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include/boost/capy/read.hpp

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read.hpp
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boost::capy::task<boost::capy::io_result<unsigned long> > boost::capy::read<boost::capy::contingent_read_stream, boost::capy::mutable_buffer>(boost::capy::contingent_read_stream&, boost::capy::mutable_buffer) :93 4x 100.0% 44.0% boost::capy::task<boost::capy::io_result<unsigned long> > boost::capy::read<boost::capy::test::read_stream, boost::capy::mutable_buffer>(boost::capy::test::read_stream&, boost::capy::mutable_buffer) :93 22x 100.0% 44.0% boost::capy::task<boost::capy::io_result<unsigned long> > boost::capy::read<boost::capy::test::read_stream, std::array<boost::capy::mutable_buffer, 2ul> >(boost::capy::test::read_stream&, std::array<boost::capy::mutable_buffer, 2ul>) :93 34x 100.0% 44.0% boost::capy::task<boost::capy::io_result<unsigned long> > boost::capy::read<boost::capy::test::stream, boost::capy::mutable_buffer>(boost::capy::test::stream&, boost::capy::mutable_buffer) :93 38x 100.0% 44.0%
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1 //
2 // Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.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/cppalliance/capy
8 //
9
10 #ifndef BOOST_CAPY_READ_HPP
11 #define BOOST_CAPY_READ_HPP
12
13 #include <boost/capy/detail/config.hpp>
14 #include <boost/capy/cond.hpp>
15 #include <boost/capy/io_task.hpp>
16 #include <boost/capy/buffers.hpp>
17 #include <boost/capy/buffers/consuming_buffers.hpp>
18 #include <boost/capy/concept/read_stream.hpp>
19
20 #include <algorithm>
21 #include <cstddef>
22
23 namespace boost {
24 namespace capy {
25
26 /** Read data from a stream until the buffer sequence is full.
27
28 @par Await-effects
29
30 Reads data from `stream` via awaiting `stream.read_some` repeatedly
31 until:
32
33 @li either the entire buffer sequence @c buffers is filled,
34 @li or a contingency occurs on `stream.read_some`.
35
36 If `buffer_size(buffers) == 0` then no awaiting `stream.read_some`
37 is performed. This is not a contingency.
38
39 @par Await-returns
40 An object of type `io_result<std::size_t>` destructuring as `[ec, n]`.
41
42 Upon a contingency, `n` represents the number of bytes read so far,
43 inclusive of the last partial read.
44
45 Contingencies:
46
47 @li The first contingency reported from awaiting @c stream.read_some
48 while `buffers` is not yet filled. A contingency that accompanies
49 the read which fills `buffers` is not reported: a completed
50 transfer is a success.
51
52 Notable conditions:
53
54 @li @c cond::canceled — Operation was cancelled,
55 @li @c cond::eof — Stream reached end before @c buffers was filled.
56
57 @par Await-postcondition
58 If `n == buffer_size(buffers)` the transfer completed and `ec` is
59 success; otherwise `ec` is set.
60
61 @param stream The stream to read from. If the lifetime of `stream` ends
62 before the coroutine finishes, the behavior is undefined.
63
64 @param buffers The buffer sequence to fill. If the lifetime of the buffer
65 sequence represented by `buffers` ends before the coroutine finishes, the behavior is undefined.
66
67
68 @par Remarks
69 Supports _IoAwaitable cancellation_.
70
71
72 @par Example
73
74 @code
75 capy::task<> process_message(capy::ReadStream auto& stream)
76 {
77 std::vector<char> header(16); // known header size for some protocol
78 auto [ec, n] = co_await capy::read(stream, capy::make_buffer(header));
79 if (ec == capy::cond::eof)
80 co_return; // Connection closed
81 if (ec)
82 throw std::system_error(ec);
83
84 // at this point `header` contains exactly 16 bytes
85 }
86 @endcode
87
88 @see ReadStream, MutableBufferSequence
89 */
90 template <typename S, typename MB>
91 requires ReadStream<S> && MutableBufferSequence<MB>
92 auto
93 98x read(S& stream, MB buffers) ->
94 io_task<std::size_t>
95 {
96 consuming_buffers consuming(buffers);
97 std::size_t const total_size = buffer_size(buffers);
98 std::size_t total_read = 0;
99
100 while(total_read < total_size)
101 {
102 auto [ec, n] = co_await stream.read_some(consuming.data());
103 consuming.consume(n);
104 total_read += n;
105 // A contingency that still completed the transfer is a success:
106 // report it only when the buffer was not filled.
107 if(ec && total_read < total_size)
108 co_return {ec, total_read};
109 }
110
111 co_return {{}, total_read};
112 196x }
113
114 } // namespace capy
115 } // namespace boost
116
117 #endif
118