Am 02.03.2020 um 22:39 schrieb Andreas Lehmkuehler:
Hi,
this is a follow-up on PDFBOX-4778.
The pdf govdocs1/444/444988.pdf contains a broken stream with a lot of
broken matrix operations. Many of them have to few or to much
operands, the later are simply skipped. In the end this leads to
illegal results when concatenating matrices and a very long, maybe
endless time of rendering.
PDFBOX-4778 added an additional check of the result which throws an
unchecked exception if any of the matrix elements is either infinite
or NaN, so that in the end the rendering simply stops.
Tilman proposes in the 2.0.19 thread to catch the exception in
org.apache.pdfbox.contentstream.operator.state.Concatenate.process()
and, I guess, to continue processing.
IMHO that won't really work for different reasons:
- there are several other places in the code where the exception might
occur
- once the exception is thrown the resulting matrix is broken as at
least one element is infinite or NaN and will lead to even more broken
matrix values
Instead of throwing an exception my first idea was to replace such
illegal values with legal ones, but which ones? NaN with 0 and
infinite with MAX? Or maybe replacing the whole resulting matrix with
one of the input matrices or with an identity matrix?
Do you see any more or less reasonable approach to avoid the exception?
I can't really contribute any idea, I'm unhappy with all and don't have
better ones.
Tilman
Andreas
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