golang websocket how to be notified when browser closed unexpectly

I am writing a websocket service in golang.
The program use gollira websocket to accept ws request, and in each request handler, it listen to rabbitmq queue for messages.

The problem is, when i close browser window, the handler thread is still running, i guess there is an mechanism to be notified when connection disconnected.

I try to listen to channel request.Context().Done(), when i doesn't work.

package main
import (
"fmt"
"log"
"net/http"
"github.com/gorilla/websocket"
"github.com/streadway/amqp"
)
var (
addr     = "localhost:9999"
upgrader = websocket.Upgrader{
CheckOrigin: func(r *http.Request) bool { return true },
}
)
var conn *amqp.Connection
func watch(w http.ResponseWriter, r *http.Request) {
ns := r.URL.Query().Get("ns")
if ns == "" {
return
}
c, err := upgrader.Upgrade(w, r, nil)
if err != nil {
log.Print("upgrade:", err)
return
}
defer c.Close()
ch, err := conn.Channel()
failOnError(err, "Failed to open a channel")
defer ch.Close()
err = ch.ExchangeDeclare(
"notify", // name
"fanout",           // type
true,               // durable
false,              // auto-deleted
false,              // internal
false,              // no-wait
nil,                // arguments
)
failOnError(err, "Failed to declare an exchange")
q, err := ch.QueueDeclare(
"",    // name
false, // durable
false, // delete when usused
true,  // exclusive
false, // no-wait
nil,   // arguments
)
failOnError(err, "Failed to declare a queue")
err = ch.QueueBind(
q.Name,             // queue name
ns,                 // routing key
"dsm_tasks_notify", // exchange
false,
nil)
failOnError(err, "Failed to bind a queue")
msgs, err := ch.Consume(
q.Name, // queue
"",     // consumer
true,   // auto-ack
false,  // exclusive
false,  // no-local
false,  // no-wait
nil,    // args
)
failOnError(err, "Failed to register a consumer")
for {
select {
case d := <-msgs:
err = c.WriteMessage(websocket.TextMessage, d.Body)
if err != nil {
log.Println("write:", err)
break
}
case <-r.Context().Done():
log.Println("Disconnect")
return
}
}
}
func failOnError(err error, msg string) {
if err != nil {
log.Fatalf("%s: %s", msg, err)
panic(fmt.Sprintf("%s: %s", msg, err))
}
}
func main() {
var err error
conn, err = amqp.Dial("amqp://guest:guest@localhost:5672/")
failOnError(err, "Failed to connect to RabbitMQ")
defer conn.Close()
http.HandleFunc("/watch", watch)
log.Fatal(http.ListenAndServe(addr, nil))
}

If the browser cleanly closes the connection, then read on the webssocket connection returns an error. Cleanup the websocket connection as you would on any read error.

The application must PING the connection and expect the corresponding PONGs to detect other situations. The chat example shows how to send PINGs and receive PONGs.