ZMQ dealer does not receive message with asyncio

Question

I'm setting up a listener for Hyperledger Sawtooth events with a pyzmq dealer socket and the provided asyncio functionality. Currently futures are returned but only sometimes finished, even though messages are sent to the Socket.

Weirdly this works for the connection message (only when sleeping before it as shown below) but not for event messages. I implemented this already with JavaScript and it works without problems. It seems that the issue does not lie with Sawtooth but rather in pyzmq's implementation of asyncio functionality or in my code.

class EventListener:
    def __init__(self):
        ...
        ctx = Context.instance()
        self._socket = ctx.socket(zmq.DEALER)
        self._socket.connect("tcp://127.0.0.1:4004")

    async def subscribe(self):
        ...
        await self._socket.send_multipart([connection_msg])

    async def receive(self):
        # Necessary wait otherwise the future is never finished
        await asyncio.sleep(0.1)
        resp = await self._socket.recv_multipart()
        handle_response(resp)

    async def listen(self):
        while True:
            # here sleep is not helping
            # await asyncio.sleep(0.1)

            # follwing await is never finished
            resp = await self._socket.recv_multipart()
            handle_response(resp)

...
listener = listener.EventListener()
await asyncio.gather(
    listener.receive(), listener.subscribe())
await asyncio.create_task(listener.listen())
...

Debugging shows that the returned Future object is never changed from a pending to a finished state. So, is my code incorrect, do I need to await messages differently or is it possible that something is wrong with pyzmq's asyncio functionality? Also, why do I need to sleep in receive(), isn't that why we have asyncio?

Answer 1

There are too many queries, this answer may not address all of them. Hope at least this will help others looking for a way to setup event listeners.

The Hyperledger Sawtooth python SDK provides option for clients to subscribe to the events. The SDK part of code that does what you're trying to do can be found at https://github.com/hyperledger/sawtooth-sdk-python/blob/master/sawtooth_sdk/messaging/stream.py

The example code to use the Hyperledger Sawtooth python SDK for event subscription can be found here https://github.com/danintel/sawtooth-cookiejar/blob/master/events/events_client.py