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/detail/op_base.hpp>
15		#include <boost/corosio/io/io_object.hpp>
16		#include <boost/corosio/detail/buffer_param.hpp>
17		#include <boost/capy/results.hpp>
18		#include <boost/capy/ex/executor_ref.hpp>
19		#include <boost/capy/ex/await_context.hpp>
20
21		#include <boost/capy/continuation.hpp>
22
23		#include <coroutine>
24		#include <cstddef>
25		#include <stop_token>
26		#include <system_error>
27
28		namespace boost::corosio {
29
30		/** Writes bytes to a stream asynchronously.
31
32		Provides the `write_some` operation via a pure virtual
33		`do_write_some` dispatch point. Concrete classes override
34		`do_write_some` to route through their implementation.
35
36		Uses virtual inheritance from @ref io_object so that
37		@ref io_stream can combine this with @ref io_read_stream
38		without duplicating the `io_object` base.
39
40		@par Thread Safety
41		Distinct objects: Safe.
42		Shared objects: Unsafe.
43
44		@see io_read_stream, io_stream, io_object
45		*/
46		class BOOST_COROSIO_DECL io_write_stream : virtual public io_object
47		{
48		protected:
49		/// Awaitable for async write operations.
50		template<class ConstBufferSequence>
51		struct write_some_awaitable
52		: detail::bytes_op_base<write_some_awaitable<ConstBufferSequence>>
53		{
54		private:
55		friend io_write_stream;
56
57	236483x	write_some_awaitable(
58		io_write_stream& ios, ConstBufferSequence buffers) noexcept
59	236483x	: ios_(ios)
60	236483x	, buffers_(std::move(buffers))
61		{
62	236483x	}
63
64		friend detail::bytes_op_base<write_some_awaitable<ConstBufferSequence>>;
65		io_write_stream& ios_;
66		ConstBufferSequence buffers_;
67
68		std::coroutine_handle<>
69	236452x	dispatch(capy::continuation& cont, capy::executor_ref ex) const
70		{
71	472904x	return ios_.do_write_some(
72	709356x	cont, ex, buffers_, this->token_, &this->ec_, &this->bytes_);
73		}
74		};
75
76		/** Dispatch a write through the concrete implementation.
77
78		@param cont Continuation to resume on completion; it lives in
79		the awaiting frame until then.
80		@param ex Executor for dispatching the completion.
81		@param buffers Source buffer sequence.
82		@param token Stop token for cancellation.
83		@param ec Output error code.
84		@param bytes Output bytes transferred.
85
86		@return Coroutine handle to resume immediately.
87		*/
88		virtual std::coroutine_handle<> do_write_some(
89		capy::continuation& cont,
90		capy::executor_ref ex,
91		buffer_param buffers,
92		std::stop_token token,
93		std::error_code* ec,
94		std::size_t* bytes) = 0;
95
96		/// Default construct; the handle is supplied through @ref io_object.
97	26592x	io_write_stream() noexcept = default;
98
99		/// Move construct; the handle moves with @ref io_object.
100		io_write_stream(io_write_stream&&) noexcept = default;
101		/// Move assignment is disabled; reseating a live stream is not supported.
102		io_write_stream& operator=(io_write_stream&&) noexcept = delete;
103		/// Copy construction is disabled; the handle is uniquely owned.
104		io_write_stream(io_write_stream const&) = delete;
105		/// Copy assignment is disabled; the handle is uniquely owned.
106		io_write_stream& operator=(io_write_stream const&) = delete;
107
108		public:
109		/** Asynchronously write data to the stream.
110
111		Suspends the calling coroutine and initiates a kernel-level
112		write. The coroutine resumes when at least one byte is written,
113		an error occurs, or the operation is cancelled.
114
115		This stream must outlive the returned awaitable. The memory
116		referenced by @p buffers must remain valid until the operation
117		completes.
118
119		A closed stream completes with `errc::bad_file_descriptor`.
120
121		@param buffers The buffer sequence containing data to write.
122
123		@return An awaitable yielding `(error_code, std::size_t)`.
124
125		@see io_stream::read_some
126		*/
127		template<capy::ConstBufferSequence CB>
128	236483x	[[nodiscard]] auto write_some(CB const& buffers)
129		{
130	236483x	return write_some_awaitable<CB>(*this, buffers);
131		}
132		};
133
134		} // namespace boost::corosio
135
136		#endif
137