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LibPDF: Don't check for startxref after trailer dict

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Several files have a comment after the trailer dict and the
`startxref` after it.

We really should add a consume_whitespace_and_comments() function
and call that in most places we currently call consume_whitespace().

But in this case, for non-linearized files, we first jump to the
end of the file, read `startxref`, then jump to `xref` from the
offset there, and then read the trailer after the `xref`,
only to read `startxref` again. So we can just not do that.

(For linearized files, we now completely ignore `startxref`.
But we don't use the data in `startxref` in linearized files
anyways, so it's fine to not read it there too.)

Reduces number of crashes on 300 random PDFs from the web (the first 300
from 0000.zip from
https://pdfa.org/new-large-scale-pdf-corpus-now-publicly-available/)
from 25 (8%) to 23 (7%).
This commit is contained in:
Nico Weber 2023-10-21 16:30:33 -04:00 committed by Tim Flynn
parent acf668e234
commit e7f7c434f7
Notes: sideshowbarker 2024-07-17 04:09:56 +09:00 
Author: https://github.com/nico
Commit: https://github.com/SerenityOS/serenity/commit/e7f7c434f7
Pull-request: https://github.com/SerenityOS/serenity/pull/21536
1 changed files with 1 additions and 15 deletions
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16
Userland/Libraries/LibPDF/DocumentParser.cpp
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@ -525,21 +525,7 @@ PDFErrorOr<NonnullRefPtr<DictObject>> DocumentParser::parse_file_trailer()
return error("Expected \"trailer\" keyword");
m_reader.move_by(7);
m_reader.consume_whitespace();
auto dict = TRY(parse_dict());
if (!m_reader.matches("startxref"))
return error("Expected \"startxref\"");
m_reader.move_by(9);
m_reader.consume_whitespace();
m_reader.move_until([&](auto) { return m_reader.matches_eol(); });
VERIFY(m_reader.consume_eol());
if (!m_reader.matches("%%EOF"))
return error("Expected \"%%EOF\"");
m_reader.move_by(5);
m_reader.consume_whitespace();
return dict;
return parse_dict();
}
PDFErrorOr<Value> DocumentParser::parse_compressed_object_with_index(u32 index)