buffer_stuffer.h

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/*
* (C) 2023-2024 René Meusel - Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#ifndef BOTAN_BUFFER_STUFFER_H_
#define BOTAN_BUFFER_STUFFER_H_
 
#include <botan/assert.h>
#include <botan/strong_type.h>
#include <botan/types.h>
#include <span>
 
namespace Botan {
 
/**
 * @brief Helper class to ease in-place marshalling of concatenated fixed-length
 *        values.
 *
 * The size of the final buffer must be known from the start, reallocations are
 * not performed.
 */
class BufferStuffer final {
   public:
      constexpr explicit BufferStuffer(std::span<uint8_t> buffer) : m_buffer(buffer) {}
 
      /**
       * @returns a span for the next @p bytes bytes in the concatenated buffer.
       *          Checks that the buffer is not exceeded.
       */
      constexpr std::span<uint8_t> next(size_t bytes) {
         BOTAN_STATE_CHECK(m_buffer.size() >= bytes);
 
         auto result = m_buffer.first(bytes);
         m_buffer = m_buffer.subspan(bytes);
         return result;
      }
 
      template <size_t bytes>
      constexpr std::span<uint8_t, bytes> next() {
         BOTAN_STATE_CHECK(m_buffer.size() >= bytes);
 
         auto result = m_buffer.first<bytes>();
         m_buffer = m_buffer.subspan(bytes);
         return result;
      }
 
      template <concepts::contiguous_strong_type StrongT>
      StrongSpan<StrongT> next(size_t bytes) {
         return StrongSpan<StrongT>(next(bytes));
      }
 
      /**
       * @returns a reference to the next single byte in the buffer
       */
      constexpr uint8_t& next_byte() { return next(1)[0]; }
 
      constexpr void append(std::span<const uint8_t> buffer) {
         auto sink = next(buffer.size());
         std::copy(buffer.begin(), buffer.end(), sink.begin());
      }
 
      constexpr void append(uint8_t b, size_t repeat = 1) {
         auto sink = next(repeat);
         std::fill(sink.begin(), sink.end(), b);
      }
 
      constexpr bool full() const { return m_buffer.empty(); }
 
      constexpr size_t remaining_capacity() const { return m_buffer.size(); }
 
   private:
      std::span<uint8_t> m_buffer;
};
 
}  // namespace Botan
 
#endif