IoT Platform:Connect a client to IoT Platform by using the SDK for Go

Development environment

In this example, Go 1.12.7 is used.

Download the SDK

You can run the following command to import the AMQP SDK for Go:

import "pack.ag/amqp"

For more information about how to use the SDK, see package amqp.

Sample code

package main

import (
	"os"
    "context"
    "crypto/hmac"
    "crypto/sha1"
    "encoding/base64"
    "fmt"
    "pack.ag/amqp"
    "time"
)
// For more information about the parameters, see the "Connect an AMQP client to IoT Platform" topic. 
const consumerGroupId = "${YourConsumerGroupId}"
const clientId = "${YourClientId}"
// iotInstanceId: The ID of the IoT Platform instance. 
const iotInstanceId = "${YourIotInstanceId}"
// The endpoint. For more information, see the "Connect an AMQP client to IoT Platform" topic. 
const host = "${YourHost}"

func main() {
	// If you hard-code the AccessKey pair in the project code, the AccessKey pair may be disclosed if the project code is leaked. In this case, the resources within your account become insecure. The following sample code provides an example on how to obtain the AccessKey pair from environment variables. This example is for reference only.
	accessKey := os.Getenv("ALIBABA_CLOUD_ACCESS_KEY_ID")
	accessSecret := os.Getenv("ALIBABA_CLOUD_ACCESS_KEY_SECRET")
    address := "amqps://" + host + ":5671"
    timestamp := time.Now().Nanosecond() / 1000000
    // The structure of the userName parameter. For more information, see the "Connect an AMQP client to IoT Platform" topic. 
    userName := fmt.Sprintf("%s|authMode=aksign,signMethod=Hmacsha1,consumerGroupId=%s,authId=%s,iotInstanceId=%s,timestamp=%d|", 
        clientId, consumerGroupId, accessKey, iotInstanceId, timestamp)
    stringToSign := fmt.Sprintf("authId=%s&timestamp=%d", accessKey, timestamp)
    hmacKey := hmac.New(sha1.New, []byte(accessSecret))
    hmacKey.Write([]byte(stringToSign))
    // Calculate a signature. For more information about how to construct the password, see the "Connect an AMQP client to IoT Platform" topic. 
    password := base64.StdEncoding.EncodeToString(hmacKey.Sum(nil))

    amqpManager := &AmqpManager{
        address:address,
        userName:userName,
        password:password,
    }

    // If you need to enable or disable the message receiving feature, you can create a context by using the Background() function. 
    ctx := context.Background()

    amqpManager.startReceiveMessage(ctx)
}

// The function that implements your business logic. The function is a user-defined function that is asynchronously called. Before you configure this function, we recommend that you consider the consumption of system resources. 
func (am *AmqpManager) processMessage(message *amqp.Message) {
    fmt.Println("data received:", string(message.GetData()), " properties:", message.ApplicationProperties)
}

type AmqpManager struct {
    address     string
    userName     string
    password     string
    client       *amqp.Client
    session     *amqp.Session
    receiver     *amqp.Receiver
}

func (am *AmqpManager) startReceiveMessage(ctx context.Context)  {

    childCtx, _ := context.WithCancel(ctx)
    err := am.generateReceiverWithRetry(childCtx)
    if nil != err {
        return
    }
    defer func() {
        am.receiver.Close(childCtx)
        am.session.Close(childCtx)
        am.client.Close()
    }()

    for {
        // Block message receiving. If ctx is the new context that is created based on the Background() function, message receiving is not blocked. 
        message, err := am.receiver.Receive(ctx)

        if nil == err {
            go am.processMessage(message)
            message.Accept()
        } else {
            fmt.Println("amqp receive data error:", err)

            // If message receiving is manually disabled, exit the program. 
            select {
            case <- childCtx.Done(): return
            default:
            }

            // If message receiving is not manually disabled, re-establish the connection. 
            err := am.generateReceiverWithRetry(childCtx)
            if nil != err {
                return
            }
        }
    }
}

func (am *AmqpManager) generateReceiverWithRetry(ctx context.Context) error {
    // Retry with exponential backoff, from 10 ms to 20s. 
    duration := 10 * time.Millisecond
    maxDuration := 20000 * time.Millisecond
    times := 1

    // If exceptions occur, retry with exponential backoff. 
    for {
        select {
        case <- ctx.Done(): return amqp.ErrConnClosed
        default:
        }

        err := am.generateReceiver()
        if nil != err {
            time.Sleep(duration)
            if duration < maxDuration {
                duration *= 2
            }
            fmt.Println("amqp connect retry,times:", times, ",duration:", duration)
            times ++
        } else {
            fmt.Println("amqp connect init success")
            return nil
        }
    }
}

// The states of the connection and session cannot be determined because the packets are unavailable. Re-establish the connection to obtain the information. 
func (am *AmqpManager) generateReceiver() error {

    if am.session != nil {
        receiver, err := am.session.NewReceiver(
            amqp.LinkSourceAddress("/queue-name"),
            amqp.LinkCredit(20),
        )
        // If a network disconnection error occurs, the connection is closed and the session fails to be established. Otherwise, the connection is established. 
        if err == nil {
            am.receiver = receiver
            return nil
        }
    }

    // Delete the previous connection. 
    if am.client != nil {
        am.client.Close()
    }

    client, err := amqp.Dial(am.address, amqp.ConnSASLPlain(am.userName, am.password), )
    if err != nil {
        return err
    }
    am.client = client

    session, err := client.NewSession()
    if err != nil {
        return err
    }
    am.session = session

    receiver, err := am.session.NewReceiver(
        amqp.LinkSourceAddress("/queue-name"),
        amqp.LinkCredit(20),
    )
    if err != nil {
        return err
    }
    am.receiver = receiver

    return nil
}

You can configure the parameters in the preceding code based on the parameter description in the following table. For more information about other parameters, see Connect an AMQP client to IoT Platform.

Sample results

• If information similar to the following output is displayed, the AMQP client is connected to IoT Platform and can receive messages.

• If information similar to the following output is displayed, the AMQP client fails to connect to IoT Platform.

  You can check the code or network environment based on logs, solve the problem, and then run the code again.

  

References

For more information about the error codes that are related to the server-side subscription feature, see the Error codes that are related to messages section of the "IoT Platform logs" topic.