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.
Related
I have two websocket servers, call them Main and Worker, and this is the desired workflow:
Client sends message to Main
Main sends message to Worker
Worker responds to Main
Main responds to Client
Is this doable? I couldn't find any WS client functionality in Channels. I tried naively to do this (in consumers.py):
import websockets
class SampleConsumer(AsyncWebsocketConsumer):
async def receive(self, text_data):
async with websockets.connect(url) as worker_ws:
await worker_ws.send(json.dumps({ 'to': 'Worker' }))
result = json.loads(await worker_ws.recv())
await self.send(text_data=json.dumps({ 'to': 'Client' })
However, it seems that the with section blocks (Main doesn't seem to accept any further messages until the response is received from Worker). I suspect it is because websockets runs its own loop, but I don't know for sure. (EDIT: I compared id(asyncio.get_running_loop()) and it seems to be the same loop. I have no clue why it is blocking then.)
The response { "to": "Client" } does not need to be here, I would be okay even if it is in a different method, as long as it triggers when the response from Worker is received.
Is there a way to do this, or am I barking up the wrong tree?
If there is no way to do this, I was thinking of having a thread (or process? or a separate application?) that communicates with Worker, and uses channel_layer to talk to Main. Would this be viable? I would be grateful if I could get a confirmation (and even more so for a code sample).
EDIT I think I see what is going on (though still investigating), but — I believe one connection from Client instantiates one consumer, and while different instances can all run at the same time, within one consumer instance it seems the instance doesn't allow a second method to start until one method has finished. Is this correct? Looking now if moving the request-and-wait-for-response code into a thread would work.
I was in the same position where I wanted to process the message in my Django app whenever I receive it from another WebSocket server.
I took the idea of using the WebSockets client library and keeping it running as a separate process using the manage.py command from this post on the Django forum.
You can define an async coroutine client(websocket_url) to listen to messages received from the WebSocket server.
import asyncio
import websockets
async def client(websocket_url):
async for websocket in websockets.connect(uri):
print("Connected to Websocket server")
try:
async for message in websocket:
# Process message received on the connection.
print(message)
except websockets.ConnectionClosed:
print("Connection lost! Retrying..")
continue #continue will retry websocket connection by exponential back off
In the above code connect() acts as an infinite asynchronous iterator. More on that here.
You can run the above coroutine inside handle() method of the custom management command class.
runwsclient.py
from django.core.management.base import BaseCommand
class Command(BaseCommand):
def handle(self, *args, **options):
URL = "ws://example.com/messages"
print(f"Connecting to websocket server {URL}")
asyncio.run(client(URL))
Finally, run the manage.py command.
python manage.py runwsclient
You can also pass handler to client(ws_url, msg_handler) which will process the message so that processing logic will remain outside of the client.
Update 31/05/2022:
I have created a django package to integrate the above functionality with the minimal setup: django-websocketclient
Yes, Django Channels does not provide a websocket client as it is used as a server mainly.
From your code, it doesn't seem like you really need a websocket communication between the Main and Worker, as you just fire up a socket, send a single message, receive the response and close the socket. This is the classical use case for regular HTTP, so if you do not really need to keep the connection alive, I suggest you use a regular HTTP endpoint instead and use aioHTTP as a client.
However, if you do really need a client, then you should open the socket once on client connection and close it when the client disconnects. You can do something like this.
import websockets
async def create_ws(on_create, on_message):
uri = "wss://localhost:8765"
async with websockets.connect(uri) as websocket:
await on_create(websocket)
while True:
message = await websocket.recv()
if message:
await on_message(message)
class WebsocketClient:
asyn def __init__(self, channel):
self.channel = channel
self.ws = None
await creat_ws(self.on_message)
async def on_create(self, was):
self.ws = ws
async def on_message(self, ws, message):
await self.channel.send(text_data=json.dumps(message)
async def send(self, message):
self.ws.send(message)
asunc def close(self):
self.ws.close()
Then in your consumer, you can use the client as follows:
class SampleConsumer(AsyncWebsocketConsumer):
async def connect(self):
self.ws_client = WebsocketClient(self)
async def receive(self, text_data):
await self.ws_client.send(text_data)
async def disconnect(self, code):
await self.ws_client.close()
It seems I managed to do it using the latest idea I posted — launching a thread to handle the connection to Worker. Something like this:
class SampleConsumer(AsyncWebsocketConsumer):
async def receive(self, text_data):
threading.Thread(
target=asyncio.run,
args=(self.talk_to_worker(
url,
{ 'to': 'Worker' },
),)
).start()
async def talk_to_worker(self, url, message):
async with websockets.connect(url) as worker_ws:
await worker_ws.send(json.dumps(message))
result = json.loads(await worker_ws.recv())
await self.send(text_data=json.dumps({ 'to': 'Client' })
It may actually be smarter to do it with HTTP requests in each direction (since both endpoints can be HTTP servers), but this seems to work.
I'm new to websockets. I've been using the examples on the Getting Started page of the websockets docs, mainly the Synchronization Example.
In this use case, I have a sqlite3 database on localhost. I edit that database from a python GUI program on localhost which just imports the database code layer directly. The client then tells the websocket server to send out some extracted data to all clients.
(Eventually this will be on a LAN, with the server machine running a Flask API.)
This is working, with the code below, but it's not clear if I'm doing it correctly. Basically I want to send websockets messages when certain database activity takes place, and I'm confused about how to do a 'simple' non-async send, when invoked from code, ultimately in response to a GUI interaction, as opposed to doing a send in response to an incoming websocket message. In pseudo-code:
def send(ws,msg):
ws.send(msg)
send(ws,'OK!')
The way I'm accomplishing that is wrapping the async def that does the sending in a non-async 'vanilla' def.
The websocket server code:
# modified from https://websockets.readthedocs.io/en/stable/intro.html#synchronization-example
import asyncio
import websockets
USERS = set()
async def register(websocket):
print("register: "+str(websocket))
USERS.add(websocket)
async def unregister(websocket):
print("unregister: "+str(websocket))
USERS.remove(websocket)
# each new connection calls trackerHandler, resulting in a new USERS entry
async def trackerHandler(websocket, path):
await register(websocket)
try:
async for message in websocket:
await asyncio.wait([user.send(message) for user in USERS])
finally:
await unregister(websocket)
start_server = websockets.serve(trackerHandler, "localhost", 8765)
asyncio.get_event_loop().run_until_complete(start_server)
asyncio.get_event_loop().run_forever()
in the database interface code (on localhost, this file is just imported directly to the GUI app; but on the LAN server, this is the file specified in the WSGI call in Flask):
import asyncio
import websockets
# uri = "ws://localhost:8765"
# wrap the asynchronous send function inside a synchronous function
def wsSend(uri,msg):
async def send():
async with websockets.connect(uri) as websocket:
# await websocket.send(str.encode(str(msg)))
await websocket.send(json.dumps({"msg":msg}))
# print(f"> {msg}")
# greeting = await websocket.recv()
# print(f"< {greeting}")
asyncio.get_event_loop().run_until_complete(send())
...
...
def tdbPushTables(uri,teamsViewList=None,assignmentsViewList=None,teamsCountText="---",assignmentsCountText="---"):
# uri = "ws://localhost:8765"
if not teamsViewList:
teamsViewList=tdbGetTeamsView()
if not assignmentsViewList:
assignmentsViewList=tdbGetAssignmentsView()
if uri=='pusher':
pusher_client.trigger('my-channel','teamsViewUpdate',teamsViewList)
pusher_client.trigger('my-channel','assignmentsViewUpdate',teamsViewList)
else:
wsSend(uri,json.dumps({
"teamsView":teamsViewList,
"assignmentsView":assignmentsViewList,
"teamsCount":teamsCountText,
"assignmentsCount":assignmentsCountText}))
it's actually the client that initiates the call to tdbPushTables:
def buildLists(self):
self.teamsList=tdbGetTeamsView()
self.assignmentsList=tdbGetAssignmentsView()
self.updateCounts()
tdbPushTables('ws://localhost:8765',self.teamsList,self.assignmentsList,self.teamsCountText,self.assignmentsCountText)
Feels spooky. Is it spooky or is this actually the right way to do it? Should I be using the websockets module for the server, but a different module to do the 'simple'/synchronous sending of the websocket message to the server?
Two known side effects of this solution: 1) it opens and closes the websocket connection on every call - probably not really a problem...?, and 2) it results in non-fatal handled messages like this in the server transcript:
register: <websockets.server.WebSocketServerProtocol object at 0x041C46F0>
Task exception was never retrieved
future: <Task finished coro=<WebSocketCommonProtocol.send() done, defined at C:\Users\caver\AppData\Roaming\Python\Python37\site-packages\websockets\protocol.py:521> exception=ConnectionClosedOK('code = 1000 (OK), no reason')>
Traceback (most recent call last):
File "C:\Users\caver\AppData\Roaming\Python\Python37\site-packages\websockets\protocol.py", line 555, in send
await self.ensure_open()
File "C:\Users\caver\AppData\Roaming\Python\Python37\site-packages\websockets\protocol.py", line 812, in ensure_open
raise self.connection_closed_exc()
websockets.exceptions.ConnectionClosedOK: code = 1000 (OK), no reason
unregister: <websockets.server.WebSocketServerProtocol object at 0x041C46F0>
EDIT: looks like the websocket (singular) module has a synchronous interface, and the websockets (plural) docs explain that if you want to go synchronous you should use a different module; so, this works:
(instead of importing asyncio and websockets)
from websocket import create_connection
def wsSend(uri,msg):
ws=create_connection(uri)
ws.send(json.dumps({"msg":msg}))
ws.close()
It does still result in the same handled traceback showing up in the server transcript each time wsSend is called; there's probably a way to silence that traceback output, but, regardless, it still doesn't seem to affect anything.
Your code feels spooky, because you are mixing async code with synchronous code.
Based on personal experience, the code is simpler to follow if you keep most of the code asynchronous.
The structure will become something like:
import asyncio
import websockets
async def main():
# Create websocket connection
async with websockets.connect(uri) as websocket:
await your_function_that_does_some_processing(websocket)
asyncio.get_event_loop().run_until_complete(main())
Have in mind that big sections of blocking code can generate trouble.
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().
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.
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()