New submission from Serhiy Storchaka <storchaka+cpyt...@gmail.com>:

When the ZIP archive is opened for appending, it reads the Central Directory at 
opening and writes existing entries back at closing. The Zip64 Extra Field is 
appended to existing Extra Fields if necessary. This leads to increasing the 
size of the Extra Fields data every time when append to the ZIP archive. Since 
the total size of Extra Fields is limited by 0xffff bytes, this can cause the 
failure.

The proposed PR removes the Zip64 Extra Field before adding a new Zip64 Extra 
Field.

----------
assignee: serhiy.storchaka
components: Library (Lib)
messages: 323181
nosy: alanmcintyre, serhiy.storchaka, twouters
priority: normal
severity: normal
status: open
title: Appending to ZIP archive blows up existing Central Directory entries
type: behavior
versions: Python 2.7, Python 3.7, Python 3.8

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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue34341>
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