ApsaraMQ for RocketMQ:Send and receive scheduled and delayed messages

Background information

• Delayed messages are messages that are delivered by ApsaraMQ for RocketMQ brokers to consumers after a specific period of time.

• Scheduled messages are messages that are delivered by ApsaraMQ for RocketMQ brokers to consumers at a specific point in time.

The code configurations of scheduled messages are the same as the code configurations of delayed messages over HTTP. Both types of messages are delivered to consumers after a specific period of time based on the attributes of messages.

For more information, see Scheduled messages and delayed messages.

Prerequisites

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

• Install the SDK for Node.js. For more information, see Set up the Node.js 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.

Send scheduled and delayed messages

The following sample code provides an example on how to send scheduled and delayed 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 = "${HTTP_ENDPOINT}";
// Make sure that the environment variables ALIBABA_CLOUD_ACCESS_KEY_ID and ALIBABA_CLOUD_ACCESS_KEY_SECRET are configured. 
// The AccessKey ID that is used for authentication. 
const accessKeyId = process.env['ALIBABA_CLOUD_ACCESS_KEY_ID'];
// The AccessKey secret that is used for authentication. 
const accessKeySecret = process.env['ALIBABA_CLOUD_ACCESS_KEY_SECRET'];// The AccessKey ID that is used for authentication. 
const accessKeyId = "${ACCESS_KEY}";
// The AccessKey secret that is used for authentication. 
const accessKeySecret = "${SECRET_KEY}";

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 = "${TOPIC}";
// The ID of the instance to which the topic belongs. You must create the instance in the ApsaraMQ for RocketMQ console. 
// If the instance has a namespace, specify the ID of the instance. If the instance does not have a namespace, set the instanceId parameter to null or an empty string. You can obtain the namespace of the instance on the Instance Details page in the ApsaraMQ for RocketMQ console. 
const instanceId = "${INSTANCE_ID}";

const producer = client.getProducer(instanceId, topic);

(async function(){
  try {
    // Cyclically send four 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 period of time after which the broker delivers the message to the consumer. In this example, the broker delivers the message to the consumer after a delay of 10 seconds. Set this parameter to a timestamp in milliseconds. 
      // If you want to send a scheduled message, set the parameter to the time difference between the scheduled point in time and the current point in time. 
      msgProps.startDeliverTime(Date.now() + 10 * 1000);
      // The body and tag of the message. 
      res = await producer.publishMessage("hello mq. timer msg!", "TagA", msgProps);
      console.log("Publish message: MessageID:%s,BodyMD5:%s", res.body.MessageId, res.body.MessageBodyMD5);
    }

  } 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)
  }
})();

Subscribe to scheduled and delayed messages

The following sample code provides an example on how to subscribe to scheduled and delayed messages by using the HTTP client SDK for Node.js:

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

   // HTTP endpoint of your ApsaraMQ for RocketMQ instance.
   const endpoint = "<http-endpoint>";
   // Read credentials from environment variables.
   const accessKeyId = process.env['ALIBABA_CLOUD_ACCESS_KEY_ID'];
   const accessKeySecret = process.env['ALIBABA_CLOUD_ACCESS_KEY_SECRET'];

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

   // Topic to consume from.
   const topic = "<topic>";
   // Consumer group ID. Create this in the console first.
   const groupId = "<group-id>";
   // Instance ID. Set to null or "" if the instance has no namespace.
   const instanceId = "<instance-id>";

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

   (async function () {
     while (true) {
       try {
         // consumeMessage(batchSize, pollingSeconds)
         //   batchSize:      max messages per request (1-16)
         //   pollingSeconds: long-polling timeout in seconds (max 30)
         const res = await consumer.consumeMessage(3, 3);

         if (res.code === 200) {
           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;
           });

           // Acknowledge consumed messages. If the broker does not receive
           // an ACK before NextConsumeTime, the message is delivered again.
           const ackRes = await consumer.ackMessage(handles);
           if (ackRes.code !== 204) {
             // If the handle of the message times out, the broker fails to receive an ACK.
             console.log("Ack failed:");
             const failHandles = ackRes.body.map((error) => {
               console.log(
                 "\tErrorHandle:%s, Code:%s, Reason:%s",
                 error.ReceiptHandle, error.ErrorCode, error.ErrorMessage
               );
               return error.ReceiptHandle;
             });
             handles.forEach((handle) => {
               if (failHandles.indexOf(handle) < 0) {
                 console.log("\tSucHandle:%s", handle);
               }
             });
           } else {
             console.log("Ack succeeded, requestId: %s\n\t", ackRes.requestId, handles.join(','));
           }
         }
       } catch (e) {
         if (e.Code && e.Code.indexOf("MessageNotExist") > -1) {
           // No messages available -- long polling continues on next iteration.
           console.log("No new messages. requestId: %s, Code: %s", e.RequestId, e.Code);
         } else {
           console.log(e);
         }
       }
     }
   })();