how i con use flutter_local_notification package in terminated state ????
how i con use flutter_local_notification package in terminated state ????
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Minimal reproducible example:
import asyncio
import aiopg
from fastapi import FastAPI, WebSocket
dsn = "dbname=aiopg user=aiopg password=passwd host=127.0.0.1"
app = FastAPI()
class ConnectionManager:
self.count_connections = 0
# other class functions and variables are taken from FastAPI docs
...
manager = ConnectionManager()
async def send_and_receive_data(websocket: WebSocket):
data = await websocket.receive_json()
await websocket.send_text('Thanks for the message')
# then process received data
# taken from official aiopg documentation
# the function listens to PostgreSQL notifications
async def listen(conn):
async with conn.cursor() as cur:
await cur.execute("LISTEN channel")
while True:
msg = await conn.notifies.get()
async def postgres_listen():
async with aiopg.connect(dsn) as listenConn:
listener = listen(listenConn)
await listener
#app.get("/")
def read_root():
return {"Hello": "World"}
#app.websocket("/")
async def websocket_endpoint(websocket: WebSocket):
await manager.connect(websocket)
manager.count_connections += 1
if manager.count_connections == 1:
await asyncio.gather(
send_and_receive_data(websocket),
postgres_listen()
)
else:
await send_and_receive_data(websocket)
Description of the problem:
I am building an app with Vue.js, FastAPI and PostgreSQL. In this example I attempt to use listen/notify from Postgres and implement it in the websocket. I also use a lot of usual http endpoints along with the websocket endpoint.
I want to run a permanent background asynchronous function at the start of the FastAPI app that will then send messages to all websocket clients/connections. So, when I use uvicorn main:app it should not only run the FastAPI app but also my background function postgres_listen(), which notifies all websocket users, when a new row is added to the table in the database.
I know that I can use asyncio.create_task() and place it in the on_* event, or even place it after the manager = ConnectionManager() row, but it will not work in my case! Because after any http request (for instance, read_root() function), I will get the same error described below.
You see that I use a strange way to run my postgres_listen() function in my websocket_endpoint() function only when the first client connects to the websocket. Any subsequent client connection does not run/trigger this function again. And everything works fine... until the first client/user disconnects (for example, closes browser tab). When it happens, I immediately get the GeneratorExit error caused by psycopg2.OperationalError:
Future exception was never retrieved
future: <Future finished exception=OperationalError('Connection closed')>
psycopg2.OperationalError: Connection closed
Task was destroyed but it is pending!
task: <Task pending name='Task-18' coro=<Queue.get() done, defined at
/home/user/anaconda3/lib/python3.8/asyncio/queues.py:154> wait_for=<Future cancelled>>
The error comes from the listen() function. After this error, I will not get any notification from the database as the asyncio's Task is cancelled. There is nothing wrong with the psycopg2, aiopg or asyncio. The problem is that I don't understand where to put the postgres_listen() function so it will not be cancelled after the first client disconnects. From my understanding, I can easily write a python script that will connect to the websocket (so I will be the first client of the websocket) and then run forever so I will not get the psycopg2.OperationalError exception again, but it does not seem right to do so.
My question is: where should I put postgres_listen() function, so the first connection to websocket may be disconnected with no consequences?
P.S. asyncio.shield() also does not work
I have answered this on Github as well, so I am reposting it here.
A working example can be found here:
https://github.com/JarroVGIT/fastapi-github-issues/tree/master/5015
# app.py
import queue
from typing import Any
from fastapi import FastAPI, WebSocket, WebSocketDisconnect
from asyncio import Queue, Task
import asyncio
import uvicorn
import websockets
class Listener:
def __init__(self):
#Every incoming websocket conneciton adds it own Queue to this list called
#subscribers.
self.subscribers: list[Queue] = []
#This will hold a asyncio task which will receives messages and broadcasts them
#to all subscribers.
self.listener_task: Task
async def subscribe(self, q: Queue):
#Every incoming websocket connection must create a Queue and subscribe itself to
#this class instance
self.subscribers.append(q)
async def start_listening(self):
#Method that must be called on startup of application to start the listening
#process of external messages.
self.listener_task = asyncio.create_task(self._listener())
async def _listener(self) -> None:
#The method with the infinite listener. In this example, it listens to a websocket
#as it was the fastest way for me to mimic the 'infinite generator' in issue 5015
#but this can be anything. It is started (via start_listening()) on startup of app.
async with websockets.connect("ws://localhost:8001") as websocket:
async for message in websocket:
for q in self.subscribers:
#important here: every websocket connection has its own Queue added to
#the list of subscribers. Here, we actually broadcast incoming messages
#to all open websocket connections.
await q.put(message)
async def stop_listening(self):
#closing off the asyncio task when stopping the app. This method is called on
#app shutdown
if self.listener_task.done():
self.listener_task.result()
else:
self.listener_task.cancel()
async def receive_and_publish_message(self, msg: Any):
#this was a method that was called when someone would make a request
#to /add_item endpoint as part of earlier solution to see if the msg would be
#broadcasted to all open websocket connections (it does)
for q in self.subscribers:
try:
q.put_nowait(str(msg))
except Exception as e:
raise e
#Note: missing here is any disconnect logic (e.g. removing the queue from the list of subscribers
# when a websocket connection is ended or closed.)
global_listener = Listener()
app = FastAPI()
#app.on_event("startup")
async def startup_event():
await global_listener.start_listening()
return
#app.on_event("shutdown")
async def shutdown_event():
await global_listener.stop_listening()
return
#app.get('/add_item/{item}')
async def add_item(item: str):
#this was a test endpoint, to see if new items where actually broadcasted to all
#open websocket connections.
await global_listener.receive_and_publish_message(item)
return {"published_message:": item}
#app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
await websocket.accept()
q: asyncio.Queue = asyncio.Queue()
await global_listener.subscribe(q=q)
try:
while True:
data = await q.get()
await websocket.send_text(data)
except WebSocketDisconnect:
return
if __name__ == "__main__":
uvicorn.run(app, host="0.0.0.0", port=8000)
As I didn't have access to a stream of message I could have subscribed to, I created a quick script that produces a websocket, so that the app.py above could listen to that (indefinitely) to mimic your use case.
# generator.py
from fastapi import FastAPI, WebSocket, WebSocketDisconnect
import asyncio
import uvicorn
app = FastAPI()
#app.websocket("/")
async def ws(websocket: WebSocket):
await websocket.accept()
i = 0
while True:
try:
await websocket.send_text(f"Hello - {i}")
await asyncio.sleep(2)
i+=1
except WebSocketDisconnect:
pass
if __name__ == "__main__":
uvicorn.run(app, host="0.0.0.0", port=8001)
The app.py will listen to a websocket and publishes all incoming messages to all connections to the websockets in app.py.
The generator.py is a simple FastAPI app that has a websocket (that our example app.py above listens to) that emits a message every 2 seconds to every connection it gets.
To try this out:
Start generator.py (e.g. python3 generator.py on your command line when in your working folder)
Start app.py (either debug mode in VScode or same as above)
Listen to http://localhost:8000/ws (= endpoint in app.py) with several clients, you will see that they will all join in the same message streak.
NOTE: lots of this logic was inspired by Broadcaster (a python module)
I'm using the Geolocator version 7.0.3 flutter package in my project and wanted to listen for the service status changes. In the documentation they are stating:
To listen for service status changes you can call the getServiceStatusStream. This will return a Stream which can be listened to, to receive location service status updates.
import 'package:geolocator/geolocator.dart';
StreamSubscription<ServiceStatus> serviceStatusStream = Geolocator.getServiceStatusStream().listen(
(ServiceStatus status) {
print(status);
});
But when calling Geolocator.getServiceStatusStream(); this error is shown:
The method 'getServiceStatusStream' isn't defined for the type 'Geolocator'.
Try correcting the name to the name of an existing method, or defining a method named 'getServiceStatusStream'.
Even in the breaking changes in 7.0.0
there is nothing saying that they moved it somewhere else or removed it.
Make sure to use version 7.1.0 or higher
I have a Web application that is using Flask-socketIO.
__init__.py
import flask
import flask_socketio
app = flask.Flask(__name__)
socketio = flask_socketio.SocketIO()
socketio.init_app(app, manage_session=False)
I have this in my manage.py
socketio.run(app, host='0.0.0.0', port=80)
I have this in my socket_IO.py
#WebApp.socketio.on('disconnect', namespace='/all')
def disconnect():
"""Socket disconnected."""
print('Disconnected')
If i now set the system clock ( Ubuntu 16.04 ) for example 1 day forward i get socket disconnect. I can set the clock backwards to whatever i want it does not effect the socket.
What i expect to happen is for the socket not to fire the disconnect function on a change in the system clock.
Does flask-socketIO use the system clock and because of that makes the socket disconnect if it's set forward and not backwards?
Thanks in advance
I am using rabbitmctl using pika library.
I use the following code to create a Producer
#!/usr/bin/env python
import pika
import time
import json
import datetime
connection = pika.BlockingConnection(pika.ConnectionParameters(
host='localhost'))
channel = connection.channel()
channel.queue_declare(queue='hello')
def callback(ch, method, properties, body):
#print " current time: %s " % (str(int((time.time())*1000)))
print body
channel.basic_consume(callback,
queue='hello',
no_ack=True)
channel.start_consuming()
Since I create an existing queue everytime (Over-write the creation of queue in case if queue is not created) The queue has been corrupted due to this.and now I want to delete the queue..how do i do that?
Since this seems to be a maintenance procedure, and not something you'll be doing routinely on your code, you should probably be using the RabbitMQ management plugin and delete the queue from there.
Anyway, you can delete it from pika with:
channel.queue_delete(queue='hello')
https://pika.readthedocs.org/en/latest/modules/channel.html#pika.channel.Channel.queue_delete
The detailed answer is as follows (with reference to above very helpful and useful answer)
import pika
connection = pika.BlockingConnection(pika.ConnectionParameters(
'localhost'))
channel = connection.channel()
channel.queue_delete(queue='hello')
connection.close()
GUI rabbitMQ mgm't made that easy
$ sudo rabbitmq-plugins enable rabbitmq_management
http://localhost:15672/#/queues
Username : guest
password : guest
inspired by this
I would like to write some code to monitor events for domains running under QEMU, managed by libvirt. However, trying to register an event handler yields the following error:
>>> import libvirt
>>> conn = libvirt.openReadOnly('qemu:///system')
>>> conn.domainEventRegister(callback, None)
libvir: Remote error : this function is not supported by the connection driver: no event support
("callback" in this case is a stub function that simply prints its arguments.)
The examples I've been able to find regarding libvirt's event handling don't seem to be specific as to which backend hypervisors support which features. Is this expected to work for QEMU backends?
I'm running a Fedora 16 system, which includes libvirt 0.9.6 and qemu-kvm 0.15.1.
For folks finding themselves here via <searchengine>:
UPDATE 2013-10-04
Many months and a few Fedora releases later, the event-test.py code in the libvirt git repository runs correctly on Fedora 19.
Make sure you have registered in the libvirt event loop (or set up your own) before registering for events.
There is a nice example of event handling shipped with the libvirt source (file is called event-test.py). I'm attaching an example based on that code;
import libvirt
import time
import threading
def callback(conn, dom, event, detail, opaque):
print "EVENT: Domain %s(%s) %s %s" % (dom.name(),
dom.ID(),
event,
detail)
eventLoopThread = None
def virEventLoopNativeRun():
while True:
libvirt.virEventRunDefaultImpl()
def virEventLoopNativeStart():
global eventLoopThread
libvirt.virEventRegisterDefaultImpl()
eventLoopThread = threading.Thread(target=virEventLoopNativeRun,
name="libvirtEventLoop")
eventLoopThread.setDaemon(True)
eventLoopThread.start()
if __name__ == '__main__':
virEventLoopNativeStart()
conn = libvirt.openReadOnly('qemu:///system')
conn.domainEventRegister(callback, None)
conn.setKeepAlive(5, 3)
while conn.isAlive() == 1:
time.sleep(1)
Good luck!
//Seto