Jakob Heher created PDFBOX-6271:
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Summary: `getNormalAppearanceStream` marks annotation appearance
stream as dirty
Key: PDFBOX-6271
URL: https://issues.apache.org/jira/browse/PDFBOX-6271
Project: PDFBox
Issue Type: Bug
Affects Versions: 3.0.6 PDFBox
Reporter: Jakob Heher
Attachments: Repro2FormXObjectConstructor.java, double-signed.pdf
Calling `getNormalAppearanceStream` on an annotation marks the appearance
stream as dirty. This causes it to be re-emitted in a subsequent incremental
update save.
In particular, Renderer's `renderPageToGraphics` can also trigger this bug
down-stack (which is how we ran into it; we render the document page to
determine where to place a subsequent signature annotation, and the previous
signature annotation's appearance stream was re-emitted).
The cause is that the `PDXObject` constructor taking `COSStream` (which the
`PDFormXObject` constructor delegates to) unconditionally calls `setName` ->
`setItem` to set the correct type/subtype values. `setItem` then
unconditionally marks the dictionary as dirty. This is the same fundamental
cause as PDFBOX-6270.
A minimal reproducer is attached. A sample PDF file exhibiting this bug is also
attached.
A suggested fix would be to make the `setItem` invocations conditional. This
likely applies to more than just PDFormXObject, it is just the context in which
we encountered the bug.
*AI disclaimer:* I used ChatGPT to perform the cause analysis after noticing
the erroneous behavior in production, and to generate an initial reproducer.
However, I have manually refined the reproducer, and have manually verified the
erroneous behavior in the source tree. I have written this bug report by hand.
I am confident that this is a real bug.
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