Add mutex to prevent concurrent connection write

examples/chat/client.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"log"
 	"net/http"
+	"sync"
 	"time"
 
 	"github.com/gorilla/websocket"
@@ -46,6 +47,9 @@ type Client struct {
 
 	// Buffered channel of outbound messages.
 	send chan []byte
+
+	// Mutex to prevent concurrent connection write
+	mu sync.Mutex
 }
 
 // readPump pumps messages from the websocket connection to the hub.
@@ -72,6 +76,8 @@ func (c *Client) readPump() {
 
 // write writes a message with the given message type and payload.
 func (c *Client) write(mt int, payload []byte) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
 	c.conn.SetWriteDeadline(time.Now().Add(writeWait))
 	return c.conn.WriteMessage(mt, payload)
 }