How to manage setup/teardown of resources in async views? #4163
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Is it possible to attach an async resource that requires setup/teardown operations to i.e. The The flask docs have shown ways of dealing with this for database connections. Is there an idiomatic way to do this with the new async view function support? Here's a small example that shows a bit of the issue: It'd be nice if I could pass the Suggestions/discussion appreciated. |
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Replies: 1 comment 8 replies
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Hi Kyle! Interesting problem. I think you should be able to put the aiohttp session in First, in a @app.before_request
async def before():
g.session = aiohttp.ClientSession(
headers=[("User-Agent", "Kyle Lawlor - spacestationbot")],
raise_for_status=True,
)Then in your request you can use # ...
weather_report = await fetch_weather(g.session, lat, lon)
# ...Finally, an @app.teardown_request
async def teardown(exc):
await g.session.close() |
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I spoke a bit too soon earlier, the app had not reloaded the changes. I'm seeing this error when I make a request to the application: After making these changes: index e396f57..6278277 100644
--- a/app/main.py
+++ b/app/main.py
@@ -5,7 +5,7 @@ import aiohttp
from common.nominatim import fetch_nominatim
from functools import wraps
-from flask import abort, Request
+from flask import abort, g, Request
from nacl.signing import VerifyKey
from nacl.exceptions import BadSignatureError
@@ -54,6 +54,19 @@ async def fetch_weather(session, lat, lon):
return weather_report
+@app.before_request
+async def before():
+ g.session = aiohttp.ClientSession(
+ headers=[("User-Agent", "Kyle Lawlor - spacestationbot")],
+ raise_for_status=True,
+ )
+
+
+@app.teardown_request
+async def teardown(exc):
+ await g.session.close()
+
+
@app.post("/")
@ack_reply_or_abort(public_key)
async def slash_command_endpoint():
@@ -64,31 +77,27 @@ async def slash_command_endpoint():
cmd = request.json["data"]["name"]
opts = request.json["data"]["options"]
result = {}
- async with aiohttp.ClientSession(
- headers=[("User-Agent", "Kyle Lawlor - spacestationbot")],
- raise_for_status=True,
- ) as session:
- if cmd == "weather":
- for opt in opts:
- if opt["name"] == "location":
- query = opt["value"]
- result = await fetch_nominatim(session, query, cache=cache)
- lat = result.get("lat")
- lon = result.get("lon")
- if lat and lon:
- weather_report = await fetch_weather(session, lat, lon)
- return {
- "tts": True,
- "type": 4,
- "data": {
- "embeds": weather_report[:5],
- }
+ if cmd == "weather":
+ for opt in opts:
+ if opt["name"] == "location":
+ query = opt["value"]
+ result = await fetch_nominatim(g.session, query, cache=cache)
+ lat = result.get("lat")
+ lon = result.get("lon")
+ if lat and lon:
+ weather_report = await fetch_weather(g.session, lat, lon)
+ return {
+ "tts": True,
+ "type": 4,
+ "data": {
+ "embeds": weather_report[:5],
}
- else:
- return {
- "tts": True,
- "type": 4,
- "data": {
- "content": "Sorry! There was an issue looking up your location.",
- }
+ }
+ else:
+ return {
+ "tts": True,
+ "type": 4,
+ "data": {
+ "content": "Sorry! There was an issue looking up your location.",
}
+ }I'm running the app with the built-in development server ( |
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It is possible to reproduce this error with a simpler example, just by following the index 6278277..ab6be52 100644
--- a/app/main.py
+++ b/app/main.py
@@ -76,6 +76,9 @@ async def slash_command_endpoint():
logger.debug(f"{request.data=}\n")
cmd = request.json["data"]["name"]
opts = request.json["data"]["options"]
+ async with g.session.get('http://httpbin.org/get') as resp:
+ print(resp.status)
+ print(await resp.text())
result = {}
if cmd == "weather":
for opt in opts:Thanks for you for any help and I apologize if I'm missing something silly. |
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It looks like the event loop used in each handler is different. I thought the same loop was reused in all handlers, but it appears that is not the case, so unfortunately what you want to do does not seem possible with the current implementation. |
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Update: after the realization that this is not going to work with Flask, I tried the same with my aioflask package. This led me to find a small bug in how I was handling the app context, but with that fix everything works. I have created a small example that demonstrates this: https://github.com/miguelgrinberg/aioflask/blob/main/examples/g/app.py. |
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@pgjones would it be possible to keep the same event loop once one is created during a request? |
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Hi Kyle!
Interesting problem. I think you should be able to put the aiohttp session in
flask.g. I'm writing this from memory, so you'll need to test it, but I think this should work.First, in a
before_requesthandler you create the session:Then in your request you can use
g.sessionto send your request:Finally, an
teardown_requesthandler does the cleanup: