regression - mimetypes guess_type is confused by ; in the filename

[YaroslavHalchenko]

BPO	38449
Nosy	@ned-deily, @ambv, @vadmium, @maxking, @corona10, @miss-islington, @kyleam
PRs	bpo-38449: Revert "bpo-22347: Update mimetypes.guess_type to allow oper parsing of URLs (GH-15522)" #16724 [3.7] bpo-38449: Revert "bpo-22347: Update mimetypes.guess_type to allow oper parsing of URLs (GH-15522)" (GH-16724) #16725 [3.7] bpo-38449: Revert "bpo-22347: Update mimetypes.guess_type to allow oper parsing of URLs (GH-15685)" (GH-16724) #16727 [3.8] bpo-38449: Revert "bpo-22347: Update mimetypes.guess_type to allow oper parsing of URLs (GH-15685)" (GH-16724) #16728 bpo-38449: Add URL delimiters test cases #16729 [3.7] bpo-38449: Add URL delimiters test cases (GH-16729) #17431 [3.8] bpo-38449: Add URL delimiters test cases (GH-16729) #17432

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-12-12.15:24:35.429>
created_at = <Date 2019-10-11.14:06:40.678>
labels = ['3.7', '3.8', 'type-bug', 'library', '3.9']
title = 'regression - mimetypes guess_type is confused by ; in the filename'
updated_at = <Date 2019-12-12.15:24:35.339>
user = 'https://bugs.python.org/YaroslavHalchenko'

bugs.python.org fields:

activity = <Date 2019-12-12.15:24:35.339>
actor = 'corona10'
assignee = 'none'
closed = True
closed_date = <Date 2019-12-12.15:24:35.429>
closer = 'corona10'
components = ['Library (Lib)']
creation = <Date 2019-10-11.14:06:40.678>
creator = 'Yaroslav.Halchenko'
dependencies = []
files = []
hgrepos = []
issue_num = 38449
keywords = ['patch', '3.7regression']
message_count = 24.0
messages = ['354455', '354456', '354465', '354470', '354488', '354500', '354505', '354513', '354522', '354523', '354524', '354536', '354537', '354539', '354544', '354545', '354546', '354665', '354696', '354705', '357694', '357695', '357696', '358302']
nosy_count = 8.0
nosy_names = ['ned.deily', 'Yaroslav.Halchenko', 'lukasz.langa', 'martin.panter', 'maxking', 'corona10', 'miss-islington', 'kyleam']
pr_nums = ['16724', '16725', '16727', '16728', '16729', '17431', '17432']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38449'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[YaroslavHalchenko]

Our tests in DataLad started to fail while building on Debian with Python 3.7.5rc1 whenever they passed just fine previously with 3.7.3rc1. Analysis boiled down to mimetypes

$> ./python3.9 -c 'import mimetypes; mimedb = mimetypes.MimeTypes(strict=False); print(mimedb.guess_type(";1.tar.gz"))'                           
(None, None)

$> ./python3.9 -c 'import mimetypes; mimedb = mimetypes.MimeTypes(strict=False); print(mimedb.guess_type("1.tar.gz"))' 
('application/x-tar', 'gzip')

$> git describe
v3.8.0b1-1174-g2b7dc40b2af

Ref:

• original issue in DataLad: patool dislikes tricky filenames datalad/datalad#3769

[YaroslavHalchenko]

FWIW, our more complete test filename is

# python3 -c 'import patoolib.util as ut; print(ut.guess_mime(r" \"\`;b&b&c |.tar.gz"))'
(None, None)

which works fine with older versions

[kyleam]

I've performed a bisect the issue with the following script:

#!/bin/sh
make -j3 || exit 125
./python <<\EOF || exit 1
import sys
import mimetypes
res = mimetypes.MimeTypes(strict=False).guess_type(";1.tar.gz")
if res[0] is None:
    sys.exit(1)
EOF

That points to 87bd207 (bpo-22347: Update mimetypes.guess_type to allow proper parsing of URLs (GH-15522), 2019-09-05). That commit was included in 3.7.5rc1 when it was cherry picked by 8873bff.

[ned-deily]

Marking as regression release blocker for 3.7.5 final and 3.8.0 final.

[maxking]

I am looking into the issue.

[maxking]

The bug is interesting due to some of the implementation details of "guess_type". The documentation says that it can parse either a URL or a filename.

Switching from urllib.parse._splittype to urllib.parse.urlparse changed what a valid "path" is. _splittype doesn't care about the rest of the URL except the scheme, but urlparse does. Previously, we used to split things like:

   >>> print(urllib.parse._splittype(';1.tar.gz')
   (None, ';1.tar.gz')

Then, we'd just treat the 2nd part as a filesystem path, which would rightfully guess the extension as .tar.gz

However, switching to using parsing via urllib.parse.urlparse, we get:

    >>> print(urllib.parse.urlparse(';1.tar.gz')
    ParseResult(scheme='', netloc='', path='', params='1.tar.gz', query='', fragment='')

And then we get the ".path" attribute for further processing, which being empty, returns (None, None).

The format of all these parts is:

scheme://netloc/path;parameters?query#fragment

A simple fix would be to just merge path, parameters, query and fragment together (with appropriate delimiters) and the proceed with further processing. That would fix parsing of Filesystem paths but would break (again) parsing of URLs like:

    >>> mimetypes.guess_type('http://example.com/index.html;1.tar.gz')
    ('application/x-tar', 'gzip')

It should return 'text/html' as the type, since this is a URL and everything after the ';' should not be used to determine the mimetype. But, if there is no scheme provided, we should treat it as a filesystem path and in that case 'application/x-tar' is the right type.

I hope I am not confusing everyone here.

The right fix IMO would be to make "guess_type" not treat URLs and filesytem paths alike.

[ned-deily]

Thanks for looking into this, @maxking. With both 3.8.0 final and 3.7.5 final scheduled for just a few days away, I wonder if the best thing to do at this point is to revert them and work on a more robust fix targeted for the next maintenance releases since the original issue was not identified as being a security issue or otherwise critical.

[maxking]

Yeah, I agree. I'll submit a PR for reverting the commits.

[miss-islington]

New changeset 19a3d87 by Miss Islington (bot) (Abhilash Raj) in branch 'master':
bpo-38449: Revert "bpo-22347: Update mimetypes.guess_type to allow oper parsing of URLs (GH-15522)" (GH-16724)
19a3d87