classification
Title: cgi module, parse_multipart fails
Type: behavior Stage:
Components: Library (Lib) Versions: Python 3.8, Python 3.7
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: Magnus Johnsson, ethan.furman, gvanrossum
Priority: normal Keywords:

Created on 2020-07-26 09:58 by Magnus Johnsson, last changed 2020-08-03 21:23 by gvanrossum.

Files
File name Uploaded Description Edit
60_Request.txt Magnus Johnsson, 2020-07-26 09:58 The request that fails.
Messages (5)
msg374307 - (view) Author: Magnus Johnsson (Magnus Johnsson) Date: 2020-07-26 09:58
When using the cgi module, parse_multipart fails with the supplied file with the error:

Invalid boundary in multipart form: b''

A sample program that demonstrates the error:
import cgi
f = open("60_Request.txt", "r")
print(cgi.parse_multipart(f, {'boundary': b'BgTzK0jM20UH01naJdsmAWUj7sqqeoikGZvh3mo9', 'CONTENT-LENGTH': 3992}))

This affects for instance Twisted, and all its dependencies.
msg374374 - (view) Author: Magnus Johnsson (Magnus Johnsson) Date: 2020-07-27 12:49
https://github.com/yohanboniface/falcon-multipart/issues/8

It would seem that the same issue pops up elsewhere. We do indeed set the content-type, as per the default examples for unity.
msg374705 - (view) Author: Guido van Rossum (gvanrossum) * (Python committer) Date: 2020-08-03 00:31
So per the stackoverflow explanation you shouldn’t do that? Should we close this?
msg374753 - (view) Author: Magnus Johnsson (Magnus Johnsson) Date: 2020-08-03 20:10
No, of course not.
The request is completely valid. Python's cgi library parses it wrong.

The 'resolution' that needs to be done is to fix it in python's source.
That, and the libraries that depend on it, like twisted, probably needs to move away from using python's cgi library at all, given the age of this bug.

As it stands, we have had to patch 16 separate calls, and will be moving away from the twisted-based server over it anyway, since it seems sketchy.

Going to have a peek at the source, but I am a bit hesitant to touch things that have that large a userbase.
msg374757 - (view) Author: Guido van Rossum (gvanrossum) * (Python committer) Date: 2020-08-03 21:23
Could you submit a PR then? I don't think I've looked at that module in 20 years.
History
Date User Action Args
2020-08-03 21:23:52gvanrossumsetmessages: + msg374757
2020-08-03 20:10:34Magnus Johnssonsetmessages: + msg374753
2020-08-03 00:31:54gvanrossumsetnosy: + gvanrossum
messages: + msg374705
2020-07-27 12:49:17Magnus Johnssonsetmessages: + msg374374
2020-07-26 11:55:16SilentGhostsetnosy: + ethan.furman
type: behavior
components: + Library (Lib)
2020-07-26 09:58:23Magnus Johnssoncreate