. /include/boost/capy /read.hpp
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1   // 1   //
2   // Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com) 2   // Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com)
  3 + // Copyright (c) 2026 Michael Vandeberg
3   // 4   //
4   // Distributed under the Boost Software License, Version 1.0. (See accompanying 5   // 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   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6   // 7   //
7   // Official repository: https://github.com/cppalliance/capy 8   // Official repository: https://github.com/cppalliance/capy
8   // 9   //
9   10  
10   #ifndef BOOST_CAPY_READ_HPP 11   #ifndef BOOST_CAPY_READ_HPP
11   #define BOOST_CAPY_READ_HPP 12   #define BOOST_CAPY_READ_HPP
12   13  
13   #include <boost/capy/detail/config.hpp> 14   #include <boost/capy/detail/config.hpp>
14   #include <boost/capy/cond.hpp> 15   #include <boost/capy/cond.hpp>
15   #include <boost/capy/io_task.hpp> 16   #include <boost/capy/io_task.hpp>
16   #include <boost/capy/buffers.hpp> 17   #include <boost/capy/buffers.hpp>
17   #include <boost/capy/buffers/consuming_buffers.hpp> 18   #include <boost/capy/buffers/consuming_buffers.hpp>
18   #include <boost/capy/concept/read_stream.hpp> 19   #include <boost/capy/concept/read_stream.hpp>
19   20  
20   #include <algorithm> 21   #include <algorithm>
21   #include <cstddef> 22   #include <cstddef>
22   23  
23   namespace boost { 24   namespace boost {
24   namespace capy { 25   namespace capy {
25   26  
26   /** Read data from a stream until the buffer sequence is full. 27   /** Read data from a stream until the buffer sequence is full.
27   28  
28   @par Await-effects 29   @par Await-effects
29   30  
30   Reads data from `stream` via awaiting `stream.read_some` repeatedly 31   Reads data from `stream` via awaiting `stream.read_some` repeatedly
31   until: 32   until:
32   33  
33   @li either the entire buffer sequence @c buffers is filled, 34   @li either the entire buffer sequence @c buffers is filled,
34   @li or a contingency occurs on `stream.read_some`. 35   @li or a contingency occurs on `stream.read_some`.
35   36  
36   If `buffer_size(buffers) == 0` then no awaiting `stream.read_some` 37   If `buffer_size(buffers) == 0` then no awaiting `stream.read_some`
37   is performed. This is not a contingency. 38   is performed. This is not a contingency.
38   39  
39   @par Await-returns 40   @par Await-returns
40   An object of type `io_result<std::size_t>` destructuring as `[ec, n]`. 41   An object of type `io_result<std::size_t>` destructuring as `[ec, n]`.
41   42  
42   Upon a contingency, `n` represents the number of bytes read so far, 43   Upon a contingency, `n` represents the number of bytes read so far,
43   inclusive of the last partial read. 44   inclusive of the last partial read.
44   45  
45   Contingencies: 46   Contingencies:
46   47  
47   @li The first contingency reported from awaiting @c stream.read_some 48   @li The first contingency reported from awaiting @c stream.read_some
48   while `buffers` is not yet filled. A contingency that accompanies 49   while `buffers` is not yet filled. A contingency that accompanies
49   the read which fills `buffers` is not reported: a completed 50   the read which fills `buffers` is not reported: a completed
50   transfer is a success. 51   transfer is a success.
51   52  
52   Notable conditions: 53   Notable conditions:
53   54  
54   @li @c cond::canceled — Operation was cancelled, 55   @li @c cond::canceled — Operation was cancelled,
55   @li @c cond::eof — Stream reached end before @c buffers was filled. 56   @li @c cond::eof — Stream reached end before @c buffers was filled.
56   57  
57   @par Await-postcondition 58   @par Await-postcondition
58   If `n == buffer_size(buffers)` the transfer completed and `ec` is 59   If `n == buffer_size(buffers)` the transfer completed and `ec` is
59   success; otherwise `ec` is set. 60   success; otherwise `ec` is set.
60   61  
61   @param stream The stream to read from. If the lifetime of `stream` ends 62   @param stream The stream to read from. If the lifetime of `stream` ends
62   before the coroutine finishes, the behavior is undefined. 63   before the coroutine finishes, the behavior is undefined.
63   64  
64   @param buffers The buffer sequence to fill. If the lifetime of the buffer 65   @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   sequence represented by `buffers` ends before the coroutine finishes, the behavior is undefined.
66   67  
  68 + @return A task yielding `io_result<std::size_t>` whose second element
  69 + is the number of bytes read.
67   70  
68   @par Remarks 71   @par Remarks
69   Supports _IoAwaitable cancellation_. 72   Supports _IoAwaitable cancellation_.
70   73  
71   74  
72   @par Example 75   @par Example
73   76  
74   @code 77   @code
75   capy::task<> process_message(capy::ReadStream auto& stream) 78   capy::task<> process_message(capy::ReadStream auto& stream)
76   { 79   {
77   std::vector<char> header(16); // known header size for some protocol 80   std::vector<char> header(16); // known header size for some protocol
78   auto [ec, n] = co_await capy::read(stream, capy::make_buffer(header)); 81   auto [ec, n] = co_await capy::read(stream, capy::make_buffer(header));
79   if (ec == capy::cond::eof) 82   if (ec == capy::cond::eof)
80   co_return; // Connection closed 83   co_return; // Connection closed
81   if (ec) 84   if (ec)
82   throw std::system_error(ec); 85   throw std::system_error(ec);
83   86  
84   // at this point `header` contains exactly 16 bytes 87   // at this point `header` contains exactly 16 bytes
85   } 88   }
86   @endcode 89   @endcode
87   90  
88   @see ReadStream, MutableBufferSequence 91   @see ReadStream, MutableBufferSequence
89   */ 92   */
90   template <typename S, typename MB> 93   template <typename S, typename MB>
91   requires ReadStream<S> && MutableBufferSequence<MB> 94   requires ReadStream<S> && MutableBufferSequence<MB>
92   auto 95   auto
HITCBC 93   99 read(S& stream, MB buffers) -> 96   99 read(S& stream, MB buffers) ->
94   io_task<std::size_t> 97   io_task<std::size_t>
95   { 98   {
96   consuming_buffers consuming(buffers); 99   consuming_buffers consuming(buffers);
97   std::size_t const total_size = buffer_size(buffers); 100   std::size_t const total_size = buffer_size(buffers);
98   std::size_t total_read = 0; 101   std::size_t total_read = 0;
99   102  
100   while(total_read < total_size) 103   while(total_read < total_size)
101   { 104   {
102   auto [ec, n] = co_await stream.read_some(consuming.data()); 105   auto [ec, n] = co_await stream.read_some(consuming.data());
103   consuming.consume(n); 106   consuming.consume(n);
104   total_read += n; 107   total_read += n;
105   // A contingency that still completed the transfer is a success: 108   // A contingency that still completed the transfer is a success:
106   // report it only when the buffer was not filled. 109   // report it only when the buffer was not filled.
107   if(ec && total_read < total_size) 110   if(ec && total_read < total_size)
108   co_return {ec, total_read}; 111   co_return {ec, total_read};
109   } 112   }
110   113  
111   co_return {{}, total_read}; 114   co_return {{}, total_read};
HITCBC 112   198 } 115   198 }
113   116  
114   } // namespace capy 117   } // namespace capy
115   } // namespace boost 118   } // namespace boost
116   119  
117   #endif 120   #endif