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RPC: Remote procedure call implementation
=========================================
This tutorial will try to implement the RPC as in the RabbitMQ's tutorial.
The API will probably look like:
.. code-block:: python
fibonacci_rpc = FibonacciRpcClient()
result = await fibonacci_rpc.call(4)
print("fib(4) is %r" % result)
Client
------
In this case it's no more a producer but a Client: we will send a message in a queue and wait for a response in another.
For that purpose, we publish a message to the `rpc_queue` and add a `reply_to` properties to let the server know where to respond.
.. code-block:: python
result = await channel.queue_declare(exclusive=True)
callback_queue = result['queue']
channel.basic_publish(
exchange='',
routing_key='rpc_queue',
properties={
'reply_to': callback_queue,
},
body=request,
)
Note: the client use a `waiter` (an asyncio.Event) which will be set when receiving a response from the previously sent message.
Server
------
When unqueing a message, the server will publish a response directly in the callback. The `correlation_id` is used to let the client know it's a response from this request.
.. code-block:: python
async def on_request(channel, body, envelope, properties):
n = int(body)
print(" [.] fib(%s)" % n)
response = fib(n)
await channel.basic_publish(
payload=str(response),
exchange_name='',
routing_key=properties.reply_to,
properties={
'correlation_id': properties.correlation_id,
},
)
await channel.basic_client_ack(delivery_tag=envelope.delivery_tag)
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