ceph/src/Beast/include/beast/core/consuming_buffers.hpp

   1 //
   2 // Copyright (c) 2013-2017 Vinnie Falco (vinnie dot falco at gmail dot com)
   3 //
   4 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   5 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6 //
   7
   8 #ifndef BEAST_CONSUMING_BUFFERS_HPP
   9 #define BEAST_CONSUMING_BUFFERS_HPP
  10
  11 #include <beast/config.hpp>
  12 #include <beast/core/buffer_concepts.hpp>
  13 #include <boost/asio/buffer.hpp>
  14 #include <cstdint>
  15 #include <iterator>
  16 #include <type_traits>
  17 #include <utility>
  18
  19 namespace beast {
  20
  21 /** Adapter to trim the front of a `BufferSequence`.
  22
  23     This adapter wraps a buffer sequence to create a new sequence
  24     which may be incrementally consumed. Bytes consumed are removed
  25     from the front of the buffer. The underlying memory is not changed,
  26     instead the adapter efficiently iterates through a subset of
  27     the buffers wrapped.
  28
  29     The wrapped buffer is not modified, a copy is made instead.
  30     Ownership of the underlying memory is not transferred, the application
  31     is still responsible for managing its lifetime.
  32
  33     @tparam BufferSequence The buffer sequence to wrap.
  34 */
  35 template<class BufferSequence>
  36 class consuming_buffers
  37 {
  38     using iter_type =
  39         typename BufferSequence::const_iterator;
  40
  41     BufferSequence bs_;
  42     iter_type begin_;
  43     iter_type end_;
  44     std::size_t skip_ = 0;
  45
  46     template<class Deduced>
  47     consuming_buffers(Deduced&& other, std::size_t nbegin)
  48         : bs_(std::forward<Deduced>(other).bs_)
  49         , begin_(std::next(bs_.begin(), nbegin))
  50         , skip_(other.skip_)
  51     {
  52     }
  53
  54 public:
  55     /** The type for each element in the list of buffers.
  56
  57         If the buffers in the underlying sequence are convertible to
  58         `boost::asio::mutable_buffer`, then this type will be
  59         `boost::asio::mutable_buffer`, else this type will be
  60         `boost::asio::const_buffer`.
  61     */
  62 #if BEAST_DOXYGEN
  63     using value_type = ...;
  64 #else
  65     using value_type = typename std::conditional<
  66         std::is_convertible<typename
  67             std::iterator_traits<iter_type>::value_type,
  68                 boost::asio::mutable_buffer>::value,
  69                     boost::asio::mutable_buffer,
  70                         boost::asio::const_buffer>::type;
  71 #endif
  72
  73 #if BEAST_DOXYGEN
  74     /// A bidirectional iterator type that may be used to read elements.
  75     using const_iterator = implementation_defined;
  76
  77 #else
  78     class const_iterator;
  79
  80 #endif
  81
  82     /// Move constructor.
  83     consuming_buffers(consuming_buffers&&);
  84
  85     /// Copy constructor.
  86     consuming_buffers(consuming_buffers const&);
  87
  88     /// Move assignment.
  89     consuming_buffers& operator=(consuming_buffers&&);
  90
  91     /// Copy assignment.
  92     consuming_buffers& operator=(consuming_buffers const&);
  93
  94     /** Construct to represent a buffer sequence.
  95
  96         A copy of the buffer sequence is made. Ownership of the
  97         underlying memory is not transferred or copied.
  98     */
  99     explicit
 100     consuming_buffers(BufferSequence const& buffers);
 101
 102     /// Get a bidirectional iterator to the first element.
 103     const_iterator
 104     begin() const;
 105
 106     /// Get a bidirectional iterator to one past the last element.
 107     const_iterator
 108     end() const;
 109
 110     /** Remove bytes from the beginning of the sequence.
 111
 112         @param n The number of bytes to remove. If this is
 113         larger than the number of bytes remaining, all the
 114         bytes remaining are removed.
 115     */
 116     void
 117     consume(std::size_t n);
 118 };
 119
 120 } // beast
 121
 122 #include <beast/core/impl/consuming_buffers.ipp>
 123
 124 #endif