TLA Line data Source code
1 : //
2 : // Copyright (c) 2026 Michael Vandeberg
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_WRITE_AT_LEAST_HPP
11 : #define BOOST_CAPY_WRITE_AT_LEAST_HPP
12 :
13 : #include <boost/capy/detail/config.hpp>
14 : #include <boost/capy/io_task.hpp>
15 : #include <boost/capy/buffers.hpp>
16 : #include <boost/capy/buffers/consuming_buffers.hpp>
17 : #include <boost/capy/concept/write_stream.hpp>
18 :
19 : #include <cstddef>
20 : #include <system_error>
21 :
22 : namespace boost {
23 : namespace capy {
24 :
25 : /** Write at least a minimum number of bytes to a stream.
26 :
27 : This is a straightforward extension of @ref write. While @ref write
28 : transfers exactly `buffer_size(buffers)` bytes, `write_at_least`
29 : transfers at least `n` bytes. The loop stops as soon as `n` bytes
30 : have been written, even if `buffers` has not been fully consumed.
31 : Any bytes beyond `n` that a single `stream.write_some` happens to
32 : transfer are counted. No further awaiting is performed to write the
33 : remainder.
34 :
35 : Provided for symmetry with @ref read_at_least.
36 :
37 : @par Await-effects
38 :
39 : If `n > buffer_size(buffers)` the request is impossible to satisfy
40 : and the operation fails immediately with
41 : `{std::errc::invalid_argument, 0}` without awaiting `stream.write_some`.
42 :
43 : Otherwise writes the contents of `buffers` to `stream` via awaiting
44 : `stream.write_some` with consecutive portions of data from `buffers`
45 : until:
46 :
47 : @li either at least `n` bytes have been written,
48 : @li or a contingency in `stream.write_some` occurs.
49 :
50 : If `n == 0` then no awaiting `stream.write_some` is performed. This is
51 : not a contingency.
52 :
53 : @par Await-returns
54 : An object of type `io_result<std::size_t>` destructuring as `[ec, n]`.
55 :
56 : Upon a contingency, the count represents the number of bytes written
57 : so far.
58 :
59 : Contingencies:
60 :
61 : @li The first contingency reported from awaiting @c stream.write_some
62 : while fewer than `n` bytes have been written. A contingency that
63 : accompanies the write which reaches `n` is not reported: a
64 : satisfied request is a success.
65 :
66 : Notable conditions:
67 :
68 : @li @c std::errc::invalid_argument — `n` exceeds `buffer_size(buffers)`,
69 : @li @c cond::canceled — Operation was cancelled,
70 : @li @c std::errc::broken_pipe — Peer closed connection.
71 :
72 : @par Await-postcondition
73 : On success the returned count is greater than or equal to `n` and
74 : less than or equal to `buffer_size(buffers)`, and `ec` is success.
75 : Otherwise `ec` is set.
76 :
77 : @param stream The stream to write to. If the lifetime of `stream` ends
78 : before the coroutine finishes, the behavior is undefined.
79 :
80 : @param buffers The buffer sequence to write. If the lifetime of the
81 : buffer sequence represented by `buffers` ends before the coroutine
82 : finishes, the behavior is undefined.
83 :
84 : @param n The minimum number of bytes to write. Must not exceed
85 : `buffer_size(buffers)`.
86 :
87 : @return A task yielding `io_result<std::size_t>` whose second element
88 : is the number of bytes written.
89 :
90 : @par Remarks
91 : Supports _IoAwaitable cancellation_.
92 :
93 : @par Example
94 :
95 : @code
96 : capy::task<> flush_at_least(capy::WriteStream auto& stream, std::string_view data)
97 : {
98 : auto [ec, n] = co_await capy::write_at_least(
99 : stream, capy::make_buffer(data), 8);
100 : if(ec)
101 : throw std::system_error(ec);
102 :
103 : // at least 8 bytes written; n may be larger
104 : }
105 : @endcode
106 :
107 : @see write, WriteStream, ConstBufferSequence
108 : */
109 : template <WriteStream S, ConstBufferSequence CB>
110 : auto
111 HIT 33 : write_at_least(S& stream, CB buffers, std::size_t n) -> io_task<std::size_t>
112 : {
113 : consuming_buffers consuming(buffers);
114 : std::size_t const total_size = buffer_size(buffers);
115 :
116 : if(n > total_size)
117 : co_return {make_error_code(std::errc::invalid_argument), 0};
118 :
119 : std::size_t total_written = 0;
120 :
121 : while(total_written < n)
122 : {
123 : auto [ec, m] = co_await stream.write_some(consuming.data());
124 : consuming.consume(m);
125 : total_written += m;
126 : // A contingency that still satisfied the request is a success:
127 : // report it only when fewer than n bytes were written.
128 : if(ec && total_written < n)
129 : co_return {ec, total_written};
130 : }
131 :
132 : co_return {{}, total_written};
133 66 : }
134 :
135 : } // namespace capy
136 : } // namespace boost
137 :
138 : #endif
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