I have a couple different needs for asynchrony in my Python 3.6 Flask RESTful web service running under Gunicorn.
1) I'd like for one of my service's routes to be able to send an HTTP request to another HTTP service and, without waiting for the response, send a response back to the client that called my service.
Some example code:
#route
def fire_and_forget():
# Send request to other server without waiting
# for it to send a response.
# Return my own response.
2) I'd like for another one of my service's routes to be able to send 2 or more asynchronous HTTP requests to other HTTP services and wait for them all to reply before my service sends a response.
Some example code:
#route
def combine_results():
# Send request to service A
# Send request to service B
# Wait for both to return.
# Do something with both responses
# Return my own response.
Thanks in advance.
EDIT: I am trying to avoid the additional complexity of using a queue (e.g. celery).
You can use eventlets for the the second use case. It's pretty easy to do:
import eventlet
providers = [EventfulPump(), MeetupPump()]
try:
pool = eventlet.GreenPool()
pile = eventlet.GreenPile(pool)
for each in providers:
pile.spawn(each.get, [], 5, loc) # call the interface method
except (PumpFailure, PumpOverride):
return abort(503)
results = []
for res in pile:
results += res
You can wrap each of your api endpoints in a class that implements a "common interface" (in the above it is the get method) and you can make the calls in parallel. I just place them all in a list.
Your other use case is harder to accomplish in straight python. At least a few years ago you would be forced to introduce some sort of worker process like celery to get something like that done. This question seems to cover all the issues:
Making an asynchronous task in Flask
Perhaps things have changed in flask land?
Related
I have encountered an issue, as I have to create a cookie in the backend, which I will later use to send a request from the frontend. Both apps are on the same domain. This is the general idea behind it: https://levelup.gitconnected.com/secure-frontend-authorization-67ae11953723.
Frontend - Sending GET request to Backend
#app.get('/')
async def homepage(request: Request, response_class=HTMLResponse):
keycloak_code = 'sksdkssdk'
data = {'code': keycloak_code}
url_post = 'http://127.0.0.1:8002/keycloak_code'
post_token=requests.get(url=url_post, json = data )
return 'Sent'
if __name__ == '__main__':
uvicorn.run(app, host='local.me.me', port=7999,debug=True)
Backend
#app.get("/keycloak_code")
def get_tokens(response: Response, data: dict):
code = data['code']
print(code)
....
requests.get(url='http://local.me.me:8002/set')
return True
#app.get("/set")
async def createcookie(response: Response):
r=response.set_cookie(key='tokic3', value='helloworld', httponly=True)
return True
if __name__ == '__main__':
uvicorn.run(app, host='local.me.me', port=8002, log_level="debug")
When I open the browser and access http://local.me.me:8002/set, I can see that the cookie is created.
But when I make a GET request from my frontend to backend to the same URL, the request is received—as I can see in the terminal—but the backend does not create the cookie. Does anyone know what I might be doing wrong?
I have tried different implementations from FastAPI docs, but none has similar use cases.
127.0.0.1 and localhost (or local.me.me in your case) are two different domains (and origins). Hence, when making a request you need to use the same domain you used for creating the cookie. For example, if the cookie was created for local.me.me domain, then you should use that domain when sending the request. See related posts here, as well as here and here.
You also seem to have a second FastAPI app (listenning on a different port) acting as your frontend (as you say). If that's what you are trying to do, you would need to use Session Objects in Python requests module, or preferably, use a Client instance from httpx library, in order to persist cookies across requests. The advantage of httpx is that it offers an asynchronous API as well, using the httpx.AsyncClient(). You can find more details and examples in this answer, as well as here and here.
I built an web application using Python Bottle framework.
I used bottle-websocket plugin for WebSocket communication with clients.
Here is a part of my code.
from bottle import Bottle, request, run
from bottle.ext.websocket import GeventWebSocketServer, websocket
class MyHandler():
...
class MyServer(Bottle):
...
def _serve_websocket(self, ws):
handler = MyHandler()
some_data = request.cookies.get('some_key') # READ SOME DATA FROM HTTP REQUEST
while True:
msg = ws.receive()
handler.do_sth_on(msg, some_data) # USE THE DATA FROM HTTP REQUEST
ws.send(msg)
del(handler)
if __name__ == '__main__':
run(app=MyServer(), server=GeventWebSocketServer, host=HOST, port=PORT)
As the code shows, I need to read some data from the browser (cookies or anything in the HTTP request headers) and use it for WebSocket message processing.
How can I ensure the request is from the same browser session as the one where WebSocket connection comes?
NOTE
As I do not have much knowledge of HTTP and WebSocket, I'd love to here detailed answere as much as possible.
How can I ensure the request is from the same browser session as the one where WebSocket connection comes?
Browser session is a bit abstract since HTTP does not have a concept of sessions. HTTP and RESTful APIs is designed to be stateless, but there is options.
Usually, what you usually want to know is what user the request comes from. This is usually solved by authentication e.g. by using OpenID Connect and let the user send his JWT-token in the Authorization: header, this works for all HTTP requests, including when setting up a Websocket connection.
bottle-oauthlib seem to be a library for authenticating end-users using OAuth2 / OpenID Connect.
Another option is to identify the "browser session" using cookies but this depends on a state somewhere on the server side and is harder to implement on cloud native platforms like e.g. Kubernetes that prefer stateless workloads.
I've struggled for two days to understand how REST API Gateways should return GET requests to browsers when the backend service runs on AMQP (without using Web Sockets or polling).
Have successfully RPC'ed betweeen AMQP service (with RabbitMqs reply_to & correlation_id), but with Flask HTTP request waiting I'm still lost.
gateway.py - Response Handler Inside The HTTP Handler, Times out
def products_get():
def handler(ch=None, method=None, properties=None, body=None):
if body:
return body
return False
return_queue = 'products.get.return'
broker.channel.queue_declare(return_queue)
broker.channel.basic_consume(handler, return_queue)
broker.publish(exchange='', routing_key='products.get', body='Request data', properties=pika.BasicProperties(reply_to=return_queue))
now = time.time() # for timeout. Not having this returns 'no content' immediately
while time.time() < now + 1:
if handler():
return handler()
return 'Time out'
POST/PUT can simply send the AMQP message, return 200/201/201 immediately and the service work at its own pace. A separate REST interface just for GET requests seems implausible, but don't know the other options.
Regards
I think what you're asking is "how to perform asynchronous GET requests". and I reckon that the answer is - you can't. and should not. its bad practice or bad design. and it does not scale.
Why are you trying to get your GET response payload from AMQP?
If the paylaod (the content of the response) can be pulled from some DB, just pull it from there. that's called a synchronous request.
If the payload must be processed in some backend, send it away and don't have the requester wait for a response. You could assign some ID and have the requester ask again later (or collect some callback URL from the requester and have your backend POST the response once its ready - less common design).
EDIT:
so, given that you have to work with AMQP-backed backend, I would do something a little more elaborate: spawn a thread or a process in your front end that would constantly consume from AMQP and store the results locally or in some db. and serve GET results based on data that you stored locally. if the data isn't yet available, just return 404. ideally you'll need to re-shape your API: split it into "post" requests (that would trigger work at the backend) and "get" requests (that would return the results if they're available).
I'm working on my first Flask app (version 0.10.1), and also my first Python (version 3.5) app. One of its pieces needs to work like this:
Submit a form
Run a Celery task (which makes some third-party API calls)
When the Celery task's API calls complete, send a JSON post to another URL in the app
Get that JSON data and update a database record with it
Here's the relevant part of the Celery task:
if not response['errors']: # response comes from the Salesforce API call
# do something to notify that the task was finished successfully
message = {'flask_id' : flask_id, 'sf_id' : response['id']}
message = json.dumps(message)
print('call endpoint now and update it')
res = requests.post('http://0.0.0.0:5000/transaction_result/', json=message)
And here's the endpoint it calls:
#app.route('/transaction_result/', methods=['POST'])
def transaction_result():
result = jsonify(request.get_json(force=True))
print(result.flask_id)
return result.flask_id
So far I'm just trying to get the data and print the ID, and I'll worry about the database after that.
The error I get though is this: requests.exceptions.ConnectionError: None: Max retries exceeded with url: /transaction_result/ (Caused by None)
My reading indicates that my data might not be coming over as JSON, hence the Force=True on the result, but even this doesn't seem to work. I've also tried doing the same request in CocoaRestClient, with a Content-Type header of application/json, and I get the same result.
Because both of these attempts break, I can't tell if my issue is in the request or in the attempt to parse the response.
First of all request.get_json(force=True) returns an object (or None if silent=True). jsonify converts objects to JSON strings. You're trying to access str_val.flask_id. It's impossible. However, even after removing redundant jsonify call, you'll have to change result.flask_id to result['flask_id'].
So, eventually the code should look like this:
#app.route('/transaction_result/', methods=['POST'])
def transaction_result():
result = request.get_json()
return result['flask_id']
And you are absolutely right when you're using REST client to test the route. It crucially simplifies testing process by reducing involved parts. One well-known problem during sending requests from a flask app to the same app is running this app under development server with only one thread. In such case a request will always be blocked by an internal request because the current thread is serving the outermost request and cannot handle the internal one. However, since you are sending a request from the Celery task, it's not likely your scenario.
UPD: Finally, the last one reason was an IP address 0.0.0.0. Changing it to the real one solved the problem.
I am using a web service that will send a url callback when a particular external event happens (that service is monitoring it 24-7)
I need to have a python script running (locally on my own computer) and waiting (possibly just looping) to receive that callback and then do something with the data.
How do I do this? Do I need to have a webserver running? Where do I look for the data? I am pretty experienced with python, but not much in the use of HTTP and other web related things.
I have looked at other stackoverflow posts but they all seem to presume some prior knowledge.... I need the basics!
Here is a simple server using Bottle Microframework .
from bottle import Bottle, run, route, request
app = Bottle()
#app.route('/listener')
def my_listener():
data = request.query.your_data
#do_something_with_data(data)
return data
run(app, host="0.0.0.0", port=8080)
You can send data to server requesting http://sever_ip:8080/listener?your_data=some_data
Look into setting up a Flask server that will run in the background and listen for the callback request