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.
Related
I've been facing this issue where I have a gRPC AIO python client sending bunch of configuration changes to the gRPC server, though it's a bi-directional RPC, client is not expecting any message from gRPC server. So whenever there is a configuration change the client sends gRPC message containing the configuration. It keeps the channel open and it's not closed (not calling done_writing()) . But when it doesn't have anything to send, it polls a queue for any new message in a tight loop. During that time if the server goes down, the client is not able to detect that. But, as soon as some data is available in the queue, while pushing it to server, client is able to detect that server went down(exception thrown).
How to detect server went down while there is no data to send and client is waiting for data availability. Is there any gRPC API I can call on the channel while the client is waiting for data to send, in order to detect channel failure(basically if there is any api call which throws exception while the server went down is also good for me, I was not able to find any useful API)? I tried gRPC keepalive, but it didn't work for my scenario.
async with grpc.aio.insecure_channel('127.0.0.1:51234') as channel:
stream = hello_pb2.HelloStub(channel).Configure()
await stream.wait_for_connection()
while True:
if queue.empty():
continue
if not queue.empty():
item = queue.get()
await asyncio.sleep(0.001)
queue.task_done()
await stream.write(item)
await asyncio.sleep(0.01)
await stream.done_writing()
I tried to enable gRPS keepalive while forming insecure_channel. It didn't have desired effect.
Subsequently I tried calling channel_ready() inside the tight loop during queue empty, was expecting to throw some exception and come out of that loop, but it didn't work.
async with grpc.aio.insecure_channel('127.0.0.1:51234',
options = [
('grpc.keepalive_time_ms', 60000),
('grpc.keepalive_timeout_ms', 600000),
('grpc.keepalive_permit_without_calls', 1),
('grpc.http2.max_pings_without_data', 0),
('grpc.http2.min_time_between_pings_ms', 10000),
('grpc.http2.min_ping_interval_without_data_ms', 60000),
('grpc.max_connection_age_ms', 2147483647),
]) as channel:
I was able to solve it using channel.get_state(). Below is the code snippet
if queue.empty():
if channel.get_state() != grpc.ChannelConnectivity.READY:
break
time.sleep(5)
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'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 try to create a client which uses a asyncio.Queue to feed the messages I want to send to the server. Receiving data from websocket server works great. Sending data which is just generated by the producer works, too. For explaning what works and what fails, first here's my code:
import sys
import asyncio
import websockets
class WebSocketClient:
def __init__(self):
self.send_queue = asyncio.Queue()
#self.send_queue.put_nowait('test-message-1')
async def startup(self):
await self.connect_websocket()
consumer_task = asyncio.create_task(
self.consumer_handler()
)
producer_task = asyncio.create_task(
self.producer_handler()
)
done, pending = await asyncio.wait(
[consumer_task, producer_task],
return_when=asyncio.ALL_COMPLETED
)
for task in pending:
task.cancel()
async def connect_websocket(self):
try:
self.connection = await websockets.client.connect('ws://my-server')
except ConnectionRefusedError:
sys.exit('error: cannot connect to backend')
async def consumer_handler(self):
async for message in self.connection:
await self.consumer(message)
async def consumer(self, message):
self.send_queue.put_nowait(message)
# await self.send_queue.put(message)
print('mirrored message %s now in queue, queue size is %s' % (message, self.send_queue.qsize()))
async def producer_handler(self):
while True:
message = await self.producer()
await self.connection.send(message)
async def producer(self):
result = await self.send_queue.get()
self.send_queue.task_done()
#await asyncio.sleep(10)
#result = 'test-message-2'
return result
if __name__ == '__main__':
wsc = WebSocketClient()
asyncio.run(wsc.startup())
Connecting works great. If I send something from my server to the client, this works great too and prints the message in consumer(). But producer never gets any message I put in send_queue inside consumer().
The reason why I chose send_queue.put_nowait in consumer() was that I wanted to prevent deadlocks. If I use the line await self.send_queue.put(message) line instead of self.send_queue.put_nowait(message) it makes no difference.
I thought, maybe the queue dos not work at all, so I filled something to the queue just at creation in __init__(): self.send_queue.put_nowait("test-message-1"). This works and is sent to my server. So the basic concept of the queue and await queue.get() works.
I als thought, maybe there is some issue with the producer, so let's just randomly generate messages during runtime: result = "test-message-2" instead of result = await self.send_queue.get(). This works too: every 10 seconds 'test-message-2' is sent to my server.
EDIT: This also happens if I try to add stuff from another source to the queue on the fly. I build a small asyncio socket server which pushes any message to the queue, which works great, and you can see the messages I added from the other source with qsize() in consumer(), but still no successfull queue.get(). So the queue itself seems to work, just not get(). This is btw the reason for the queue, too: I would like to send data from quite different sources.
So, this is the point where I'm stuck. My wild guess is that the queue I use in producer() is not the same as in consumer(), something which happens at threading quite easily if you use non-thread-safe queues like asyncio.Queue, but as I understood it I don't use threading at all, just coroutines. So, what else went wrong here?
Just for the context: it's a Ubuntu 20.04 python 3.8.2 inside a docker container.
Thanks,
Ernesto
Just for the records - the solution for my problem was quite simple: I defined send_queue outside the event loop created by my websocket client. So it called events.get_event_loop() and got its own loop - which was not part of the main loop and therefore never called, therefore await queue.get() really never got anything back.
In normal mode, you don't see any message which is a hint to this issue. But, python documentation to the rescue: for course they mentioned it at https://docs.python.org/3/library/asyncio-dev.html : logging.DEBUG gave the hints I needed to find the problem.
It should look like this:
class WebSocketClient:
async def startup(self):
self.send_queue = asyncio.Queue()
await self.connect_websocket()
Then the queue is defined inside the main loop.
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().