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LibPDF: Improve hex string parsing

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A local (non-public) PDF I have lying around contains this in
a page's operator stream:

```
[<00b4003e> 3 <002600480051> 3 <005700550044004f0003> -29
<00330044> 3 <0055> -3 <004e0040> 4 <0003> -29 <004c00560003> -31
<0057004b> 4 <00480003> -37 <0050
>] TJ
```

That is, there's a newline in a hexstring after a character.

This led to `Parser error at offset 5184: Unexpected character`.

The spec says in 3.2.3 String Objects, Hexadecimal Strings:
"""Each pair of hexadecimal digits defines one byte of the string.
White-space characters (such as space, tab, carriage return, line feed,
and form feed) are ignored."""

But we didn't ignore whitespace before or after a character, only
in between the bytes.

The spec also says:
"""If the final digit of a hexadecimal string is missing—that is, if
there is an odd number of digits—the final digit is assumed to be 0."""

In that case, we were skipping the closing `>` twice -- or, more
accurately, we ignored the character after it too. This has been
wrong all the way back in #6974.

Add a test that fails if either of the two changes isn't present.
This commit is contained in:
Nico Weber 2024-01-01 19:31:27 -05:00 committed by Andreas Kling
parent d11c7a19da
commit 9495f64f91
Notes: sideshowbarker 2024-07-17 02:39:10 +09:00 
Author: https://github.com/nico
Commit: https://github.com/SerenityOS/serenity/commit/9495f64f91
Pull-request: https://github.com/SerenityOS/serenity/pull/22535
2 changed files with 22 additions and 1 deletions
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21
Tests/LibPDF/TestPDF.cpp
View File

@ -15,6 +15,27 @@
#include <LibTest/Macros.h>
#include <LibTest/TestCase.h>
TEST_CASE(parse_value)
{
// document isn't really used for anything, only to check there's no security_handler.
auto file = MUST(Core::MappedFile::map("linearized.pdf"sv));
auto document = MUST(PDF::Document::create(file->bytes()));
auto contents = "<50607><10\n>"sv;
PDF::Parser parser(contents.bytes());
parser.set_document(document->make_weak_ptr());
auto value1 = MUST(parser.parse_value(PDF::Parser::CanBeIndirectValue::No));
auto string1 = value1.get<NonnullRefPtr<PDF::Object>>()->cast<PDF::StringObject>();
EXPECT(string1->is_binary());
EXPECT_EQ(string1->string(), "\x50\x60\x70"sv);
auto value2 = MUST(parser.parse_value(PDF::Parser::CanBeIndirectValue::No));
auto string2 = value2.get<NonnullRefPtr<PDF::Object>>()->cast<PDF::StringObject>();
EXPECT(string2->is_binary());
EXPECT_EQ(string2->string(), "\x10"sv);
}
TEST_CASE(linearized_pdf)
{
auto file = MUST(Core::MappedFile::map("linearized.pdf"sv));

2
Userland/Libraries/LibPDF/Parser.cpp
View File

@ -352,6 +352,7 @@ PDFErrorOr<ByteString> Parser::parse_hex_string()
StringBuilder builder;
while (true) {
m_reader.consume_whitespace();
if (m_reader.matches('>')) {
m_reader.consume();
return builder.to_byte_string();
@ -364,7 +365,6 @@ PDFErrorOr<ByteString> Parser::parse_hex_string()
if (ch == '>') {
// The hex string contains an odd number of characters, and the last character
// is assumed to be '0'
m_reader.consume();
hex_value *= 16;
builder.append(static_cast<char>(hex_value));
return builder.to_byte_string();