boost/asio/read_at.hpp
//
// read_at.hpp
// ~~~~~~~~~~~
//
// Copyright (c) 2003-2024 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#ifndef BOOST_ASIO_READ_AT_HPP
#define BOOST_ASIO_READ_AT_HPP
#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
#include <boost/asio/detail/config.hpp>
#include <cstddef>
#include <boost/asio/async_result.hpp>
#include <boost/asio/completion_condition.hpp>
#include <boost/asio/detail/cstdint.hpp>
#include <boost/asio/error.hpp>
#if !defined(BOOST_ASIO_NO_EXTENSIONS)
# include <boost/asio/basic_streambuf_fwd.hpp>
#endif // !defined(BOOST_ASIO_NO_EXTENSIONS)
#include <boost/asio/detail/push_options.hpp>
namespace boost {
namespace asio {
namespace detail {
template <typename> class initiate_async_read_at;
#if !defined(BOOST_ASIO_NO_IOSTREAM)
template <typename> class initiate_async_read_at_streambuf;
#endif // !defined(BOOST_ASIO_NO_IOSTREAM)
} // namespace detail
/**
* @defgroup read_at boost::asio::read_at
*
* @brief The @c read_at function is a composed operation that reads a certain
* amount of data at the specified offset before returning.
*/
/*@{*/
/// Attempt to read a certain amount of data at the specified offset before
/// returning.
/**
* This function is used to read a certain number of bytes of data from a
* random access device at the specified offset. The call will block until one
* of the following conditions is true:
*
* @li The supplied buffers are full. That is, the bytes transferred is equal to
* the sum of the buffer sizes.
*
* @li An error occurred.
*
* This operation is implemented in terms of zero or more calls to the device's
* read_some_at function.
*
* @param d The device from which the data is to be read. The type must support
* the SyncRandomAccessReadDevice concept.
*
* @param offset The offset at which the data will be read.
*
* @param buffers One or more buffers into which the data will be read. The sum
* of the buffer sizes indicates the maximum number of bytes to read from the
* device.
*
* @returns The number of bytes transferred.
*
* @throws boost::system::system_error Thrown on failure.
*
* @par Example
* To read into a single data buffer use the @ref buffer function as follows:
* @code boost::asio::read_at(d, 42, boost::asio::buffer(data, size)); @endcode
* See the @ref buffer documentation for information on reading into multiple
* buffers in one go, and how to use it with arrays, boost::array or
* std::vector.
*
* @note This overload is equivalent to calling:
* @code boost::asio::read_at(
* d, 42, buffers,
* boost::asio::transfer_all()); @endcode
*/
template <typename SyncRandomAccessReadDevice, typename MutableBufferSequence>
std::size_t read_at(SyncRandomAccessReadDevice& d,
uint64_t offset, const MutableBufferSequence& buffers);
/// Attempt to read a certain amount of data at the specified offset before
/// returning.
/**
* This function is used to read a certain number of bytes of data from a
* random access device at the specified offset. The call will block until one
* of the following conditions is true:
*
* @li The supplied buffers are full. That is, the bytes transferred is equal to
* the sum of the buffer sizes.
*
* @li An error occurred.
*
* This operation is implemented in terms of zero or more calls to the device's
* read_some_at function.
*
* @param d The device from which the data is to be read. The type must support
* the SyncRandomAccessReadDevice concept.
*
* @param offset The offset at which the data will be read.
*
* @param buffers One or more buffers into which the data will be read. The sum
* of the buffer sizes indicates the maximum number of bytes to read from the
* device.
*
* @param ec Set to indicate what error occurred, if any.
*
* @returns The number of bytes transferred.
*
* @par Example
* To read into a single data buffer use the @ref buffer function as follows:
* @code boost::asio::read_at(d, 42,
* boost::asio::buffer(data, size), ec); @endcode
* See the @ref buffer documentation for information on reading into multiple
* buffers in one go, and how to use it with arrays, boost::array or
* std::vector.
*
* @note This overload is equivalent to calling:
* @code boost::asio::read_at(
* d, 42, buffers,
* boost::asio::transfer_all(), ec); @endcode
*/
template <typename SyncRandomAccessReadDevice, typename MutableBufferSequence>
std::size_t read_at(SyncRandomAccessReadDevice& d,
uint64_t offset, const MutableBufferSequence& buffers,
boost::system::error_code& ec);
/// Attempt to read a certain amount of data at the specified offset before
/// returning.
/**
* This function is used to read a certain number of bytes of data from a
* random access device at the specified offset. The call will block until one
* of the following conditions is true:
*
* @li The supplied buffers are full. That is, the bytes transferred is equal to
* the sum of the buffer sizes.
*
* @li The completion_condition function object returns 0.
*
* This operation is implemented in terms of zero or more calls to the device's
* read_some_at function.
*
* @param d The device from which the data is to be read. The type must support
* the SyncRandomAccessReadDevice concept.
*
* @param offset The offset at which the data will be read.
*
* @param buffers One or more buffers into which the data will be read. The sum
* of the buffer sizes indicates the maximum number of bytes to read from the
* device.
*
* @param completion_condition The function object to be called to determine
* whether the read operation is complete. The signature of the function object
* must be:
* @code std::size_t completion_condition(
* // Result of latest read_some_at operation.
* const boost::system::error_code& error,
*
* // Number of bytes transferred so far.
* std::size_t bytes_transferred
* ); @endcode
* A return value of 0 indicates that the read operation is complete. A non-zero
* return value indicates the maximum number of bytes to be read on the next
* call to the device's read_some_at function.
*
* @returns The number of bytes transferred.
*
* @throws boost::system::system_error Thrown on failure.
*
* @par Example
* To read into a single data buffer use the @ref buffer function as follows:
* @code boost::asio::read_at(d, 42, boost::asio::buffer(data, size),
* boost::asio::transfer_at_least(32)); @endcode
* See the @ref buffer documentation for information on reading into multiple
* buffers in one go, and how to use it with arrays, boost::array or
* std::vector.
*/
template <typename SyncRandomAccessReadDevice, typename MutableBufferSequence,
typename CompletionCondition>
std::size_t read_at(SyncRandomAccessReadDevice& d,
uint64_t offset, const MutableBufferSequence& buffers,
CompletionCondition completion_condition,
constraint_t<
is_completion_condition<CompletionCondition>::value
> = 0);
/// Attempt to read a certain amount of data at the specified offset before
/// returning.
/**
* This function is used to read a certain number of bytes of data from a
* random access device at the specified offset. The call will block until one
* of the following conditions is true:
*
* @li The supplied buffers are full. That is, the bytes transferred is equal to
* the sum of the buffer sizes.
*
* @li The completion_condition function object returns 0.
*
* This operation is implemented in terms of zero or more calls to the device's
* read_some_at function.
*
* @param d The device from which the data is to be read. The type must support
* the SyncRandomAccessReadDevice concept.
*
* @param offset The offset at which the data will be read.
*
* @param buffers One or more buffers into which the data will be read. The sum
* of the buffer sizes indicates the maximum number of bytes to read from the
* device.
*
* @param completion_condition The function object to be called to determine
* whether the read operation is complete. The signature of the function object
* must be:
* @code std::size_t completion_condition(
* // Result of latest read_some_at operation.
* const boost::system::error_code& error,
*
* // Number of bytes transferred so far.
* std::size_t bytes_transferred
* ); @endcode
* A return value of 0 indicates that the read operation is complete. A non-zero
* return value indicates the maximum number of bytes to be read on the next
* call to the device's read_some_at function.
*
* @param ec Set to indicate what error occurred, if any.
*
* @returns The number of bytes read. If an error occurs, returns the total
* number of bytes successfully transferred prior to the error.
*/
template <typename SyncRandomAccessReadDevice, typename MutableBufferSequence,
typename CompletionCondition>
std::size_t read_at(SyncRandomAccessReadDevice& d,
uint64_t offset, const MutableBufferSequence& buffers,
CompletionCondition completion_condition, boost::system::error_code& ec,
constraint_t<
is_completion_condition<CompletionCondition>::value
> = 0);
#if !defined(BOOST_ASIO_NO_EXTENSIONS)
#if !defined(BOOST_ASIO_NO_IOSTREAM)
/// Attempt to read a certain amount of data at the specified offset before
/// returning.
/**
* This function is used to read a certain number of bytes of data from a
* random access device at the specified offset. The call will block until one
* of the following conditions is true:
*
* @li An error occurred.
*
* This operation is implemented in terms of zero or more calls to the device's
* read_some_at function.
*
* @param d The device from which the data is to be read. The type must support
* the SyncRandomAccessReadDevice concept.
*
* @param offset The offset at which the data will be read.
*
* @param b The basic_streambuf object into which the data will be read.
*
* @returns The number of bytes transferred.
*
* @throws boost::system::system_error Thrown on failure.
*
* @note This overload is equivalent to calling:
* @code boost::asio::read_at(
* d, 42, b,
* boost::asio::transfer_all()); @endcode
*/
template <typename SyncRandomAccessReadDevice, typename Allocator>
std::size_t read_at(SyncRandomAccessReadDevice& d,
uint64_t offset, basic_streambuf<Allocator>& b);
/// Attempt to read a certain amount of data at the specified offset before
/// returning.
/**
* This function is used to read a certain number of bytes of data from a
* random access device at the specified offset. The call will block until one
* of the following conditions is true:
*
* @li An error occurred.
*
* This operation is implemented in terms of zero or more calls to the device's
* read_some_at function.
*
* @param d The device from which the data is to be read. The type must support
* the SyncRandomAccessReadDevice concept.
*
* @param offset The offset at which the data will be read.
*
* @param b The basic_streambuf object into which the data will be read.
*
* @param ec Set to indicate what error occurred, if any.
*
* @returns The number of bytes transferred.
*
* @note This overload is equivalent to calling:
* @code boost::asio::read_at(
* d, 42, b,
* boost::asio::transfer_all(), ec); @endcode
*/
template <typename SyncRandomAccessReadDevice, typename Allocator>
std::size_t read_at(SyncRandomAccessReadDevice& d,
uint64_t offset, basic_streambuf<Allocator>& b,
boost::system::error_code& ec);
/// Attempt to read a certain amount of data at the specified offset before
/// returning.
/**
* This function is used to read a certain number of bytes of data from a
* random access device at the specified offset. The call will block until one
* of the following conditions is true:
*
* @li The completion_condition function object returns 0.
*
* This operation is implemented in terms of zero or more calls to the device's
* read_some_at function.
*
* @param d The device from which the data is to be read. The type must support
* the SyncRandomAccessReadDevice concept.
*
* @param offset The offset at which the data will be read.
*
* @param b The basic_streambuf object into which the data will be read.
*
* @param completion_condition The function object to be called to determine
* whether the read operation is complete. The signature of the function object
* must be:
* @code std::size_t completion_condition(
* // Result of latest read_some_at operation.
* const boost::system::error_code& error,
*
* // Number of bytes transferred so far.
* std::size_t bytes_transferred
* ); @endcode
* A return value of 0 indicates that the read operation is complete. A non-zero
* return value indicates the maximum number of bytes to be read on the next
* call to the device's read_some_at function.
*
* @returns The number of bytes transferred.
*
* @throws boost::system::system_error Thrown on failure.
*/
template <typename SyncRandomAccessReadDevice, typename Allocator,
typename CompletionCondition>
std::size_t read_at(SyncRandomAccessReadDevice& d,
uint64_t offset, basic_streambuf<Allocator>& b,
CompletionCondition completion_condition,
constraint_t<
is_completion_condition<CompletionCondition>::value
> = 0);
/// Attempt to read a certain amount of data at the specified offset before
/// returning.
/**
* This function is used to read a certain number of bytes of data from a
* random access device at the specified offset. The call will block until one
* of the following conditions is true:
*
* @li The completion_condition function object returns 0.
*
* This operation is implemented in terms of zero or more calls to the device's
* read_some_at function.
*
* @param d The device from which the data is to be read. The type must support
* the SyncRandomAccessReadDevice concept.
*
* @param offset The offset at which the data will be read.
*
* @param b The basic_streambuf object into which the data will be read.
*
* @param completion_condition The function object to be called to determine
* whether the read operation is complete. The signature of the function object
* must be:
* @code std::size_t completion_condition(
* // Result of latest read_some_at operation.
* const boost::system::error_code& error,
*
* // Number of bytes transferred so far.
* std::size_t bytes_transferred
* ); @endcode
* A return value of 0 indicates that the read operation is complete. A non-zero
* return value indicates the maximum number of bytes to be read on the next
* call to the device's read_some_at function.
*
* @param ec Set to indicate what error occurred, if any.
*
* @returns The number of bytes read. If an error occurs, returns the total
* number of bytes successfully transferred prior to the error.
*/
template <typename SyncRandomAccessReadDevice, typename Allocator,
typename CompletionCondition>
std::size_t read_at(SyncRandomAccessReadDevice& d,
uint64_t offset, basic_streambuf<Allocator>& b,
CompletionCondition completion_condition, boost::system::error_code& ec,
constraint_t<
is_completion_condition<CompletionCondition>::value
> = 0);
#endif // !defined(BOOST_ASIO_NO_IOSTREAM)
#endif // !defined(BOOST_ASIO_NO_EXTENSIONS)
/*@}*/
/**
* @defgroup async_read_at boost::asio::async_read_at
*
* @brief The @c async_read_at function is a composed asynchronous operation
* that reads a certain amount of data at the specified offset.
*/
/*@{*/
/// Start an asynchronous operation to read a certain amount of data at the
/// specified offset.
/**
* This function is used to asynchronously read a certain number of bytes of
* data from a random access device at the specified offset. It is an
* initiating function for an @ref asynchronous_operation, and always returns
* immediately. The asynchronous operation will continue until one of the
* following conditions is true:
*
* @li The supplied buffers are full. That is, the bytes transferred is equal to
* the sum of the buffer sizes.
*
* @li An error occurred.
*
* This operation is implemented in terms of zero or more calls to the device's
* async_read_some_at function.
*
* @param d The device from which the data is to be read. The type must support
* the AsyncRandomAccessReadDevice concept.
*
* @param offset The offset at which the data will be read.
*
* @param buffers One or more buffers into which the data will be read. The sum
* of the buffer sizes indicates the maximum number of bytes to read from the
* device. Although the buffers object may be copied as necessary, ownership of
* the underlying memory blocks is retained by the caller, which must guarantee
* that they remain valid until the completion handler is called.
*
* @param token The @ref completion_token that will be used to produce a
* completion handler, which will be called when the read completes.
* Potential completion tokens include @ref use_future, @ref use_awaitable,
* @ref yield_context, or a function object with the correct completion
* signature. The function signature of the completion handler must be:
* @code void handler(
* // Result of operation.
* const boost::system::error_code& error,
*
* // Number of bytes copied into the buffers. If an error
* // occurred, this will be the number of bytes successfully
* // transferred prior to the error.
* std::size_t bytes_transferred
* ); @endcode
* Regardless of whether the asynchronous operation completes immediately or
* not, the completion handler will not be invoked from within this function.
* On immediate completion, invocation of the handler will be performed in a
* manner equivalent to using boost::asio::async_immediate().
*
* @par Completion Signature
* @code void(boost::system::error_code, std::size_t) @endcode
*
* @par Example
* To read into a single data buffer use the @ref buffer function as follows:
* @code
* boost::asio::async_read_at(d, 42, boost::asio::buffer(data, size), handler);
* @endcode
* See the @ref buffer documentation for information on reading into multiple
* buffers in one go, and how to use it with arrays, boost::array or
* std::vector.
*
* @note This overload is equivalent to calling:
* @code boost::asio::async_read_at(
* d, 42, buffers,
* boost::asio::transfer_all(),
* handler); @endcode
*
* @par Per-Operation Cancellation
* This asynchronous operation supports cancellation for the following
* boost::asio::cancellation_type values:
*
* @li @c cancellation_type::terminal
*
* @li @c cancellation_type::partial
*
* if they are also supported by the @c AsyncRandomAccessReadDevice type's
* async_read_some_at operation.
*/
template <typename AsyncRandomAccessReadDevice, typename MutableBufferSequence,
BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
std::size_t)) ReadToken = default_completion_token_t<
typename AsyncRandomAccessReadDevice::executor_type>>
inline auto async_read_at(AsyncRandomAccessReadDevice& d,
uint64_t offset, const MutableBufferSequence& buffers,
ReadToken&& token = default_completion_token_t<
typename AsyncRandomAccessReadDevice::executor_type>(),
constraint_t<
!is_completion_condition<ReadToken>::value
> = 0)
-> decltype(
async_initiate<ReadToken,
void (boost::system::error_code, std::size_t)>(
declval<detail::initiate_async_read_at<AsyncRandomAccessReadDevice>>(),
token, offset, buffers, transfer_all()))
{
return async_initiate<ReadToken,
void (boost::system::error_code, std::size_t)>(
detail::initiate_async_read_at<AsyncRandomAccessReadDevice>(d),
token, offset, buffers, transfer_all());
}
/// Start an asynchronous operation to read a certain amount of data at the
/// specified offset.
/**
* This function is used to asynchronously read a certain number of bytes of
* data from a random access device at the specified offset. It is an
* initiating function for an @ref asynchronous_operation, and always returns
* immediately. The asynchronous operation will continue until one of the
* following conditions is true:
*
* @li The supplied buffers are full. That is, the bytes transferred is equal to
* the sum of the buffer sizes.
*
* @li The completion_condition function object returns 0.
*
* @param d The device from which the data is to be read. The type must support
* the AsyncRandomAccessReadDevice concept.
*
* @param offset The offset at which the data will be read.
*
* @param buffers One or more buffers into which the data will be read. The sum
* of the buffer sizes indicates the maximum number of bytes to read from the
* device. Although the buffers object may be copied as necessary, ownership of
* the underlying memory blocks is retained by the caller, which must guarantee
* that they remain valid until the completion handler is called.
*
* @param completion_condition The function object to be called to determine
* whether the read operation is complete. The signature of the function object
* must be:
* @code std::size_t completion_condition(
* // Result of latest async_read_some_at operation.
* const boost::system::error_code& error,
*
* // Number of bytes transferred so far.
* std::size_t bytes_transferred
* ); @endcode
* A return value of 0 indicates that the read operation is complete. A non-zero
* return value indicates the maximum number of bytes to be read on the next
* call to the device's async_read_some_at function.
*
* @param token The @ref completion_token that will be used to produce a
* completion handler, which will be called when the read completes.
* Potential completion tokens include @ref use_future, @ref use_awaitable,
* @ref yield_context, or a function object with the correct completion
* signature. The function signature of the completion handler must be:
* @code void handler(
* // Result of operation.
* const boost::system::error_code& error,
*
* // Number of bytes copied into the buffers. If an error
* // occurred, this will be the number of bytes successfully
* // transferred prior to the error.
* std::size_t bytes_transferred
* ); @endcode
* Regardless of whether the asynchronous operation completes immediately or
* not, the completion handler will not be invoked from within this function.
* On immediate completion, invocation of the handler will be performed in a
* manner equivalent to using boost::asio::async_immediate().
*
* @par Completion Signature
* @code void(boost::system::error_code, std::size_t) @endcode
*
* @par Example
* To read into a single data buffer use the @ref buffer function as follows:
* @code boost::asio::async_read_at(d, 42,
* boost::asio::buffer(data, size),
* boost::asio::transfer_at_least(32),
* handler); @endcode
* See the @ref buffer documentation for information on reading into multiple
* buffers in one go, and how to use it with arrays, boost::array or
* std::vector.
*
* @par Per-Operation Cancellation
* This asynchronous operation supports cancellation for the following
* boost::asio::cancellation_type values:
*
* @li @c cancellation_type::terminal
*
* @li @c cancellation_type::partial
*
* if they are also supported by the @c AsyncRandomAccessReadDevice type's
* async_read_some_at operation.
*/
template <typename AsyncRandomAccessReadDevice,
typename MutableBufferSequence, typename CompletionCondition,
BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
std::size_t)) ReadToken = default_completion_token_t<
typename AsyncRandomAccessReadDevice::executor_type>>
inline auto async_read_at(AsyncRandomAccessReadDevice& d,
uint64_t offset, const MutableBufferSequence& buffers,
CompletionCondition completion_condition,
ReadToken&& token = default_completion_token_t<
typename AsyncRandomAccessReadDevice::executor_type>(),
constraint_t<
is_completion_condition<CompletionCondition>::value
> = 0)
-> decltype(
async_initiate<ReadToken,
void (boost::system::error_code, std::size_t)>(
declval<detail::initiate_async_read_at<AsyncRandomAccessReadDevice>>(),
token, offset, buffers,
static_cast<CompletionCondition&&>(completion_condition)))
{
return async_initiate<ReadToken,
void (boost::system::error_code, std::size_t)>(
detail::initiate_async_read_at<AsyncRandomAccessReadDevice>(d),
token, offset, buffers,
static_cast<CompletionCondition&&>(completion_condition));
}
#if !defined(BOOST_ASIO_NO_EXTENSIONS)
#if !defined(BOOST_ASIO_NO_IOSTREAM)
/// Start an asynchronous operation to read a certain amount of data at the
/// specified offset.
/**
* This function is used to asynchronously read a certain number of bytes of
* data from a random access device at the specified offset. It is an
* initiating function for an @ref asynchronous_operation, and always returns
* immediately. The asynchronous operation will continue until one of the
* following conditions is true:
*
* @li An error occurred.
*
* This operation is implemented in terms of zero or more calls to the device's
* async_read_some_at function.
*
* @param d The device from which the data is to be read. The type must support
* the AsyncRandomAccessReadDevice concept.
*
* @param offset The offset at which the data will be read.
*
* @param b A basic_streambuf object into which the data will be read. Ownership
* of the streambuf is retained by the caller, which must guarantee that it
* remains valid until the completion handler is called.
*
* @param token The @ref completion_token that will be used to produce a
* completion handler, which will be called when the read completes.
* Potential completion tokens include @ref use_future, @ref use_awaitable,
* @ref yield_context, or a function object with the correct completion
* signature. The function signature of the completion handler must be:
* @code void handler(
* // Result of operation.
* const boost::system::error_code& error,
*
* // Number of bytes copied into the buffers. If an error
* // occurred, this will be the number of bytes successfully
* // transferred prior to the error.
* std::size_t bytes_transferred
* ); @endcode
* Regardless of whether the asynchronous operation completes immediately or
* not, the completion handler will not be invoked from within this function.
* On immediate completion, invocation of the handler will be performed in a
* manner equivalent to using boost::asio::async_immediate().
*
* @par Completion Signature
* @code void(boost::system::error_code, std::size_t) @endcode
*
* @note This overload is equivalent to calling:
* @code boost::asio::async_read_at(
* d, 42, b,
* boost::asio::transfer_all(),
* handler); @endcode
*
* @par Per-Operation Cancellation
* This asynchronous operation supports cancellation for the following
* boost::asio::cancellation_type values:
*
* @li @c cancellation_type::terminal
*
* @li @c cancellation_type::partial
*
* if they are also supported by the @c AsyncRandomAccessReadDevice type's
* async_read_some_at operation.
*/
template <typename AsyncRandomAccessReadDevice, typename Allocator,
BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
std::size_t)) ReadToken = default_completion_token_t<
typename AsyncRandomAccessReadDevice::executor_type>>
inline auto async_read_at(AsyncRandomAccessReadDevice& d,
uint64_t offset, basic_streambuf<Allocator>& b,
ReadToken&& token = default_completion_token_t<
typename AsyncRandomAccessReadDevice::executor_type>(),
constraint_t<
!is_completion_condition<ReadToken>::value
> = 0)
-> decltype(
async_initiate<ReadToken,
void (boost::system::error_code, std::size_t)>(
declval<detail::initiate_async_read_at_streambuf<
AsyncRandomAccessReadDevice>>(),
token, offset, &b, transfer_all()))
{
return async_initiate<ReadToken,
void (boost::system::error_code, std::size_t)>(
detail::initiate_async_read_at_streambuf<AsyncRandomAccessReadDevice>(d),
token, offset, &b, transfer_all());
}
/// Start an asynchronous operation to read a certain amount of data at the
/// specified offset.
/**
* This function is used to asynchronously read a certain number of bytes of
* data from a random access device at the specified offset. It is an
* initiating function for an @ref asynchronous_operation, and always returns
* immediately. The asynchronous operation will continue until one of the
* following conditions is true:
*
* @li The completion_condition function object returns 0.
*
* This operation is implemented in terms of zero or more calls to the device's
* async_read_some_at function.
*
* @param d The device from which the data is to be read. The type must support
* the AsyncRandomAccessReadDevice concept.
*
* @param offset The offset at which the data will be read.
*
* @param b A basic_streambuf object into which the data will be read. Ownership
* of the streambuf is retained by the caller, which must guarantee that it
* remains valid until the completion handler is called.
*
* @param completion_condition The function object to be called to determine
* whether the read operation is complete. The signature of the function object
* must be:
* @code std::size_t completion_condition(
* // Result of latest async_read_some_at operation.
* const boost::system::error_code& error,
*
* // Number of bytes transferred so far.
* std::size_t bytes_transferred
* ); @endcode
* A return value of 0 indicates that the read operation is complete. A non-zero
* return value indicates the maximum number of bytes to be read on the next
* call to the device's async_read_some_at function.
*
* @param token The @ref completion_token that will be used to produce a
* completion handler, which will be called when the read completes.
* Potential completion tokens include @ref use_future, @ref use_awaitable,
* @ref yield_context, or a function object with the correct completion
* signature. The function signature of the completion handler must be:
* @code void handler(
* // Result of operation.
* const boost::system::error_code& error,
*
* // Number of bytes copied into the buffers. If an error
* // occurred, this will be the number of bytes successfully
* // transferred prior to the error.
* std::size_t bytes_transferred
* ); @endcode
* Regardless of whether the asynchronous operation completes immediately or
* not, the completion handler will not be invoked from within this function.
* On immediate completion, invocation of the handler will be performed in a
* manner equivalent to using boost::asio::async_immediate().
*
* @par Completion Signature
* @code void(boost::system::error_code, std::size_t) @endcode
*
* @par Per-Operation Cancellation
* This asynchronous operation supports cancellation for the following
* boost::asio::cancellation_type values:
*
* @li @c cancellation_type::terminal
*
* @li @c cancellation_type::partial
*
* if they are also supported by the @c AsyncRandomAccessReadDevice type's
* async_read_some_at operation.
*/
template <typename AsyncRandomAccessReadDevice,
typename Allocator, typename CompletionCondition,
BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
std::size_t)) ReadToken = default_completion_token_t<
typename AsyncRandomAccessReadDevice::executor_type>>
inline auto async_read_at(AsyncRandomAccessReadDevice& d, uint64_t offset,
basic_streambuf<Allocator>& b, CompletionCondition completion_condition,
ReadToken&& token = default_completion_token_t<
typename AsyncRandomAccessReadDevice::executor_type>(),
constraint_t<
is_completion_condition<CompletionCondition>::value
> = 0)
-> decltype(
async_initiate<ReadToken,
void (boost::system::error_code, std::size_t)>(
declval<detail::initiate_async_read_at_streambuf<
AsyncRandomAccessReadDevice>>(),
token, offset, &b,
static_cast<CompletionCondition&&>(completion_condition)))
{
return async_initiate<ReadToken,
void (boost::system::error_code, std::size_t)>(
detail::initiate_async_read_at_streambuf<AsyncRandomAccessReadDevice>(d),
token, offset, &b,
static_cast<CompletionCondition&&>(completion_condition));
}
#endif // !defined(BOOST_ASIO_NO_IOSTREAM)
#endif // !defined(BOOST_ASIO_NO_EXTENSIONS)
/*@}*/
} // namespace asio
} // namespace boost
#include <boost/asio/detail/pop_options.hpp>
#include <boost/asio/impl/read_at.hpp>
#endif // BOOST_ASIO_READ_AT_HPP