Using Quart I am trying to receive data from one client via a websocket, then have the Quart websocket server send it to a different client via websocket.
The two clients will be alone sharing the same url, other pairs of clients will have their own urls. This echo test works for both clients individually:
#copilot_ext.websocket('/ws/<unique_id>')
async def ws(unique_id):
while True:
data = await websocket.receive()
await websocket.send(f"echo {data}")
I have tried broadcasting using the example here https://pgjones.gitlab.io/quart/tutorials/websocket_tutorial.html#broadcasting although I can catch and print the different websockets, have not had much luck sending data from one client to the other :(
connected_websockets = set()
def collect_websocket(func):
#wraps(func)
async def wrapper(*args, **kwargs):
global connected_websockets
send_channel, receive_channel = trio.open_memory_channel(2)
connected_websockets.add(send_channel)
try:
return await func(send_channel, *args, **kwargs)
finally:
connected_websockets.remove(send_channel)
return wrapper
#copilot_ext.websocket('/ws/<unique_id>')
#collect_websocket
async def ws(que, unique_id):
while True:
data = await websocket.receive()
for send_channel in connected_websockets:
await send_channel.send(f"message {data}")
print(send_channel)
Just storing the websocket object and iterating through them doesn't work either
connected_websockets = set()
#copilot_ext.websocket('/ws/<unique_id>')
async def ws(unique_id):
global connected_websockets
while True:
data = await websocket.receive()
connected_websockets.add(websocket)
for websockett in connected_websockets:
await websockett.send(f"message {data}")
print(type(websockett))
I think this snippet can form the basis of what you want to achieve. The idea is that rooms are a collection of queues keyed by the room id. Then each connected client has a queue in the room which any other clients put messages to. The send_task then runs in the background to send any messages to the client that are on its queue. I hope this makes sense,
import asyncio
from collections import defaultdict
from quart import Quart, websocket
app = Quart(__name__)
websocket_rooms = defaultdict(set)
async def send_task(ws, queue):
while True:
message = await queue.get()
await ws.send(message)
#app.websocket("/ws/<id>/")
async def ws(id):
global websocket_rooms
queue = asyncio.Queue()
websocket_rooms[id].add(queue)
try:
task = asyncio.ensure_future(send_task(websocket._get_current_object(), queue))
while True:
message = await websocket.receive()
for other in websocket_rooms[id]:
if other is not queue:
await other.put(message)
finally:
task.cancel()
await task
websocket_rooms[id].remove(queue)
Related
I want to send two different messages to a websocket server but with different time intervalls.
For example:
The first message should be send every 2 seconds.
The second message should send every 5 seconds.
async def send_first_message(websocket):
while True:
await websocket.send("FIRST MESSAGE")
response = await websocket.recv()
await asyncio.sleep(2)
async def send_second_message():
while True:
async with websockets.connect(f"ws://{IP}:{PORT}") as websocket:
asyncio.create_task(send_first_message(websocket))
while True:
await websocket.send("SECOND MESSAGE")
response = await websocket.recv()
await asyncio.sleep(5)
asyncio.run(send_second_message())
If I run the code like this I get:
"RuntimeError: cannot call recv while another coroutine is already waiting for the next message"
If I comment out one of the "await websocket.recv()" it works fine for a few seconds and then it throws:
"RuntimeError no close frame received or sent"
There's a bit of a disconnect between what you are trying to do in the tasks (synchronous request-response interaction) and what the protocol and the library expects you to do (asynchronous messages).
When writing asynchronous code, you need to look at what the library/protocol/service expects to be an atomic operation that can happen asynchronously to everything else, and what you want to be a synchronous series of operations. Then you need to find the primitive in the library that will support that. In the case of websockets, the atomic operation is a message being sent in either direction. So you can't expect websockets to synchronize flow over two messages.
Or to put it another way, you are expecting synchronous responses for each send message, but websockets are not designed to handle interleaved synchronous requests. You've sent a message to the websocket server, and you want to get a response to that message. But you've also sent another message on the same websocket and want a response to that too. Your client websocket library can't differentiate between a message intended for the first request and a message intended for the second request (because from the websocket protocol layer, that is a meaningless concept - so the library enforces this by limiting the recv operations on a websocket that can be blocking to one).
So ...
Option 1 - multiple tasks on separate sockets
From the fact the library limits a websocket to one blocking recv, a primitive in the protocol that meets the requirement is the websocket itself. If these are separate requests that you need separate blocking responses to (so only continue in the requesting task once those responses are available) then you could have separate websocket connections and block for the response in each.
client1.py
async def send_first_message():
async with websockets.connect(f"ws://{IP}:{PORT}") as websocket:
while True:
await websocket.send("FIRST MESSAGE")
response = await websocket.recv()
print(response)
await asyncio.sleep(2)
async def send_second_message():
async with websockets.connect(f"ws://{IP}:{PORT}") as websocket:
while True:
await websocket.send("SECOND MESSAGE")
response = await websocket.recv()
print(response)
await asyncio.sleep(5)
async def main():
asyncio.create_task(send_first_message())
asyncio.create_task(send_second_message())
await asyncio.Future()
asyncio.run(main())
Option 1 is however not really the websocket or asynchronous way.
Option 2 - embrace the asynchronous
To do this on a single websocket, you will need to receive the response asynchronous to both sending tasks.
If you don't actually care that the send_* functions get the response, you can do this easily...
client2.py
async def send_first_message(websocket):
while True:
await websocket.send("FIRST MESSAGE")
await asyncio.sleep(2)
async def send_second_message(websocket):
while True:
await websocket.send("SECOND MESSAGE")
await asyncio.sleep(5)
async def receive_message(websocket):
while True:
response = await websocket.recv()
print(response)
async def main():
async with websockets.connect(f"ws://{IP}:{PORT}") as websocket:
asyncio.create_task(send_first_message(websocket))
asyncio.create_task(send_second_message(websocket))
asyncio.create_task(receive_message(websocket))
await asyncio.Future()
asyncio.run(main())
Option 3
But what if you want to line up responses to requests and keep on a single websocket? You need some way of knowing which request any particular response is for. Most web services that need this sort of interaction will have you send an ID in the message to the server, and it will respond once a response is ready using the ID as a reference.
There's also a way of getting your message tasks to block and wait for the response with the right ID by queuing up the responses and checking them periodically.
client3.py
unhandled_responses = {}
async def send_first_message(websocket):
while True:
req_id = random.randint(0,65535)
message = json.dumps({'id': req_id, 'message': 'FIRST MESSAGE'})
await websocket.send(message)
response = await block_for_response(req_id)
print(response)
await asyncio.sleep(2)
async def send_second_message(websocket):
while True:
req_id = random.randint(0,65535)
message = json.dumps({'id': req_id, 'message': 'SECOND MESSAGE'})
await websocket.send(message)
response = await block_for_response(req_id)
print(response)
await asyncio.sleep(5)
async def block_for_response(id):
while True:
response = unhandled_responses.pop(id, None)
if response:
return response
await asyncio.sleep(0.1)
async def receive_message(websocket):
while True:
response = json.loads(await websocket.recv())
unhandled_responses[response['id']] = response
async def main():
async with websockets.connect(f"ws://{IP}:{PORT}") as websocket:
asyncio.create_task(send_first_message(websocket))
asyncio.create_task(send_second_message(websocket))
asyncio.create_task(receive_message(websocket))
await asyncio.Future()
asyncio.run(main())
For completeness, the server code the clients were talking to in my tests.
server.py
import asyncio
import websockets
async def server_endpoint(websocket):
try:
while True:
recv_msg = await websocket.recv()
response = recv_msg
await websocket.send(response)
except Exception as ex:
print(str(ex))
async def main():
async with websockets.serve(server_endpoint, "localhost", 8765):
await asyncio.Future() # run forever
if __name__ == "__main__":
asyncio.run(main())
Quart is a Python web framework which re-implements the Flask API on top of the asyncio coroutine system of Python. In my particular case, I have a Quart websocket endpoint which is supposed to have not just one source of incoming events, but two possible sources of events which are supposed to continue the asynchronous loop.
An example with one event source:
from quart import Quart, websocket
app = Quart(__name__)
#app.websocket("/echo")
def echo():
while True:
incoming_message = await websocket.receive()
await websocket.send(incoming_message)
Taken from https://pgjones.gitlab.io/quart/
This example has one source: the incoming message stream. But what is the correct pattern if I had two possible sources, one being await websocket.receive() and another one being something along the lines of await system.get_next_external_notification() .
If either of them arrives, I'd like to send a websocket message.
I think I'll have to use asyncio.wait(..., return_when=FIRST_COMPLETED), but how do I make sure that I miss no data (i.e. for the race condition that websocket.receive() and system.get_next_external_notification() both finish almost exactly at the same time) ? What's the correct pattern in this case?
An idea you could use is a Queue to join the events together from different sources, then have an async function listening in the background to that queue for requests. Something like this might get you started:
import asyncio
from quart import Quart, websocket
app = Quart(__name__)
#app.before_serving
async def startup():
print(f'starting')
app.q = asyncio.Queue(1)
asyncio.ensure_future(listener(app.q))
async def listener(q):
while True:
returnq, msg = await q.get()
print(msg)
await returnq.put(f'hi: {msg}')
#app.route("/echo/<message>")
async def echo(message):
while True:
returnq = asyncio.Queue(1)
await app.q.put((returnq, message))
response = await returnq.get()
return response
#app.route("/echo2/<message>")
async def echo2(message):
while True:
returnq = asyncio.Queue(1)
await app.q.put((returnq, message))
response = await returnq.get()
return response
I am using websocket library in python for one of my projects. It works for me but I am curious to know how it works. I could not find this in the documentation. Specifically, for the example given in the docs,
#!/usr/bin/env python
# WS server example that synchronizes state across clients
import asyncio
import json
import logging
import websockets
logging.basicConfig()
STATE = {"value": 0}
USERS = set()
def state_event():
return json.dumps({"type": "state", **STATE})
def users_event():
return json.dumps({"type": "users", "count": len(USERS)})
async def notify_state():
if USERS: # asyncio.wait doesn't accept an empty list
message = state_event()
await asyncio.wait([user.send(message) for user in USERS])
async def notify_users():
if USERS: # asyncio.wait doesn't accept an empty list
message = users_event()
await asyncio.wait([user.send(message) for user in USERS])
async def register(websocket):
USERS.add(websocket)
await notify_users()
async def unregister(websocket):
USERS.remove(websocket)
await notify_users()
async def counter(websocket, path):
# register(websocket) sends user_event() to websocket
await register(websocket)
try:
await websocket.send(state_event())
async for message in websocket:
data = json.loads(message)
if data["action"] == "minus":
STATE["value"] -= 1
await notify_state()
elif data["action"] == "plus":
STATE["value"] += 1
await notify_state()
else:
logging.error("unsupported event: {}", data)
finally:
await unregister(websocket)
start_server = websockets.serve(counter, "localhost", 6789)
asyncio.get_event_loop().run_until_complete(start_server)
asyncio.get_event_loop().run_forever()
Whenever, I disconnect, the event unregister() gets fired. How does websocket come to know that I have disconnected?
My guess is the line async for message in websocket: has to do something with it but I do not know the details. Any insight on it will be appreciated.
With the websockets module, disconnections are handled as exceptions. For example, if you wanted to handle different kinds of disconnections, you could do something like this:
try:
await websocket.send(state_event())
async for message in websocket:
# Your code...
except websockets.exceptions.ConnectionClosedOK:
print("Client disconnected OK")
except websockets.exceptions.ConnectionClosedError:
print("Client disconnected unexpectedly")
finally:
await unregister(websocket)
More information can be found in the documentation.
I'm trying to read messages from Azure ServiceBus Topics using async/await and then forward the content to another application via HTTP. My code is simple:
import asyncio
from aiohttp import ClientSession
from azure.servicebus.aio.async_client import ServiceBusService
bus_service = ServiceBusService(service_namespace=..., shared_access_key_name=..., shared_access_key_value=...)
async def watch(topic_name, subscription_name):
print('{} started'.format(topic_name))
message = bus_service.receive_subscription_message(topic_name, subscription_name, peek_lock=False, timeout=1)
if message.body is not None:
async with ClientSession() as session:
await session.post('ip:port/endpoint',
headers={'Content-type': 'application/x-www-form-urlencoded'},
data={'data': message.body.decode()})
async def do():
while True:
for topic in ['topic1', 'topic2', 'topic3']:
await watch(topic, 'watcher')
if __name__ == "__main__":
asyncio.run(do())
I want to look for messages (forever) from various topics and when a message arrives send the POST. I import the aio package from azure which should work in an async way. After many attempts, the only solution I got is this with while True and setting the timeout=1. This is not what I wanted, I'm doing it sequentially.
azure-servicebus version 0.50.3.
This is my first time with async/await probably I'm missing something...
Any solution/suggestions?
Here's how you'll do it with the latest major version v7 of servicebus
Please take a look a the async samples to send and receive subscription messages
https://github.com/Azure/azure-sdk-for-python/blob/04290863fa8963ec525a0b2f4079595287e15d93/sdk/servicebus/azure-servicebus/samples/async_samples/sample_code_servicebus_async.py
import os
import asyncio
from aiohttp import ClientSession
from azure.servicebus.aio import ServiceBusClient
connstr = os.environ['SERVICE_BUS_CONNECTION_STR']
topic_name = os.environ['SERVICE_BUS_TOPIC_NAME']
subscription_name = os.environ['SERVICE_BUS_SUBSCRIPTION_NAME']
async def watch(topic_name, subscription_name):
async with ServiceBusClient.from_connection_string(conn_str=servicebus_connection_str) as servicebus_client:
subscription_receiver = servicebus_client.get_subscription_receiver(
topic_name=topic_name,
subscription_name=subscription_name,
)
async with subscription_receiver:
message = await subscription_receiver.receive_messages(max_wait_time=1)
if message.body is not None:
async with ClientSession() as session:
await session.post('ip:port/endpoint',
headers={'Content-type': 'application/x-www-form-urlencoded'},
data={'data': message.body.decode()})
async def do():
while True:
for topic in ['topic1', 'topic2', 'topic3']:
await watch(topic, 'watcher')
if __name__ == "__main__":
loop = asyncio.get_event_loop()
loop.run_until_complete(do())
You will have to use the package : azure.servicebus.aio
They have the below modules for async :
We will have to use the Receive handler class - it can instantiated with get_receiver() method. With this object you will be able to iterate through the message Asynchronously. Spun up a sample script which does that you could further optimise it :
from azure.servicebus.aio import SubscriptionClient
import asyncio
import nest_asyncio
nest_asyncio.apply()
Receiving = True
#Topic 1 receiver :
conn_str= "<>"
name="Allmessages1"
SubsClient = SubscriptionClient.from_connection_string(conn_str, name)
receiver = SubsClient.get_receiver()
#Topic 2 receiver :
conn_str2= "<>"
name2="Allmessages2"
SubsClient2 = SubscriptionClient.from_connection_string(conn_str2, name2)
receiver2 = SubsClient2.get_receiver()
#obj= SubscriptionClient("svijayservicebus","mytopic1", shared_access_key_name="RootManageSharedAccessKey", shared_access_key_value="ySr+maBCmIRDK4I1aGgkoBl5sNNxJt4HTwINo0FQ/tc=")
async def receive_message_from1():
await receiver.open()
print("Opening the Receiver for Topic1")
async with receiver:
while(Receiving):
msgs = await receiver.fetch_next()
for m in msgs:
print("Received the message from topic 1.....")
print(str(m))
await m.complete()
async def receive_message_from2():
await receiver2.open()
print("Opening the Receiver for Topic2")
async with receiver2:
while(Receiving):
msgs = await receiver2.fetch_next()
for m in msgs:
print("Received the message from topic 2.....")
print(str(m))
await m.complete()
loop = asyncio.get_event_loop()
topic1receiver = loop.create_task(receive_message_from1())
topic2receiver = loop.create_task(receive_message_from2())
I have created two tasks to facilitate the concurrency. You could refer this post to get more clarity on them.
Output :
http://websockets.readthedocs.io/en/stable/intro.html#consumer contains the following example:
async def consumer_handler(websocket, path):
while True:
message = await websocket.recv()
await consumer(message)
and http://websockets.readthedocs.io/en/stable/intro.html#producer
async def producer_handler(websocket, path):
while True:
message = await producer()
await websocket.send(message)
But there is no example for consumer() and producer() implementation or any explanation. Can somebody provide any simple example for that?
In the first example, consumer_handler listens for the messages from a websocket connection. It then passes the messages to a consumer. In its simplest form, a consumer can look like this:
async def consumer(message):
# do something with the message
In the second example, producer_handler receives a message from a producer and sends it to the websocket connection. A producer can look like this:
async def producer():
message = "Hello, World!"
await asyncio.sleep(5) # sleep for 5 seconds before returning message
return message