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 rough 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 may be all you need too.
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
def publisher():
"""publish time.time() every second"""
with Client(name="publisher") as client:
while True:
time.sleep(1)
client.publish(subject=b"time.time", payload=f"{time.time()}".encode())
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=b"today")
client.subscribe(subject=b"add")
while True:
for request in client.get():
if request.subject == b"today":
# slow responder
time.sleep(2)
# will format the date according to payload or defaults to ...
format = request.payload.decode() if request.payload else "%Y-%m-%d"
response = f"{dt.date.today():{format}}".encode()
elif request.subject == b"add":
response = _int_to_bytes(sum(json.loads(request.payload)))
else:
continue
client.publish(
subject=request.inbox,
payload=response,
)
threading.Thread(target=responder, daemon=True).start()
# application
with Client(name="consumer") as client:
print("--- one ---")
print(one(subject=b"time.time"))
print("--- client.subscribe + client.request ---")
client.subscribe(subject=b"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:
# publish
publish(subject=b"time.time", payload=b"hijack")
# request response are blocking
response = client.request(subject=b"today", payload=b"%Y%m%d")
print(response)
print("--- request ---")
print(request(subject=b"add", payload=b"[1, 2, 3]"))
try:
print(request(subject=b"today", wait=100))
except TimeoutError as e:
print(e)
# UserWarning: NOP - out of context manager
client.publish(subject=b"out.of.context.manager")>>> from goingnats import one
>>> one(subject=b">")
Message(...)one is a very handy little helper that waits to receive a message on a given subject and returns it.
>>> from goingnats import request
>>> request(subject=b"add", payload=b"[1, 2, 3]")
Message(payload=b"6")request is another handy helper when developing services running on NATS.
>>> from goingnats import publish
>>> publish(subject=b"something.important", payload=b"OR_NOT")publish is similar to request but does not expect a response ... another convenient helper.
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