Normal messages are messages that have no special features in Message Queue for Apache RocketMQ. They are different from featured messages, such as scheduled messages, delayed messages, ordered messages, and transactional messages. This topic provides the sample code about how to send and subscribe to normal messages by using HTTP client SDK for Go.

Prerequisites

Before you begin, make sure that the following operations are complete:

  • SDK for Go is installed. For more information, see Prepare the environment.
  • Resources are created. The resources that you want to specify in the code are created in advance. For example, the instance, topic, and group ID that you want to specify in the code are created in the Message Queue for Apache RocketMQ console in advance. For more information, see Create resources.

Send normal messages

The following sample code provides an example on how to send normal messages:

package main

import (
    "fmt"
    "time"
    "strconv"

    "github.com/aliyunmq/mq-http-go-sdk"
)

func main() {
    // The HTTP endpoint. To obtain the HTTP endpoint, log on to the Message Queue for Apache RocketMQ console. In the left-side navigation pane, click Instances. On the Instances page, click the name of your instance. On the Instance Details page, scroll to the Basic Information section and view the endpoint on the Endpoints tab. 
    endpoint := "${HTTP_ENDPOINT}"
    // The AccessKey ID that you created in the Resource Access Management (RAM) console for identity authentication. 
    accessKey := "${ACCESS_KEY}"
    // The AccessKey secret that you created in the RAM console for identity authentication. 
    secretKey := "${SECRET_KEY}"
    // The topic of the message. The topic is created in the Message Queue for Apache RocketMQ console. 
    topic := "${TOPIC}"
    // The ID of the instance to which the topic belongs. The instance is created in the Message Queue for Apache RocketMQ console. 
    // If the instance has a namespace, the instance ID must be passed in. If the instance does not have a namespace, pass in null or an empty string. Check whether your instance has a namespace on the Instance Details page in the Message Queue for Apache RocketMQ console. 
    instanceId := "${INSTANCE_ID}"

    client := mq_http_sdk.NewAliyunMQClient(endpoint, accessKey, secretKey, "")

    mqProducer := client.GetProducer(instanceId, topic)
    // Cyclically send four messages. 
    for i := 0; i < 4; i++ {
        var msg mq_http_sdk.PublishMessageRequest

        msg = mq_http_sdk.PublishMessageRequest{
        MessageBody: "hello mq!",         // The content of the message. 
        MessageTag:  "",                  // The message tag. 
        Properties:  map[string]string {}, // The message attributes. 
        }
        // The key of the message. 
        msg.MessageKey = "MessageKey"
        // The custom attributes of the message. 
        msg.Properties["a"] = strconv.Itoa(i)

        ret, err := mqProducer.PublishMessage(msg)

        if err != nil {
            fmt.Println(err)
            return
        } else {
            fmt.Printf("Publish ---->\n\tMessageId:%s, BodyMD5:%s, \n", ret.MessageId, ret.MessageBodyMD5)
        }
        time.Sleep(time.Duration(100) * time.Millisecond)
    }
}

Subscribe to normal messages

The following sample code provides an example on how to subscribe to normal messages:

package main

import (
    "fmt"
    "github.com/gogap/errors"
    "strings"
    "time"

    "github.com/aliyunmq/mq-http-go-sdk"
)

func main() {
    // The HTTP endpoint. To obtain the HTTP endpoint, log on to the Message Queue for Apache RocketMQ console. In the left-side navigation pane, click Instances. On the Instances page, click the name of your instance. On the Instance Details page, scroll to the Basic Information section and view the endpoint on the Endpoints tab. 
    endpoint := "${HTTP_ENDPOINT}"
    // The AccessKey ID that you created in the RAM console for identity authentication. 
    accessKey := "${ACCESS_KEY}"
    // The AccessKey secret that you created in the RAM console for identity authentication. 
    secretKey := "${SECRET_KEY}"
    // The topic of the message. The topic is created in the Message Queue for Apache RocketMQ console. 
    // Each topic can be used to send and subscribe to messages of a specific type. For example, a topic that is used to send and subscribe to normal messages cannot be used to send and subscribe to messages of other types. 
    topic := "${TOPIC}"
    // The ID of the instance to which the topic belongs. The instance is created in the Message Queue for Apache RocketMQ console. 
    // If the instance has a namespace, the instance ID must be passed in. If the instance does not have a namespace, pass in null or an empty string. Check whether your instance has a namespace on the Instance Details page in the Message Queue for Apache RocketMQ console. 
    instanceId := "${INSTANCE_ID}"
    // The ID of the group that you created in the Message Queue for Apache RocketMQ console. 
    groupId := "${GROUP_ID}"

    client := mq_http_sdk.NewAliyunMQClient(endpoint, accessKey, secretKey, "")

    mqConsumer := client.GetConsumer(instanceId, topic, groupId, "")

    for {
        endChan := make(chan int)
        respChan := make(chan mq_http_sdk.ConsumeMessageResponse)
        errChan := make(chan error)
        go func() {
            select {
            case resp := <-respChan:
                {
                    // Specify the business processing logic. 
                    var handles []string
                    fmt.Printf("Consume %d messages---->\n", len(resp.Messages))
                    for _, v := range resp.Messages {
                        handles = append(handles, v.ReceiptHandle)
                        fmt.Printf("\tMessageID: %s, PublishTime: %d, MessageTag: %s\n"+
                            "\tConsumedTimes: %d, FirstConsumeTime: %d, NextConsumeTime: %d\n"+
                            "\tBody: %s\n"+
                            "\tProps: %s\n",
                            v.MessageId, v.PublishTime, v.MessageTag, v.ConsumedTimes,
                            v.FirstConsumeTime, v.NextConsumeTime, v.MessageBody, v.Properties)
                    }

                    // If the broker does not receive an acknowledgment (ACK) for a message from the consumer before the period of time specified by the NextConsumeTime parameter elapses, the message will be consumed again. 
                    // A unique timestamp is specified for the handle of a message each time the message is consumed. 
                    ackerr := mqConsumer.AckMessage(handles)
                    if ackerr != nil {
                        // The broker may fail to receive an ACK for a message from the consumer if the handle of the message times out. 
                        fmt.Println(ackerr)
                        if errAckItems, ok := ackerr.(errors.ErrCode).Context()["Detail"].([]mq_http_sdk.ErrAckItem); ok {
                           for _, errAckItem := range errAckItems {
                             fmt.Printf("\tErrorHandle:%s, ErrorCode:%s, ErrorMsg:%s\n",
                               errAckItem.ErrorHandle, errAckItem.ErrorCode, errAckItem.ErrorMsg)
                           }
                        } else {
                           fmt.Println("ack err =", ackerr)
                        }
                        time.Sleep(time.Duration(3) * time.Second)
                    } else {
                        fmt.Printf("Ack ---->\n\t%s\n", handles)
                    }

                    endChan <- 1
                }
            case err := <-errChan:
                {
                    // No messages in the topic are available for consumption. 
                    if strings.Contains(err.(errors.ErrCode).Error(), "MessageNotExist") {
                        fmt.Println("\nNo new message, continue!")
                    } else {
                        fmt.Println(err)
                        time.Sleep(time.Duration(3) * time.Second)
                    }
                    endChan <- 1
                }
            case <-time.After(35 * time.Second):
                {
                    fmt.Println("Timeout of consumer message ??")
                    endChan <- 1
                }
            }
        }()

        // Consume messages in long polling mode. 
        // In long polling mode, if no message in the topic is available for consumption, the request is suspended on the broker for a specified period of time. If a message is available for consumption within the duration, a response is immediately sent to the consumer. In this example, the duration is 3 seconds. 
        mqConsumer.ConsumeMessage(respChan, errChan,
            3, // The maximum number of messages that can be consumed at a time. In this example, the value is set to 3. The largest value you can set is 16. 
            3, // The duration of a long polling cycle. Unit: seconds. In this example, the value is set to 3. The largest value you can set is 30. 
        )
        <-endChan
    }
}