I have a websocket server written in python tornado. the server will receive many connections from clients and as you know, we have on_message function that is fired when a websocket message is received. so, here is my question that if a message(say request from client) need 5 sec to be processed then when the server is processing some request, the server goes in blocking mode and can't accept or receive more connection or data. after some research i figure out that Asyncio can resolve my problem but i don't now know to use it. so, how do i call process method to avoid blocking?
following is my code:
class WavesClient(tornado.websocket.WebSocketHandler):
def check_origin(self, origin):
return True
def open(self):
print("New client connected")
def on_message(self, message):
self.process(message)
def on_close(self):
print("Client disconnected")
def process(self,message):
#it takes 5 sec to complete
I use tornado primarily to host my webapps, therefore I can tell you if any part of your code in tornado is blocking, the whole server will block.
Now to your code:
#tornado.gen.coroutine
def on_message(self, message):
process_results = yield self.process(message)
self.write_message(process_results)
#tornado.gen.coroutine
def process(self, message):
# a long process, this is the equivalent of time.sleep(2) which is blocking
yield tornado.gen.sleep(2)
return 'finished'
With tornado you have to yield from a function to get the return value.
Also, if your function is yielding, you must wrap it using the tornado.gen.coroutine decorator
This question is similar to yours. And the answer is informative as well.
Related
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.
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 am new to web-sockets. I am using tornado/python for my back-end and written the following code.
class BaseWebSocketHandler(websocket.WebSocketHandler):
"""Base Class to establish an websocket connection."""
def open(self):
"""Opening the web socket connection."""
self.write_message('Connection Established.')
def on_message(self, message):
"""On message module send the response."""
pass
def on_close(self):
"""Close the connection."""
self.write_message('bye')
class MeterInfo(BaseWebSocketHandler):
"""Establish an websocket connection and send meter readings."""
def on_message(self, message):
"""On message module send to the response."""
self.write_message({'A': get_meter_reading()})
My JavaScript code is like the following,
var meter = new WebSocket("ws://"+window.location.host+"/socket/meterstatus/");
meter.onopen = function() {
$('#meter-well').text('Establishing connection...');
};
meter.onmessage = function (evt) {
var data = JSON.parse(evt.data)
var text = "<div class='meter'><h2>" + data.A +"</h2></div>";
$('#meter-pre').html(text);
};
meter.onclose = function (evt) {
console.log(JSON.parse(evt.data))
$('#meter-pre').append('\n'+evt.data);
};
window.setInterval(function(){ meter.send('') }, 100);
I am making a blank web-socket request request to the back-end every 100 millisecond. this seems a very bad solution to me. Is there any better way to do it without making multiple send() to the back-end and only notifying the user only on any changes in the meter reading?
Also i have gone through MQTT protocol to do this in a better way, can someone suggest how can i implement that?
You almost found the solution to your issue here:
class MeterInfo(BaseWebSocketHandler):
"""Establish an websocket connection and send meter readings."""
def on_message(self, message):
"""On message module send to the response."""
self.write_message({'A': get_meter_reading()})
As you could notice tornado needs some event to ping client through write_message method. You are using new message from client as such event, try to change to simple timeout call as event, like this:
# BaseWebSocketHandler removed, because we need to track all opened
# sockets in the class. You could change this later.
class MeterInfo(websocket.WebSocketHandler):
"""Establish an websocket connection and send meter readings."""
opened_sockets = []
previous_meter_reading = 0
def open(self):
"""Opening the web socket connection."""
self.write_message('Connection Established.')
MeterInfo.opened_sockets.append(self)
def on_close(self):
"""Close the connection."""
self.write_message('bye')
MeterInfo.opened_sockets.remove(self)
#classmethod
def try_send_new_reading(cls):
"""Send new reading to all connected clients"""
new_reading = get_meter_reading()
if new_reading == cls.previous_meter_reading:
return
cls.previous_meter_reading = new_reading
for socket in cls.opened_sockets:
socket.write_message({'A': new_reading})
if __name__ == '__main__':
# add this after all set up and before starting ioloop
METER_CHECK_INTERVAL = 100 # ms
ioloop.PeriodicCallback(MeterInfo.try_send_new_reading,
METER_CHECK_INTERVAL).start()
# start loop
ioloop.IOLoop.instance().start()
Check out tornado.ioloop documentation for more about PeriodicCallback and other options.
If you want to use tornado to MQTT protocol, it's not possible with tornado. You could try emqtt server for example, but this is actual server, not framework to write apps, so IMHO it would be more comprehensive that ping through web socket with tornado.
I am currently building a client-server-type application with Pythons autobahn (asyncio) framework on both ends. I already have the basic setup of the server, which consists of the server itself and a database managing module. For the client I want to have the networking in a separate module, so I can call <networkingModule>.sendMessage("msg") for example. Is that a good way to do it?
My problem however is, the code used to initialize the client doesn't give me a real object to work with.
import asyncio
factory = WebSocketClientFactory("ws://localhost:9000", debug = False)
factory.protocol = <ClientProtocolName>
loop = asyncio.get_event_loop()
coro = loop.create_connection(factory, '127.0.0.1', 9000)
loop.run_until_complete(coro)
loop.run_forever()
loop.close()
The class itself is:
class <ClientProtocolName>(WebSocketClientProtocol):
def onConnect(self, response):
print("Server connected: {0}".format(response.peer))
def onOpen(self):
print("WebSocket connection open.")
self.sendInput()
def _sendMessage(self, msg):
self.sendMessage(bytes(msg, "utf-8"))
def onMessage(self, payload, isBinary):
if isBinary:
print("Binary message received: {0} bytes".format(len(payload)))
else:
print("Text message received: {0}".format(payload.decode('utf8')))
def onClose(self, wasClean, code, reason):
print("WebSocket connection closed: {0}".format(reason))
So my question is: Is there a way to build a "networking module" so I can access the sendMessage method from outside and would that be a good way to go about this problem, or should I just stuff all my programm logic into the client itself?
I need to send system logs to the browser and so I have a tornado-based websocket server running like so.
class WSHandler(tornado.websocket.WebSocketHandler):
def check_origin(self, origin):
return True
def get(self, *args, **kwargs):
self.ip = self.get_argument('ip', None)
self.action = self.get_argument('action', None)
super(WSHandler, self).get(self, *args, **kwargs)
def open(self, *args, **kwargs):
clients.append(self)
def on_message(self, message):
ll = eval(message)
for cl in clients:
if cl.ip and cl.ip != ll.user:
continue
if cl.action and cl.action != ll.action:
continue
message = '%s %s' % (ll.action, ll.url)
cl.write_message(message)
def on_close(self):
try:
clients.remove(self)
except ValueError:
pass
The examples I've encountered so far revolve around Tornado-based servers and js-based clients.
What I need, however, is an easy way to connect to this websocket from a Python client, preferably powered by Tornado. The client does not need to receive messages - only send them. I thought I had my answer with this SO post,
How to run functions outside websocket loop in python (tornado)
...but I need to send a message whenever a log event occurs, and preferably from my code that's parsing the events. The examples I've encountered so far revolve around Tornado-based servers and js-based clients. Is there a short & sweet tornado-based client that only sends messages, that can be called from a for-loop?
Also, I developed a complete Tornado WebSocket Client/Server example.
https://github.com/ilkerkesen/tornado-websocket-client-example
If you want WebSocket Authentication/Authorization, look at my other projects trebol and sugar.
There is tornad-websocket-client project. Pay attention on it.
Also there is simple websocket-client to just send messages.
Tornado includes a websocket client: http://www.tornadoweb.org/en/stable/websocket.html#client-side-support