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https://issues.apache.org/jira/browse/PDFBOX-1000?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13052652#comment-13052652
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Adam Nichols commented on PDFBOX-1000:
--------------------------------------
I haven't had time to go back to this lately, but I'm still following the
mailing list. The comments in PDFBOX-1016 do a great job at explaining how the
xref tables should be read/parsed. So when I (or anyone else) comes back to
the conforming parser, it'd be good to confirm that we're doing it properly and
old references are overwritten by new ones (PDFBOX-1042). I think the current
code (attached above) is only reading the last xref table and ignoring all the
previous ones, which is very wrong. However, it should be easy to put a loop
in there to handle this. Linearized documents will be another thing to add
support for in the future, but we'll cross that bridge when we come to it.
> Conforming parser
> -----------------
>
> Key: PDFBOX-1000
> URL: https://issues.apache.org/jira/browse/PDFBOX-1000
> Project: PDFBox
> Issue Type: New Feature
> Components: Parsing
> Reporter: Adam Nichols
> Assignee: Adam Nichols
> Attachments: COSUnread.java, ConformingPDDocument.java,
> ConformingPDFParser.java, ConformingPDFParserTest.java, XrefEntry.java,
> conforming-parser.patch, gdb-refcard.pdf
>
>
> A conforming parser will start at the end of the file and read backward until
> it has read the EOF marker, the xref location, and trailer[1]. Once this is
> read, it will read in the xref table so it can locate other objects and
> revisions. This also allows skipping objects which have been rendered
> obsolete (per the xref table)[2]. It also allows the minimum amount of
> information to be read when the file is loaded, and then subsequent
> information will be loaded if and when it is requested. This is all laid out
> in the official PDF specification, ISO 32000-1:2008.
> Existing code will be re-used where possible, but this will require new
> classes in order to accommodate the lazy reading which is a very different
> paradigm from the existing parser. Using separate classes will also
> eliminate the possibility of regression bugs from making their way into the
> PDDocument or BaseParser classes. Changes to existing classes will be kept
> to a minimum in order to prevent regression bugs.
> [1] Section 7.5.5 "Conforming readers should read a PDF file from its end"
> [2] Section 7.5.4 "the entire file need not be read to locate any particular
> object"
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