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LibCore: Fix corner case for files without newlines

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When BufferedFile.can_read_line() was invoked on files with no newlines,
t incorrectly returned a false result for this single line that, even
though doesn't finish with a newline character, is still a line. Since
this method is usually used in tandem with read_line(), users would miss
reading this line (and hence all the file contents).

This commit fixes this corner case by adding another check after a
negative result from finding a newline character. This new check does
the same as the check that is done *before* looking for newlines, which
takes care of this problem, but only works for files that have at least
one newline (hence the buffer has already been filled).

A new unit test has been added that shows the use case. Without the
changes in this commit the test fails, which is a testament that this
commit really fixes the underlying issue.
This commit is contained in:
Rodrigo Tobar 2023-03-17 00:46:21 +08:00 committed by Andrew Kaster
parent 371974ed4a
commit 5a8373c6b9
Notes: sideshowbarker 2024-07-17 02:28:18 +09:00 
Author: https://github.com/rtobar
Commit: https://github.com/SerenityOS/serenity/commit/5a8373c6b9
Pull-request: https://github.com/SerenityOS/serenity/pull/16788
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/alimpfard
2 changed files with 22 additions and 1 deletions
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5
AK/BufferedStream.h
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@ -193,7 +193,10 @@ public:
if (stream().is_eof())
return m_buffer.used_space() > 0;
return TRY(find_and_populate_until_any_of(Array<StringView, 1> { "\n"sv })).has_value();
auto maybe_match = TRY(find_and_populate_until_any_of(Array { "\n"sv }));
if (maybe_match.has_value())
return true;
return stream().is_eof() && m_buffer.used_space() > 0;
}
bool is_eof() const

18
Tests/LibCore/TestLibCoreStream.cpp
View file

@ -553,6 +553,24 @@ TEST_CASE(buffered_file_tell_and_seek)
}
}
constexpr auto new_newlines_message = "Hi, look, no newlines"sv;
TEST_CASE(buffered_file_without_newlines)
{
constexpr auto filename = "/tmp/file-without-newlines"sv;
auto file_wo_newlines = Core::File::open(filename, Core::File::OpenMode::Write).release_value();
EXPECT(!file_wo_newlines->write_until_depleted(new_newlines_message.bytes()).is_error());
file_wo_newlines->close();
auto ro_file = Core::BufferedFile::create(Core::File::open(filename, Core::File::OpenMode::Read).release_value(), new_newlines_message.length() + 1).release_value();
auto maybe_can_read_line = ro_file->can_read_line();
EXPECT(!maybe_can_read_line.is_error());
EXPECT(maybe_can_read_line.release_value());
Array<u8, new_newlines_message.length() + 1> buffer;
EXPECT(ro_file->read_line(buffer).release_value() == new_newlines_message);
}
constexpr auto buffered_sent_data = "Well hello friends!\n:^)\nThis shouldn't be present. :^("sv;
constexpr auto first_line = "Well hello friends!"sv;
constexpr auto second_line = ":^)"sv;