ladybird/AK/CircularBuffer.cpp
Lucas CHOLLET 3b824ec8c9 AK+Test: Fix a logic error in CircularBuffer::offset_of()
This error was introduced by 9a7accdd and had a significant impact on
`BufferedFile` behavior. Hence, we started seeing crash in test262.

By itself, the issue was a wrong calculation of the internal reading
spans when using the `read` and `until` parameters. Which can lead to
at worse crash in VERIFY and at least weird behaviors as missed needles
or detections out of bounds.

It was also accompanied by an erroneous test.

This patch fixes the bug, the test and also provides more tests.
2023-01-15 23:23:24 +00:00

188 lines
5.1 KiB
C++

/*
* Copyright (c) 2022, Lucas Chollet <lucas.chollet@free.fr>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/CircularBuffer.h>
#include <AK/MemMem.h>
namespace AK {
CircularBuffer::CircularBuffer(ByteBuffer buffer)
: m_buffer(move(buffer))
{
}
ErrorOr<CircularBuffer> CircularBuffer::create_empty(size_t size)
{
auto temporary_buffer = TRY(ByteBuffer::create_uninitialized(size));
CircularBuffer circular_buffer { move(temporary_buffer) };
return circular_buffer;
}
ErrorOr<CircularBuffer> CircularBuffer::create_initialized(ByteBuffer buffer)
{
CircularBuffer circular_buffer { move(buffer) };
circular_buffer.m_used_space = circular_buffer.m_buffer.size();
return circular_buffer;
}
size_t CircularBuffer::empty_space() const
{
return capacity() - m_used_space;
}
size_t CircularBuffer::used_space() const
{
return m_used_space;
}
size_t CircularBuffer::capacity() const
{
return m_buffer.size();
}
bool CircularBuffer::is_wrapping_around() const
{
return capacity() <= m_reading_head + m_used_space;
}
Optional<size_t> CircularBuffer::offset_of(StringView needle, Optional<size_t> from, Optional<size_t> until) const
{
auto const read_from = from.value_or(0);
auto const read_until = until.value_or(m_used_space);
VERIFY(read_from <= read_until);
Array<ReadonlyBytes, 2> spans {};
spans[0] = next_read_span();
auto const original_span_0_size = spans[0].size();
if (read_from > 0)
spans[0] = spans[0].slice(min(spans[0].size(), read_from));
if (spans[0].size() + read_from > read_until)
spans[0] = spans[0].trim(read_until - read_from);
else if (is_wrapping_around())
spans[1] = m_buffer.span().slice(max(original_span_0_size, read_from) - original_span_0_size, min(read_until, m_used_space) - original_span_0_size);
auto maybe_found = AK::memmem(spans.begin(), spans.end(), needle.bytes());
if (maybe_found.has_value())
*maybe_found += read_from;
return maybe_found;
}
void CircularBuffer::clear()
{
m_reading_head = 0;
m_used_space = 0;
m_seekback_limit = 0;
}
Bytes CircularBuffer::next_write_span()
{
if (is_wrapping_around())
return m_buffer.span().slice(m_reading_head + m_used_space - capacity(), capacity() - m_used_space);
return m_buffer.span().slice(m_reading_head + m_used_space, capacity() - (m_reading_head + m_used_space));
}
ReadonlyBytes CircularBuffer::next_read_span() const
{
return m_buffer.span().slice(m_reading_head, min(capacity() - m_reading_head, m_used_space));
}
ReadonlyBytes CircularBuffer::next_read_span_with_seekback(size_t distance) const
{
VERIFY(m_seekback_limit <= capacity());
VERIFY(distance <= m_seekback_limit);
// Note: We are adding the capacity once here to ensure that we can wrap around the negative space by using modulo.
auto read_offset = (capacity() + m_reading_head + m_used_space - distance) % capacity();
return m_buffer.span().slice(read_offset, min(capacity() - read_offset, m_seekback_limit));
}
size_t CircularBuffer::write(ReadonlyBytes bytes)
{
auto remaining = bytes.size();
while (remaining > 0) {
auto const next_span = next_write_span();
if (next_span.size() == 0)
break;
auto const written_bytes = bytes.slice(bytes.size() - remaining).copy_trimmed_to(next_span);
m_used_space += written_bytes;
m_seekback_limit += written_bytes;
if (m_seekback_limit > capacity())
m_seekback_limit = capacity();
remaining -= written_bytes;
}
return bytes.size() - remaining;
}
Bytes CircularBuffer::read(Bytes bytes)
{
auto remaining = bytes.size();
while (remaining > 0) {
auto const next_span = next_read_span();
if (next_span.size() == 0)
break;
auto written_bytes = next_span.copy_trimmed_to(bytes.slice(bytes.size() - remaining));
m_used_space -= written_bytes;
m_reading_head += written_bytes;
if (m_reading_head >= capacity())
m_reading_head -= capacity();
remaining -= written_bytes;
}
return bytes.trim(bytes.size() - remaining);
}
ErrorOr<Bytes> CircularBuffer::read_with_seekback(Bytes bytes, size_t distance)
{
if (distance > m_seekback_limit)
return Error::from_string_literal("Tried a seekback read beyond the seekback limit");
auto remaining = bytes.size();
while (remaining > 0) {
auto const next_span = next_read_span_with_seekback(distance);
if (next_span.size() == 0)
break;
auto written_bytes = next_span.copy_trimmed_to(bytes.slice(bytes.size() - remaining));
distance -= written_bytes;
remaining -= written_bytes;
}
return bytes.trim(bytes.size() - remaining);
}
ErrorOr<void> CircularBuffer::discard(size_t discarding_size)
{
if (m_used_space < discarding_size)
return Error::from_string_literal("Can not discard more data than what the buffer contains");
m_used_space -= discarding_size;
m_reading_head = (m_reading_head + discarding_size) % capacity();
return {};
}
}