bugfix(client): Fix the panic due to concurrent writing (#180)

The bug:
	panic: concurrent write to websocket connection
	goroutine 66624 [running]:
	github.com/gorilla/websocket.(*messageWriter).flushFrame(0xc001ad7ef0, 0x1, {0x0?, 0x0?, 0x0?})
		/home/streampanel/go/pkg/mod/github.com/gorilla/[email protected]/conn.go:617 +0x4b8
	github.com/gorilla/websocket.(*messageWriter).Close(0xc001e12f60?)
		/home/streampanel/go/pkg/mod/github.com/gorilla/[email protected]/conn.go:731 +0x35
	github.com/gorilla/websocket.(*Conn).beginMessage(0xc001e034a0, 0xc001e12f60, 0x8)
		/home/streampanel/go/pkg/mod/github.com/gorilla/[email protected]/conn.go:480 +0x3a
	github.com/gorilla/websocket.(*Conn).NextWriter(0xc001e034a0, 0x8)
		/home/streampanel/go/pkg/mod/github.com/gorilla/[email protected]/conn.go:520 +0x3f
	github.com/gorilla/websocket.(*Conn).WriteMessage(0x37d2cb0?, 0x1e5f71c?, {0xc000945490, 0x5, 0x5})
		/home/streampanel/go/pkg/mod/github.com/gorilla/[email protected]/conn.go:773 +0x137
	github.com/andreykaipov/goobs.(*Client).Disconnect(0xc001c26fc0)
		/home/streampanel/go/pkg/mod/github.com/xaionaro-go/[email protected]/client.go:123 +0xe5

The documentation of github.com/gorilla/websocket explicitly forbids concurrent writing and reading.
See section "Concurrency" in:

	https://pkg.go.dev/github.com/gorilla/websocket#hdr-Concurrency

client.go

@@ -32,6 +32,8 @@ type Client struct {
 	Categories
 
 	conn               *websocket.Conn
+	connWLocker        sync.Mutex
+	connRLocker        sync.Mutex
 	scheme             string
 	host               string
 	password           string
@@ -120,7 +122,7 @@ func (c *Client) Disconnect() error {
 	c.client.Log.Printf("[DEBUG] Sending disconnect message")
 	c.markDisconnected()
 
-	if err := c.conn.WriteMessage(
+	if err := c.writeMessage(
 		websocket.CloseMessage,
 		websocket.FormatCloseMessage(websocket.CloseNormalClosure, "Bye"),
 	); err != nil {
@@ -131,6 +133,15 @@ func (c *Client) Disconnect() error {
 	return nil
 }
 
+func (c *Client) writeMessage(messageType int, data []byte) error {
+	c.connWLocker.Lock()
+	defer c.connWLocker.Unlock()
+	return c.conn.WriteMessage(
+		messageType,
+		data,
+	)
+}
+
 func (c *Client) markDisconnected() {
 	c.once.Do(func() {
 		select {
@@ -222,13 +233,19 @@ func (c *Client) connect() (err error) {
 	}
 }
 
+func (c *Client) readJSON(v any) error {
+	c.connRLocker.Lock()
+	defer c.connRLocker.Unlock()
+	return c.conn.ReadJSON(v)
+}
+
 // translates raw server messages into opcodes
 func (c *Client) handleRawServerMessages(auth chan<- error) {
 	defer c.client.Log.Printf("[TRACE] Finished handling raw server messages")
 
 	for {
 		raw := json.RawMessage{}
-		if err := c.conn.ReadJSON(&raw); err != nil {
+		if err := c.readJSON(&raw); err != nil {
 			switch t := err.(type) {
 			case *json.UnmarshalTypeError:
 				c.client.Log.Printf("[ERROR] Reading from connection: %s: %s", t, raw)
@@ -323,7 +340,7 @@ func (c *Client) handleOpcodes(auth chan<- error) {
 			c.client.Log.Printf("[INFO] Identify;")
 
 			msg := opcodes.Wrap(val).Bytes()
-			if err := c.conn.WriteMessage(websocket.TextMessage, msg); err != nil {
+			if err := c.writeMessage(websocket.TextMessage, msg); err != nil {
 				auth <- fmt.Errorf("sending Identify to server `%s`: %w", msg, err)
 			}
 
@@ -354,7 +371,7 @@ func (c *Client) handleOpcodes(auth chan<- error) {
 			c.client.Log.Printf("[TRACE] Got %s Request with ID %s", val.Type, val.ID)
 
 			msg := opcodes.Wrap(val).Bytes()
-			if err := c.conn.WriteMessage(websocket.TextMessage, msg); err != nil {
+			if err := c.writeMessage(websocket.TextMessage, msg); err != nil {
 				c.client.Log.Printf("[ERROR] Sending Request to server `%s`: %s", msg, err)
 			}