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. In this topic, HTTP client SDK for Node.js is used as an example.

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 Node.js 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:

const {
  MQClient,
  MessageProperties
} = require('@aliyunmq/mq-http-sdk');

// 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. 
const endpoint = "${HTTP_ENDPOINT}";
// The AccessKey ID that you created in the Resource Access Management (RAM) console for identity authentication. 
const accessKeyId = "${ACCESS_KEY}";
// The AccessKey secret that you created in the RAM console for identity authentication. 
const accessKeySecret = "${SECRET_KEY}";

var client = new MQClient(endpoint, accessKeyId, accessKeySecret);

// The topic of the message. The topic must have been created in the Message Queue for Apache RocketMQ console. 
const topic = "${TOPIC}";
// The group ID that you created in the Message Queue for Apache RocketMQ console. 
const groupId = "${GROUP_ID}";
// The ID of the instance to which the topic belongs. The instance must have been 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.
const instanceId = "${INSTANCE_ID}";

const mqTransProducer = client.getTransProducer(instanceId, topic, groupId);

async function processTransResult(res, msgId) {
    if (!res) {
        return;
    }
    if (res.code != 204) {
      // 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. 
      console.log("Commit/Rollback Message Fail:");
      const failHandles = res.body.map((error) => {
        console.log("\tErrorHandle:%s, Code:%s, Reason:%s\n", error.ReceiptHandle, error.ErrorCode, error.ErrorMessage);
        return error.ReceiptHandle;
      });
    } else {
      console.log("Commit/Rollback Message suc!!! %s", msgId);
    }
}

var halfMessageCount = 0;
var halfMessageConsumeCount = 0;

(async function(){
  try {
    // Cyclically send four transactional messages. 
    for(var i = 0; i < 4; i++) {
      let res;
      msgProps = new MessageProperties();
      // The custom attributes of the message. 
      msgProps.putProperty("a", i);
      // The key of the message. 
      msgProps.messageKey("MessageKey");
      // The time interval between the sending time of the transactional message and the start time of the first back-check for the status of 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 local transaction, the broker initiates a back-check request for the status of local transaction every 10 seconds within the 24 hours. 
      msgProps.transCheckImmunityTime(10);
      res = await mqTransProducer.publishMessage("hello mq.", "tagA", msgProps);
      console.log("Publish message: MessageID:%s,BodyMD5:%s,Handle:%s", res.body.MessageId, res.body.MessageBodyMD5, res.body.ReceiptHandle);
      if (res && 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. 
          const msgId = res.body.MessageId;
          res = await mqTransProducer.commit(res.body.ReceiptHandle);
          console.log("Commit msg when publish, %s", msgId);
          // If the transactional message is committed or rolled back after the time specified by the TransCheckImmunityTime parameter elapses, the commit or rollback fails. 
        processTransResult(res, msgId);
      }
    }
  } catch(e) {
    // Specify the logic to resend or persist the message if the message fails to be sent. 
    console.log(e)
  }
})();

// The producer needs a thread or process to process unacknowledged transactional messages. 
// Process unacknowledged transactional messages. 
(async function() {
  // Cyclically check half messages. This is similar to consuming normal messages. 
  while(halfMessageCount < 3 && halfMessageConsumeCount < 15) {
    try {
        halfMessageConsumeCount++;
      res = await mqTransProducer.consumeHalfMessage(3, 3);
      if (res.code == 200) {
        // Specify the message consumption logic. 
        console.log("Consume Messages, requestId:%s", res.requestId);
        res.body.forEach(async (message) => {
          console.log("\tMessageId:%s,Tag:%s,PublishTime:%d,NextConsumeTime:%d,FirstConsumeTime:%d,ConsumedTimes:%d,Body:%s" +
            ",Props:%j,MessageKey:%s,Prop-A:%s",
              message.MessageId, message.MessageTag, message.PublishTime, message.NextConsumeTime, message.FirstConsumeTime, message.ConsumedTimes,
              message.MessageBody,message.Properties,message.MessageKey,message.Properties.a);

          var propA = message.Properties && message.Properties.a ? parseInt(message.Properties.a) : 0;
                  var opResp;
                  if (propA == 1 || (propA == 2 && message.ConsumedTimes > 1)) {
                      opResp = await mqTransProducer.commit(message.ReceiptHandle);
                      console.log("Commit msg when check half, %s", message.MessageId);
                      halfMessageCount++;
                  } else if (propA == 3) {
                      opResp = await mqTransProducer.rollback(message.ReceiptHandle);
                      console.log("Rollback msg when check half, %s", message.MessageId);
                      halfMessageCount++;
                  }
                  processTransResult(opResp, message.MessageId);
        });
      }
    } catch(e) {
      if (e.Code && e.Code.indexOf("MessageNotExist") > -1) {
        // If no messages in the topic are available for consumption, the consumer requests the broker in long polling mode. 
        console.log("Consume Transaction Half msg: no new message, RequestId:%s, Code:%s", e.RequestId, e.Code);
      } else {
        console.log(e);
      }
    }
  }
})();  

Subscribe to transactional messages

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

const {
  MQClient
} = require('@aliyunmq/mq-http-sdk');

// 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. 
const endpoint = "${HTTP_ENDPOINT}";
// The AccessKey ID that you created in the RAM console for identity authentication. 
const accessKeyId = "${ACCESS_KEY}";
// The AccessKey secret that you created in the RAM console for identity authentication. 
const accessKeySecret = "${SECRET_KEY}";

var client = new MQClient(endpoint, accessKeyId, accessKeySecret);

// The topic of the message. The topic must have been created in the Message Queue for Apache RocketMQ console. 
const topic = "${TOPIC}";
// The group ID that you created in the Message Queue for Apache RocketMQ console. 
const groupId = "${GROUP_ID}";
// The ID of the instance to which the topic belongs. The instance must have been 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.
const instanceId = "${INSTANCE_ID}";

const consumer = client.getConsumer(instanceId, topic, groupId);

(async function(){
  // Cyclically consume messages. 
  while(true) {
    try {
      // 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. 
      res = await consumer.consumeMessage(
          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. 
          );

      if (res.code == 200) {
        // Specify the message consumption logic. 
        console.log("Consume Messages, requestId:%s", res.requestId);
        const handles = res.body.map((message) => {
          console.log("\tMessageId:%s,Tag:%s,PublishTime:%d,NextConsumeTime:%d,FirstConsumeTime:%d,ConsumedTimes:%d,Body:%s" + 
            ",Props:%j,MessageKey:%s,Prop-A:%s",
              message.MessageId, message.MessageTag, message.PublishTime, message.NextConsumeTime, message.FirstConsumeTime, message.ConsumedTimes,
              message.MessageBody,message.Properties,message.MessageKey,message.Properties.a);
          return message.ReceiptHandle;
        });

        // If the broker does not receive an acknowledgment (ACK) from the consumer before the period of time specified by the message.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. 
        res = await consumer.ackMessage(handles);
        if (res.code != 204) {
          // The broker may fail to receive an ACK for a message from the consumer if the handle of the message times out. 
          console.log("Ack Message Fail:");
          const failHandles = res.body.map((error)=>{
            console.log("\tErrorHandle:%s, Code:%s, Reason:%s\n", error.ReceiptHandle, error.ErrorCode, error.ErrorMessage);
            return error.ReceiptHandle;
          });
          handles.forEach((handle)=>{
            if (failHandles.indexOf(handle) < 0) {
              console.log("\tSucHandle:%s\n", handle);
            }
          });
        } else {
          // Obtain an ACK from the consumer. 
          console.log("Ack Message suc, RequestId:%s\n\t", res.requestId, handles.join(','));
        }
      }
    } catch(e) {
      if (e.Code.indexOf("MessageNotExist") > -1) {
        // If no messages in the topic are available for consumption, the consumer requests the broker in long polling mode. 
        console.log("Consume Message: no new message, RequestId:%s, Code:%s", e.RequestId, e.Code);
      } else {
        console.log(e);
      }
    }
  }
})();