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Give a repeatable PDF the same document id however the project was made (#1178)

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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>
This commit is contained in:
ispyisail
2026-10-04 08:54:13 +13:00
parent f09be8007f
commit ef96b7d948
4 changed files with 98 additions and 14 deletions
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sources/cli_export.cpp
+11 -13
View File
@@ -42,7 +42,6 @@
#include <QDir>
#include <QDirIterator>
#include <QDomDocument>
#include <QCryptographicHash>
#include <QDate>
#include <QDateTime>
#include <QFile>
@@ -63,7 +62,6 @@
#include <QTextStream>
#include <QTimeZone>
#include <QTransform>
#include <QUuid>
namespace {
@@ -189,18 +187,16 @@ int exportPdf(QETProject &project, const QString &output,
// SOURCE_DATE_EPOCH (reproducible-builds.org) asks for the same file
// from the same input: the time it names instead of now, and a document
// id from the project file instead of a random one. Qt has no setter for
// the dates, so they are rewritten once the file is written. Before
// Qt 6.8 there is no document id to set: it is only written for PDF/A.
// id from what the PDF shows instead of a random one. Qt has no setter
// for the dates, and the content is not known yet, so both are
// rewritten once the file is written; Qt writes a fixed id until then.
// The id does not come from the project file, whose uuids are new each
// time a project is generated again from the same data. Before Qt 6.8
// there is no document id to set: it is only written for PDF/A.
const QDateTime sourceDate = sourceDateEpoch();
#if QT_VERSION >= QT_VERSION_CHECK(6, 8, 0)
if (sourceDate.isValid()) {
QCryptographicHash hash(QCryptographicHash::Sha256);
QFile file(project.filePath());
if (file.open(QIODevice::ReadOnly))
hash.addData(&file);
writer.setDocumentId(QUuid::createUuidV5(project.uuid(), hash.result()));
}
if (sourceDate.isValid())
writer.setDocumentId(PdfLinks::placeholderDocumentId());
#endif
QPainter painter;
@@ -277,8 +273,10 @@ int exportPdf(QETProject &project, const QString &output,
// the cross-references jump inside the document in any PDF viewer.
PdfLinks::convertUriToGoTo(output);
PdfLinks::removeUnusedPdfxNamespace(output);
if (sourceDate.isValid())
if (sourceDate.isValid()) {
PdfLinks::setDocumentDate(output, sourceDate);
PdfLinks::setDocumentIdFromContent(output);
}
out << "Exported " << diagrams.size() << " page(s) -> " << output << "\n";
return 0;