TypeError swallowed in decorated handlers

If a TypeError is raised within a handler, which has been decorated by a “wrapper” function whose first argument is not called self, the TypeError is swallowed and a 404 HTTP Error is returned instead.

from functools import wraps
import cherrypy


def dec(f):
    @wraps(f)
    def wrapper(handler, *args, **kwargs):
        return f(handler, *args, **kwargs)
    return wrapper


class HelloWorld(object):

    @dec
    def index(self, *args, **kwargs):
        raise TypeError('OOPS')
        return "Hello world!"

    index.exposed = True


if __name__ == '__main__':
    cherrypy.quickstart(HelloWorld())

Response is a 404:

> curl -sD - 'http://localhost:8080/' -o /dev/null
HTTP/1.1 404 Not Found
Server: CherryPy/8.1.2
Content-Length: 1267
Content-Type: text/html;charset=utf-8
Date: Fri, 16 Dec 2016 16:05:18 GMT

Without the decorator @dec, one correctly gets a 500.

The problem is here: https://github.com/cherrypy/cherrypy/blob/master/cherrypy/_cpdispatch.py#L105 When inspecting the “callable”, CherryPy checks for the name of the first argument and strips it out if it’s called self. It then goes on inspecting the other arguments and raises a 404 if some arguments are missing or unknown. But if the “callable”'s first argument is not called “self”, as in the decorated handler above (where it’s called “handler”), then CherryPy mistakenly returns a “404 argument ‘handler’ is unknown”.

[lbolla]

One option, that would only work on Python3, though, is to check if the “callable” has a __wrapped__ attribute when checking if it’s been wrapped or not and call getargspec on __wrapped__ if so:

>>> getargspec(callable.__wrapped__) (['self'], 'args', 'kwargs', None)

See https://docs.python.org/3/library/functools.html#functools.update_wrapper

For Python2, at leasts the docs should suggest to set the __wrapped__ attribute manually to the original wrapper.

[lbolla]

PR available here: https://github.com/cherrypy/cherrypy/pull/1531