TLA  Line data    Source code

       1                 : //
       2                 : // Copyright (c) 2026 Steve Gerbino
       3                 : // Copyright (c) 2026 Michael Vandeberg
       4                 : //
       5                 : // Distributed under the Boost Software License, Version 1.0. (See accompanying
       6                 : // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
       7                 : //
       8                 : // Official repository: https://github.com/cppalliance/capy
       9                 : //
      10                 : 
      11                 : #ifndef BOOST_CAPY_BUFFERS_CONSUMING_BUFFERS_HPP
      12                 : #define BOOST_CAPY_BUFFERS_CONSUMING_BUFFERS_HPP
      13                 : 
      14                 : #include <boost/capy/detail/config.hpp>
      15                 : #include <boost/capy/buffers.hpp>
      16                 : #include <boost/capy/detail/slice_of.hpp>
      17                 : 
      18                 : #include <cstddef>
      19                 : #include <utility>
      20                 : 
      21                 : namespace boost {
      22                 : namespace capy {
      23                 : 
      24                 : /** A cursor that drives consumption of a buffer sequence.
      25                 : 
      26                 :     `consuming_buffers` is the dedicated driver for `read_some`/`write_some`
      27                 :     loops. It presents the not-yet-consumed bytes of a buffer sequence via
      28                 :     `data()`, and `consume(n)` advances past `n` transferred bytes **in
      29                 :     place**.
      30                 : 
      31                 :     It is deliberately **not** itself a buffer sequence — it hands out the
      32                 :     remaining bytes through `data()` (returning a `slice_of` view). It
      33                 :     **borrows** the underlying sequence (iterators + a consumed-byte offset).
      34                 :     The sequence must outlive the cursor. That is the natural case when the
      35                 :     cursor is a local of a composed operation that took its buffers by value.
      36                 : 
      37                 :     @par Example
      38                 :     @par !example example
      39                 : 
      40                 : 
      41                 :     @see buffer_slice, slice_of
      42                 : */
      43                 : template<class Seq>
      44                 :     requires MutableBufferSequence<Seq> || ConstBufferSequence<Seq>
      45                 : class consuming_buffers
      46                 : {
      47                 : public:
      48                 :     /// Names the buffer type the underlying sequence `Seq` yields.
      49                 :     using buffer_type = capy::buffer_type<Seq>;
      50                 : 
      51                 : private:
      52                 :     using iterator_type =
      53                 :         decltype(capy::begin(std::declval<Seq const&>()));
      54                 : 
      55                 :     iterator_type first_{};
      56                 :     iterator_type last_{};
      57                 :     std::size_t   front_skip_ = 0;  // bytes consumed from *first_
      58                 : 
      59                 : public:
      60                 :     /** Construct a cursor over `s`.
      61                 : 
      62                 :         @param s The sequence to consume. Must outlive the cursor.
      63                 :     */
      64 HIT         315 :     explicit consuming_buffers(Seq const& s) noexcept
      65             315 :         : first_(capy::begin(s))
      66             315 :         , last_(capy::end(s))
      67                 :     {
      68             315 :     }
      69                 : 
      70                 :     /** Reject construction from a temporary (the view would dangle).
      71                 : 
      72                 :         @param s The sequence that would be consumed.
      73                 :     */
      74                 :     consuming_buffers(Seq const&& s) = delete;
      75                 : 
      76                 :     /** Return the remaining (unconsumed) bytes as a buffer sequence.
      77                 : 
      78                 :         @return The bytes not yet consumed, as a buffer sequence.
      79                 :     */
      80                 :     detail::slice_of<Seq>
      81             362 :     data() const noexcept
      82                 :     {
      83             362 :         return detail::slice_of<Seq>(first_, last_, front_skip_, 0);
      84                 :     }
      85                 : 
      86                 :     /** Discard `n` bytes from the front, in place.
      87                 : 
      88                 :         Advances past `min(n, remaining)` bytes.
      89                 : 
      90                 :         @param n The number of bytes consumed.
      91                 :     */
      92                 :     void
      93             272 :     consume(std::size_t n) noexcept
      94                 :     {
      95             415 :         while (n > 0 && first_ != last_)
      96                 :         {
      97             214 :             std::size_t const sz    = buffer_type(*first_).size();
      98             214 :             std::size_t const avail = sz - front_skip_;
      99             214 :             if (n < avail)
     100                 :             {
     101              71 :                 front_skip_ += n;
     102              71 :                 return;
     103                 :             }
     104             143 :             n -= avail;
     105             143 :             ++first_;
     106             143 :             front_skip_ = 0;
     107                 :         }
     108                 :     }
     109                 : };
     110                 : 
     111                 : /** Deduce the sequence type from the constructor argument.
     112                 : 
     113                 :     @tparam Seq The buffer sequence type.
     114                 : */
     115                 : template<class Seq>
     116                 : consuming_buffers(Seq const&) -> consuming_buffers<Seq>;
     117                 : 
     118                 : } // namespace capy
     119                 : } // namespace boost
     120                 : 
     121                 : #endif