include/boost/corosio/io/io_write_stream.hpp

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io_write_stream.hpp

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1			//
2			// Copyright (c) 2026 Steve Gerbino
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/corosio
8			//
9
10			#ifndef BOOST_COROSIO_IO_IO_WRITE_STREAM_HPP
11			#define BOOST_COROSIO_IO_IO_WRITE_STREAM_HPP
12
13			#include <boost/corosio/detail/config.hpp>
14			#include <boost/corosio/io/io_object.hpp>
15			#include <boost/corosio/detail/buffer_param.hpp>
16			#include <boost/capy/io_result.hpp>
17			#include <boost/capy/ex/executor_ref.hpp>
18			#include <boost/capy/ex/io_env.hpp>
19
20			#include <coroutine>
21			#include <cstddef>
22			#include <stop_token>
23			#include <system_error>
24
25			namespace boost::corosio {
26
27			/** Abstract base for streams that support async writes.
28
29			Provides the `write_some` operation via a pure virtual
30			`do_write_some` dispatch point. Concrete classes override
31			`do_write_some` to route through their implementation.
32
33			Uses virtual inheritance from @ref io_object so that
34			@ref io_stream can combine this with @ref io_read_stream
35			without duplicating the `io_object` base.
36
37			@par Thread Safety
38			Distinct objects: Safe.
39			Shared objects: Unsafe.
40
41			@see io_read_stream, io_stream, io_object
42			*/
43			class BOOST_COROSIO_DECL io_write_stream : virtual public io_object
44			{
45			protected:
46			/// Awaitable for async write operations.
47			template<class ConstBufferSequence>
48			struct write_some_awaitable
49			{
50			io_write_stream& ios_;
51			ConstBufferSequence buffers_;
52			std::stop_token token_;
53			mutable std::error_code ec_;
54			mutable std::size_t bytes_transferred_ = 0;
55
56		233454x	write_some_awaitable(
57			io_write_stream& ios, ConstBufferSequence buffers) noexcept
58		233454x	: ios_(ios)
59		233454x	, buffers_(std::move(buffers))
60			{
61		233454x	}
62
63		233454x	bool await_ready() const noexcept
64			{
65		233454x	return token_.stop_requested();
66			}
67
68		233454x	capy::io_result<std::size_t> await_resume() const noexcept
69			{
70	2/2 ✓ Branch 3 → 4 taken 2 times. ✓ Branch 3 → 6 taken 233452 times.	233454x	if (token_.stop_requested())
71		2x	return {make_error_code(std::errc::operation_canceled), 0};
72		233452x	return {ec_, bytes_transferred_};
73			}
74
75		233454x	auto await_suspend(std::coroutine_handle<> h, capy::io_env const* env)
76			-> std::coroutine_handle<>
77			{
78		233454x	token_ = env->stop_token;
79	1/1 ✓ Branch 5 → 6 taken 233454 times.	466908x	return ios_.do_write_some(
80		700362x	h, env->executor, buffers_, token_, &ec_, &bytes_transferred_);
81			}
82			};
83
84			/** Dispatch a write through the concrete implementation.
85
86			@param h Coroutine handle to resume on completion.
87			@param ex Executor for dispatching the completion.
88			@param buffers Source buffer sequence.
89			@param token Stop token for cancellation.
90			@param ec Output error code.
91			@param bytes Output bytes transferred.
92
93			@return Coroutine handle to resume immediately.
94			*/
95			virtual std::coroutine_handle<> do_write_some(
96			std::coroutine_handle<>,
97			capy::executor_ref,
98			buffer_param,
99			std::stop_token,
100			std::error_code*,
101			std::size_t*) = 0;
102
103		4653x	io_write_stream() noexcept = default;
104
105			/// Construct from a handle.
106			explicit io_write_stream(handle h) noexcept : io_object(std::move(h)) {}
107
108			io_write_stream(io_write_stream&&) noexcept = default;
109			io_write_stream& operator=(io_write_stream&&) noexcept = delete;
110			io_write_stream(io_write_stream const&) = delete;
111			io_write_stream& operator=(io_write_stream const&) = delete;
112
113			public:
114			/** Asynchronously write data to the stream.
115
116			Suspends the calling coroutine and initiates a kernel-level
117			write. The coroutine resumes when at least one byte is written,
118			an error occurs, or the operation is cancelled.
119
120			This stream must outlive the returned awaitable. The memory
121			referenced by @p buffers must remain valid until the operation
122			completes.
123
124			@param buffers The buffer sequence containing data to write.
125
126			@return An awaitable yielding `(error_code, std::size_t)`.
127
128			@see io_stream::read_some
129			*/
130			template<capy::ConstBufferSequence CB>
131		233454x	auto write_some(CB const& buffers)
132			{
133		233454x	return write_some_awaitable<CB>(*this, buffers);
134			}
135			};
136
137			} // namespace boost::corosio
138
139			#endif
140