py-amqprpc

Async RPC library based on AMQP protocol.

This library allows easy integration with go-amqprpc. Clients or servers written in go-amqprpc can interact with clients or servers written in py-amqprpc. See examples for more details.

Usage

Server

A python class or function can be used as RPC server. For this purpose it should be registered using an instance of server_codec (the name comes from golang net/rpc library).

Let's assume we have the following python class:

class Server:

    def mul(self, args):
        return args["A"] * args["B"]

And we are going to use it as RPC server. To do that we should connect AMQP broker, create server codec and register instance of this class in the codec.

import aioamqp

async def example_server(**amqp_settings):
    transport, protocol = await aioamqp.connect(**amqp_settings)
    codec = await amqprpc.server_codec(protocol, "testrpc", amqprpc.Json)
    codec.register(Server())
    # Now server is regisered and can accept requests to the method `mul`.
    # Codec should be closed before function exits.

NOTE: this example uses the library aioamqp but py-amqprpc can work with other async AMQP implementation so aioamqp will not be installed as py-amqprpc dependency.

Here testrpc is the routing key that will be used for routing requests to services registered in the codec. The parameter amqprpc.Json specifies that messages should be encoded in JSON. See Messages format for more details.

When a class instance is registered all its public methods will be available for remote call. But either class method or function should accept only 1 argument. Such interface make interopability with services in other languages more easy.

Client

To make requests to RPC server we have to create a client instance. Let's assume we would like to call the remote method mul of the class Server from the previous example. To do that we should connect AMQP broker, create client codec and create a client - proxy for the remote instance of the Server class.

async def example_client(**amqp_settings):
    transport, protocol = await aioamqp.connect(**amqp_settings)
    codec = await amqprpc.client_codec(protocol, "testrpc", amqprpc.Json)
    client = codec.client("Server")

    try:
        result = client.Mul({"A": 2, "B": 3})
        print(result)
    except amqprpc.RPCError as ex:
        print(ex)

Mind the second and third arguments of the function client_codec. They should be the same as in the server.

The argument of the method client.codec is the name of the RPC service. If RPC service is registered as a class isntance, it will be the class name, if it's registered as a function, it will be the function name.

Messages format

The py-amqprpc allows to specify how RPC requests and responses should be encoded. The argument formatter of the functions server_codec, client_codec should be an object with the following methods:

class SomeFormatter:

    def pack(pyobj):
        # Translate python object to the binary representation.

    def unpack(binrepr):
        # Translate binary representation to the python object.

The py-amqprpc library provides 2 default implementations:

• Json - JSON formatter
• MsgPack - msgpack formatter

Licence

See the LICENCE file.