Source/WTF/wtf/persistence/PersistentDecoder.h

/*
 * Copyright (C) 2014-2021 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include <span>
#include <wtf/EnumTraits.h>
#include <wtf/SHA1.h>
#include <wtf/persistence/PersistentCoders.h>

namespace WTF::Persistence {

template<typename> struct Coder;

class Decoder {
    WTF_DEPRECATED_MAKE_FAST_ALLOCATED(Decoder);
public:
    WTF_EXPORT_PRIVATE Decoder(std::span<const uint8_t>);
    WTF_EXPORT_PRIVATE ~Decoder();

    size_t length() const { return m_buffer.size(); }
    size_t currentOffset() const { return static_cast<size_t>(std::distance(m_buffer.begin(), m_bufferPosition)); }
    
    [[nodiscard]] WTF_EXPORT_PRIVATE bool rewind(size_t);

    [[nodiscard]] WTF_EXPORT_PRIVATE bool verifyChecksum();

    [[nodiscard]] WTF_EXPORT_PRIVATE bool decodeFixedLengthData(std::span<uint8_t>);

    WTF_EXPORT_PRIVATE Decoder& operator>>(std::optional<bool>&);
    WTF_EXPORT_PRIVATE Decoder& operator>>(std::optional<uint8_t>&);
    WTF_EXPORT_PRIVATE Decoder& operator>>(std::optional<uint16_t>&);
    WTF_EXPORT_PRIVATE Decoder& operator>>(std::optional<uint32_t>&);
    WTF_EXPORT_PRIVATE Decoder& operator>>(std::optional<uint64_t>&);
    WTF_EXPORT_PRIVATE Decoder& operator>>(std::optional<int16_t>&);
    WTF_EXPORT_PRIVATE Decoder& operator>>(std::optional<int32_t>&);
    WTF_EXPORT_PRIVATE Decoder& operator>>(std::optional<int64_t>&);
    WTF_EXPORT_PRIVATE Decoder& operator>>(std::optional<float>&);
    WTF_EXPORT_PRIVATE Decoder& operator>>(std::optional<double>&);

    template<typename T>
        requires (!std::is_arithmetic_v<typename std::remove_const<T>> && !std::is_enum_v<T>)
    Decoder& operator>>(std::optional<T>& result)
    {
        result = Coder<T>::decodeForPersistence(*this);
        return *this;
    }

    template<typename E>
        requires (std::is_enum_v<E>)
    Decoder& operator>>(std::optional<E>& result)
    {
        static_assert(sizeof(E) <= 8, "Enum type T must not be larger than 64 bits!");
        std::optional<uint64_t> value;
        *this >> value;
        if (!value)
            return *this;
        if (!isValidEnumForPersistence<E>(*value))
            return *this;
        result = static_cast<E>(*value);
        return *this;
    }

    template<typename T> [[nodiscard]]
    bool bufferIsLargeEnoughToContain(size_t numElements) const
    {
        static_assert(std::is_arithmetic<T>::value, "Type T must have a fixed, known encoded size!");
        return numElements <= std::numeric_limits<size_t>::max() / sizeof(T) && bufferIsLargeEnoughToContain(numElements * sizeof(T));
    }

    [[nodiscard]] WTF_EXPORT_PRIVATE std::span<const uint8_t> bufferPointerForDirectRead(size_t numBytes);

private:
    [[nodiscard]] WTF_EXPORT_PRIVATE bool bufferIsLargeEnoughToContain(size_t) const;
    template<typename Type> Decoder& decodeNumber(std::optional<Type>&);

    const std::span<const uint8_t> m_buffer;
    std::span<const uint8_t>::iterator m_bufferPosition;

    SHA1 m_sha1;
};

}