flask.abort() behavioral change in debug mode

[pypingou]

Expected Behavior

In flask 1.0, calling flask.abort(400) returns a 500 error in debug mode

import flask
import werkzeug

APP = flask.Flask(__name__)
print(flask.__version__)
print(werkzeug.__version__)

@APP.route('/<arg>')
def index(arg):
    return flask.abort(400)

APP.debug = True
APP.run()

Actual Behavior

When App.debug = True is set:

127.0.0.1 - - [27/Apr/2018 17:39:16] "GET /tes HTTP/1.1" 500 -
Traceback (most recent call last):
  File "/home/pingou/.local/share/virtualenvs/pag/lib/python2.7/site-packages/flask/app.py", line 2301, in __call__
    return self.wsgi_app(environ, start_response)
  File "/home/pingou/.local/share/virtualenvs/pag/lib/python2.7/site-packages/flask/app.py", line 2287, in wsgi_app
    response = self.handle_exception(e)
  File "/home/pingou/.local/share/virtualenvs/pag/lib/python2.7/site-packages/flask/app.py", line 1733, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/home/pingou/.local/share/virtualenvs/pag/lib/python2.7/site-packages/flask/app.py", line 2284, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/pingou/.local/share/virtualenvs/pag/lib/python2.7/site-packages/flask/app.py", line 1807, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/pingou/.local/share/virtualenvs/pag/lib/python2.7/site-packages/flask/app.py", line 1710, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/home/pingou/.local/share/virtualenvs/pag/lib/python2.7/site-packages/flask/app.py", line 1805, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/pingou/.local/share/virtualenvs/pag/lib/python2.7/site-packages/flask/app.py", line 1791, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/pingou/reproducer.py", line 12, in index
    return flask.abort(400)
  File "/home/pingou/.local/share/virtualenvs/pag/lib/python2.7/site-packages/werkzeug/exceptions.py", line 707, in abort
    return _aborter(status, *args, **kwargs)
  File "/home/pingou/.local/share/virtualenvs/pag/lib/python2.7/site-packages/werkzeug/exceptions.py", line 687, in __call__
    raise self.mapping[code](*args, **kwargs)
BadRequest: 400 Bad Request: The browser (or proxy) sent a request that this server could not understand.

Calling the endpoint via requests show:

>>> requests.get('http://127.0.0.1:5000/tes')
<Response [500]>

When App.debug = True is commented out, I get the expected behavior:

>>> requests.get('http://127.0.0.1:5000/tes')
<Response [400]>

Environment

• Python version: in this case 2.7.14
• Flask version: 1.0
• Werkzeug version: 0.14.1

[davidism]

Stop setting app.debug manually. Not sure if that's related, but don't do it anyway. Use the FLASK_ENV=development env var.

[lepture]

@davidism It it still reproducible. I think it is a real bug.

[davidism]

This is due to #2348, which started trapping bad requests in debug mode, in order to help debug form data.

flask/flask/app.py

Lines 1666 to 1668 in ea316d2

	# if unset, trap based on debug mode
	if (trap_bad_request is None and self.debug) or trap_bad_request:
	return isinstance(e, BadRequest)

I should have checked that it's a BadRequestKeyError for the default behavior, instead of all BadRequest errors.

Fixing this now.

[pypingou]

Thanks for the quick fix :)