ladybird/AK/MemoryStream.h

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/*
* Copyright (c) 2021, kleines Filmröllchen <filmroellchen@serenityos.org>.
* Copyright (c) 2023, Sam Atkins <atkinssj@serenityos.org>.
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Error.h>
#include <AK/OwnPtr.h>
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#include <AK/Stream.h>
#include <AK/Vector.h>
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namespace AK {
/// A stream class that allows for reading/writing on a preallocated memory area
/// using a single read/write head.
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class FixedMemoryStream : public SeekableStream {
public:
enum class Mode {
ReadOnly,
ReadWrite,
};
explicit FixedMemoryStream(Bytes bytes, Mode mode = Mode::ReadWrite);
explicit FixedMemoryStream(ReadonlyBytes bytes);
virtual bool is_eof() const override;
virtual bool is_open() const override;
virtual void close() override;
virtual ErrorOr<void> truncate(size_t) override;
virtual ErrorOr<Bytes> read_some(Bytes bytes) override;
virtual ErrorOr<void> read_until_filled(Bytes bytes) override;
virtual ErrorOr<size_t> seek(i64 offset, SeekMode seek_mode = SeekMode::SetPosition) override;
virtual ErrorOr<size_t> write_some(ReadonlyBytes bytes) override;
virtual ErrorOr<void> write_until_depleted(ReadonlyBytes bytes) override;
size_t offset() const;
size_t remaining() const;
/// Read a value, but referring to the stream's underlying data instead of copying it.
/// Of course, only use this if you know the lifetime of the data will exceed the value's.
// FIXME: Would be nicer to be able to return T& but Variant (and thus ErrorOr) can't hold references.
template<typename T>
requires(Traits<T>::is_trivially_serializable())
ErrorOr<T*> read_in_place()
{
if constexpr (!IsConst<T>) {
if (!m_writing_enabled)
return Error::from_string_view_or_print_error_and_return_errno("Tried to obtain a non-const reference from a read-only FixedMemoryStream"sv, EINVAL);
}
T* value = reinterpret_cast<T*>(m_bytes.offset_pointer(m_offset));
TRY(discard(sizeof(T)));
return value;
}
/// Read a span of values, referring to the stream's underlying data instead of copying it.
/// Of course, only use this if you know the lifetime of the data will exceed the span's.
template<typename T>
requires(Traits<T>::is_trivially_serializable())
ErrorOr<Span<T>> read_in_place(size_t count)
{
if constexpr (!IsConst<T>) {
if (!m_writing_enabled)
return Error::from_string_view_or_print_error_and_return_errno("Tried to obtain a non-const span from a read-only FixedMemoryStream"sv, EINVAL);
}
Span<T> span { reinterpret_cast<T*>(m_bytes.offset_pointer(m_offset)), count };
TRY(discard(sizeof(T) * count));
return span;
}
private:
Bytes m_bytes;
size_t m_offset { 0 };
bool m_writing_enabled { true };
};
/// A stream class that allows for writing to an automatically allocating memory area
/// and reading back the written data afterwards.
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class AllocatingMemoryStream final : public Stream {
public:
static constexpr size_t CHUNK_SIZE = 4096;
virtual ErrorOr<Bytes> read_some(Bytes) override;
virtual ErrorOr<size_t> write_some(ReadonlyBytes) override;
virtual ErrorOr<void> discard(size_t) override;
virtual bool is_eof() const override;
virtual bool is_open() const override;
virtual void close() override;
size_t used_buffer_size() const;
ErrorOr<Optional<size_t>> offset_of(ReadonlyBytes needle) const;
private:
// Note: We set the inline buffer capacity to zero to make moving chunks as efficient as possible.
using Chunk = AK::Detail::ByteBuffer<0>;
ErrorOr<ReadonlyBytes> next_read_range();
ErrorOr<Bytes> next_write_range();
void cleanup_unused_chunks();
Vector<Chunk> m_chunks;
size_t m_read_offset = 0;
size_t m_write_offset = 0;
};
}
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#if USING_AK_GLOBALLY
using AK::AllocatingMemoryStream;
using AK::FixedMemoryStream;
#endif