Use the Paho MQTT Go client - Best Practices| Alibaba Cloud Documentation Center

Prepare the development environment

Install the Go language package.

On macOS, run the following command:
```
brew install go
```
On Ubuntu, run the following command:
```
sudo apt-get install golang-go
```
On Windows, download the installation package from the Go official website and install the Go language package.

Note If you are in the Chinese mainland, you must use a virtual private network (VPN) to access the Go official website.

Download the Paho MQTT library for Go

For more information about the Paho project and supported programming languages, see Eclipse Paho Downloads.

Run the following commands to download the Paho MQTT library for Go and the related dependencies:

go get github.com/eclipse/paho.mqtt.golang
go get github.com/gorilla/websocket
go get golang.org/x/net/proxy

Connect the client to IoT Platform

Click MqttSign.go and copy the source code that is provided by Alibaba Cloud to obtain the MQTT connection parameters. Then, create the MqttSign.go file on premises and paste the code to the file.

The MqttSign.go file defines the function to obtain the MQTT connection parameters. You must call this function to connect your client with IoT Platform.

Definition:

type AuthInfo struct {
    password, username, mqttClientId string;
}

func calculate_sign(clientId, productKey, deviceName, deviceSecret, timeStamp string) AuthInfo;

Description:
This function is used to obtain the following MQTT connection parameters: username, password, and mqttClientId.

Input parameters:


Parameter	Type	Description
productKey	String	The ProductKey of the product to which the device belongs. This parameter is used to identify the device in IoT Platform.
deviceName	String	The DeviceName of the device. This parameter is used to identify the device in IoT Platform.
deviceSecret	String	The DeviceSecret of the device. This parameter is used to identify the device in IoT Platform.
clientId	String	The ID of the device. The ID can contain up to 64 characters in length. We recommend that you use the MAC address or serial number (SN) of the device as the ID.
timeStamp	String	The timestamp that indicates the current time, in milliseconds.

Output parameters:

This function returns an AuthInfo structure that contains the parameters that are described in the following table.


Parameter	Type	Description
username	String	The username that is used to establish the MQTT connection.
password	String	The password that is used to establish the MQTT connection.
mqttClientId	String	The ID of the MQTT client.

Add a program file that can connect a device to IoT Platform.

To obtain MQTT connection parameters, you must write a program to call the function in the MqttSign.go file.

This section provides the development instructions and sample code.

Specify the device information.

// set the device info, include product key, device name, and device secret
    var productKey string = "a1Zd7n5***"
    var deviceName string = "testdevice"
    var deviceSecret string = "UrwclDV33NaFSmk0JaBxNTqgSrJW****"

    // set timestamp, clientid, subscribe topic and publish topic
    var timeStamp string = "1528018257135"
    var clientId string = "192.168.****"
    var subTopic string = "/" + productKey + "/" + deviceName + "/user/get";
    var pubTopic string = "/" + productKey + "/" + deviceName + "/user/update";

Specify the MQTT connection information.
Call the calculate_sign() function in MqttSign.go file. This function returns the username, password, and mqttClientId parameters based on the clientId, productKey, deviceName, deviceSecret, and timeStamp input parameters. Then, add the result to the opts structure.
```
    // set the login broker url
    var raw_broker bytes.Buffer
    raw_broker.WriteString("tls://")
    raw_broker.WriteString(productKey)
    raw_broker.WriteString(".iot-as-mqtt.cn-shanghai.aliyuncs.com:1883")
    opts := MQTT.NewClientOptions().AddBroker(raw_broker.String());

    // calculate the login auth info, and set it into the connection options
    auth := calculate_sign(clientId, productKey, deviceName, deviceSecret, timeStamp)
    opts.SetClientID(auth.mqttClientId)
    opts.SetUsername(auth.username)
    opts.SetPassword(auth.password)
    opts.SetKeepAlive(60 * 2 * time.Second)
    opts.SetDefaultPublishHandler(f)
```
Notice
- If you are using public instances, replace cn-shanghai in raw_broker.WriteString(".iot-as-mqtt.cn-shanghai.aliyuncs.com:1883") with the ID of the region in which your device resides. For more information about region IDs, see Regions and zones.
- If you are using Enterprise Edition instances, replace raw_broker.String() in opts := MQTT.NewClientOptions().AddBroker(raw_broker.String()); with <Endpoint of MQTT>:1833. Example: opts := MQTT.NewClientOptions().AddBroker("iot-***.mqtt.iothub.aliyuncs.com:1883");.
  To obtain the MQTT endpoint, perform the following steps: Log on to the IoT Platform. On the Overview page, click the card of the instance that you want to manage. The MQTT endpoint is displayed on the Instance Details page. For more information, see View the endpoint of an instance.
For more information about instances, see Overview.

Call the Connect() function to connect the MQTT client with IoT Platform.

    // 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())
    }
    fmt.Print("Connect aliyun IoT Cloud Success\n");

Call the Publish() function to publish messages. You must specify the topic to which messages are published and the payloads of the messages.

    // publish 5 messages to pubTopic("/a1Zd7n5****/deng/user/update")
    for i := 0; i < 5; i++ {
        fmt.Println("publish msg:", i)
        text := fmt.Sprintf("ABC #%d", i)
        token := c.Publish(pubTopic, 0, false, text)
        fmt.Println("publish msg: ", text)
        token.Wait()
        time.Sleep(2 * time.Second)
    }

For more information about topics, see What is a topic?.

Call the Subscribe() function to subscribe to the topic and receive messages from IoT Platform.

    // subscribe to subTopic("/a1Zd7n5***/deng/user/get") and request messages to be delivered
    if token := c.Subscribe(subTopic, 0, nil); token.Wait() && token.Error() != nil {
        fmt.Println(token.Error())
        os.Exit(1)
    }
    fmt.Print("Subscribe topic " + subTopic + " success\n");

For more information about the communication methods of devices, servers, and IoT Platform, see Overview.

Compile the project.

Sample code

You can use the sample code to connect to IoT Platform.

Download and decompress the demo package.

The following table describes the files that are contained in the aiot-go-demo package.


File	Description
MqttSign.go	This file contains the code that is used to obtain the MQTT connection parameters. When you execute the iot.go file, the calculate_sign() function is called to obtain the username, password, and mqttClientId parameters.
iot.go	This file contains the logic code that is used to connect to and communicate with IoT Platform.
x509	The root certificate of IoT Platform. This certificate is required to connect devices with IoT Platform.

In the iot.go file, replace the device information with your device information.
You can use tools such as Linux vi to modify the iot.go file.
- Replace the values of the productKey, deviceName, and deviceSecret parameters with your device certificate information.
- Optional. Configure the timeStamp and clientId parameters. You can replace the value of the clientId parameter with the MAC address or SN of your device.
  If you do not configure the two parameters, you can still connect to IoT Platform. However, we recommend that you replace the values of the parameters with actual values.
- - If you are using public instances, replace cn-shanghai in raw_broker.WriteString(".iot-as-mqtt.cn-shanghai.aliyuncs.com:1883") with the ID of the region in which your device resides.
  - If you are using Enterprise Edition instances, replace raw_broker.String() in opts := MQTT.NewClientOptions().AddBroker(raw_broker.String()); with <Endpoint of MQTT>:1833.
  For more information, see Step 2 in the Connect the client to IoT Platform section.

Run the following command in the Command Prompt to execute the iot.go file:

go run iot.go MqttSign.go

After you execute the file, the following local logs are generated:

clientId192.168.****deviceNametestdeviceproductKeya1Zd7n5****timestamp1528018257135
1b865320fc183cc747041c9faffc9055fc45****
Connect aliyun IoT Cloud Sucess
Subscribe topic /a1Zd7n5****/testdevice/user/get success
publish msg: 0
publish msg:  ABC #0
publish msg: 1
publish msg:  ABC #1
publish msg: 2
publish msg:  ABC #2
publish msg: 3
publish msg:  ABC #3
publish msg: 4
publish msg:  ABC #4
publish msg: 5
publish msg:  ABC #5

Log on to the IoT Platform console.View device status and logs.

Choose Devices > Devices. You can find that the status of the device is Online.
Choose Maintenance > Device Log. Then, click the Cloud run log or Device local log tab to view logs. For more information, see IoT Platform logs and Local device logs.

Error codes

If a device fails to establish an MQTT connection to IoT Platform, you can troubleshoot the issue based on the error code. For more information, see Troubleshooting.

Prerequisites

Prepare the development environment

Download the Paho MQTT library for Go

Connect the client to IoT Platform

Sample code

Error codes