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* Several assertions in linearization were not always true; change them to run time errors * Handle a few cases of uninitialized objects * Handle pages with no contents when doing form operations * Handle invalid page tree nodes when traversing pages
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This makes all integer type conversions that have potential data loss explicit with calls that do range checks and raise an exception. After this commit, qpdf builds with no warnings when -Wsign-conversion -Wconversion is used with gcc or clang or when -W3 -Wd4800 is used with MSVC. This significantly reduces the likelihood of potential crashes from bogus integer values. There are some parts of the code that take int when they should take size_t or an offset. Such places would make qpdf not support files with more than 2^31 of something that usually wouldn't be so large. In the event that such a file shows up and is valid, at least qpdf would raise an error in the right spot so the issue could be legitimately addressed rather than failing in some weird way because of a silent overflow condition.
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Bounding box X coordinates could be truncated, causing them to be off by a fraction of a point. This was most likely not visible, but it was still wrong.
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If we end up using our fallback font size when generating appearances for text fields, reflect that in the Tf operator used in the appearance stream.
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When generating appearance streams for variable text annotations, properly handle the cases of there being no appearance dictionary, no appearance stream, or an appearance stream with no BMC..EMC marker.
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Also add some additional methods for detecting form field types to assist in the json creation and for later use.