This topic provides sample code on how to send and receive scheduled messages and delayed messages by using the HTTP client SDK for Python.
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 Python. 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 or delayed messages by using the HTTP client SDK for Python:
import sys
from mq_http_sdk.mq_exception import MQExceptionBase
from mq_http_sdk.mq_producer import *
from mq_http_sdk.mq_client import *
import time
# Initialize the producer client.
mq_client = 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.
"${HTTP_ENDPOINT}",
# Make sure that the environment variables ALIBABA_CLOUD_ACCESS_KEY_ID and ALIBABA_CLOUD_ACCESS_KEY_SECRET are configured.
# The AccessKey ID that is used for authentication.
os.environ['ALIBABA_CLOUD_ACCESS_KEY_ID'],
# The AccessKey secret that is used for authentication.
os.environ['ALIBABA_CLOUD_ACCESS_KEY_SECRET']
)
# The topic in which the message is produced. You must create the topic in the ApsaraMQ for RocketMQ console.
topic_name = "${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, the instance ID must be specified. If the instance does not have a namespace, set the instanceID parameter to an empty string. You can obtain the namespace of the instance on the Instance Details page in the ApsaraMQ for RocketMQ console.
instance_id = "${INSTANCE_ID}"
producer = mq_client.get_producer(instance_id, topic_name)
# Cyclically send four messages.
msg_count = 4
print("%sPublish Message To %s\nTopicName:%s\nMessageCount:%s\n" % (10 * "=", 10 * "=", topic_name, msg_count))
try:
for i in range(msg_count):
msg = TopicMessage(
# The message content.
"I am test message %s.hello" % i,
# The message tag.
"tag1"
)
# The message attributes.
msg.put_property("a", "i")
# The message key.
msg.set_message_key("MessageKey")
# The period of time after which the broker delivers the message to the consumer. In this example, the broker delivers the message to the consumer after a delay of 10 seconds. Set this parameter to a timestamp in milliseconds.
# If the producer sends a scheduled message, set the parameter to the time difference between the scheduled point in time and the current point in time.
msg.set_start_deliver_time(int(round(time.time() * 1000)) + 10 * 1000)
re_msg = producer.publish_message(msg)
print("Publish Timer Message Succeed. MessageID:%s, BodyMD5:%s" % (re_msg.message_id, re_msg.message_body_md5))
except MQExceptionBase as e:
if e.type == "TopicNotExist":
print("Topic not exist, please create it.")
sys.exit(1)
print("Publish Message Fail. Exception:%s" % e)Subscribe to scheduled messages and delayed messages
The following sample code provides an example on how to subscribe to scheduled messages and delayed messages by using the HTTP client SDK for Python:
from mq_http_sdk.mq_exception import MQExceptionBase
from mq_http_sdk.mq_consumer import *
from mq_http_sdk.mq_client import *
# Initialize the consumer client.
mq_client = MQClient(
# The HTTP endpoint. You can obtain the endpoint in the HTTP Endpoint section of the Instance Details page in the ApsaraMQ for RocketMQ console.
"${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.
os.environ['ALIBABA_CLOUD_ACCESS_KEY_ID'],
# The AccessKey secret that is used for authentication.
os.environ['ALIBABA_CLOUD_ACCESS_KEY_SECRET']
)
# The topic in which the message is produced. You must create the topic in the ApsaraMQ for RocketMQ console.
topic_name = "${TOPIC}"
# The ID of the consumer group that you created in the ApsaraMQ for RocketMQ console.
group_id = "${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, the instance ID must be specified. If the instance does not have a namespace, set the instanceID parameter to an empty string. You can obtain the namespace of the instance on the Instance Details page in the ApsaraMQ for RocketMQ console.
instance_id = "${INSTANCE_ID}"
consumer = mq_client.get_consumer(instance_id, topic_name, group_id)
# 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, a response is immediately sent to the consumer. In this example, the value is specified as 3 seconds.
# The long polling period. Unit: seconds. In this example, the value is specified as 3. The maximum value that you can specify is 30.
wait_seconds = 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.
batch = 3
print(("%sConsume And Ak Message From Topic%s\nTopicName:%s\nMQConsumer:%s\nWaitSeconds:%s\n" \
% (10 * "=", 10 * "=", topic_name, group_id, wait_seconds)))
while True:
try:
# Consume messages in long polling mode.
recv_msgs = consumer.consume_message(batch, wait_seconds)
for msg in recv_msgs:
print(("Receive, MessageId: %s\nMessageBodyMD5: %s \
\nMessageTag: %s\nConsumedTimes: %s \
\nPublishTime: %s\nBody: %s \
\nNextConsumeTime: %s \
\nReceiptHandle: %s \
\nProperties: %s\n" % \
(msg.message_id, msg.message_body_md5,
msg.message_tag, msg.consumed_times,
msg.publish_time, msg.message_body,
msg.next_consume_time, msg.receipt_handle, msg.properties)))
except MQExceptionBase as e:
# No message in the topic is available for consumption.
if e.type == "MessageNotExist":
print(("No new message! RequestId: %s" % e.req_id))
continue
print(("Consume Message Fail! Exception:%s\n" % e))
time.sleep(2)
continue
# If the broker fails to receive an acknowledgement (ACK) for a message from the consumer before the period of time specified by the msg.next_consume_time 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.
try:
receipt_handle_list = [msg.receipt_handle for msg in recv_msgs]
consumer.ack_message(receipt_handle_list)
print(("Ak %s Message Succeed.\n\n" % len(receipt_handle_list)))
except MQExceptionBase as e:
print(("\nAk Message Fail! Exception:%s" % e))
# If the handle of a message times out, the broker cannot receive an ACK for the message from the consumer.
if e.sub_errors:
for sub_error in e.sub_errors:
print(("\tErrorHandle:%s,ErrorCode:%s,ErrorMsg:%s" % \
(sub_error["ReceiptHandle"], sub_error["ErrorCode"], sub_error["ErrorMessage"])))