MM-25516: Changed to byte slice instead of string for cluster messages (#17998)

* MM-25516: Changed to byte slice instead of string for cluster messages

https://mattermost.atlassian.net/browse/MM-25116

Testing:
Manually tested.
Load-tested with Cluster Controller.

I looked into changing the serialization method to use msgpack,
but the ClusterMessage struct was mainly used for only 3 fields
which didn't lead to much of a CPU time improvement, whereas
actually led to more allocations using msgpack. Hence, I chose
to remain with JSON.

```
name              old time/op    new time/op    delta
ClusterMarshal-8    3.51µs ± 1%    3.10µs ± 2%  -11.59%  (p=0.000 n=9+10)

name              old alloc/op   new alloc/op   delta
ClusterMarshal-8      776B ± 0%     1000B ± 0%  +28.87%  (p=0.000 n=10+10)

name              old allocs/op  new allocs/op  delta
ClusterMarshal-8      12.0 ± 0%      13.0 ± 0%   +8.33%  (p=0.000 n=10+10)
```

```release-note
Changed the field type of Data in model.ClusterMessage to []byte from string.
```

* Trigger CI
```release-note
NONE
```

model/cluster_message.go

@@ -3,11 +3,6 @@
 
 package model
 
-import (
-	"encoding/json"
-	"io"
-)
-
 type ClusterEvent string
 
 const (
@@ -62,17 +57,6 @@ type ClusterMessage struct {
 	Event            ClusterEvent      `json:"event"`
 	SendType         string            `json:"-"`
 	WaitForAllToSend bool              `json:"-"`
-	Data             string            `json:"data,omitempty"`
+	Data             []byte            `json:"data,omitempty"`
 	Props            map[string]string `json:"props,omitempty"`
 }
-
-func (o *ClusterMessage) ToJson() string {
-	b, _ := json.Marshal(o)
-	return string(b)
-}
-
-func ClusterMessageFromJson(data io.Reader) *ClusterMessage {
-	var o *ClusterMessage
-	json.NewDecoder(data).Decode(&o)
-	return o
-}

model/cluster_message_test.go

@@ -1,27 +0,0 @@
-// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
-// See LICENSE.txt for license information.
-
-package model
-
-import (
-	"strings"
-	"testing"
-
-	"github.com/stretchr/testify/require"
-)
-
-func TestClusterMessage(t *testing.T) {
-	m := ClusterMessage{
-		Event:    ClusterEventPublish,
-		SendType: ClusterSendBestEffort,
-		Data:     "hello",
-	}
-	json := m.ToJson()
-	result := ClusterMessageFromJson(strings.NewReader(json))
-
-	require.Equal(t, "hello", result.Data)
-
-	badresult := ClusterMessageFromJson(strings.NewReader("junk"))
-
-	require.Nil(t, badresult, "should not have parsed")
-}

model/websocket_message.go

@@ -77,7 +77,7 @@ const (
 )
 
 type WebSocketMessage interface {
-	ToJson() string
+	ToJson() []byte
 	IsValid() bool
 	EventType() string
 }
@@ -199,9 +199,9 @@ func (ev *WebSocketEvent) EventType() string {
 	return ev.event
 }
 
-func (ev *WebSocketEvent) ToJson() string {
+func (ev *WebSocketEvent) ToJson() []byte {
 	if ev.precomputedJSON != nil {
-		return fmt.Sprintf(`{"event": %s, "data": %s, "broadcast": %s, "seq": %d}`, ev.precomputedJSON.Event, ev.precomputedJSON.Data, ev.precomputedJSON.Broadcast, ev.GetSequence())
+		return []byte(fmt.Sprintf(`{"event": %s, "data": %s, "broadcast": %s, "seq": %d}`, ev.precomputedJSON.Event, ev.precomputedJSON.Data, ev.precomputedJSON.Broadcast, ev.GetSequence()))
 	}
 	b, _ := json.Marshal(webSocketEventJSON{
 		ev.event,
@@ -209,7 +209,7 @@ func (ev *WebSocketEvent) ToJson() string {
 		ev.broadcast,
 		ev.sequence,
 	})
-	return string(b)
+	return b
 }
 
 // Encode encodes the event to the given encoder.
@@ -280,9 +280,9 @@ func (m *WebSocketResponse) EventType() string {
 	return WebsocketEventResponse
 }
 
-func (m *WebSocketResponse) ToJson() string {
+func (m *WebSocketResponse) ToJson() []byte {
 	b, _ := json.Marshal(m)
-	return string(b)
+	return b
 }
 
 func WebSocketResponseFromJson(data io.Reader) *WebSocketResponse {

model/websocket_message_test.go

@@ -4,7 +4,7 @@
 package model
 
 import (
-	"strings"
+	"bytes"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -20,7 +20,7 @@ func TestWebSocketEvent(t *testing.T) {
 	}
 	m.Add("user", user)
 	json := m.ToJson()
-	result := WebSocketEventFromJson(strings.NewReader(json))
+	result := WebSocketEventFromJson(bytes.NewReader(json))
 
 	require.True(t, m.IsValid(), "should be valid")
 	require.Equal(t, m.GetBroadcast().TeamId, result.GetBroadcast().TeamId, "Team ids do not match")
@@ -73,10 +73,10 @@ func TestWebSocketEventImmutable(t *testing.T) {
 }
 
 func TestWebSocketEventFromJson(t *testing.T) {
-	ev := WebSocketEventFromJson(strings.NewReader("junk"))
+	ev := WebSocketEventFromJson(bytes.NewReader([]byte("junk")))
 	require.Nil(t, ev, "should not have parsed")
-	data := `{"event": "test", "data": {"key": "val"}, "seq": 45, "broadcast": {"user_id": "userid"}}`
-	ev = WebSocketEventFromJson(strings.NewReader(data))
+	data := []byte(`{"event": "test", "data": {"key": "val"}, "seq": 45, "broadcast": {"user_id": "userid"}}`)
+	ev = WebSocketEventFromJson(bytes.NewReader(data))
 	require.NotNil(t, ev, "should have parsed")
 	require.Equal(t, ev.EventType(), "test")
 	require.Equal(t, ev.GetSequence(), int64(45))
@@ -89,11 +89,11 @@ func TestWebSocketResponse(t *testing.T) {
 	e := NewWebSocketError(1, &AppError{})
 	m.Add("RootId", NewId())
 	json := m.ToJson()
-	result := WebSocketResponseFromJson(strings.NewReader(json))
+	result := WebSocketResponseFromJson(bytes.NewReader(json))
 	json2 := e.ToJson()
-	WebSocketResponseFromJson(strings.NewReader(json2))
+	WebSocketResponseFromJson(bytes.NewReader(json2))
 
-	badresult := WebSocketResponseFromJson(strings.NewReader("junk"))
+	badresult := WebSocketResponseFromJson(bytes.NewReader([]byte("junk")))
 	require.Nil(t, badresult, "should not have parsed")
 
 	require.True(t, m.IsValid(), "should be valid")
@@ -109,10 +109,10 @@ func TestWebSocketEvent_PrecomputeJSON(t *testing.T) {
 	event.PrecomputeJSON()
 	after := event.ToJson()
 
-	assert.JSONEq(t, before, after)
+	assert.Equal(t, before, after)
 }
 
-var stringSink string
+var stringSink []byte
 
 func BenchmarkWebSocketEvent_ToJson(b *testing.B) {
 	event := NewWebSocketEvent(WebsocketEventPosted, "foo", "bar", "baz", nil)