I am using flask and flask-restx try to create a protocol to get a specific string from another service. I am trying to figure out a way to run the function in server in different threads. Here's my code sample:
from flask_restx import Api,fields,Resource
from flask import Flask
app = Flask(__name__)
api = Api(app)
parent = api.model('Parent', {
'name': fields.String(get_answer(a,b)),
'class': fields.String(discriminator=True)
})
#api.route('/language')
class Language(Resource):
# #api.marshal_with(data_stream_request)
#api.marshal_with(parent)
#api.response(403, "Unauthorized")
def get(self):
return {"happy": "good"}
What I expect:
In Client side, first the server should run, i.e., we should able to make curl -i localhost:8080 work. Then when a specific condition is true, the client side should receive a GET request with the parent JSON data I have in server. However, if that condition is true, the GET request should not be able to return the correct result.
What I did:
One of the method I used is wrap up the decorator and Class Language(Resource) part in a different function and wrong that function in a different thread, and put that thread under a condition check. Not sure if that's the right way to do.I was seeing anyone said celery might be a good choice but not sure if that can work in flask-restx.
I have the answer for you. to run a process in the background with flask, schedule it to run using another process using APScheduler. A very simple package that helps you schedule tasks to run functions at an interval, in your case one time at utcnow().
here is the link to Flask-APScheduler.
job = scheduler.add_job(myfunc, 'interval', minutes=2)
In your case use 'date' instead of 'interval' and specify run_date
job = scheduler.add_job(myfunc, 'date', run_date=datetime.utcnow())
You can send arguments to the function:
job = scheduler.add_job(myfunc, 'date', args = (your args), run_date=datetime.utcnow())
here is the documentation:
User Guide
Related
I'm trying to implement a service that will get a request from an external API, do some work (which might take time) and then return a response to the external API with the parsed data. However I'm at a loss on how to achieve this. I'm using FastAPI as my API service and have been looking at the following documentation: OpenAPI Callbacks
By following that documentation I can get the OpenAPI docs looking all pretty and nice. However I'm stumped on how to implement the actual callback and the docs don't have much information about that.
My current implementation is as follows:
from typing import Union
from fastapi import APIRouter, FastAPI
from pydantic import BaseModel, AnyHttpUrl
import requests
import time
from threading import Thread
app = FastAPI()
class Invoice(BaseModel):
id: str
title: Union[str, None] = None
customer: str
total: float
class InvoiceEvent(BaseModel):
description: str
paid: bool
class InvoiceEventReceived(BaseModel):
ok: bool
invoices_callback_router = APIRouter()
#invoices_callback_router.post(
"{$callback_url}/invoices/{$request.body.id}", response_model=InvoiceEventReceived
)
def invoice_notification(body: InvoiceEvent):
pass
#app.post("/invoices/", callbacks=invoices_callback_router.routes)
async def create_invoice(invoice: Invoice, callback_url: Union[AnyHttpUrl, None] = None):
# Send the invoice, collect the money, send the notification (the callback)
thread = Thread(target=do_invoice(invoice, callback_url))
thread.start()
return {"msg": "Invoice received"}
def do_invoice(invoice: Invoice, callback_url: AnyHttpUrl):
time.sleep(10)
url = callback_url + "/invoices/" + invoice.id
json = {
"data": ["Payment celebration"],
}
requests.post(url=url, json=json)
I thought putting the actual callback in a separate thread might work and that the {"msg": "Invoice received"} would be returned immediately and then 10s later the external api would recieve the result from the do_invoice function. But this doesn't seem to be the case so perhaps I'm doing something wrong.
I've also tried putting the logic in the invoice_notification function but that doesn't seem to do anything at all.
So what is the correct to implement a callback like the one I want? Thankful for any help!
I thought putting the actual callback in a separate thread might work and that the {"msg": "Invoice received"} would be returned
immediately and then 10s later the external api would recieve the
result from the do_invoice function. But this doesn't seem to be the case so perhaps I'm doing something wrong.
If you would like to run a task after the response has been sent, you could use a BackgroundTask, as demonstrated in this answer, as well as here and here. If you instead would like to wait for the task to finish before returning the response, you could run the task in either an external ThreadPool or ProcessPool (depending on the nature of the task) and await it, as explained in this detailed answer.
I would also strongly recommend using the httpx library in an async environment such as FastAPI, instead of using Python requests—you may find details and working examples here, as well as here and here.
I am trying to build REST API with only one call.
Sometimes it takes up to 30 seconds for a program to return a response. But if user thinks that service is lagging - he makes a new call and my app returns response with error code 500 (Internal Server Error).
For now it is enough for me to block any new requests if last one is not ready. Is there any simple way to do it?
I know that there is a lot of queueing managers like Celery, but I prefer not to overload my app with any large dependencies/etc.
You could use Flask-Limiter to ignore new requests from that remote address.
pip install Flask-Limiter
Check this quickstart:
from flask import Flask
from flask_limiter import Limiter
from flask_limiter.util import get_remote_address
app = Flask(__name__)
limiter = Limiter(
app,
key_func=get_remote_address,
default_limits=["200 per day", "50 per hour"]
)
#app.route("/slow")
#limiter.limit("1 per day")
def slow():
return "24"
#app.route("/fast")
def fast():
return "42"
#app.route("/ping")
#limiter.exempt
def ping():
return "PONG"
As you can see, you could ignore the remote IP address for a certain amount of time meanwhile you finish the process you´re running
DOCS
Check these two links:
Flasf-Limiter Documentation
Flasf-Limiter Quick start
I have a REST API, which returns a JSON response. I need to keep track of one of the fields of the response, and listen for any changes in the value of this field. If the value reaches a certain threshold, I need to perform some task (say print an alert message). How can I accomplish this? Right now, I have a daemon which runs periodically, making an HTTP request and obtaining the value. What is the correct approach to do this, if I want to perform the action the moment the variable reaches the threshold?
This is what I currently have -
import daemon, time
from daemon import runner
NUMBER_OF_MINUTES = 10
def doSomething():
print "Yay, we got there"
def getSomeData():
url = "www.somewebsite.com/getdata?id=somevalue&name=someothervalue"
response = requests.get(url)
json_data = response.json()
myField = json_data['somefield']
if myField > threshold:
doSomething()
def run()
while True:
getSomeData()
time.sleep(60*NUMBER_OF_MINUTES)
if __name__ == '__main__':
run()
Do you have control of the API? If so, add a websocket endpoint that your frontend app can connect to. Your API can then let your frontend app know whenever the value changes, through whatever data structure is appropriate.
If you don't have control of the API, your current polling solution is about as good as it gets.
Just to give a context here, I'm a node.JS developer, but I'm on a project that I need to work with Python using Flask framework.
The problem is, when a client request to an endpoint of my rest flask app, I need to emit an event using socket.IO, and get some data from the socket server, then this data is the response of the endpoint. But I didn't figured out how to send this, because flask needs a "return" statement saying what is the response, and my callback is in another context.
Sample of what I'm trying to do: (There's some comments explaining)
import socketio
import eventlet
from flask import Flask, request
sio = socketio.Server()
app = Flask(__name__)
#app.route('/test/<param>')
def get(param):
def ack(data):
print (data) #Should be the response
sio.emit('event', param, callback=ack) # Socket server call my ack function
#Without a return statement, the endpoint return 500
if __name__ == '__main__':
app = socketio.Middleware(sio, app)
eventlet.wsgi.server(eventlet.listen(('', 8000)), app)
Maybe, the right question here is: Is this possible?
I'm going to give you one way to implement what you want specifically, but I believe you have an important design flaw in this, as I explain in a comment above. In the way you have this coded, your socketio.Server() object will broadcast to all your clients, so will not be able to get a callback. If you want to emit to one client (hopefully not the same one that sent the HTTP request), then you need to add a room=client_sid argument to the emit. Or, if you are contacting a Socket.IO server, then you need to use a Socket.IO client here, not a server.
In any case, to block your HTTP route until the callback function is invoked, you can use an Event object. Something like this:
from threading import Event
from flask import jsonify
#app.route('/test/<param>')
def get(param):
ev = threading.Event()
result = None
def ack(data):
nonlocal result
nonlocal ev
result = {'data': data}
ev.set() # unblock HTTP route
sio.emit('event', param, room=some_client_sid, callback=ack)
ev.wait() # blocks until ev.set() is called
return jsonify(result)
I had a similar problem using FastAPI + socketIO (async version) and I was stuck at the exact same point. No eventlet so could not try out the monkey patching option.
After a lot of head bangings it turns out that, for some reason, adding asyncio.sleep(.1) just before ev.wait() made everything work smoothly. Without that, emitted event actually never reach the other side (socketio client, in my scenario)
I have a python server that is currently keeping track of the location of all the buses in my university and generating predictions of arrivals to specific locations.
Now, I wanted to attach a lightweight REST API to this server but I have been running intro problems.
I tried using flask with the following code:
from flask import Flask, jsonify
from PredictionWrapper import *
import threading
class RequestHandler():
def __init__(self,predictionWrapper):
self.app = Flask(__name__)
self.predictor = predictionWrapper
self.app.debug = False
self.app.add_url_rule('/<route>/<int:busStop>','getSinglePrediction',self.getSinglePrediction)
t = threading.Thread(target=self.app.run, kwargs={'host':'0.0.0.0', 'port':80, 'threaded':True})
t.start()
def getSinglePrediction(self, route, busStop):
# TODO Get the actual prediction with given parameters
prediction = self.predictor.getPredictionForStop(route, busStop)
return jsonify({'busStop': busStop, 'prediction': prediction})
def getStopPrediction(self, busStop):
# TODO Get the actual prediction with given parameters
return jsonify({'busStop': busStop, 'prediction': 2})
def run(self):
self.app.run(host='0.0.0.0', port=80, threaded=True)
The problem is that I have been encountering the error below after about half a day of running the server. Note that no requests were made to the server around the time it failed with the following error:
ERROR:werkzeug: - - [01/May/2016 09:55:55] code 400, message Bad request syntax ('\x02\xfd\xb1\xc5!')
After investigating I believe I need to deploy to a WSGI production server. But I have no clue what it means in this specific approach given that 1)the flask server is being threaded in order to run the rest of the prediction application, and 2)I am using classes which none of the documentation uses.
Any help on how to setup the wsgi file with apache, gunicorn, or the technology of your choice would be appreciated. Also, any comments on a better approach on making a non-blocking REST API would be helpful.
Let me know if you need any further clarification!
Not sure if this can actually solve your problem but you can use the coroutine based web server gevent. They have a WSGI server that you can use if that's what you meant by saying that you need to deploy a WSGI production server.
If you want to implement the server to your flask application just do the following:
from gevent.pywsgi import WSGIServer
app = Flask(__name__)
http_server = WSGIServer(('', 5000), app)
http_server.serve_forever()
Gevent in general is a very powerful tool and by issuing context switches as necessary it can handle multiple clients very easily. Also, gevent fully supports flask.
First thing to do would be to put exception handling to deal with bad JSON request data (which maybe is what's happening) something like
def getSinglePrediction(self, route, busStop):
try:
prediction = self.predictor.getPredictionForStop(route, busStop)
return jsonify({'busStop': busStop, 'prediction': prediction})
except:
return jsonify({'busStop': 'error', 'prediction': 'error'})