Expected Behavior

When using copy_current_request_context in the middle of a request, I'm expecting it to copy the current state of flask.request and flask.session at the time it's called.

Actual Behavior

The current state of flask.request is copied, but flask.session is from before the current request and doesn't contain changes made during the current request, before copy_current_request_context was called. To me this seems like unexpected behaviour. If it's not I'd like to understand a bit more about why, and also to find out whether there's any workaround or alternative approach I can take.

Example

Here's a fully functional example you can save and run. It adds a test value to flask.request and flask.session during the request, then uses copy_current_request_context to decorate a method that will retrieve those same values in another thread. Two requests are made; on the first request the copied context can find the new value added to flask.request but cannot find the value added to flask.session. On the second request, the copied context can find the value added to flask.request, and now finds the value that was previously added to flask.session in the first request.

import concurrent.futures
import random
from flask import Flask, copy_current_request_context, request, session
app = Flask(__name__)
app.config['SECRET_KEY'] = 'test'
executor = concurrent.futures.ThreadPoolExecutor()
@app.route('/')
def session_context():
    test_value = random.randint(1, 1001)
    request.test_value = test_value
    session['TEST_VALUE'] = test_value
    original_context = (
        ('request', request.test_value),
        ('session', session.get('TEST_VALUE'))
    )
    @copy_current_request_context
    def debug_session():
        return (
            ('request', request.test_value),
            ('session', session.get('TEST_VALUE'))
        )
    future = executor.submit(debug_session)
    print('original_context:', original_context)
    print('copied_context:', future.result())
    return 'ok'
if __name__ == '__main__':
    client = app.test_client()
    print('### First request ###')
    client.get('/')
    print('### Second request ###')
    client.get('/')

Example output:

$ python session_context.py
### First request ###
original_context: (('request', 27), ('session', 27))
copied_context: (('request', 27), ('session', None))
### Second request ###
original_context: (('request', 63), ('session', 63))
copied_context: (('request', 63), ('session', 27))

Environment

• Python version: 3.7.0
• Flask version: Flask==1.0.2
• Werkzeug version: Werkzeug==0.14.1

Also, for whatever it's worth: I'm investigating this as part of improving this project: https://github.com/dchevell/flask-executor