Guard ParentTree allocation against pathological MCID - #94
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A self-review of #93 (v1.5.5) found a regression: the per-page ParentTree array is sized by (max MCID + 1), and PdfStructElem.Mcid is a public setter, so a hand-built structure tree with a huge MCID (or int.MaxValue) would attempt a multi-gigabyte allocation or overflow the length to a negative value — crashing mid-Save instead of failing cleanly. Cap the per-page MCID at 1,000,000 (far above any real page's marked-content count, which is bounded by content-stream size) and throw a clear InvalidOperationException above it, before the array is sized. Documents tagged through the canvas are unaffected: their per-page MCIDs are dense and sequential. Bump to 1.5.6.
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Follow-up to a self-review of #93 (v1.5.5).
Problem
The v1.5.5 MCID ParentTree change sizes the per-page array by
max(MCID) + 1. SincePdfStructElem.Mcidis a public setter, a hand-built structure tree with a very large MCID (orint.MaxValue) would attempt a multi-gigabyte allocation, or overflowmax(MCID)+1to a negative length — crashing mid-Saverather than failing cleanly. Documents tagged through the canvas are safe (their per-page MCIDs are dense and sequential); this only affected hand-built trees.Fix
Cap the per-page MCID at
1_000_000(per-page marked content is bounded by content-stream size, so this is ~100× beyond any real page) and throw a clearInvalidOperationExceptionabove it, before the array is sized — so neither the overflow nor the large allocation is reachable. It is a robustness guard, not a conformance limit.Tests
StructureTree_pathologicalMcid_throwsInsteadOfOom(assertsint.MaxValuethrowsInvalidOperationException, not OOM/overflow).dotnet format --verify-no-changesclean; AOT smoke passes.Bumps version to 1.5.6.