// Copyright (c) 2019, The Monero Project
//
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#pragma once
#include <cstddef>
#include <cstdint>
#include <memory>
#include <string>
#include <vector>
#include "span.h"
namespace epee
{
struct byte_slice_data;
struct release_byte_slice
{
void operator()(byte_slice_data*) const noexcept;
};
/*! Inspired by slices in golang. Storage is thread-safe reference counted,
allowing for cheap copies or range selection on the bytes. The bytes
owned by this class are always immutable.
The functions `operator=`, `take_slice` and `remove_prefix` may alter the
reference count for the backing store, which will invalidate pointers
previously returned if the reference count is zero. Be careful about
"caching" pointers in these circumstances. */
class byte_slice
{
/* A custom reference count is used instead of shared_ptr because it allows
for an allocation optimization for the span constructor. This also
reduces the size of this class by one pointer. */
std::unique_ptr<byte_slice_data, release_byte_slice> storage_;
span<const std::uint8_t> portion_; // within storage_
//! Internal use only; use to increase `storage` reference count.
byte_slice(byte_slice_data* storage, span<const std::uint8_t> portion) noexcept;
struct adapt_buffer{};
template<typename T>
explicit byte_slice(const adapt_buffer, T&& buffer);
public:
using value_type = std::uint8_t;
using size_type = std::size_t;
using difference_type = std::ptrdiff_t;
using pointer = const std::uint8_t*;
using const_pointer = const std::uint8_t*;
using reference = std::uint8_t;
using const_reference = std::uint8_t;
using iterator = pointer;
using const_iterator = const_pointer;
//! Construct empty slice.
byte_slice() noexcept
: storage_(nullptr), portion_()
{}
//! Construct empty slice
byte_slice(std::nullptr_t) noexcept
: byte_slice()
{}
//! Scatter-gather (copy) multiple `sources` into a single allocated slice.
explicit byte_slice(std::initializer_list<span<const std::uint8_t>> sources);
//! Convert `buffer` into a slice using one allocation for shared count.
explicit byte_slice(std::vector<std::uint8_t>&& buffer);
//! Convert `buffer` into a slice using one allocation for shared count.
explicit byte_slice(std::string&& buffer);
byte_slice(byte_slice&& source) noexcept;
~byte_slice() noexcept = default;
//! \note May invalidate previously retrieved pointers.
byte_slice& operator=(byte_slice&&) noexcept;
//! \return A shallow (cheap) copy of the data from `this` slice.
byte_slice clone() const noexcept { return {storage_.get(), portion_}; }
iterator begin() const noexcept { return portion_.begin(); }
const_iterator cbegin() const noexcept { return portion_.begin(); }
iterator end() const noexcept { return portion_.end(); }
const_iterator cend() const noexcept { return portion_.end(); }
bool empty() const noexcept { return storage_ == nullptr; }
const std::uint8_t* data() const noexcept { return portion_.data(); }
std::size_t size() const noexcept { return portion_.size(); }
/*! Drop bytes from the beginning of `this` slice.
\note May invalidate previously retrieved pointers.
\post `this->size() = this->size() - std::min(this->size(), max_bytes)`
\post `if (this->size() <= max_bytes) this->data() = nullptr`
\return Number of bytes removed. */
std::size_t remove_prefix(std::size_t max_bytes) noexcept;
/*! "Take" bytes from the beginning of `this` slice.
\note May invalidate previously retrieved pointers.
\post `this->size() = this->size() - std::min(this->size(), max_bytes)`
\post `if (this->size() <= max_bytes) this->data() = nullptr`
\return Slice containing the bytes removed from `this` slice. */
byte_slice take_slice(std::size_t max_bytes) noexcept;
/*! Return a shallow (cheap) copy of a slice from `begin` and `end` offsets.
\throw std::out_of_range If `end < begin`.
\throw std::out_of_range If `size() < end`.
\return Slice starting at `data() + begin` of size `end - begin`. */
byte_slice get_slice(std::size_t begin, std::size_t end) const;
};
} // epee
