RabbitMQ之tutorial-6

发表于 2020-12-11 更新于 2020-12-29 分类于 RabbitMQ

RabbitMQ之tutorial-6

Tutorial Six

we need to run a function on a remote computer and wait for the result? - RPC

callback queue

A client sends a request message and a server replies with a response message. In order to receive a response the client needs to send a 'callback' queue address with the request.

create callback queue per client
use correlation_id , match response with request; unknown correlation_id , simply discard

workflow

When the client starts up, it creates an anonymous exclusive callback queue.
For an RPC request, the Client sends a message with two properties: reply_to, which is set to the callback queue and correlation_id, which is set to a unique value for every request.
The request is sent to an rpc_queue queue.
The RPC worker (aka: server) is waiting for requests on that queue. When a request appears, it does the job and sends a message with the result back to the Client, using the queue from the reply_to field.
the client waits for data on the callback queue. When a message appears, it checks the correlation_id property. If it matches the value from the request it returns the response to the application.

rpc_client

import pika
import uuid


class FibonacciRpcClient(object):

    def __init__(self):
        self.connection = pika.BlockingConnection(
            pika.ConnectionParameters(host='localhost'))

        self.channel = self.connection.channel()

        result = self.channel.queue_declare(queue='', exclusive=True)
        self.callback_queue = result.method.queue

        self.channel.basic_consume(
            queue=self.callback_queue,
            on_message_callback=self.on_response,
            auto_ack=True)

    def on_response(self, ch, method, props, body):
        if self.corr_id == props.correlation_id:
            self.response = body

    def call(self, n):
        self.response = None
        self.corr_id = str(uuid.uuid4())
        self.channel.basic_publish(
            exchange='',
            routing_key='rpc_queue',
            properties=pika.BasicProperties(
                reply_to=self.callback_queue,
                correlation_id=self.corr_id,
            ),
            body=str(n))
        while self.response is None:
            self.connection.process_data_events()
        return int(self.response)


fibonacci_rpc = FibonacciRpcClient()

print(" [x] Requesting fib(30)")
response = fibonacci_rpc.call(30)
print(" [.] Got %r" % response)

rpc_server

import pika

connection = pika.BlockingConnection(
  pika.ConnectionParameters(host='localhost'))


channel = connection.channel()

channel.queue_declare(queue='rpc_queue')

def fib(n):
  if n == 0:
    return 0
  elif n == 1:
    return 1
  else:
    return fib(n-1) + fib(n-2)


  def on_request(ch, method, props, body):
    n = int(body)
    print(" [.] fib(%s)" % n)
    response = fib(n)

    ch.basic_publish(exchange='',
                     routing_key=props.reply_to,
                     properties=pika.BasicProperties(correlation_id=props.correlation_id),body=str(response))
    ch.basic_ack(delivery_tag=method.delivery_tag)


    channel.basic_qos(prefetch_count=1)
    channel.basic_consume(queue='rpc_queue', on_message_callback=on_request)

    print(" [x] Awaiting RPC requests")
    channel.start_consuming()

Testing


python rpc_server.py

python rpc_client.py