Message Queue for Apache RocketMQ provides a distributed transaction processing feature similar to X/Open XA to ensure transaction consistency in Message Queue for Apache RocketMQ. This topic provides the sample code about how to send and subscribe to transactional messages by using HTTP client SDK for Go.

Background information

The following figure shows the interaction process of transactional messages. 事务消息流程图For more information, see Transactional messages.

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 transactional messages

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

package main

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

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

var loopCount = 0

func ProcessError(err error) {
    // If the transactional message is committed or rolled back after the time specified by the TransCheckImmunityTime parameter for the handle of the transactional message elapses or after the timeout period specified for the handle of consumeHalfMessage elapses, the commit or rollback fails. In this example, the timeout period is set to 10 seconds for the handle of consumeHalfMessage. 
    if err == nil {
        return
    }
    fmt.Println(err)
    for _, errAckItem := range err.(errors.ErrCode).Context()["Detail"].([]mq_http_sdk.ErrAckItem) {
        fmt.Printf("\tErrorHandle:%s, ErrorCode:%s, ErrorMsg:%s\n",
            errAckItem.ErrorHandle, errAckItem.ErrorCode, errAckItem.ErrorMsg)
    }
}

func ConsumeHalfMsg(mqTransProducer *mq_http_sdk.MQTransProducer) {
    for {
        if loopCount >= 10 {
            return
        }
        loopCount++
        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"+
                            "\tProperties:%s, Key:%s, Timer:%d, Trans:%d\n",
                            v.MessageId, v.PublishTime, v.MessageTag, v.ConsumedTimes,
                            v.FirstConsumeTime, v.NextConsumeTime, v.MessageBody,
                            v.Properties, v.MessageKey, v.StartDeliverTime, v.TransCheckImmunityTime)

                        a, _ := strconv.Atoi(v.Properties["a"])
                        var comRollErr error
                        if a == 1 {
                            // Confirm to commit the transactional message. 
                            comRollErr = (*mqTransProducer).Commit(v.ReceiptHandle)
                            fmt.Println("Commit---------->")
                        } else if a == 2 && v.ConsumedTimes > 1 {
                            // Confirm to commit the transactional message. 
                            comRollErr = (*mqTransProducer).Commit(v.ReceiptHandle)
                            fmt.Println("Commit---------->")
                        } else if a == 3 {
                            // Confirm to roll back the transactional message. 
                            comRollErr = (*mqTransProducer).Rollback(v.ReceiptHandle)
                            fmt.Println("Rollback---------->")
                        } else {
                            // Check the status next time. 
                            fmt.Println("Unknown---------->")
                        }
                        ProcessError(comRollErr)
                    }
                    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 ??")
                    return
                }
            }
        }()

        // Check the status of the half message 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. 
        (*mqTransProducer).ConsumeHalfMessage(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
    }
}

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 := "${SECRET_KEY}"
    // The topic of the message. The topic is created in the Message Queue for Apache RocketMQ console.    
    // Each topic can be used to send and subscribe to messages of a specific type. For example, a topic that is used to send and subscribe to normal messages cannot be used to send and subscribe to messages of other types. 
    topic := "${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, "")

    mqTransProducer := client.GetTransProducer(instanceId, topic, groupId)

    // The producer needs a thread or process to process unacknowledged transactional messages. 
    // Start a goroutine to process unacknowledged transactional messages. 
    go ConsumeHalfMsg(&mqTransProducer)

    // Send four transactional messages. Commit one message after the message is sent. Check the status of the half messages that correspond to the other three transactional messages after the three messages are sent. 
    for i := 0; i < 4; i++ {
        msg := mq_http_sdk.PublishMessageRequest{
            MessageBody:"I am transaction msg!",
            Properties: map[string]string{"a":strconv.Itoa(i)},
        }
        // The time interval between the sending time of the transactional message and the start time of the first back-check for the status of the local transaction. The time interval is a relative time interval. Unit: seconds. Valid values: 10 to 300. 
        // If the message is not committed or rolled back after the first back-check for the status of the local transaction, the broker initiates a back-check request for the status of the local transaction every 10 seconds within 24 hours. 
        msg.TransCheckImmunityTime = 10

        resp, pubErr := mqTransProducer.PublishMessage(msg)
        if pubErr != nil {
            fmt.Println(pubErr)
            return
        }
        fmt.Printf("Publish ---->\n\tMessageId:%s, BodyMD5:%s, Handle:%s\n",
            resp.MessageId, resp.MessageBodyMD5, resp.ReceiptHandle)
        if i == 0 {
            // After the producer sends the transactional message, the broker obtains the handle of the half message that corresponds to the transactional message, and can directly commit or roll back the half message. 
            ackErr := mqTransProducer.Commit(resp.ReceiptHandle)
            fmt.Println("Commit---------->")
            ProcessError(ackErr)
        }
    }

    for ; loopCount < 10 ; {
        time.Sleep(time.Duration(1) * time.Second)
    }
}

Subscribe to transactional messages

The following sample code provides an example on how to subscribe to transactional 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
    }
}