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fq/format/zip/zip.md
Mattias Wadman a83cac6021 zip: Fix incorrect time/date, add extended timestamp and refactor
MSDOS time/date was read in wrong order and also did not take into account
that the bit ranges in the shortis are in little-endian.

Remodel modification_time/date to be one struct with fat_time, fat_date LE shorts
and then synthetic values for day, hours, minute etc and also a unix field with the
timestamp as unix time.

Also refactor and clenaup extra fields/extended code a bit.

Fixes #792
2023-10-23 11:11:27 +02:00

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745 B
Markdown

Supports ZIP64.
## Timestamp and time zones
The timestamp accessed via `.local_files[].last_modification` is encoded in ZIP files using [MS-DOS representation](https://learn.microsoft.com/en-us/windows/win32/api/oleauto/nf-oleauto-dosdatetimetovarianttime) which lacks a known time zone. Probably the local time/date was used at creation. The `unix_guess` field in `last_modification` is a guess assuming the local time zone was UTC at creation.
### References
- https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT
- https://opensource.apple.com/source/zip/zip-6/unzip/unzip/proginfo/extra.fld
- https://formats.kaitai.io/dos_datetime/
- https://learn.microsoft.com/en-us/windows/win32/api/oleauto/nf-oleauto-dosdatetimetovarianttime