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_DETAIL_CONSUMING_BUFFERS_HPP
      12                 : #define BOOST_CAPY_DETAIL_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                 : namespace detail {
      24                 : 
      25                 : /** A cursor that drives consumption of a buffer sequence.
      26                 : 
      27                 :     `consuming_buffers` is the dedicated driver for `read_some`/`write_some`
      28                 :     loops. It presents the not-yet-consumed bytes of a buffer sequence via
      29                 :     `data()`, and `consume(n)` advances past `n` transferred bytes **in
      30                 :     place**.
      31                 : 
      32                 :     It is deliberately **not** itself a buffer sequence — it hands out the
      33                 :     remaining bytes through `data()` (returning a `slice_of` view). It
      34                 :     **borrows** the underlying sequence (iterators + a consumed-byte offset).
      35                 :     The sequence must outlive the cursor. That is the natural case when the
      36                 :     cursor is a local of a composed operation that took its buffers by value.
      37                 : */
      38                 : template<class Seq>
      39                 :     requires ConstBufferSequence<Seq>
      40                 : class consuming_buffers
      41                 : {
      42                 : public:
      43                 :     /// Names the buffer type the underlying sequence `Seq` yields.
      44                 :     using buffer_type = capy::buffer_type<Seq>;
      45                 : 
      46                 : private:
      47                 :     using iterator_type =
      48                 :         decltype(capy::buffer_sequence_begin(std::declval<Seq const&>()));
      49                 : 
      50                 :     iterator_type first_{};
      51                 :     iterator_type last_{};
      52                 :     std::size_t   front_skip_ = 0;  // bytes consumed from *first_
      53                 : 
      54                 : public:
      55                 :     /** Construct a cursor over `s`.
      56                 : 
      57                 :         @param s The sequence to consume. Must outlive the cursor.
      58                 :     */
      59 HIT         306 :     explicit consuming_buffers(Seq const& s) noexcept
      60             306 :         : first_(capy::buffer_sequence_begin(s))
      61             306 :         , last_(capy::buffer_sequence_end(s))
      62                 :     {
      63             306 :     }
      64                 : 
      65                 :     /** Reject construction from a temporary (the view would dangle).
      66                 : 
      67                 :         @param s The sequence that would be consumed.
      68                 :     */
      69                 :     consuming_buffers(Seq const&& s) = delete;
      70                 : 
      71                 :     /** Return the remaining (unconsumed) bytes as a buffer sequence.
      72                 : 
      73                 :         @return The bytes not yet consumed, as a buffer sequence.
      74                 :     */
      75                 :     slice_of<Seq>
      76             354 :     data() const noexcept
      77                 :     {
      78             354 :         return slice_of<Seq>(first_, last_, front_skip_, 0);
      79                 :     }
      80                 : 
      81                 :     /** Discard `n` bytes from the front, in place.
      82                 : 
      83                 :         Advances past `min(n, remaining)` bytes.
      84                 : 
      85                 :         @param n The number of bytes consumed.
      86                 :     */
      87                 :     void
      88             262 :     consume(std::size_t n) noexcept
      89                 :     {
      90             387 :         while (n > 0 && first_ != last_)
      91                 :         {
      92             199 :             std::size_t const sz    = buffer_type(*first_).size();
      93             199 :             std::size_t const avail = sz - front_skip_;
      94             199 :             if (n < avail)
      95                 :             {
      96              74 :                 front_skip_ += n;
      97              74 :                 return;
      98                 :             }
      99             125 :             n -= avail;
     100             125 :             ++first_;
     101             125 :             front_skip_ = 0;
     102                 :         }
     103                 :     }
     104                 : };
     105                 : 
     106                 : /** Deduce the sequence type from the constructor argument.
     107                 : 
     108                 :     @tparam Seq The buffer sequence type.
     109                 : */
     110                 : template<class Seq>
     111                 : consuming_buffers(Seq const&) -> consuming_buffers<Seq>;
     112                 : 
     113                 : } // namespace detail
     114                 : } // namespace capy
     115                 : } // namespace boost
     116                 : 
     117                 : #endif