include/boost/corosio/io/io_read_stream.hpp

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io_read_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_READ_STREAM_HPP
11		#define BOOST_COROSIO_IO_IO_READ_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		/** Reads bytes from a stream asynchronously.
31
32		Provides the `read_some` operation via a pure virtual
33		`do_read_some` dispatch point. Concrete classes override
34		`do_read_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_write_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_write_stream, io_stream, io_object
45		*/
46		class BOOST_COROSIO_DECL io_read_stream : virtual public io_object
47		{
48		protected:
49		/// Awaitable for async read operations.
50		template<class MutableBufferSequence>
51		struct read_some_awaitable
52		: detail::bytes_op_base<read_some_awaitable<MutableBufferSequence>>
53		{
54		private:
55		friend io_read_stream;
56
57	238212x	read_some_awaitable(
58		io_read_stream& ios, MutableBufferSequence buffers) noexcept
59	238212x	: ios_(ios)
60	238212x	, buffers_(std::move(buffers))
61		{
62	238212x	}
63
64		friend detail::bytes_op_base<
65		read_some_awaitable<MutableBufferSequence>>;
66		io_read_stream& ios_;
67		MutableBufferSequence buffers_;
68
69		std::coroutine_handle<>
70	238184x	dispatch(capy::continuation& cont, capy::executor_ref ex) const
71		{
72	476368x	return ios_.do_read_some(
73	714552x	cont, ex, buffers_, this->token_, &this->ec_, &this->bytes_);
74		}
75		};
76
77		/** Dispatch a read through the concrete implementation.
78
79		@param cont Continuation to resume on completion; it lives in
80		the awaiting frame until then.
81		@param ex Executor for dispatching the completion.
82		@param buffers Target buffer sequence.
83		@param token Stop token for cancellation.
84		@param ec Output error code.
85		@param bytes Output bytes transferred.
86
87		@return Coroutine handle to resume immediately.
88		*/
89		virtual std::coroutine_handle<> do_read_some(
90		capy::continuation& cont,
91		capy::executor_ref ex,
92		buffer_param buffers,
93		std::stop_token token,
94		std::error_code* ec,
95		std::size_t* bytes) = 0;
96
97		/// Default construct; the handle is supplied through @ref io_object.
98	26592x	io_read_stream() noexcept = default;
99
100		/// Move construct; the handle moves with @ref io_object.
101		io_read_stream(io_read_stream&&) noexcept = default;
102		/// Move assignment is disabled; reseating a live stream is not supported.
103		io_read_stream& operator=(io_read_stream&&) noexcept = delete;
104		/// Copy construction is disabled; the handle is uniquely owned.
105		io_read_stream(io_read_stream const&) = delete;
106		/// Copy assignment is disabled; the handle is uniquely owned.
107		io_read_stream& operator=(io_read_stream const&) = delete;
108
109		public:
110		/** Asynchronously read data from the stream.
111
112		Suspends the calling coroutine and initiates a kernel-level
113		read. The coroutine resumes when at least one byte is read,
114		an error occurs, or the operation is cancelled.
115
116		This stream must outlive the returned awaitable. The memory
117		referenced by @p buffers must remain valid until the operation
118		completes.
119
120		A closed stream completes with `errc::bad_file_descriptor`.
121
122		@param buffers The buffer sequence to read data into.
123
124		@return An awaitable yielding `(error_code, std::size_t)`.
125
126		@see io_stream::write_some
127		*/
128		template<capy::MutableBufferSequence MB>
129	238212x	[[nodiscard]] auto read_some(MB const& buffers)
130		{
131	238212x	return read_some_awaitable<MB>(*this, buffers);
132		}
133		};
134
135		} // namespace boost::corosio
136
137		#endif
138