Asyncio + aiohttp - 单个处理程序中的 redis Pub/Sub 和 websocket read/write

Question

我目前正在使用 aiohttp 看看它作为具有 websocket 连接的移动应用程序的服务器应用程序如何执行。

这是简单的 "Hello world" 示例 (as gist here):

import asyncio
import aiohttp
from aiohttp import web


class WebsocketEchoHandler:

    @asyncio.coroutine
    def __call__(self, request):
        ws = web.WebSocketResponse()
        ws.start(request)

        print('Connection opened')
        try:
            while True:
                msg = yield from ws.receive()
                ws.send_str(msg.data + '/answer')
        except:
            pass
        finally:
            print('Connection closed')
        return ws


if __name__ == "__main__":
    app = aiohttp.web.Application()
    app.router.add_route('GET', '/ws', WebsocketEchoHandler())

    loop = asyncio.get_event_loop()
    handler = app.make_handler()

    f = loop.create_server(
        handler,
        '127.0.0.1',
        8080,
    )

    srv = loop.run_until_complete(f)
    print("Server started at {sock[0]}:{sock[1]}".format(
        sock=srv.sockets[0].getsockname()
    ))
    try:
        loop.run_forever()
    except KeyboardInterrupt:
        pass
    finally:
        loop.run_until_complete(handler.finish_connections(1.0))
        srv.close()
        loop.run_until_complete(srv.wait_closed())
        loop.run_until_complete(app.finish())
    loop.close()

问题

现在我想使用下面描述的结构 (node server = python aiohttp)。更具体地说，使用 Redis Pub/Sub mechanism with asyncio-redis 在我的 WebsocketEchoHandler.

中读取和写入 websocket 连接和 Redis

WebsocketEchoHandler 是一个非常简单的循环，所以我不确定应该如何完成。使用 Tornado and brükva 我只会使用回调。

额外的（可能是题外话）问题

由于我已经在使用 Redis，我应该采用以下两种方法中的哪一种：

就像在 "classic" 网络应用程序中一样，对所有内容都有一个 controller/view，使用 Redis 仅用于消息传递等。
Web 应用程序应该只是客户端和 Redis 之间的一个层，也用作任务队列（最简单的 Python RQ）。每个请求都应该委托给工人。

编辑

图片来自http://goldfirestudios.com/blog/136/Horizontally-Scaling-Node.js-and-WebSockets-with-Redis

编辑 2

看来我需要澄清一下

仅 Websocket 处理程序如上所示

Redis Pub/Sub 处理程序可能看起来像这样：

class WebsocketEchoHandler:

    @asyncio.coroutine
    def __call__(self, request):
        ws = web.WebSocketResponse()
        ws.start(request)

        connection = yield from asyncio_redis.Connection.create(host='127.0.0.1', port=6379)
        subscriber = yield from connection.start_subscribe()
        yield from subscriber.subscribe(['ch1', 'ch2'])

        print('Connection opened')
        try:
            while True:
                msg = yield from subscriber.next_published()
                ws.send_str(msg.value + '/answer')
        except:
            pass
        finally:
            print('Connection closed')
        return ws

此处理程序仅订阅 Redis 通道 ch1 和 ch2 并将从这些通道收到的每条消息发送到 websocket。

我想要这个处理程序：

class WebsocketEchoHandler:

    @asyncio.coroutine
    def __call__(self, request):
        ws = web.WebSocketResponse()
        ws.start(request)

        connection = yield from asyncio_redis.Connection.create(host='127.0.0.1', port=6379)
        subscriber = yield from connection.start_subscribe()
        yield from subscriber.subscribe(['ch1', 'ch2'])

        print('Connection opened')
        try:
            while True:
                # If message recived from redis OR from websocket
                msg_ws = yield from ws.receive()
                msg_redis = yield from subscriber.next_published()
                if msg_ws:
                    # push to redis / do something else
                    self.on_msg_from_ws(msg_ws)
                if msg_redis:
                    self.on_msg_from_redis(msg_redis)
        except:
            pass
        finally:
            print('Connection closed')
        return ws

但是以下代码总是按顺序调用，因此从 websocket 读取会阻止从 Redis 读取：

msg_ws = yield from ws.receive()
msg_redis = yield from subscriber.next_published()

我想在事件上完成阅读，其中事件是从两个来源之一收到的消息。

Answer 1

您应该使用两个 while 循环 - 一个处理来自 websocket 的消息，一个处理来自 redis 的消息。您的主处理程序可以启动两个协同程序，一个处理每个循环，然后等待 both 个：

class WebsocketEchoHandler:
    @asyncio.coroutine
    def __call__(self, request):
        ws = web.WebSocketResponse()
        ws.start(request)

        connection = yield from asyncio_redis.Connection.create(host='127.0.0.1', port=6379)
        subscriber = yield from connection.start_subscribe()
        yield from subscriber.subscribe(['ch1', 'ch2'])

        print('Connection opened')
        try:
            # Kick off both coroutines in parallel, and then block
            # until both are completed.
            yield from asyncio.gather(self.handle_ws(ws), self.handle_redis(subscriber))
        except Exception as e:  # Don't do except: pass
            import traceback
            traceback.print_exc()
        finally:
            print('Connection closed')
        return ws

    @asyncio.coroutine
    def handle_ws(self, ws):
        while True:
            msg_ws = yield from ws.receive()
            if msg_ws:
                self.on_msg_from_ws(msg_ws)

    @asyncio.coroutine
    def handle_redis(self, subscriber):
        while True:
            msg_redis = yield from subscriber.next_published()
            if msg_redis:
                self.on_msg_from_redis(msg_redis)

这样您就可以从两个潜在来源中的任何一个阅读，而不必关心另一个。

Answer 2

最近我们可以在 python 3.5 及更高版本中使用异步等待..

async def task1(ws):
    async for msg in ws:
        if msg.type == WSMsgType.TEXT:
            data = msg.data
            print(data)
            if data:
                await ws.send_str('pong')
## ch is a redis channel
async def task2(ch):
    async for msg in ch1.iter(encoding="utf-8", decoder=json.loads):
        print("receving", msg)
        user_token = msg['token']
        if user_token in r_cons.keys():
            _ws = r_cons[user_token]
            await  _ws.send_json(msg)

coroutines = list()
coroutines.append(task1(ws))
coroutines.append(task2(ch1))

await asyncio.gather(*coroutines)

这就是我 do.when websockets 需要等待来自多个源的消息。

这里的要点是使用 asyncio.gather 到运行两个 corotine 在一起就像 @dano 提到。

Asyncio + aiohttp - 单个处理程序中的 redis Pub/Sub 和 websocket read/write

Asyncio + aiohttp - redis Pub/Sub and websocket read/write in single handler

python

redis

python-asyncio

aiohttp

问题

额外的（可能是题外话）问题

编辑

编辑 2