ladybird/AK/CircularBuffer.h

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/*
* Copyright (c) 2022, Lucas Chollet <lucas.chollet@free.fr>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/ByteBuffer.h>
#include <AK/Error.h>
#include <AK/HashMap.h>
#include <AK/Noncopyable.h>
#include <AK/Vector.h>
namespace AK {
class CircularBuffer {
AK_MAKE_NONCOPYABLE(CircularBuffer);
AK_MAKE_DEFAULT_MOVABLE(CircularBuffer);
public:
static ErrorOr<CircularBuffer> create_empty(size_t size);
static ErrorOr<CircularBuffer> create_initialized(ByteBuffer);
~CircularBuffer() = default;
size_t write(ReadonlyBytes bytes);
Bytes read(Bytes bytes);
ErrorOr<void> discard(size_t discarded_bytes);
ErrorOr<size_t> fill_from_stream(Stream&);
ErrorOr<size_t> flush_to_stream(Stream&);
/// Compared to `read()`, this starts reading from an offset that is `distance` bytes
/// before the current write pointer and allows for reading already-read data.
ErrorOr<Bytes> read_with_seekback(Bytes bytes, size_t distance) const;
ErrorOr<size_t> copy_from_seekback(size_t distance, size_t length);
[[nodiscard]] size_t empty_space() const;
[[nodiscard]] size_t used_space() const;
[[nodiscard]] size_t capacity() const;
[[nodiscard]] size_t seekback_limit() const;
Optional<size_t> offset_of(StringView needle, Optional<size_t> from = {}, Optional<size_t> until = {}) const;
void clear();
protected:
CircularBuffer(ByteBuffer);
[[nodiscard]] bool is_wrapping_around() const;
[[nodiscard]] Bytes next_write_span();
[[nodiscard]] ReadonlyBytes next_read_span(size_t offset = 0) const;
[[nodiscard]] ReadonlyBytes next_seekback_span(size_t distance) const;
ByteBuffer m_buffer {};
size_t m_reading_head {};
size_t m_used_space {};
size_t m_seekback_limit {};
};
class SearchableCircularBuffer : public CircularBuffer {
public:
static ErrorOr<SearchableCircularBuffer> create_empty(size_t size);
static ErrorOr<SearchableCircularBuffer> create_initialized(ByteBuffer);
[[nodiscard]] size_t search_limit() const;
// These functions update the read pointer, so we need to hash any data that we have processed.
ErrorOr<Bytes> read(Bytes bytes);
ErrorOr<void> discard(size_t discarded_bytes);
ErrorOr<size_t> flush_to_stream(Stream& stream);
struct Match {
size_t distance;
size_t length;
};
/// This searches the seekback buffer (between read head and limit) for occurrences where it matches the next `length` bytes from the read buffer.
/// Supplying any hints will only consider those distances, in case existing offsets need to be validated.
/// Note that, since we only start searching at the read head, the length between read head and write head is excluded from the distance.
Optional<Match> find_copy_in_seekback(size_t maximum_length, size_t minimum_length = 2);
Optional<Match> find_copy_in_seekback(ReadonlySpan<size_t> distances, size_t maximum_length, size_t minimum_length = 2) const;
// The chunk size for which the hash table holds hashes.
// This is nice for users to know, as picking a minimum match length that is
// equal or greater than this allows us to completely skip a slow memory search.
static constexpr size_t HASH_CHUNK_SIZE = 3;
private:
// Note: This function has a similar purpose as next_seekback_span, but they differ in their reference point.
// Seekback operations start counting their distance at the write head, while search operations start counting their distance at the read head.
[[nodiscard]] ReadonlyBytes next_search_span(size_t distance) const;
SearchableCircularBuffer(ByteBuffer);
HashMap<unsigned, size_t> m_hash_location_map;
HashMap<size_t, size_t> m_location_chain_map;
ErrorOr<void> insert_location_hash(ReadonlyBytes value, size_t raw_offset);
ErrorOr<void> hash_last_bytes(size_t count);
};
}