我正在尝试使用paho pkg通过golang构建mqtt子客户端, 当代理断开连接时我的客户端出现问题,我认为应该丢失消息appear,但这不会发生,如果我启动代理, mqtt子客户端无法获取mqtt pub客户端发送的消息。
为什么会发生这种情况以及如何解决这个问题?
代码
package main
import (
"fmt"
"os"
mqtt "github.com/eclipse/paho.mqtt.golang"
)
var (
broker = "tcp://localhost:1883"
f mqtt.MessageHandler = func(client mqtt.Client, msg mqtt.Message) {
fmt.Printf("TOPIC: %s\n", msg.Topic())
fmt.Printf("MSG: %s\n", msg.Payload())
}
)
func main() {
//create a ClientOptions
opts := mqtt.NewClientOptions().AddBroker(broker)
opts.SetClientID("group-one")
opts.SetDefaultPublishHandler(f)
//create and start a client using the above ClientOptions
c := mqtt.NewClient(opts)
if token := c.Connect(); token.Wait() && token.Error() != nil {
panic(token.Error())
}
if token := c.Subscribe("test", 0, nil); token.Wait() && token.Error() != nil {
fmt.Println(token.Error())
os.Exit(1)
}
for {
}
}
答案 0 :(得分:5)
分配自定义OnConnectionLostHandler
以捕获连接丢失事件,这样您就可以在客户端失去连接时执行其他操作。如果将AutoReconnect
选项设置为true
(这是默认行为),则客户端将在连接丢失后自动重新连接到代理。请注意,在连接丢失后,您的订阅状态/信息可能不会被代理保存,因此您将无法接收任何消息。要解决此问题,请将主题订阅移至OnConnect
处理程序。以下是一个示例实现:
package main
import (
"fmt"
"os"
"time"
mqtt "github.com/eclipse/paho.mqtt.golang"
)
func messageHandler(c mqtt.Client, msg mqtt.Message) {
fmt.Printf("TOPIC: %s\n", msg.Topic())
fmt.Printf("MSG: %s\n", msg.Payload())
}
func connLostHandler(c mqtt.Client, err error) {
fmt.Printf("Connection lost, reason: %v\n", err)
//Perform additional action...
}
func main() {
//create a ClientOptions
opts := mqtt.NewClientOptions().
AddBroker("tcp://localhost:1883").
SetClientID("group-one").
SetDefaultPublishHandler(messageHandler).
SetConnectionLostHandler(connLostHandler)
//set OnConnect handler as anonymous function
//after connected, subscribe to topic
opts.OnConnect = func(c mqtt.Client) {
fmt.Printf("Client connected, subscribing to: test/topic\n")
//Subscribe here, otherwise after connection lost,
//you may not receive any message
if token := c.Subscribe("test/topic", 0, nil); token.Wait() && token.Error() != nil {
fmt.Println(token.Error())
os.Exit(1)
}
}
//create and start a client using the above ClientOptions
c := mqtt.NewClient(opts)
if token := c.Connect(); token.Wait() && token.Error() != nil {
panic(token.Error())
}
for {
//Lazy...
time.Sleep(500 * time.Millisecond)
}
}