Thierry Guérin created TIKA-4098:
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Summary: Detection fail on PDF with garbage before header
Key: TIKA-4098
URL: https://issues.apache.org/jira/browse/TIKA-4098
Project: Tika
Issue Type: Bug
Components: core
Affects Versions: 2.8.0
Reporter: Thierry Guérin
Attachments: garbageBeforeHeader.pdf
PDF detection fails on files that contain too much garbage before the header
'PDF%-'.
Those PDFs do not respect the specification, but are nonetheless correctly
handled by PDF viewers.
The joined PDF is an example on the garbage found in a real-life PDF (looks
like email headers that 'leaked' onto the PDF file). The PDF itself is one that
I generated so that the exemple si small.
The current magic for PDFs limits the search for the '%PDF-%' header to 512
bytes, and in the joined PDF it's located after 702 garbage bytes.
I looked at the sources of PdfBox and Ghostscript to see how they handle this
case and:
* Ghostscript searches through the entire file (see
[https://github.com/ArtifexSoftware/ghostpdl/blob/master/pdf/ghostpdf.c] lines
1323-1339)
* PdfBox reads the file line by line, and stops looking for the header when
it encounters a line that starts with a digit (see
[https://github.com/apache/pdfbox/blob/trunk/pdfbox/src/main/java/org/apache/pdfbox/pdfparser/COSParser.java]
lines 1561-)
>From the doc in tika-mimetypes.xml for the application/pdf MIME type, I
>understand that increasing the maximum offset can trigger false positives. I
>increased it to 768, and the unit tests pass, but I didn't find any PDF that
>tests this particular case, so either it doesn't exist or there are
>integration tests that aren't part of this repo ?
How can I go about testing for regressions ? I can provide a pull request for
this change, but where do I put the test PDF and a unit test?
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