如何在Python中订阅NATS主题并持续接收消息？

Question

我尝试了下面的示例（来自this页面）：

nc = NATS()

await nc.connect(servers=["nats://demo.nats.io:4222"])

future = asyncio.Future()

async def cb(msg):
  nonlocal future
  future.set_result(msg)

await nc.subscribe("updates", cb=cb)
await nc.publish("updates", b'All is Well')
await nc.flush()

# Wait for message to come in
msg = await asyncio.wait_for(future, 1)

但这似乎只对接收一条消息有用。 我如何订阅并继续接收消息？

我也看过包的例子，但好像只是玩双方的对话，然后就退出了。

Answer 1

您还可以找到长时间运行的服务示例：https://github.com/nats-io/nats.py/blob/master/examples/service.py

import asyncio
from nats.aio.client import Client as NATS

async def run(loop):
    nc = NATS()

    async def disconnected_cb():
        print("Got disconnected...")

    async def reconnected_cb():
        print("Got reconnected...")

    await nc.connect("127.0.0.1",
                     reconnected_cb=reconnected_cb,
                     disconnected_cb=disconnected_cb,
                     max_reconnect_attempts=-1,
                     loop=loop)

    async def help_request(msg):
        subject = msg.subject
        reply = msg.reply
        data = msg.data.decode()
        print("Received a message on '{subject} {reply}': {data}".format(
            subject=subject, reply=reply, data=data))
        await nc.publish(reply, b'I can help')

    # Use queue named 'workers' for distributing requests
    # among subscribers.
    await nc.subscribe("help", "workers", help_request)

    print("Listening for requests on 'help' subject...")
    for i in range(1, 1000000):
        await asyncio.sleep(1)
        try:
            response = await nc.request("help", b'hi')
            print(response)
        except Exception as e:
            print("Error:", e)

if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(run(loop))
    loop.run_forever()
    loop.close()

Answer 2

对 python 不太了解，但看起来你只是在等待一条消息，然后程序结束。您应该查看订阅者示例here。正如您所看到的，有一个循环永远等待或等待 SIGTERM 信号。

Answer 3

我认为，你应该看看 FastStream - 它以完美的方式支持 NATS：https://faststream.airt.ai/latest/faststream/#fastapi-plugin