pynng / Python pattern guide

survey communication topology

SURVEYOR / RESPONDENT — Everybody Votes

SURVEYOR / RESPONDENT asks connected peers a question and collects their responses.

pynng is an independently maintained Python binding for NNG. Its maintainers and release cycle are separate from the NNG core project.

This example is sourced from the project’s default branch. See the upstream example for its current history.

survey.py

"""
The surveyor pattern is used to send a timed survey out,
responses are individually returned until the survey has expired.
This pattern is useful for service discovery and voting algorithms.
"""

import datetime
import pynng
import trio


DATE = "DATE"
address = "ipc:///tmp/survey.ipc"


def get_current_date():
    return str(datetime.datetime.now())


async def server(sock, max_survey_request=10):
    while max_survey_request:
        print(f"SERVER: SENDING DATE SURVEY REQUEST")
        await sock.asend(DATE.encode())
        while True:
            try:
                msg = await sock.arecv_msg()
                print(f'SERVER: RECEIVED "{msg.bytes.decode()}" SURVEY RESPONSE')
            except pynng.Timeout:
                break
        print("SERVER: SURVEY COMPLETE")
        max_survey_request -= 1


async def client(name, max_survey=3):
    with pynng.Respondent0() as sock:
        sock.dial(address)
        while max_survey:
            await sock.arecv_msg()
            print(f'CLIENT ({name}): RECEIVED SURVEY REQUEST"')
            print(f"CLIENT ({name}): SENDING DATE SURVEY RESPONSE")
            await sock.asend(get_current_date().encode())
            max_survey -= 1


async def main():
    with pynng.Surveyor0(listen=address) as surveyor:
        async with trio.open_nursery() as nursery:
            nursery.start_soon(server, surveyor)
            nursery.start_soon(client, "client0", 3)
            nursery.start_soon(client, "client1", 3)
            nursery.start_soon(client, "client2", 4)


if __name__ == "__main__":
    try:
        trio.run(main)
    except KeyboardInterrupt:
        # that's the way the program *should* end
        pass
Run it

python -m pip install pynng trio
python survey.py