Normal messages are messages that have no special features in Message Queue for Apache RocketMQ. They are different from featured messages, such as scheduled messages, delayed messages, ordered messages, and transactional messages. This topic provides the sample code about how to send and subscribe to normal messages by using HTTP client SDK for C#.

Prerequisites

Before you begin, make sure that the following operations are complete:

  • SDK for C# 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 normal messages

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

using System;
using System.Collections.Generic;
using System.Threading;
using Aliyun.MQ.Model;
using Aliyun.MQ.Model.Exp;
using Aliyun.MQ.Util;

namespace Aliyun.MQ.Sample
{
    public class ProducerSample
    {
        // 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. 
        private const string _endpoint = "${HTTP_ENDPOINT}";
        // The AccessKey ID that you created in the Resource Access Management (RAM) console for identity authentication. 
        private const string _accessKeyId = "${ACCESS_KEY}";
        // The AccessKey secret that you created in the RAM console for identity authentication. 
        private const string _secretAccessKey = "${SECRET_KEY}";
        // The topic of the message. The topic must have been created in the Message Queue for Apache RocketMQ console. 
        private const string _topicName = "${TOPIC}";
        // 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.
        private const string _instanceId = "${INSTANCE_ID}";

        private static MQClient _client = new Aliyun.MQ.MQClient(_accessKeyId, _secretAccessKey, _endpoint);

        static MQProducer producer = _client.GetProducer(_instanceId, _topicName);

        static void Main(string[] args)
        {
            try
            {
                // Cyclically send four messages. 
                for (int i = 0; i < 4; i++)
                {
                TopicMessage sendMsg;
                // The content of the message.     
                sendMsg = new TopicMessage("hello mq");
                // The custom attributes of the message. 
                sendMsg.PutProperty("a", i.ToString());
                // The key of the message. 
                sendMsg.MessageKey = "MessageKey";
                    
                TopicMessage result = producer.PublishMessage(sendMsg);
                Console.WriteLine("publis message success:" + result);
                }
            }
            catch (Exception ex)
            {
                Console.Write(ex);
            }
        }
    }
}

Subscribe to normal messages

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

using System;
using System.Collections.Generic;
using System.Threading;
using Aliyun.MQ.Model;
using Aliyun.MQ.Model.Exp;
using Aliyun.MQ;

namespace Aliyun.MQ.Sample
{
    public class ConsumerSample
    {
        // 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. 
        private const string _endpoint = "${HTTP_ENDPOINT}";
        // The AccessKey ID that you created in the RAM console for identity authentication. 
        private const string _accessKeyId = "${ACCESS_KEY}";
        // The AccessKey secret that you created in the RAM console for identity authentication. 
        private const string _secretAccessKey = "${SECRET_KEY}";
        // The topic of the message. The topic must have been created in the Message Queue for Apache RocketMQ console. 
        private const string _topicName = "${TOPIC}";
        // 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.
        private const string _instanceId = "${INSTANCE_ID}";
        // The group ID that you created in the Message Queue for Apache RocketMQ console. 
        private const string _groupId = "${GROUP_ID}";

        private static MQClient _client = new Aliyun.MQ.MQClient(_accessKeyId, _secretAccessKey, _endpoint);
        static MQConsumer consumer = _client.GetConsumer(_instanceId, _topicName, _groupId, null);

        static void Main(string[] args)
        {
            // Cyclically consume messages in the current thread. We recommend that you use multiple threads to concurrently 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. 
                    List<Message> messages = null;

                    try
                    {
                        messages = 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. 
                        );
                    }
                    catch (Exception exp1)
                    {
                        if (exp1 is MessageNotExistException)
                        {
                            Console.WriteLine(Thread.CurrentThread.Name + " No new message, " + ((MessageNotExistException)exp1).RequestId);
                            continue;
                        }
                        Console.WriteLine(exp1);
                        Thread.Sleep(2000);
                    }

                    if (messages == null)
                    {
                        continue;
                    }

                    List<string> handlers = new List<string>();
                    Console.WriteLine(Thread.CurrentThread.Name + " Receive Messages:");
                    // Specify the business processing logic. 
                    foreach (Message message in messages)
                    {
                        Console.WriteLine(message);
                        Console.WriteLine("Property a is:" + message.GetProperty("a"));
                        handlers.Add(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. 
                    try
                    {
                        consumer.AckMessage(handlers);
                        Console.WriteLine("Ack message success:");
                        foreach (string handle in handlers)
                        {
                            Console.Write("\t" + handle);
                        }
                        Console.WriteLine();
                    }
                    catch (Exception exp2)
                    {
                        // The broker may fail to receive an ACK for a message from the consumer if the handle of the message times out. 
                        if (exp2 is AckMessageException)
                        {
                            AckMessageException ackExp = (AckMessageException)exp2;
                            Console.WriteLine("Ack message fail, RequestId:" + ackExp.RequestId);
                            foreach (AckMessageErrorItem errorItem in ackExp.ErrorItems)
                            {
                                Console.WriteLine("\tErrorHandle:" + errorItem.ReceiptHandle + ",ErrorCode:" + errorItem.ErrorCode + ",ErrorMsg:" + errorItem.ErrorMessage);
                            }
                        }
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex);
                    Thread.Sleep(2000);
                }
            }
        }
    }
}