rippled/include/xrpl/basics/Slice.h

#ifndef XRPL_BASICS_SLICE_H_INCLUDED
#define XRPL_BASICS_SLICE_H_INCLUDED

#include <xrpl/basics/contract.h>
#include <xrpl/basics/strHex.h>
#include <xrpl/beast/utility/instrumentation.h>

#include <algorithm>
#include <array>
#include <cstdint>
#include <cstring>
#include <limits>
#include <stdexcept>
#include <string>
#include <type_traits>
#include <vector>

namespace xrpl {

/** An immutable linear range of bytes.

    A fully constructed Slice is guaranteed to be in a valid state.
    A Slice is lightweight and copyable, it retains no ownership
    of the underlying memory.
*/
class Slice
{
private:
    std::uint8_t const* data_ = nullptr;
    std::size_t size_ = 0;

public:
    using value_type = std::uint8_t;
    using const_iterator = value_type const*;

    /** Default constructed Slice has length 0. */
    Slice() noexcept = default;

    Slice(Slice const&) noexcept = default;
    Slice&
    operator=(Slice const&) noexcept = default;

    /** Create a slice pointing to existing memory. */
    Slice(void const* data, std::size_t size) noexcept
        : data_(reinterpret_cast<std::uint8_t const*>(data)), size_(size)
    {
    }

    /** Return `true` if the byte range is empty. */
    [[nodiscard]] bool
    empty() const noexcept
    {
        return size_ == 0;
    }

    /** Returns the number of bytes in the storage.

        This may be zero for an empty range.
    */
    /** @{ */
    [[nodiscard]] std::size_t
    size() const noexcept
    {
        return size_;
    }

    [[nodiscard]] std::size_t
    length() const noexcept
    {
        return size_;
    }
    /** @} */

    /** Return a pointer to beginning of the storage.
        @note The return type is guaranteed to be a pointer
              to a single byte, to facilitate pointer arithmetic.
    */
    std::uint8_t const*
    data() const noexcept
    {
        return data_;
    }

    /** Access raw bytes. */
    std::uint8_t
    operator[](std::size_t i) const noexcept
    {
        XRPL_ASSERT(
            i < size_,
            "xrpl::Slice::operator[](std::size_t) const : valid input");
        return data_[i];
    }

    /** Advance the buffer. */
    /** @{ */
    Slice&
    operator+=(std::size_t n)
    {
        if (n > size_)
            Throw<std::domain_error>("too small");
        data_ += n;
        size_ -= n;
        return *this;
    }

    Slice
    operator+(std::size_t n) const
    {
        Slice temp = *this;
        return temp += n;
    }
    /** @} */

    /** Shrinks the slice by moving its start forward by n characters. */
    void
    remove_prefix(std::size_t n)
    {
        data_ += n;
        size_ -= n;
    }

    /** Shrinks the slice by moving its end backward by n characters. */
    void
    remove_suffix(std::size_t n)
    {
        size_ -= n;
    }

    const_iterator
    begin() const noexcept
    {
        return data_;
    }

    const_iterator
    cbegin() const noexcept
    {
        return data_;
    }

    const_iterator
    end() const noexcept
    {
        return data_ + size_;
    }

    const_iterator
    cend() const noexcept
    {
        return data_ + size_;
    }

    /** Return a "sub slice" of given length starting at the given position

        Note that the subslice encompasses the range [pos, pos + rcount),
        where rcount is the smaller of count and size() - pos.

        @param pos position of the first character
        @count requested length

        @returns The requested subslice, if the request is valid.
        @throws std::out_of_range if pos > size()
     */
    Slice
    substr(
        std::size_t pos,
        std::size_t count = std::numeric_limits<std::size_t>::max()) const
    {
        if (pos > size())
            throw std::out_of_range("Requested sub-slice is out of bounds");

        return {data_ + pos, std::min(count, size() - pos)};
    }
};

//------------------------------------------------------------------------------

template <class Hasher>
inline void
hash_append(Hasher& h, Slice const& v)
{
    h(v.data(), v.size());
}

inline bool
operator==(Slice const& lhs, Slice const& rhs) noexcept
{
    if (lhs.size() != rhs.size())
        return false;

    if (lhs.size() == 0)
        return true;

    return std::memcmp(lhs.data(), rhs.data(), lhs.size()) == 0;
}

inline bool
operator!=(Slice const& lhs, Slice const& rhs) noexcept
{
    return !(lhs == rhs);
}

inline bool
operator<(Slice const& lhs, Slice const& rhs) noexcept
{
    return std::lexicographical_compare(
        lhs.data(),
        lhs.data() + lhs.size(),
        rhs.data(),
        rhs.data() + rhs.size());
}

template <class Stream>
Stream&
operator<<(Stream& s, Slice const& v)
{
    s << strHex(v);
    return s;
}

template <class T, std::size_t N>
std::enable_if_t<
    std::is_same<T, char>::value || std::is_same<T, unsigned char>::value,
    Slice>
makeSlice(std::array<T, N> const& a)
{
    return Slice(a.data(), a.size());
}

template <class T, class Alloc>
std::enable_if_t<
    std::is_same<T, char>::value || std::is_same<T, unsigned char>::value,
    Slice>
makeSlice(std::vector<T, Alloc> const& v)
{
    return Slice(v.data(), v.size());
}

template <class Traits, class Alloc>
Slice
makeSlice(std::basic_string<char, Traits, Alloc> const& s)
{
    return Slice(s.data(), s.size());
}

}  // namespace xrpl

#endif