This topic provides the sample code on how to send and receive scheduled messages and delayed messages by using the HTTP client SDK for C++.
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 C++. 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 scheduled messages and delayed messages
The following sample code provides an example on how to send scheduled messages and delayed messages by using the HTTP client SDK for C++:
#include <fstream>
#include <time.h>
#include "mq_http_sdk/mq_client.h"
using namespace std;
using namespace mq::http::sdk;
int main() {
MQClient mqClient(
// The HTTP endpoint. You can obtain the endpoint in the HTTP Endpoint section of the Instance Details page in the ApsaraMQ for RocketMQ console.
"${HTTP_ENDPOINT}",
// Make sure that the environment variables ALIBABA_CLOUD_ACCESS_KEY_ID and ALIBABA_CLOUD_ACCESS_KEY_SECRET are configured.
// The AccessKey ID that is used for authentication.
System.getenv("ALIBABA_CLOUD_ACCESS_KEY_ID"),
// The AccessKey secret that is used for authentication.
System.getenv("ALIBABA_CLOUD_ACCESS_KEY_SECRET")
);
// The topic in which the message is produced. You must create the topic in the ApsaraMQ for RocketMQ console.
string topic = "${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.
string instanceId = "${INSTANCE_ID}";
MQProducerPtr producer;
if (instanceId == "") {
producer = mqClient.getProducerRef(topic);
} else {
producer = mqClient.getProducerRef(instanceId, topic);
}
try {
// Cyclically send four messages.
for (int i = 0; i < 4; i++)
{
PublishMessageResponse pmResp;
// The message content.
TopicMessage pubMsg("Hello, mq!have key!");
// The custom attributes of the message.
pubMsg.putProperty("a",std::to_string(i));
// The message key.
pubMsg.setMessageKey("MessageKey" + std::to_string(i));
// The period of time after which the broker delivers the message to the consumer. In this example, the broker delivers the message to the consumer after a delay of 10 seconds. Set this parameter to a timestamp in milliseconds.
// If you want to send a scheduled message, set the parameter to the time difference between the scheduled point in time and the current point in time.
pubMsg.setStartDeliverTime(time(NULL) * 1000 + 10 * 1000);
producer->publishMessage(pubMsg, pmResp);
cout << "Publish mq message success. Topic is: " << topic
<< ", msgId is:" << pmResp.getMessageId()
<< ", bodyMD5 is:" << pmResp.getMessageBodyMD5() << endl;
}
} catch (MQServerException& me) {
cout << "Request Failed: " + me.GetErrorCode() << ", requestId is:" << me.GetRequestId() << endl;
return -1;
} catch (MQExceptionBase& mb) {
cout << "Request Failed: " + mb.ToString() << endl;
return -2;
}
return 0;
}Subscribe to scheduled messages and delayed messages
The following sample code provides an example on how to subscribe to scheduled messages and delayed messages by using the HTTP client SDK for C++:
#include <vector>
#include <fstream>
#include "mq_http_sdk/mq_client.h"
#ifdef _WIN32
#include <windows.h>
#else
#include <unistd.h>
#endif
using namespace std;
using namespace mq::http::sdk;
int main() {
MQClient mqClient(
// The HTTP endpoint. You can obtain the endpoint in the HTTP Endpoint section of the Instance Details page in the ApsaraMQ for RocketMQ console.
"${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.
System.getenv("ALIBABA_CLOUD_ACCESS_KEY_ID"),
// The AccessKey secret that is used for authentication.
System.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.
string topic = "${TOPIC}";
// The ID of the consumer group that you created in the ApsaraMQ for RocketMQ console.
string groupId = "${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.
string instanceId = "${INSTANCE_ID}";
MQConsumerPtr consumer;
if (instanceId == "") {
consumer = mqClient.getConsumerRef(topic, groupId);
} else {
consumer = mqClient.getConsumerRef(instanceId, topic, groupId, "");
}
do {
try {
std::vector<Message> messages;
// 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.
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 cycle. Unit: seconds. In this example, the value is specified as 3. The maximum value that you can specify is 30.
messages
);
cout << "Consume: " << messages.size() << " Messages!" << endl;
// The message consumption logic.
std::vector<std::string> receiptHandles;
for (std::vector<Message>::iterator iter = messages.begin();
iter != messages.end(); ++iter)
{
cout << "MessageId: " << iter->getMessageId()
<< " PublishTime: " << iter->getPublishTime()
<< " Tag: " << iter->getMessageTag()
<< " Body: " << iter->getMessageBody()
<< " FirstConsumeTime: " << iter->getFirstConsumeTime()
<< " NextConsumeTime: " << iter->getNextConsumeTime()
<< " ConsumedTimes: " << iter->getConsumedTimes()
<< " Properties: " << iter->getPropertiesAsString()
<< " Key: " << iter->getMessageKey() << endl;
receiptHandles.push_back(iter->getReceiptHandle());
}
// Obtain an acknowledgement (ACK) from the consumer.
// If the broker fails to receive an ACK for a message from the consumer before the period of time that is specified by the Message.NextConsumeTime parameter elapses, the broker delivers the message for consumption again.
// A unique timestamp is specified for the handle of a message each time the message is consumed.
AckMessageResponse bdmResp;
consumer->ackMessage(receiptHandles, bdmResp);
if (!bdmResp.isSuccess()) {
// If the handle of a message times out, the broker cannot receive an ACK for the message from the consumer.
const std::vector<AckMessageFailedItem>& failedItems =
bdmResp.getAckMessageFailedItem();
for (std::vector<AckMessageFailedItem>::const_iterator iter = failedItems.begin();
iter != failedItems.end(); ++iter)
{
cout << "AckFailedItem: " << iter->errorCode
<< " " << iter->receiptHandle << endl;
}
} else {
cout << "Ack: " << messages.size() << " messages suc!" << endl;
}
} catch (MQServerException& me) {
if (me.GetErrorCode() == "MessageNotExist") {
cout << "No message to consume! RequestId: " + me.GetRequestId() << endl;
continue;
}
cout << "Request Failed: " + me.GetErrorCode() + ".RequestId: " + me.GetRequestId() << endl;
#ifdef _WIN32
Sleep(2000);
#else
usleep(2000 * 1000);
#endif
} catch (MQExceptionBase& mb) {
cout << "Request Failed: " + mb.ToString() << endl;
#ifdef _WIN32
Sleep(2000);
#else
usleep(2000 * 1000);
#endif
}
} while(true);
}