include/boost/corosio/native/detail/posix/posix_stream_file.hpp

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posix_stream_file.hpp

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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/corosio
8			//
9
10			#ifndef BOOST_COROSIO_NATIVE_DETAIL_POSIX_POSIX_STREAM_FILE_HPP
11			#define BOOST_COROSIO_NATIVE_DETAIL_POSIX_POSIX_STREAM_FILE_HPP
12
13			#include <boost/corosio/detail/platform.hpp>
14
15			#if BOOST_COROSIO_POSIX
16
17			#include <boost/corosio/detail/config.hpp>
18			#include <boost/corosio/stream_file.hpp>
19			#include <boost/corosio/file_base.hpp>
20			#include <boost/corosio/detail/intrusive.hpp>
21			#include <boost/corosio/detail/dispatch_coro.hpp>
22			#include <boost/corosio/detail/scheduler_op.hpp>
23			#include <boost/corosio/detail/thread_pool.hpp>
24			#include <boost/corosio/detail/scheduler.hpp>
25			#include <boost/corosio/detail/buffer_param.hpp>
26			#include <boost/corosio/native/detail/make_err.hpp>
27			#include <boost/capy/ex/executor_ref.hpp>
28			#include <boost/capy/error.hpp>
29			#include <boost/capy/buffers.hpp>
30
31			#include <atomic>
32			#include <coroutine>
33			#include <cstddef>
34			#include <cstdint>
35			#include <filesystem>
36			#include <limits>
37			#include <memory>
38			#include <optional>
39			#include <stop_token>
40			#include <system_error>
41
42			#include <errno.h>
43			#include <fcntl.h>
44			#include <sys/stat.h>
45			#include <sys/uio.h>
46			#include <unistd.h>
47
48			/*
49			POSIX Stream File Implementation
50			=================================
51
52			Regular files cannot be monitored by epoll/kqueue/select — the kernel
53			always reports them as ready. Blocking I/O (pread/pwrite) is dispatched
54			to a shared thread pool, with completion posted back to the scheduler.
55
56			This follows the same pattern as posix_resolver: pool_work_item for
57			dispatch, scheduler_op for completion, shared_from_this for lifetime.
58
59			Completion Flow
60			---------------
61			1. read_some() sets up file_read_op, posts to thread pool
62			2. Pool thread runs preadv() (blocking)
63			3. Pool thread stores results, posts scheduler_op to scheduler
64			4. Scheduler invokes op() which resumes the coroutine
65
66			Single-Inflight Constraint
67			--------------------------
68			Only one asynchronous operation may be in flight at a time on a
69			given file object. Concurrent read and write is not supported
70			because both share offset_ without synchronization.
71			*/
72
73			namespace boost::corosio::detail {
74
75			struct scheduler;
76			class posix_stream_file_service;
77
78			/** Stream file implementation for POSIX backends.
79
80			Each instance contains embedded operation objects (read_op_, write_op_)
81			that are reused across calls. This avoids per-operation heap allocation.
82			*/
83			class posix_stream_file final
84			: public stream_file::implementation
85			, public std::enable_shared_from_this<posix_stream_file>
86			, public intrusive_list<posix_stream_file>::node
87			{
88			friend class posix_stream_file_service;
89
90			public:
91			static constexpr std::size_t max_buffers = 16;
92
93			/** Operation state for a single file read or write. */
94			struct file_op : scheduler_op
95			{
96			struct canceller
97			{
98			file_op* op;
99		2x	void operator()() const noexcept
100			{
101		2x	op->request_cancel();
102		2x	}
103			};
104
105			// Coroutine state
106			std::coroutine_handle<> h;
107			capy::continuation cont;
108			capy::executor_ref ex;
109
110			// Output pointers
111		190x	std::error_code* ec_out = nullptr;
112		190x	std::size_t* bytes_out = nullptr;
113
114			// Buffer data (copied from buffer_param at submission time)
115			iovec iovecs[max_buffers];
116		190x	int iovec_count = 0;
117
118			// Result storage (populated by worker thread)
119		190x	int errn = 0;
120		190x	std::size_t bytes_transferred = 0;
121		190x	bool is_read = false;
122
123			// Thread coordination
124		190x	std::atomic<bool> cancelled{false};
125			std::optional<std::stop_callback<canceller>> stop_cb;
126
127			/// Prevents use-after-free when file is closed with pending ops.
128			std::shared_ptr<void> impl_ref;
129
130		760x	file_op() = default;
131
132		55x	void reset() noexcept
133			{
134		55x	iovec_count = 0;
135		55x	errn = 0;
136		55x	bytes_transferred = 0;
137		55x	is_read = false;
138		55x	cancelled.store(false, std::memory_order_relaxed);
139		55x	stop_cb.reset();
140		55x	impl_ref.reset();
141		55x	ec_out = nullptr;
142		55x	bytes_out = nullptr;
143		55x	}
144
145			void operator()() override;
146			void destroy() override;
147
148		532x	void request_cancel() noexcept
149			{
150		532x	cancelled.store(true, std::memory_order_release);
151		532x	}
152
153		39x	void start(std::stop_token const& token)
154			{
155		39x	cancelled.store(false, std::memory_order_release);
156		39x	stop_cb.reset();
157	2/2 ✓ Branch 0 taken 37 times. ✓ Branch 1 taken 2 times.	39x	if (token.stop_possible())
158		2x	stop_cb.emplace(token, canceller{this});
159		39x	}
160			};
161
162			/** Pool work item for thread pool dispatch. */
163		190x	struct pool_op : pool_work_item
164			{
165		190x	posix_stream_file* file_ = nullptr;
166			std::shared_ptr<posix_stream_file> ref_;
167			};
168
169			explicit posix_stream_file(posix_stream_file_service& svc) noexcept;
170
171			// -- io_stream::implementation --
172
173			std::coroutine_handle<> read_some(
174			std::coroutine_handle<>,
175			capy::executor_ref,
176			buffer_param,
177			std::stop_token,
178			std::error_code*,
179			std::size_t*) override;
180
181			std::coroutine_handle<> write_some(
182			std::coroutine_handle<>,
183			capy::executor_ref,
184			buffer_param,
185			std::stop_token,
186			std::error_code*,
187			std::size_t*) override;
188
189			// -- stream_file::implementation --
190
191		302x	native_handle_type native_handle() const noexcept override
192			{
193		302x	return fd_;
194			}
195
196		265x	void cancel() noexcept override
197			{
198		265x	read_op_.request_cancel();
199		265x	write_op_.request_cancel();
200		265x	}
201
202			std::uint64_t size() const override;
203			std::error_code resize(std::uint64_t new_size) noexcept override;
204			std::error_code sync_data() noexcept override;
205			std::error_code sync_all() noexcept override;
206			native_handle_type release() override;
207			std::error_code assign(native_handle_type handle) noexcept override;
208			capy::io_result<std::uint64_t>
209			seek(std::int64_t offset, file_base::seek_basis origin) noexcept override;
210
211			// -- Internal --
212
213			/** Open the file and store the fd. */
214			std::error_code open_file(
215			std::filesystem::path const& path, file_base::flags mode);
216
217			/** Close the file descriptor. */
218			void close_file() noexcept;
219
220			private:
221			posix_stream_file_service& svc_;
222		95x	int fd_ = -1;
223		95x	std::uint64_t offset_ = 0;
224
225			file_op read_op_;
226			file_op write_op_;
227			pool_op read_pool_op_;
228			pool_op write_pool_op_;
229
230			static void do_read_work(pool_work_item*) noexcept;
231			static void do_write_work(pool_work_item*) noexcept;
232			};
233
234			// ---------------------------------------------------------------------------
235			// Inline implementation
236			// ---------------------------------------------------------------------------
237
238			inline
239		475x	posix_stream_file::posix_stream_file(posix_stream_file_service& svc) noexcept
240		95x	: svc_(svc)
241		380x	{
242		190x	}
243
244			inline std::error_code
245		73x	posix_stream_file::open_file(
246			std::filesystem::path const& path, file_base::flags mode)
247			{
248		73x	close_file();
249
250		73x	int oflags = 0;
251
252			// Access mode
253		73x	unsigned access = static_cast<unsigned>(mode) & 3u;
254	2/2 ✓ Branch 0 taken 4 times. ✓ Branch 1 taken 69 times.	73x	if (access == static_cast<unsigned>(file_base::read_write))
255		4x	oflags \|= O_RDWR;
256	2/2 ✓ Branch 0 taken 24 times. ✓ Branch 1 taken 45 times.	69x	else if (access == static_cast<unsigned>(file_base::write_only))
257		24x	oflags \|= O_WRONLY;
258			else
259		45x	oflags \|= O_RDONLY;
260
261			// Creation flags
262	2/2 ✓ Branch 0 taken 53 times. ✓ Branch 1 taken 20 times.	73x	if ((mode & file_base::create) != file_base::flags(0))
263		20x	oflags \|= O_CREAT;
264	2/2 ✓ Branch 0 taken 71 times. ✓ Branch 1 taken 2 times.	73x	if ((mode & file_base::exclusive) != file_base::flags(0))
265		2x	oflags \|= O_EXCL;
266	2/2 ✓ Branch 0 taken 56 times. ✓ Branch 1 taken 17 times.	73x	if ((mode & file_base::truncate) != file_base::flags(0))
267		17x	oflags \|= O_TRUNC;
268	2/2 ✓ Branch 0 taken 70 times. ✓ Branch 1 taken 3 times.	73x	if ((mode & file_base::append) != file_base::flags(0))
269		3x	oflags \|= O_APPEND;
270	2/2 ✓ Branch 0 taken 71 times. ✓ Branch 1 taken 2 times.	73x	if ((mode & file_base::sync_all_on_write) != file_base::flags(0))
271		2x	oflags \|= O_SYNC;
272
273		73x	int fd = ::open(path.c_str(), oflags, 0666);
274	2/2 ✓ Branch 0 taken 69 times. ✓ Branch 1 taken 4 times.	73x	if (fd < 0)
275		4x	return make_err(errno);
276
277		69x	fd_ = fd;
278		69x	offset_ = 0;
279
280			// Append mode: position at end-of-file (preadv/pwritev use
281			// explicit offsets, so O_APPEND alone is not sufficient).
282	2/2 ✓ Branch 0 taken 66 times. ✓ Branch 1 taken 3 times.	69x	if ((mode & file_base::append) != file_base::flags(0))
283			{
284			struct stat st;
285	1/2 ✓ Branch 0 taken 3 times. ✗ Branch 1 not taken.	3x	if (::fstat(fd, &st) < 0)
286			{
287		✗	int err = errno;
288		✗	::close(fd);
289		✗	fd_ = -1;
290		✗	return make_err(err);
291			}
292		3x	offset_ = static_cast<std::uint64_t>(st.st_size);
293		3x	}
294
295			#ifdef POSIX_FADV_SEQUENTIAL
296			::posix_fadvise(fd_, 0, 0, POSIX_FADV_SEQUENTIAL);
297			#endif
298
299		69x	return {};
300		73x	}
301
302			inline void
303		342x	posix_stream_file::close_file() noexcept
304			{
305	2/2 ✓ Branch 0 taken 269 times. ✓ Branch 1 taken 73 times.	342x	if (fd_ >= 0)
306			{
307	1/2 ✓ Branch 0 taken 73 times. ✗ Branch 1 not taken.	73x	::close(fd_);
308		73x	fd_ = -1;
309		73x	}
310		342x	}
311
312			inline std::uint64_t
313		12x	posix_stream_file::size() const
314			{
315			struct stat st;
316	1/2 ✓ Branch 0 taken 12 times. ✗ Branch 1 not taken.	12x	if (::fstat(fd_, &st) < 0)
317		✗	throw_system_error(make_err(errno), "stream_file::size");
318		12x	return static_cast<std::uint64_t>(st.st_size);
319			}
320
321			inline std::error_code
322		7x	posix_stream_file::resize(std::uint64_t new_size) noexcept
323			{
324	4/4 ✓ Branch 0 taken 2 times. ✓ Branch 1 taken 5 times. ✓ Branch 2 taken 2 times. ✓ Branch 3 taken 5 times.	14x	if (new_size >
325		7x	static_cast<std::uint64_t>((std::numeric_limits<off_t>::max)()))
326		2x	return make_err(EOVERFLOW);
327	3/4 ✓ Branch 0 taken 5 times. ✗ Branch 1 not taken. ✓ Branch 2 taken 2 times. ✓ Branch 3 taken 3 times.	5x	if (::ftruncate(fd_, static_cast<off_t>(new_size)) < 0)
328	1/2 ✓ Branch 0 taken 2 times. ✗ Branch 1 not taken.	2x	return make_err(errno);
329		3x	return {};
330		7x	}
331
332			inline std::error_code
333		5x	posix_stream_file::sync_data() noexcept
334			{
335			#if BOOST_COROSIO_HAS_POSIX_SYNCHRONIZED_IO
336			if (::fdatasync(fd_) < 0)
337			#else // BOOST_COROSIO_HAS_POSIX_SYNCHRONIZED_IO
338	3/4 ✓ Branch 0 taken 5 times. ✗ Branch 1 not taken. ✓ Branch 2 taken 2 times. ✓ Branch 3 taken 3 times.	5x	if (::fsync(fd_) < 0)
339			#endif // BOOST_COROSIO_HAS_POSIX_SYNCHRONIZED_IO
340	1/2 ✓ Branch 0 taken 2 times. ✗ Branch 1 not taken.	2x	return make_err(errno);
341		3x	return {};
342		5x	}
343
344			inline std::error_code
345		5x	posix_stream_file::sync_all() noexcept
346			{
347	3/4 ✓ Branch 0 taken 5 times. ✗ Branch 1 not taken. ✓ Branch 2 taken 2 times. ✓ Branch 3 taken 3 times.	5x	if (::fsync(fd_) < 0)
348	1/2 ✓ Branch 0 taken 2 times. ✗ Branch 1 not taken.	2x	return make_err(errno);
349		3x	return {};
350		5x	}
351
352			inline native_handle_type
353		2x	posix_stream_file::release()
354			{
355		2x	int fd = fd_;
356		2x	fd_ = -1;
357		2x	offset_ = 0;
358		2x	return fd;
359			}
360
361			inline std::error_code
362		6x	posix_stream_file::assign(native_handle_type handle) noexcept
363			{
364		6x	close_file();
365		6x	fd_ = handle;
366		6x	offset_ = 0;
367		6x	return {};
368			}
369
370			inline capy::io_result<std::uint64_t>
371		20x	posix_stream_file::seek(
372			std::int64_t offset, file_base::seek_basis origin) noexcept
373			{
374			// We track offset_ ourselves (not the kernel fd offset)
375			// because preadv/pwritev use explicit offsets.
376			std::int64_t new_pos;
377
378	2/2 ✓ Branch 0 taken 11 times. ✓ Branch 1 taken 9 times.	20x	if (origin == file_base::seek_set)
379			{
380		9x	new_pos = offset;
381		9x	}
382	2/2 ✓ Branch 0 taken 5 times. ✓ Branch 1 taken 6 times.	11x	else if (origin == file_base::seek_cur)
383			{
384		5x	new_pos = static_cast<std::int64_t>(offset_) + offset;
385		5x	}
386			else
387			{
388			struct stat st;
389	2/4 ✓ Branch 0 taken 6 times. ✗ Branch 1 not taken. ✗ Branch 2 not taken. ✓ Branch 3 taken 6 times.	6x	if (::fstat(fd_, &st) < 0)
390		✗	return {make_err(errno), 0};
391		6x	new_pos = st.st_size + offset;
392			}
393
394	2/2 ✓ Branch 0 taken 14 times. ✓ Branch 1 taken 6 times.	20x	if (new_pos < 0)
395		6x	return {make_err(EINVAL), 0};
396	2/4 ✗ Branch 0 not taken. ✓ Branch 1 taken 14 times. ✗ Branch 2 not taken. ✓ Branch 3 taken 14 times.	28x	if (new_pos >
397		14x	static_cast<std::int64_t>((std::numeric_limits<off_t>::max)()))
398		✗	return {make_err(EOVERFLOW), 0};
399
400		14x	offset_ = static_cast<std::uint64_t>(new_pos);
401
402		14x	return {std::error_code{}, offset_};
403		20x	}
404
405			// -- file_op completion handler --
406			// (read_some, write_some, do_read_work, do_write_work are
407			// defined in posix_stream_file_service.hpp after the service)
408
409			inline void
410		39x	posix_stream_file::file_op::operator()()
411			{
412		39x	stop_cb.reset();
413
414		39x	bool const was_cancelled = cancelled.load(std::memory_order_acquire);
415
416	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 39 times.	39x	if (ec_out)
417			{
418	2/2 ✓ Branch 0 taken 2 times. ✓ Branch 1 taken 37 times.	39x	if (was_cancelled)
419		2x	*ec_out = capy::error::canceled;
420	2/2 ✓ Branch 0 taken 4 times. ✓ Branch 1 taken 33 times.	37x	else if (errn != 0)
421		4x	*ec_out = make_err(errn);
422	4/4 ✓ Branch 0 taken 16 times. ✓ Branch 1 taken 17 times. ✓ Branch 2 taken 13 times. ✓ Branch 3 taken 3 times.	33x	else if (is_read && bytes_transferred == 0)
423		3x	*ec_out = capy::error::eof;
424			else
425		30x	*ec_out = {};
426		39x	}
427
428	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 39 times.	39x	if (bytes_out)
429	2/2 ✓ Branch 0 taken 2 times. ✓ Branch 1 taken 37 times.	39x	*bytes_out = was_cancelled ? 0 : bytes_transferred;
430
431			// Move impl_ref to a local so members remain valid through
432			// dispatch — impl_ref may be the last shared_ptr keeping
433			// the parent posix_stream_file (which embeds this file_op) alive.
434		39x	auto prevent_destroy = std::move(impl_ref);
435		39x	ex.on_work_finished();
436		39x	cont.h = h;
437	2/4 ✓ Branch 0 taken 39 times. ✗ Branch 1 not taken. ✓ Branch 2 taken 39 times. ✗ Branch 3 not taken.	39x	dispatch_coro(ex, cont).resume();
438		39x	}
439
440			inline void
441		✗	posix_stream_file::file_op::destroy()
442			{
443		✗	stop_cb.reset();
444		✗	auto local_ex = ex;
445		✗	impl_ref.reset();
446		✗	local_ex.on_work_finished();
447		✗	}
448
449			} // namespace boost::corosio::detail
450
451			#endif // BOOST_COROSIO_POSIX
452
453			#endif // BOOST_COROSIO_NATIVE_DETAIL_POSIX_POSIX_STREAM_FILE_HPP
454