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Implementation JSON-RPC 2.0 server and client using aiohttp on top of websockets transport

Project description

https://img.shields.io/travis/pengutronix/aiohttp-json-rpc/master.svg?label=Linux%20build%20%40%20Travis%20CI

aiohttp-json-rpc

Implements JSON-RPC 2.0 Specification using aiohttp

Protocol Support
Websocket since v0.1
POST TODO
GET TODO

Installation

pip install aiohttp-json-rpc

Usage

RPC methods can be added by using rpc.add_method().

All RPC methods are getting passed a aiohttp_json_rpc.communicaton.JsonRpcRequest.

Server

The following code implements a simple RPC server that serves the method ping on localhost:8080.

from aiohttp.web import Application
from aiohttp_json_rpc import JsonRpc
import asyncio


async def ping(request):
    return 'pong'


if __name__ == '__main__':
    loop = asyncio.get_event_loop()

    rpc = JsonRpc()
    rpc.add_methods(
        ('', ping),
    )

    app = Application(loop=loop)
    app.router.add_route('*', '/', rpc)

    handler = app.make_handler()

    server = loop.run_until_complete(
        loop.create_server(handler, '0.0.0.0', 8080))

    loop.run_forever()

Client (JS)

The following code implements a simple RPC client that connects to the server above and prints all incoming messages to the console.

<script src="//code.jquery.com/jquery-2.2.1.js"></script>
<script>
  var ws = new WebSocket("ws://localhost:8080");
  var message_id = 0;

  ws.onmessage = function(event) {
    console.log(JSON.parse(event.data));
  }

  function ws_call_method(method, params) {
    var request = {
      jsonrpc: "2.0",
      id: message_id,
      method: method,
      params: params
    }

    ws.send(JSON.stringify(request));
    message_id++;
  }
</script>

These are example responses the server would give if you call ws_call_method.

--> ws_call_method("get_methods")
<-- {"jsonrpc": "2.0", "result": ["get_methods", "ping"], "id": 1}

--> ws_call_method("ping")
<-- {"jsonrpc": "2.0", "method": "ping", "params": "pong", "id": 2}

Client (Python)

There’s also Python client, which can be used as follows:

from aiohttp_json_rpc import JsonRpcClient


async def ping_json_rpc():
    """Connect to ws://localhost:8080/rpc, call ping() and disconnect."""
    rpc_client = JsonRpcClient()
    try:
        await rpc_client.connect('localhost', 8080, '/rpc')
        call_result = await rpc_client.call('ping')
        print(call_result)  # prints 'pong' (if that's return val of ping)
    finally:
        await rpc_client.disconnect()


asyncio.get_event_loop().run_until_complete(ping_json_rpc())

Or use asynchronous context manager interface:

from aiohttp_json_rpc import JsonRpcClientContext


async def jrpc_coro():
    async with JsonRpcClientContext('ws://localhost:8000/rpc') as jrpc:
        # `some_other_method` will get request.params filled with `args` and
        # `kwargs` keys:
        method_res = await jrpc.some_other_method('arg1', key='arg2')

    return method_res

asyncio.get_event_loop().run_until_complete(jrpc_coro())

Features

Error Handling

All errors specified in the error specification but the InvalidParamsError are handled internally.

If your coroutine got called with wrong params you can raise an aiohttp_json_rpc.RpcInvalidParamsError instead of sending an error by yourself.

The JSONRPC protocol defines a range for server defined errors. aiohttp_json_rpc.RpcGenericServerDefinedError implements this feature.

from aiohttp_json_rpc import RpcInvalidParamsError


async def add(request):
    try:
        a = params.get('a')
        b = params.get('b')

        return a + b

    except KeyError:
        raise RpcInvalidParamsError


  async def add(request):
      raise RpcGenericServerDefinedError(
          error_code=-32050,
          message='Computer says no.',
      )

Error Logging

Every traceback caused by an RPC method will be caught and logged.

The RPC will send an RPC ServerError and proceed as if nothing happened.

async def divide(request):
    return 1 / 0  # will raise a ZeroDivisionError
ERROR:JsonRpc: Traceback (most recent call last):
ERROR:JsonRpc:   File "aiohttp_json_rpc/base.py", line 289, in handle_websocket_request
ERROR:JsonRpc:     rsp = yield from methods[msg['method']](ws, msg)
ERROR:JsonRpc:   File "./example.py", line 12, in divide
ERROR:JsonRpc:     return 1 / 0
ERROR:JsonRpc: ZeroDivisionError: division by zero

Publish Subscribe

Any client of an RPC object can subscribe to a topic using the built-in RPC method subscribe().

Topics can be added using rpc.add_topics.

Authentication

The auth system works like in Django with decorators. For details see the corresponding Django documentation.

Decorator Django Equivalent
aiohttp_json_rpc.django.auth.login_required django.contrib.auth.decorators.login_required
aiohttp_json_rpc.django.auth.permission_required django.contrib.auth.decorators.permission_required
aiohttp_json_rpc.django.auth.user_passes_test django.contrib.auth.decorators.user_passes_test
from aiohttp_json_rpc.auth import (
    permission_required,
    user_passes_test,
    login_required,
)

from aiohttp_json_rpc.auth.django import DjangoAuthBackend
from aiohttp_json_rpc import JsonRpc

@login_required
@permission_required('ping')
@user_passes_test(lambda user: user.is_superuser)
async def ping(request):
    return 'pong'

if __name__ == '__main__':
    rpc = JsonRpc(auth_backend=DjangoAuthBackend())

    rpc.add_methods(
        ('', ping),
    )

    rpc.add_topics(
        ('foo', [login_required, permission_required('foo')])
    )

Class References

class aiohttp_json_rpc.JsonRpc(object)

Methods

def add_methods(self, *args, prefix='')

Args have to be tuple containing a prefix as string (may be empty) and a module, object, coroutine or import string.

If second arg is module or object all coroutines in it are getting added.

async def get_methods()
Returns list of all available RPC methods.
def filter(self, topics)

Returns generator over all clients that have subscribed for given topic.

Topics can be string or a list of strings.

async def notify(self, topic, data)

Send RPC notification to all connected clients subscribed to given topic.

Data has to be JSON serializable.

Uses filter().

async def subscribe(topics)

Subscribe to a topic.

Topics can be string or a list of strings.

async def unsubscribe(topics)

Unsubscribe from a topic.

Topics can be string or a list of strings.

async def get_topics()
Get subscribable topics as list of strings.

Project details


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