ApsaraMQ for RocketMQ:Send and receive transactional messages

Background information

Prerequisites

Before you start, make sure that the following operations are performed:

• Install the SDK for Node.js. 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 Node.js:

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

// The HTTP endpoint. You can obtain the endpoint in the HTTP Endpoint section of the Instance Details page in the ApsaraMQ for RocketMQ console. 
const 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. 
const accessKeyId = process.env['ALIBABA_CLOUD_ACCESS_KEY_ID'];
// The AccessKey secret that is used for authentication. 
const accessKeySecret = process.env['ALIBABA_CLOUD_ACCESS_KEY_SECRET'];

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

// The topic in which the message is produced. You must create the topic in the ApsaraMQ for RocketMQ console. 
const topic = "${TOPIC}";
// The ID of the consumer group that you created in the ApsaraMQ for RocketMQ console. 
const groupId = "${GROUP_ID}";
// 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. 
const instanceId = "${INSTANCE_ID}";

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

async function processTransResult(res, msgId) {
    if (!res) {
        return;
    }
    if (res.code != 204) {
      // If a transactional message is not committed or rolled back before the timeout period specified by the TransCheckImmunityTime parameter for the handle of the transactional message elapses or before the timeout period specified for the handle of consumeHalfMessage elapses, the commit or rollback operation fails. In this example, the timeout period for the handle of consumeHalfMessage is specified as 10 seconds. 
      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 message key. 
      msgProps.messageKey("MessageKey");
      // The time interval between the sending time of the transactional message and the start time of the first check for the status of the local transaction. This time interval specifies the relative time when the status is first checked. 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. 
      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 commits or rolls back the transactional message based on the status of the handle. 
          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 not committed or rolled back before the timeout period specified by the TransCheckImmunityTime parameter elapses, the commit or rollback operation fails. 
        processTransResult(res, msgId);
      }
    }
  } catch(e) {
    // Specify the logic that you want to use to resend or persist the message if the message fails to be sent and needs to be sent again. 
    console.log(e)
  }
})();

// The client needs a thread or a 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) {
        // 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 message is available for consumption in the topic, the long polling mode continues to take effect. 
        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 by using the HTTP client SDK for Node.js:

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

// The HTTP endpoint. You can obtain the endpoint in the HTTP Endpoint section of the Instance Details page in the ApsaraMQ for RocketMQ console. 
const 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. 
const accessKeyId = process.env['ALIBABA_CLOUD_ACCESS_KEY_ID'];
// The AccessKey secret that is used for authentication. 
const accessKeySecret = process.env['ALIBABA_CLOUD_ACCESS_KEY_SECRET'];

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

// The topic in which the message is produced. You must create the topic in the ApsaraMQ for RocketMQ console. 
const topic = "${TOPIC}";
// The ID of the consumer group that you created in the ApsaraMQ for RocketMQ console. 
const groupId = "${GROUP_ID}";
// 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. 
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 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. 
      res = await consumer.consumeMessage(
          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. 
          );

      if (res.code == 200) {
        // 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 fails to receive an acknowledgement (ACK) for a message from the consumer before the period of time specified by the message.NextConsumeTime parameter elapses, the message is 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) {
          // If the handle of a message times out, the broker cannot receive an ACK for the message from the consumer. 
          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 message is available for consumption in the topic, the long polling mode continues to take effect. 
        console.log("Consume Message: no new message, RequestId:%s, Code:%s", e.RequestId, e.Code);
      } else {
        console.log(e);
      }
    }
  }
})();