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Python - Async callback/receiver for WebSocket

I am trying to implement WebSocket connection to a server (Python app <=> Django app)
Whole system runs in big Asyncio loop with many tasks. Code snippet is just very small testing part.
I am able to send any data to a server at any moment and many of them will be type request something and wait for response. But I would like to have some "always running" handler for all incoming messages. (When something in Django database will change I want to send changes to python app).
How can Include always running receiver/ or add callback to websocket? I am not able to find any solution for this.
My code snippet:
import asyncio, json, websockets, logging
class UpdateConnection:
async def connect(self,botName):
self.sock = await websockets.connect('ws://localhost:8000/updates/bot/'+botName)
async def send(self,data):
try:
await self.sock.send(json.dumps(data))
except:
logging.info("Websocket connection lost!")
# Find a way how to reconenct... or make socket reconnect automatically
if __name__ == '__main__':
async def DebugLoop(socketCon):
await socketCon.connect("dev")
print("Running..")
while True:
data = {"type": "debug"}
await socketCon.send(data)
await asyncio.sleep(1)
uSocket = UpdateConnection()
loop = asyncio.get_event_loop()
loop.create_task(DebugLoop(uSocket))
loop.run_forever()
My debug server after connection will start sending random messages to the client in random intervals and I would like to somehow handle them in async way.
Thanks for any help :)

You don't have to do it so complicated. First of all I suggest you use the context patterns offered by websockets module.
From the documentation:
connect() can be used as an infinite asynchronous iterator to reconnect automatically on errors:
async for websocket in websockets.connect(...):
try:
...
except websockets.ConnectionClosed:
continue
Additionally, you simply keep the connection alive by awaiting incoming messages:
my_websocket = None
async for websocket in websockets.connect('ws://localhost:8000/updates/bot/' + botName):
try:
my_websocket = websocket
async for message in websocket:
pass # here you could also process incoming messages
except websockets.ConnectionClosed:
my_websocket = None
continue
As you can see we have a nested loop here:
The outer loop constantly reconnects to the server
The inner loop processes one incoming message at a time
If you are connected, and no messages are coming in from the server, this will just sleep.
The other thing that happens here is that my_websocket is set to the active connection, and unset again when the connection is lost.
In other parts of your script you can use my_websocket to send data. Note that you will need to check if it is currently set wherever you use it:
async def send(data):
if my_websocket:
await my_websocket.send(json.dumps(data))
This is just an illustration, you can also keep the websocket object as an object member, or pass it to another component through a setter function, etc.

GRPC bidirectional stream closes after 1 minute without messages

I am opening a GRPC bidirectional stream with a server (python3.8 specifically). After I get some data from the server, I have to do a time consuming task (it takes about 3 minutes). While doing this, I am keeping the channel open to send the results to the server as soon as the task is done
Exactly 1 minute after the server's last message, my connection closes. And I get this error
<AioRpcError of RPC that terminated with:
status = StatusCode.INTERNAL
details = "Received RST_STREAM with error code 1"
debug_error_string = "{"created":"#1625250019.779494905","description":"Error received from peer ipv4:3.101.44.139:443","file":"src/core/lib/surface/call.cc","file_line":1066,"grpc_message":"Received RST_STREAM with error code 1","grpc_status":13}"
>
To me it seems like some timeout. I am a beginner to grpc. I referred to this article and gave my channel the client options as specified in the article with every number close to 5mins. But it did not change anything. Can someone please help me understand what is going on here and how I should solve this?
TL;DR
My connection to the server is an async secure channel. Please note that my two streams are independant which is why I have to do async
channel=grpc.aio.secure_channel(address, credentials=creds, options=options)
I have two coroutines, one is waiting for the long running task to be excecuted, other receiving and sensing messages on the bi directional stream
def parse_response(resp):
# collect data from server response
# make `task_available=True` when all data is received
async def stream_handler():
stub = TaskServiceStub(channel)
req_gen = get_requests() # An async generator for request messages
stream: grpc.aio.StreamStreamCall = stub.Task(req_gen)
async for resp in stream.__aiter__():
parse_response(resp)
async def task_handler():
if task_available:
do_task()
async def main():
await asyncio.gather(stream_handler(), task_handler())

Adding a read timeout to the server nginx configuration solved the issue
nginx.ingress.kubernetes.io/server-snippet: |
client_header_timeout 3h;
client_body_timeout 3h;
grpc_read_timeout 3h;
grpc_send_timeout 3h;

Asyncronously manage connected clients while continously sending data in Python

I have a server built in Python that uses Sanic and websockets to routinely broadcast data to clients:
#app.websocket("/")
async def websocket(request, ws):
app.ws_clients.add(ws)
await ws.send(json.dumps("hello from climate server!"))
while True:
try:
data = dict()
time_of_reading = time.ctime(time.time())
data['climateData'] = sensor.read_data()
data['systemData'] = get_system_data()
data['timestamp'] = time_of_reading
await broadcast(json.dumps(data))
time.sleep(10) # changing this to asyncio.sleep() causes the msgs to send sporatically
except KeyboardInterrupt:
sensor.clear()
pass
if __name__ == '__main__':
app.run(host='0.0.0.0', port=8080, workers=1, debug=False)
and my broadcast function which attempts to send a message, or removes a client from app.ws_clients if there is a ConnectionClosed error:
async def broadcast(message):
for ws in app.ws_clients:
try:
await ws.send(message)
print('attempting data send') # this line runs, but the clients don't receive the messages
except websockets.ConnectionClosed:
clients_to_remove.add(ws)
except KeyboardInterrupt:
sensor.clear()
pass
if (len(clients_to_remove) > 0):
await remove_dead_clients(clients_to_remove)
async def remove_dead_clients(clients_to_remove):
for client in clients_to_remove:
app.ws_clients.remove(client)
clients_to_remove.clear()
The client is able to connect just fine, and the server prints that it is trying to broadcast, but no message is ever received by the client.
I am using this broadcast function from another server that I wrote, and it works perfectly there. The difference with that one is that it only sends data when a client requests it. I feel the issue here is that the async cannot handle both continually broadcasting and removing clients simultaneously. I tried changing time.sleep() to asyncio.sleep(), but that only succeeded in successfully sending the messages dozens at a time, and then nothing at all for awhile.
Is there a pattern I could implement that would meet my needs, where I can send messages in an endless loop and also asynchronously manage connected clients?

For anyone that happens to stumble across this in the future - I had forgotten to use the await keyword prior to asyncio.sleep().

Sending and receiving frames over the same websocket connection without blocking

Sorry for the long post but I've been poking at this for over a week so I've tried a lot of different stuff. I know Python well enough but I don't have any experience with asyncio or non-blocking functions in Python.
I'm writing an API library/module/package/whatever for a web service that requires a websocket connection. There are many incoming messages to act on, and some control-related (web app level, not websocket control messages) that I need to send on occasion. I can easily receive messages over the connection and act on them. I can send messages, but only in response to received messages because the receive loop is always blocking waiting for messages. I don't want to wait for an incoming messages to process an outgoing one so the script doesn't have to hang on input until a new messages is received. In my struggles to get two-way communication working as desired I discovered I need to use something like Twisted, Tornado, or asyncio but so far every implementation I've tried has failed. Note that the sending has to happen over the same connection. Opening a short-lived connection outside of the receive loop will not work. Here's what I've done so far:
The first iteration of the websocket code was using the websocket-client package. It was very close to the example from the docs:
import websocket
try:
import thread
except ImportError:
import _thread as thread
import time
def on_message(ws, message):
# Send message frames to respective functions
# for sorting, objectification, and processing
def on_error(ws, error):
print(error)
def on_close(ws):
print("### closed ###")
def on_open(ws):
def run(*args):
# Send initial frames required for server to send the desired frames
thread.start_new_thread(run, ())
if __name__ == "__main__":
websocket.enableTrace(True)
ws = websocket.WebSocketApp(buildWebsocketURL()),
on_message = on_message,
on_error = on_error,
on_close = on_close)
ws.on_open = on_open
ws.run_forever()
This blocks any further execution outside of the loop. I tried learning up on the _thread module but I couldn't find any indication that I could "communicate" with the websocket thread from outside. I tried setting up a pub/sub listener function that would forward data to ws.send() from another sender function but it didn't work. No errors or anything, just no indication of any sent messages.
Next I tried the Websockets module. This one seems to be built from the ground up to utilize asyncio. Again, I got a client build that would send initial messages and act on received messages but the progress stopped there:
async def wsconnection():
async with websockets.connect(getWebsocketURL()) as websocket:
while True:
message = await websocket.recv()
if message == '{"type":"broadcaster.ready"}':
subscriptions = getSubscriptions() # Get subscriptions from ident data
logging.info('Sending bookmarks to server as subscription keys')
subscriptionupdate = '{{"type": "subscribe","subscription_keys": ["{0}"],"subscription_scope": "update"}}'.format(
'","'.join(subscriptions))
subscriptioncontent = '{{"subscription_keys": ["{0}"],"subscription_scope": "content","type": "subscribe"}}'.format(
'","'.join(subscriptions))
logging.debug(subscriptioncontent)
await websocket.send(subscriptionupdate)
await websocket.send(subscriptioncontent)
await websocket.send(
'{"type":"message_lobby.read","lobby_id":"1","message_id:"16256829"}')
sortframe(message)
asyncio.get_event_loop().run_until_complete(wsconnection())
I tried the aforementioned pub/sub listener applied here to no avail. Upon reading the docs for this module more thoroughly I tried getting the websocket protocol object (that contains the send() and recv() methods) outside of the loop then creating two coroutines(?), one listening for incoming messages and one listening for and sending outgoing messages. So far I've been completely unable to get the websocket protocol object without running the async with websockets.connect(getWebsocketURL()) as websocket: line within the scope of the wsconnection() function. I tried using websocket = websockets.client.connect() which according to the docs I thought would set the protocol object I need but it doesn't. All of the examples I can find don't seem to reveal any apparent way to structure the websockets sender and receiver in the way I require without extensive knowledge of asyncio.
I also poked around with autobahn with similar code structures as above using both asyncio and Twisted but I came up with all the same problems as above.
So far the closest I've gotten was with the Websockets package above. The docs have an example snippet for a send/recv connection but I can't really read what's going on there as it's all very specific to asyncio. I'm really having trouble wrapping my head around asyncio in general and I think a big problem is it seems to have very rapidly evolved recently so there is a ton of very version-specific information floating around that conflicts. Not good for learning, unfortunately. ~~~~This is what I tried using that example and it connects, receives initial messages, then the connection is lost/closed:
async def producer(message):
print('Sending message')
async def consumer_handler(websocket, path):
while True:
message = await websocket.recv()
await print(message)
await pub.sendMessage('sender', message)
async def producer_handler(websocket, path):
while True:
message = await producer()
await websocket.send(message)
async def wsconnect():
async with websockets.connect(getWebsocketURL()) as websocket:
path = "443"
async def handler(websocket, path):
consumer_task = asyncio.ensure_future(
consumer_handler(websocket, path))
producer_task = asyncio.ensure_future(
producer_handler(websocket, path))
done, pending = await asyncio.wait(
[consumer_task, producer_task],
return_when=asyncio.FIRST_COMPLETED,
)
for task in pending:
task.cancel()
pub.subscribe(producer, 'sender')
asyncio.get_event_loop().run_until_complete(wsconnect())
So how do I structure this code to get sending and receiving over the same websocket connection? I also have various API calls to make in the same script while the websocket connection is open which further complicates things.
I'm using Python 3.6.6 and this script is intended to be imported as a module into other scripts so the websocket functionality will need to be wrapped up in a function or class for external calls.

I am in the exact same situation as u. I know that this is a very inelegant solution
because it still isn't full-duplex but i can't seem to find any example on the internet or stackoverflow involving asyncio and the websockets module which i used.
I don't think i completely understand your websockets example (is that server-side or client-side code?) but i'm going to explain my situation and "solution" and maybe that would be usable for you too.
So i have a server main function that has a websocket listening for messages in a loop with recv(). When i send "start" it will start a function that will send data every second to the javascript client in the browser. But while the function is sending data i sometimes want to pause or stop the stream of data from my client be sending a stop message. The problem is that when i use recv() while the data sending has already begun the server stops sending data and only waits for a message. I tried threads,multiprocessing and some other stuff but eventually i came to the hopefully temporarily solution of sending a "pong" message to the server immediately after the client receives a piece of data so that the server continues sending data at the next loop iteration or stop sending data if the "pong" message is "stop" instead for example but yeah this is not real duplex just fast half-duplex...
code on my python "server"
async def start_server(self,websocket,webserver_path):
self.websocket = websocket
self.webserver_path = webserver_path
while True:
command = await self.websocket.recv()
print("received command")
if command == "start":
await self.analyze()
asyncio.sleep(1)
in my analyze function:
for i,row in enumerate(data)
await self.websocket.send(json.dumps(row))
msg = await self.websocket.recv()
if msg == "stop":
self.stopFlag = True
return
await asyncio.sleep(1)
main
start_server = websockets.serve(t.start_server, "127.0.0.1", 5678)
asyncio.get_event_loop().run_until_complete(start_server)
asyncio.get_event_loop().run_forever()
code on the javascript client
var ws = new WebSocket("ws://127.0.0.1:5678/");
ws.onmessage = function (event) {
var datapoint = JSON.parse(event.data);
console.log(counter);
counter++;
data.push(datapoint);
if (data.length > 40){
var element = data.shift();
render(data);
}
ws.send("pong");//sending dummy message to let server continue
};
I know it is not THE solution and i hope somebody else provides a better one but since i have the same or very similar problem and there are no other answers i decided to post and i hope it helps.

How do I send something to connected websocket clients from another thread?

I am writing a Python 3.5 program which handles some signals and serves this data to a small amount of websocket clients.
I want the websocket server and the signal handling to happen in the same program, therefore I am using threading.
The problem is I don't know how to send data from the worker thread to the client.
The Websocket server is implemented with a simple library called "websockets". The server is set up and clients can connect and talk to the server within the "new websocket client has connected" handler.
The server is set up with the help of an event loop:
start_server = websockets.serve(newWsHandler, host, port)
loop = asyncio.get_event_loop()
loop.run_until_complete(start_server)
loop.run_forever()
Because I want my program to do signal handling too, and loop.run_forever() is a blocking call, I create an endless worker thread before I start my server. This works as expected.
When the worker thread detects a signal change, it has to alert the connected websocket clients. But a simple client.send() does not work. Putting await in front of it does not work either (since that only works within coroutines, I think). I tried making a separate "async def" function and adding it to the event loop, but it gets a bit complicated because it's not on the same thread.
So the main question is: what is the best way send something to a websocket client from a worker thread? I don't receive anything in response.
EDIT:
It will probably help if I add some mock code.
def signalHandler():
#check signals
...
if alert:
connections[0].send("Alert") #NEED HELP HERE
async def newWsHandler(websocket, path):
connections.append(websocket)
while True:
#keep the connection open until the client disconnects
msg = await websocket.recv()
#top level
connections = []
...
start_server = websockets.serve(newWsHandler, host, port)
signalThread = Thread(target = signalHandler)
signalThread.setDaemon(True)
signalThread.start()
loop = asyncio.get_event_loop()
loop.run_until_complete(start_server)
loop.run_forever()