feat(pdf): reproducible output via a deterministic() backend option#363
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PdfFixedLayoutBackend.builder().deterministic(true) (or .deterministic(Instant)) pins the document CreationDate / ModDate and derives the PDF /ID from the document metadata instead of PDFBox's time-seeded default, so the same document renders to byte-identical PDF output across runs — for reproducible builds and byte-level output tests. Off by default; existing output keeps the live timestamp and /ID. Applied on both the render and section-render paths.
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Why
The same document rendered twice produced different PDF bytes: PDFBox seeds the document
/IDfrom the current time on every save, and that
/IDwas the only source of non-determinism(GraphCompose never set a CreationDate). That blocks reproducible builds and byte-level output
assertions.
What
PdfFixedLayoutBackend.builder().deterministic(true)— enables reproducible output: pins thedocument CreationDate / ModDate to a fixed default timestamp and sets the PDF
/IDto a stablevalue derived from the document's info dictionary (MD5), instead of PDFBox's time-seeded
/ID..deterministic(Instant)— the same, with an explicit timestamp.deterministicTimestamp == null): output is unchanged — live timestamp andPDFBox
/ID.buildDocument(render / toBytes) andbuildSectionsDocument(the@Betasection-render path).
Tests
PdfDeterministicOutputTest(3): the same document rendered twice withdeterministic(true)is byte-identical;
deterministic(Instant)pins the CreationDate to that instant; the defaultbackend leaves the CreationDate unset (proving it's opt-in).
./mvnw -f aggregator/pom.xml verify -pl :graph-compose-qa -am— full compile + javadoc gate +the qa visual/parity byte-identity suite (643): green. The default path is a no-op, so existing
rendered output is unchanged.
Architectural note: determinism is a PDF-serialization concern (
/ID, dates), so the knob lives onthe PDF backend builder rather than the canonical
DocumentSession— it keeps a format-specificdetail out of the backend-neutral document model.