_test.go

@@ -51,3 +51,80 @@ func TestSetLogger(t *testing.T) {
 		t.Fatalf("got %q, want %q", got, want)
 	}
 }
+
+type dummyHandler struct {
+	t *testing.T
+}
+
+func (h *dummyHandler) Handle(ctx context.Context, conn *jsonrpc2.Conn, req *jsonrpc2.Request) {
+	if !req.Notif {
+		err := conn.Reply(ctx, req.ID, nil)
+		if err != nil {
+			h.t.Error(err)
+			return
+		}
+	}
+}
+
+func TestLogMessages(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	rd, wr := io.Pipe()
+	defer rd.Close()
+	defer wr.Close()
+
+	buf := bufio.NewReader(rd)
+	logger := log.New(wr, "", log.Lmsgprefix)
+
+	a, b := net.Pipe()
+	connA := jsonrpc2.NewConn(
+		ctx,
+		jsonrpc2.NewBufferedStream(a, jsonrpc2.VSCodeObjectCodec{}),
+		&dummyHandler{t},
+		jsonrpc2.LogMessages(logger),
+	)
+	connB := jsonrpc2.NewConn(
+		ctx,
+		jsonrpc2.NewBufferedStream(b, jsonrpc2.VSCodeObjectCodec{}),
+		&dummyHandler{t},
+	)
+	defer connA.Close()
+	defer connB.Close()
+
+	go func() {
+		if err := connA.Call(ctx, "method1", nil, nil); err != nil {
+			t.Error(err)
+			return
+		}
+		if err := connB.Call(ctx, "method2", nil, nil); err != nil {
+			t.Error(err)
+			return
+		}
+		if err := connA.Notify(ctx, "notification1", nil); err != nil {
+			t.Error(err)
+			return
+		}
+		if err := connB.Notify(ctx, "notification2", nil); err != nil {
+			t.Error(err)
+			return
+		}
+	}()
+
+	for i, want := range []string{
+		"jsonrpc2: <-- request #0: method1: null\n",
+		"jsonrpc2: --> result #0: method1: null\n",
+		"jsonrpc2: --> request #0: method2: null\n",
+		"jsonrpc2: <-- result #0: method2: null\n",
+		"jsonrpc2: <-- notif: notification1: null\n",
+		"jsonrpc2: --> notif: notification2: null\n",
+	} {
+		got, err := buf.ReadString('\n')
+		if err != nil {
+			t.Fatal(err)
+		}
+		if got != want {
+			t.Errorf("message %v: got %q, want %q", i, got, want)
+		}
+	}
+}