tarfile zeroes ustar header fields unnecessarily

[jmroot]

BPO	45863
Nosy	@vstinner, @jmroot, @ethanfurman, @miss-islington, @sobolevn
PRs	bpo-45863: tarfile: don't zero out header fields unnecessarily #29693 [3.9] bpo-45863: tarfile: don't zero out header fields unnecessarily (GH-29693) #31232 [3.10] bpo-45863: tarfile: don't zero out header fields unnecessarily (GH-29693) #31233 Fix sphinx-lint after #31097 and b878b3a #31248

^{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 2022-02-09.17:37:25.043>
created_at = <Date 2021-11-22.08:01:20.884>
labels = ['type-bug', 'library', '3.9', '3.10', '3.11']
title = 'tarfile zeroes ustar header fields unnecessarily'
updated_at = <Date 2022-02-10.09:08:59.472>
user = 'https://github.com/jmroot'

bugs.python.org fields:

activity = <Date 2022-02-10.09:08:59.472>
actor = 'miss-islington'
assignee = 'none'
closed = True
closed_date = <Date 2022-02-09.17:37:25.043>
closer = 'vstinner'
components = ['Library (Lib)']
creation = <Date 2021-11-22.08:01:20.884>
creator = 'jmr'
dependencies = []
files = []
hgrepos = []
issue_num = 45863
keywords = ['patch']
message_count = 7.0
messages = ['406744', '409228', '412923', '412930', '412931', '412932', '412984']
nosy_count = 5.0
nosy_names = ['vstinner', 'jmr', 'ethan.furman', 'miss-islington', 'sobolevn']
pr_nums = ['29693', '31232', '31233', '31248']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue45863'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[jmroot]

When using the pax format, tarfile will zero out the field in the ustar header for any values that are represented with a float, setting the correct value only in the pax header. This mainly seems to apply to the mtime. This behaviour doesn't cause problems when using an unarchiver that understands the pax header, but unarchivers that don't will extract incorrect metadata (most obviously all mtimes set to the epoch). Compatibility with such unarchivers can easily be achieved by rounding the float value to int for the ustar header only, thus at least giving mtimes that are accurate to the nearest second instead of nothing.

[jmroot]

PR has been marked stale; friendly ping.

[vstinner]

New changeset bf2d44f by Joshua Root in branch 'main':
bpo-45863: tarfile: don't zero out header fields unnecessarily (GH-29693)
bf2d44f

[miss-islington]

New changeset 42f87d4 by Miss Islington (bot) in branch '3.10':
bpo-45863: tarfile: don't zero out header fields unnecessarily (GH-29693)
42f87d4

[miss-islington]

New changeset b0517a1 by Miss Islington (bot) in branch '3.9':
bpo-45863: tarfile: don't zero out header fields unnecessarily (GH-29693)
b0517a1