ceph/src/boost/boost/beast/core/buffers_prefix.hpp

   1 //
   2 // Copyright (c) 2016-2017 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 // Official repository: https://github.com/boostorg/beast
   8 //
   9
  10 #ifndef BOOST_BEAST_BUFFERS_PREFIX_HPP
  11 #define BOOST_BEAST_BUFFERS_PREFIX_HPP
  12
  13 #include <boost/beast/core/detail/config.hpp>
  14 #include <boost/beast/core/type_traits.hpp>
  15 #include <boost/beast/core/detail/in_place_init.hpp>
  16 #include <boost/asio/buffer.hpp>
  17 #include <cstdint>
  18 #include <type_traits>
  19
  20 namespace boost {
  21 namespace beast {
  22
  23 /** A buffer sequence adapter that shortens the sequence size.
  24
  25     The class adapts a buffer sequence to efficiently represent
  26     a shorter subset of the original list of buffers starting
  27     with the first byte of the original sequence.
  28
  29     @tparam BufferSequence The buffer sequence to adapt.
  30 */
  31 template<class BufferSequence>
  32 class buffers_prefix_view
  33 {
  34     using buffers_type = typename
  35         std::decay<BufferSequence>::type;
  36
  37     using iter_type = typename
  38         detail::buffer_sequence_iterator<buffers_type>::type;
  39
  40     BufferSequence bs_;
  41     std::size_t size_;
  42     iter_type end_;
  43
  44     template<class Deduced>
  45     buffers_prefix_view(
  46             Deduced&& other, std::size_t dist)
  47         : bs_(std::forward<Deduced>(other).bs_)
  48         , size_(other.size_)
  49         , end_(std::next(bs_.begin(), dist))
  50     {
  51     }
  52
  53     void
  54     setup(std::size_t size);
  55
  56 public:
  57     /// The type for each element in the list of buffers.
  58     using value_type = typename std::conditional<
  59         std::is_convertible<typename
  60             std::iterator_traits<iter_type>::value_type,
  61                 boost::asio::mutable_buffer>::value,
  62                     boost::asio::mutable_buffer,
  63                         boost::asio::const_buffer>::type;
  64
  65 #if BOOST_BEAST_DOXYGEN
  66     /// A bidirectional iterator type that may be used to read elements.
  67     using const_iterator = implementation_defined;
  68
  69 #else
  70     class const_iterator;
  71
  72 #endif
  73
  74     /// Move constructor.
  75     buffers_prefix_view(buffers_prefix_view&&);
  76
  77     /// Copy constructor.
  78     buffers_prefix_view(buffers_prefix_view const&);
  79
  80     /// Move assignment.
  81     buffers_prefix_view& operator=(buffers_prefix_view&&);
  82
  83     /// Copy assignment.
  84     buffers_prefix_view& operator=(buffers_prefix_view const&);
  85
  86     /** Construct a buffer sequence prefix.
  87
  88         @param size The maximum number of bytes in the prefix.
  89         If this is larger than the size of passed, buffers,
  90         the resulting sequence will represent the entire
  91         input sequence.
  92
  93         @param buffers The buffer sequence to adapt. A copy of
  94         the sequence will be made, but ownership of the underlying
  95         memory is not transferred.
  96     */
  97     buffers_prefix_view(
  98         std::size_t size,
  99         BufferSequence const& buffers);
 100
 101     /** Construct a buffer sequence prefix in-place.
 102
 103         @param size The maximum number of bytes in the prefix.
 104         If this is larger than the size of passed, buffers,
 105         the resulting sequence will represent the entire
 106         input sequence.
 107
 108         @param args Arguments forwarded to the contained buffers constructor.
 109     */
 110     template<class... Args>
 111     buffers_prefix_view(
 112         std::size_t size,
 113         boost::in_place_init_t,
 114         Args&&... args);
 115
 116     /// Get a bidirectional iterator to the first element.
 117     const_iterator
 118     begin() const;
 119
 120     /// Get a bidirectional iterator to one past the last element.
 121     const_iterator
 122     end() const;
 123 };
 124
 125 /** Returns a prefix of a constant buffer.
 126
 127     The returned buffer points to the same memory as the
 128     passed buffer, but with a size that is equal to or less
 129     than the size of the original buffer.
 130
 131     @param size The size of the returned buffer.
 132
 133     @param buffer The buffer to shorten. The underlying
 134     memory is not modified.
 135
 136     @return A new buffer that points to the first `size`
 137     bytes of the original buffer.
 138 */
 139 inline
 140 boost::asio::const_buffer
 141 buffers_prefix(std::size_t size,
 142     boost::asio::const_buffer buffer)
 143 {
 144     return {buffer.data(),
 145         (std::min)(size, buffer.size())};
 146 }
 147
 148 /** Returns a prefix of a mutable buffer.
 149
 150     The returned buffer points to the same memory as the
 151     passed buffer, but with a size that is equal to or less
 152     than the size of the original buffer.
 153
 154     @param size The size of the returned buffer.
 155
 156     @param buffer The buffer to shorten. The underlying
 157     memory is not modified.
 158
 159     @return A new buffer that points to the first `size` bytes
 160     of the original buffer.
 161 */
 162 inline
 163 boost::asio::mutable_buffer
 164 buffers_prefix(std::size_t size,
 165     boost::asio::mutable_buffer buffer)
 166 {
 167     return {buffer.data(),
 168         (std::min)(size, buffer.size())};
 169 }
 170
 171 /** Returns a prefix of a buffer sequence.
 172
 173     This function returns a new buffer sequence which when iterated,
 174     presents a shorter subset of the original list of buffers starting
 175     with the first byte of the original sequence.
 176
 177     @param size The maximum number of bytes in the wrapped
 178     sequence. If this is larger than the size of passed,
 179     buffers, the resulting sequence will represent the
 180     entire input sequence.
 181
 182     @param buffers An instance of @b ConstBufferSequence or
 183     @b MutableBufferSequence to adapt. A copy of the sequence
 184     will be made, but ownership of the underlying memory is
 185     not transferred.
 186 */
 187 template<class BufferSequence>
 188 #if BOOST_BEAST_DOXYGEN
 189 buffers_prefix_view<BufferSequence>
 190 #else
 191 inline
 192 typename std::enable_if<
 193     ! std::is_same<BufferSequence,
 194         boost::asio::const_buffer>::value &&
 195     ! std::is_same<BufferSequence,
 196         boost::asio::mutable_buffer>::value,
 197     buffers_prefix_view<BufferSequence>>::type
 198 #endif
 199 buffers_prefix(std::size_t size, BufferSequence const& buffers)
 200 {
 201     static_assert(
 202         boost::asio::is_const_buffer_sequence<BufferSequence>::value ||
 203         boost::asio::is_mutable_buffer_sequence<BufferSequence>::value,
 204             "BufferSequence requirements not met");
 205     return buffers_prefix_view<BufferSequence>(size, buffers);
 206 }
 207
 208 /** Returns the first buffer in a buffer sequence
 209
 210     This returns the first buffer in the buffer sequence.
 211     If the buffer sequence is an empty range, the returned
 212     buffer will have a zero buffer size.
 213
 214     @param buffers The buffer sequence. If the sequence is
 215     mutable, the returned buffer sequence will also be mutable.
 216     Otherwise, the returned buffer sequence will be constant.
 217 */
 218 template<class BufferSequence>
 219 typename std::conditional<
 220     boost::asio::is_mutable_buffer_sequence<BufferSequence>::value,
 221     boost::asio::mutable_buffer,
 222     boost::asio::const_buffer>::type
 223 buffers_front(BufferSequence const& buffers)
 224 {
 225     auto const first =
 226         boost::asio::buffer_sequence_begin(buffers);
 227     if(first == boost::asio::buffer_sequence_end(buffers))
 228         return {};
 229     return *first;
 230 }
 231
 232 } // beast
 233 } // boost
 234
 235 #include <boost/beast/core/impl/buffers_prefix.ipp>
 236
 237 #endif