ApsaraMQ for RocketMQ provides a distributed transaction processing feature that is similar to eXtended Architecture (X/Open XA). ApsaraMQ for RocketMQ uses transactional messages to ensure the ultimate consistency of distributed transactions. This topic provides sample code on how to send and receive transactional messages by using the HTTP client SDK for Go.
Background information
The following figure shows the interaction process of transactional messages.
For more information, see Transactional messages.
Prerequisites
Before you start, make sure that the following operations are performed:
Install the SDK for Go. For more information, see Prepare the environment.
Create the resources that you want to specify in the code in the ApsaraMQ for RocketMQ console. The resources include instances, topics, and consumer groups. For more information, see Create resources.
Obtain the AccessKey pair of your Alibaba Cloud account. For more information, see Create an AccessKey pair.
Send transactional messages
The following sample code provides an example on how to send transactional messages by using the HTTP client SDK for Go:
package main
import (
"fmt"
"github.com/gogap/errors"
"strconv"
"strings"
"time"
"os"
"github.com/aliyunmq/mq-http-go-sdk"
)
var loopCount = 0
func ProcessError(err error) {
// The timeout period. 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 specified as 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:
{
// The message consumption 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 message is available for consumption in the topic.
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 the specified period of time. If a message is available for consumption within the specified period of time, a response is immediately sent to the consumer. In this example, the period of time is specified as 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 specified as 3. The maximum value that you can specify 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. You can obtain the endpoint in the HTTP Endpoint section of the Instance Details page in the ApsaraMQ for RocketMQ console.
endpoint := "${HTTP_ENDPOINT}"
// Make sure that the environment variables ALIBABA_CLOUD_ACCESS_KEY_ID and ALIBABA_CLOUD_ACCESS_KEY_SECRET are configured.
// The AccessKey ID that is used for authentication.
accessKey := os.Getenv("ALIBABA_CLOUD_ACCESS_KEY_ID")
// The AccessKey secret that is used for authentication.
secretKey := os.Getenv("ALIBABA_CLOUD_ACCESS_KEY_SECRET")
// The topic in which the message is produced. You must create the topic in the ApsaraMQ for RocketMQ console.
// Each topic can be used to send and receive messages of a specific type. For example, a topic that is used to send and receive normal messages cannot be used to send or receive messages of other types.
topic := "${TOPIC}"
// The ID of the instance to which the topic belongs. You must create the instance in the ApsaraMQ for RocketMQ console.
// If the instance has a namespace, specify the ID of the instance. If the instance does not have a namespace, set the instanceID parameter to null or an empty string. You can obtain the namespace of the instance on the Instance Details page in the ApsaraMQ for RocketMQ console.
instanceId := "${INSTANCE_ID}"
// The ID of the consumer group that you created in the ApsaraMQ for RocketMQ console.
groupId := "${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 commits or rolls back the transactional message based on the status of the handle.
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 by using the HTTP client SDK for Go:
package main
import (
"fmt"
"github.com/gogap/errors"
"strings"
"time"
"os"
"github.com/aliyunmq/mq-http-go-sdk"
)
func main() {
// The HTTP endpoint. You can obtain the endpoint in the HTTP Endpoint section of the Instance Details page in the ApsaraMQ for RocketMQ console.
endpoint := "${HTTP_ENDPOINT}"
// Make sure that the environment variables ALIBABA_CLOUD_ACCESS_KEY_ID and ALIBABA_CLOUD_ACCESS_KEY_SECRET are configured.
// The AccessKey ID that is used for authentication.
accessKey := os.Getenv("ALIBABA_CLOUD_ACCESS_KEY_ID")
// The AccessKey secret that is used for authentication.
secretKey := os.Getenv("ALIBABA_CLOUD_ACCESS_KEY_SECRET")
// The topic in which the message is produced. You must create the topic in the ApsaraMQ for RocketMQ console.
// Each topic can be used to send and receive messages of a specific type. For example, a topic that is used to send and receive normal messages cannot be used to send or receive messages of other types.
topic := "${TOPIC}"
// The ID of the instance to which the topic belongs. You must create the instance in the ApsaraMQ for RocketMQ console.
// If the instance has a namespace, specify the ID of the instance. If the instance does not have a namespace, set the instanceID parameter to null or an empty string. You can obtain the namespace of the instance on the Instance Details page in the ApsaraMQ for RocketMQ console.
instanceId := "${INSTANCE_ID}"
// The ID of the consumer group that you created in the ApsaraMQ for RocketMQ console.
groupId := "${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:
{
// The message consumption 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 fails to receive an acknowledgment (ACK) for a message from the consumer before the period of time specified by the NextConsumeTime parameter elapses, the broker delivers the message in the partition to the consumer 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 {
// If the handle of the message times out, the broker fails to receive an ACK for the message from the consumer.
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 message is available for consumption in the topic.
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. The default network timeout period is 35 seconds.
// In long polling mode, if no message in the topic is available for consumption, the request is suspended on the broker for the specified period of time. If a message becomes available for consumption within the specified period of time, the broker immediately sends a response to the consumer. In this example, the value is specified as 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 specified as 3. The maximum value that you can specify is 16.
3, // The duration of a long polling period. Unit: seconds. In this example, the value is specified as 3. The maximum value that you can specify is 30.
)
<-endChan
}
}