Rewriting the links copied the old trailer up to %%EOF, so the old
startxref stayed in the file before the new one. Its offset is the size
the file had before the rewrite, and the links carry the output path,
so the same project exported to two folders gave different bytes, and
a different document id. Both rewrites now copy the trailer dictionary
only, through one helper; the print window's rewrite no longer leaves a
stray %%EOF either.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
With SOURCE_DATE_EPOCH set, the document id came from the project's uuid
and a hash of the .qet file. A project generated again from the same
data has new uuids, so its PDF differed in the id alone (XMP DocumentID
and trailer /ID, 120 bytes) although every page was the same.
Qt now writes a fixed placeholder id, and once the file is written the
placeholder is replaced with an id derived from the bytes of the PDF:
the same pages give the same id. Same length, so no offset changes.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
QPdfWriter::setDocumentId() is new in Qt 6.8, QTimeZone::UTC in 6.5 and
QHashSeed in 6.2, so the build failed on Qt 6.4 (Ubuntu 24.04). Qt before
6.8 also writes no /ModDate and no XMP metadata, and setDocumentDate()
then gave up and left the time of the export in the file. Those two are
now rewritten when present, and no document id is set where Qt writes
none.
tst_pdfreproducible also checks that the xref table still matches the
file after the dates are rewritten.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PJw3u5AdKQgQVPug8CzuMQ
Two exports of one project differed in the creation and modification
dates (the time of the export, in local time) and in the document id
(random). With SOURCE_DATE_EPOCH set (reproducible-builds.org),
--export-pdf now uses the time it names, in UTC, and a document id
derived from the project: version 5 of the project uuid with the
SHA-256 of the project file, so it is the same for the same file and
changes when the file does. Qt has no setter for the dates, so
PdfLinks::setDocumentDate() rewrites them in the document information
and the XMP metadata after the file is written, fixing the XMP /Length
and shifting the xref table. Without the variable nothing changes.
Only --export-pdf reads it; the print window's PDF export does not, as
a person exporting by hand wants the real date.
qet_export (misc/qet-mcp) gains "reproducible" and "source_date_epoch".
It reports whether the build honoured the variable, since an older one
ignores it.
tst_pdfreproducible exports examples/741.qet four times and requires
identical bytes and the epoch's date; it fails with either this change
or the hash seed fix reverted. Projects with cross-reference links also
need their links in a fixed order, which is a separate fix.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
ispyisail