1//
2// Copyright (c) 2016-2019 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/buffer_traits.hpp>
15#include <boost/optional/optional.hpp> // for in_place_init_t
16#include <algorithm>
17#include <cstdint>
18#include <type_traits>
19
20#if BOOST_WORKAROUND(BOOST_MSVC, < 1910)
21#include <boost/type_traits/is_convertible.hpp>
22#endif
23
24namespace boost {
25namespace beast {
26
27/** A buffer sequence adaptor that shortens the sequence size.
28
29 The class adapts a buffer sequence to efficiently represent
30 a shorter subset of the original list of buffers starting
31 with the first byte of the original sequence.
32
33 @tparam BufferSequence The buffer sequence to adapt.
34*/
35template<class BufferSequence>
36class buffers_prefix_view
37{
38 using iter_type =
39 buffers_iterator_type<BufferSequence>;
40
41 BufferSequence bs_;
42 std::size_t size_ = 0;
43 std::size_t remain_ = 0;
44 iter_type end_{};
45
46 void
47 setup(std::size_t size);
48
49 buffers_prefix_view(
50 buffers_prefix_view const& other,
51 std::size_t dist);
52
53public:
54 /** The type for each element in the list of buffers.
55
56 If the type `BufferSequence` meets the requirements of
57 <em>MutableBufferSequence</em>, then `value_type` is
58 `net::mutable_buffer`. Otherwise, `value_type` is
59 `net::const_buffer`.
60
61 @see buffers_type
62 */
63#if BOOST_BEAST_DOXYGEN
64 using value_type = __see_below__;
65#elif BOOST_WORKAROUND(BOOST_MSVC, < 1910)
66 using value_type = typename std::conditional<
67 boost::is_convertible<typename
68 std::iterator_traits<iter_type>::value_type,
69 net::mutable_buffer>::value,
70 net::mutable_buffer,
71 net::const_buffer>::type;
72#else
73 using value_type = buffers_type<BufferSequence>;
74#endif
75
76#if BOOST_BEAST_DOXYGEN
77 /// A bidirectional iterator type that may be used to read elements.
78 using const_iterator = __implementation_defined__;
79
80#else
81 class const_iterator;
82
83#endif
84
85 /// Copy Constructor
86 buffers_prefix_view(buffers_prefix_view const&);
87
88 /// Copy Assignment
89 buffers_prefix_view& operator=(buffers_prefix_view const&);
90
91 /** Construct a buffer sequence prefix.
92
93 @param size The maximum number of bytes in the prefix.
94 If this is larger than the size of passed buffers,
95 the resulting sequence will represent the entire
96 input sequence.
97
98 @param buffers The buffer sequence to adapt. A copy of
99 the sequence will be made, but ownership of the underlying
100 memory is not transferred. The copy is maintained for
101 the lifetime of the view.
102 */
103 buffers_prefix_view(
104 std::size_t size,
105 BufferSequence const& buffers);
106
107 /** Construct a buffer sequence prefix in-place.
108
109 @param size The maximum number of bytes in the prefix.
110 If this is larger than the size of passed buffers,
111 the resulting sequence will represent the entire
112 input sequence.
113
114 @param args Arguments forwarded to the contained buffer's constructor.
115 */
116 template<class... Args>
117 buffers_prefix_view(
118 std::size_t size,
119 boost::in_place_init_t,
120 Args&&... args);
121
122 /// Returns an iterator to the first buffer in the sequence
123 const_iterator
124 begin() const;
125
126 /// Returns an iterator to one past the last buffer in the sequence
127 const_iterator
128 end() const;
129
130#if ! BOOST_BEAST_DOXYGEN
131 std::size_t
132 buffer_bytes_impl() const noexcept
133 {
134 return size_;
135 }
136#endif
137};
138
139//------------------------------------------------------------------------------
140
141/** Returns a prefix of a constant or mutable buffer sequence.
142
143 The returned buffer sequence points to the same memory as the
144 passed buffer sequence, but with a size that is equal to or
145 smaller. No memory allocations are performed; the resulting
146 sequence is calculated as a lazy range.
147
148 @param size The maximum size of the returned buffer sequence
149 in bytes. If this is greater than or equal to the size of
150 the passed buffer sequence, the result will have the same
151 size as the original buffer sequence.
152
153 @param buffers An object whose type meets the requirements
154 of <em>BufferSequence</em>. The returned value will
155 maintain a copy of the passed buffers for its lifetime;
156 however, ownership of the underlying memory is not
157 transferred.
158
159 @return A constant buffer sequence that represents the prefix
160 of the original buffer sequence. If the original buffer sequence
161 also meets the requirements of <em>MutableBufferSequence</em>,
162 then the returned value will also be a mutable buffer sequence.
163*/
164template<class BufferSequence>
165buffers_prefix_view<BufferSequence>
166buffers_prefix(
167 std::size_t size, BufferSequence const& buffers)
168{
169 static_assert(
170 net::is_const_buffer_sequence<BufferSequence>::value,
171 "BufferSequence type requirements not met");
172 return buffers_prefix_view<BufferSequence>(size, buffers);
173}
174
175/** Returns the first buffer in a buffer sequence
176
177 This returns the first buffer in the buffer sequence.
178 If the buffer sequence is an empty range, the returned
179 buffer will have a zero buffer size.
180
181 @param buffers The buffer sequence. If the sequence is
182 mutable, the returned buffer sequence will also be mutable.
183 Otherwise, the returned buffer sequence will be constant.
184*/
185template<class BufferSequence>
186buffers_type<BufferSequence>
187buffers_front(BufferSequence const& buffers)
188{
189 auto const first =
190 net::buffer_sequence_begin(buffers);
191 if(first == net::buffer_sequence_end(buffers))
192 return {};
193 return *first;
194}
195
196} // beast
197} // boost
198
199#include <boost/beast/core/impl/buffers_prefix.hpp>
200
201#endif
202

source code of boost/libs/beast/include/boost/beast/core/buffers_prefix.hpp