a Python NATS client

Why?

I like NATS a lot.

asyncio less so hence never played with the official Python client.

While I got a lot out of nats-python, it has some rought edges I would rather not have to work around as an end user.

I wanted to teach myself enough socket programming and gain a deeper understanding of the NATS protocol.

a Python NATS client that fits the way I use NATS.

• Client must have a name
• Client PONGs on PING behind the scene
• Encourage to only use Client as a contextmanager
• non blocking when receiving messages from subscriptions
• blocking on request / response

It is far from feature complete.

It implements the features I use, which maybe all you need too.

How?

A contrived example illustrating how an application would interact with a publisher and a responder via NATS.

Fire up NATS on your dev box and python -m goingnats to see it run.

import datetime as dt
import time
import threading

from goingnats import Client


def publisher():
    """publish time.time() every second"""
    with Client(name="publisher") as client:
        while True:
            time.sleep(1)
            client.publish(subject="time.time", payload=f"{time.time()}")

threading.Thread(target=publisher, daemon=True).start()

def responder():
    """respond to request for today with the date"""
    with Client(name="responder") as client:
        client.subscribe(subject="today")
        while True:
            for request in client.get():
                if request.subject != "today":
                    continue
                # slow responder
                time.sleep(2)
                # will format the date according to payload or defaults to ...
                format = (
                    request.payload.decode("utf-8")
                    if request.payload
                    else "%Y-%m-%d"
                )
                client.publish(
                    subject=request.inbox,
                    payload=f"{dt.date.today():{format}}",
                )

threading.Thread(target=responder, daemon=True).start()

# application
with Client(name="consumer") as client:
    client.subscribe(subject="time.time")
    received = 0
    response = None
    while received < 5:
        # waits for at most 10 ms for messages
        for message in client.get(wait=10):
            print(message)
            received += 1
        if received == 3 and response is None:
            # request response are blocking
            response = client.request(subject="today", payload="%Y%m%d")
            print(response)

one more thing

>>> from goingnats import one
>>> one(subject=">")
Message(...)

one is a very handy little helper that waits to receive a message on a given subject and returns it.