catching errors in finished_callbacks ?

[jvanasco]

I tracked down an odd issue (which is a bit of a variant from closed #237)

this is caused by the pyramid design of finished callbacks happening after the tween egress.

If an exception is raised in a finished callback, the debugtoolbar has already considered the request to be fine -- so the client gets an error (e.g the two line waitress internal-server error) but the toolbar shows a 200.

a simple example of this is setting a value in a cookie that is too long (there is a max 4096 length due to browser header limitations)

for example, this will trigger an uncaught exception

from pyramid.session import SignedCookieSessionFactory
my_session_factory = SignedCookieSessionFactory('itsaseekreet')
config.set_session_factory(my_session_factory)
...
def a_view(request):
    request.session['a'] = "1" * 5000
    return {}

i don't think it's possible to catch these exceptions with the current design of pyramid or the toolbar, but i think it would be good to remember this type of situation as future plans are made.