zipfile: does not include optional descriptor signature

[silas]

BPO	34472
Nosy	@serhiy-storchaka, @silas
PRs	bpo-34472: Add data descriptor signature to zipfile #8871 [3.6] bpo-34472: Add data descriptor signature to zipfile (GH-8871) #9398 [3.7] bpo-34472: Add data descriptor signature to zipfile (GH-8871) #9399 [2.7] bpo-34472: Add data descriptor signature to zipfile (GH-8871) #9407
Files	zip_stream_example.py: Example code showing issue

^{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 2018-09-22.18:03:34.606>
created_at = <Date 2018-08-23.12:57:59.166>
labels = ['3.7', '3.8', 'type-bug', 'library']
title = 'zipfile: does not include optional descriptor signature'
updated_at = <Date 2018-09-22.18:03:48.081>
user = 'https://github.com/silas'

bugs.python.org fields:

activity = <Date 2018-09-22.18:03:48.081>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2018-09-22.18:03:34.606>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2018-08-23.12:57:59.166>
creator = 'silas'
dependencies = []
files = ['47760']
hgrepos = []
issue_num = 34472
keywords = ['patch']
message_count = 6.0
messages = ['323943', '325664', '325667', '326101', '326104', '326105']
nosy_count = 2.0
nosy_names = ['serhiy.storchaka', 'silas']
pr_nums = ['8871', '9398', '9399', '9407']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue34472'
versions = ['Python 2.7', 'Python 3.6', 'Python 3.7', 'Python 3.8']

[silas]

When adding a fileobj that is not seekable to a zip using the zipfile module, the optional signature value 0x08074b50 is not included. This breaks certain zip implementations, including the builtin MacOS Archive Utility.

See https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT sections 4.3.9.3 and 4.3.9.4

[serhiy-storchaka]

New changeset 4ba3b50 by Serhiy Storchaka (Silas Sewell) in branch 'master':
bpo-34472: Add data descriptor signature to zipfile (GH-8871)
4ba3b50

[serhiy-storchaka]

Thank you for your contribution Silas.

Since popular ZIP file implementation like Info-ZIP and Java write this signature unconditionally, I think most unzipping software support it if they support reading ZIP files in streaming mode at all, at it is safe to backport this change to all maintained versions.

[serhiy-storchaka]

New changeset 6ec2981 by Serhiy Storchaka in branch '2.7':
[2.7] bpo-34472: Add data descriptor signature to zipfile (GH-8871) (ПР-9407)
6ec2981

[serhiy-storchaka]

New changeset ed21919 by Serhiy Storchaka (Miss Islington (bot)) in branch '3.6':
bpo-34472: Add data descriptor signature to zipfile (GH-8871) (GH-9398)
ed21919

[serhiy-storchaka]

New changeset 44989bc by Serhiy Storchaka (Miss Islington (bot)) in branch '3.7':
bpo-34472: Add data descriptor signature to zipfile (GH-8871) (GH-9399)
44989bc