https://bugs.documentfoundation.org/show_bug.cgi?id=174246
Bug ID: 174246
Summary: Support SOURCE_DATE_EPOCH for reproducible PDF export
Product: LibreOffice
Version: 27.2.0.0 alpha0+ master
Hardware: All
OS: All
Status: UNCONFIRMED
Severity: enhancement
Priority: medium
Component: Printing and PDF export
Assignee: [email protected]
Reporter: [email protected]
Description:
PDF export currently embeds the current time in the exported file: the
info-dictionary CreationDate (and modification date), the XMP metadata
dates, and the trailer /ID all derive from the wall clock, so two
exports of the same document seconds apart differ byte for byte. That
breaks reproducible-build verification and content-addressed archiving
of exported documents.
The reproducible-builds convention is the SOURCE_DATE_EPOCH environment
variable (a Unix timestamp). When it is set, exporters use it in place
of the current time.
A patch implementing this for the PDF writer is in review:
https://gerrit.libreoffice.org/c/core/+/213278
With SOURCE_DATE_EPOCH set, two exports of the same document are
byte-identical; unset or invalid values keep the current behaviour.
Steps to Reproduce:
1. Export any document to PDF.
2. Wait a few seconds and export the same unchanged document again to a second
file.
3. Compare the two files byte for byte (for example with sha256sum).
Actual Results:
The two files differ. The info-dictionary CreationDate and modification date,
the XMP metadata dates, and the trailer /ID all derive from the wall clock at
export time, so two exports of the same document seconds apart are never
byte-identical. That breaks reproducible-build verification and
content-addressed archiving of exported documents.
Expected Results:
The PDF exporter should honour the SOURCE_DATE_EPOCH environment variable (the
reproducible-builds convention, a Unix timestamp): when it is set, use it in
place of the current time for those fields, so two exports of the same document
are byte-identical. Unset or invalid values keep the current behaviour.
Reproducible: Always
User Profile Reset: No
Additional Info:
Filed at the request of Ilmari Lauhakangas on Gerrit change 213278.
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