Boost C++ Libraries

boost/asio/basic_random_access_file.hpp

//
// basic_random_access_file.hpp
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2022 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_BASIC_RANDOM_ACCESS_FILE_HPP
#define BOOST_ASIO_BASIC_RANDOM_ACCESS_FILE_HPP

#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)

#include <boost/asio/detail/config.hpp>

#if defined(BOOST_ASIO_HAS_FILE) \
  || defined(GENERATING_DOCUMENTATION)

#include <cstddef>
#include <boost/asio/async_result.hpp>
#include <boost/asio/basic_file.hpp>
#include <boost/asio/detail/handler_type_requirements.hpp>
#include <boost/asio/detail/non_const_lvalue.hpp>
#include <boost/asio/detail/throw_error.hpp>
#include <boost/asio/error.hpp>

#include <boost/asio/detail/push_options.hpp>

namespace boost {
namespace asio {

#if !defined(BOOST_ASIO_BASIC_RANDOM_ACCESS_FILE_FWD_DECL)
#define BOOST_ASIO_BASIC_RANDOM_ACCESS_FILE_FWD_DECL

// Forward declaration with defaulted arguments.
template <typename Executor = any_io_executor>
class basic_random_access_file;

#endif // !defined(BOOST_ASIO_BASIC_RANDOM_ACCESS_FILE_FWD_DECL)

/// Provides random-access file functionality.
/**
 * The basic_random_access_file class template provides asynchronous and
 * blocking random-access file functionality.
 *
 * @par Thread Safety
 * @e Distinct @e objects: Safe.@n
 * @e Shared @e objects: Unsafe.
 *
 * Synchronous @c read_some_at and @c write_some_at operations are thread safe
 * with respect to each other, if the underlying operating system calls are
 * also thread safe. This means that it is permitted to perform concurrent
 * calls to these synchronous operations on a single file object. Other
 * synchronous operations, such as @c open or @c close, are not thread safe.
 */
template <typename Executor>
class basic_random_access_file
  : public basic_file<Executor>
{
public:
  /// The type of the executor associated with the object.
  typedef Executor executor_type;

  /// Rebinds the file type to another executor.
  template <typename Executor1>
  struct rebind_executor
  {
    /// The file type when rebound to the specified executor.
    typedef basic_random_access_file<Executor1> other;
  };

  /// The native representation of a file.
#if defined(GENERATING_DOCUMENTATION)
  typedef implementation_defined native_handle_type;
#else
  typedef typename basic_file<Executor>::native_handle_type native_handle_type;
#endif

  /// Construct a basic_random_access_file without opening it.
  /**
   * This constructor initialises a file without opening it. The file needs to
   * be opened before data can be read from or or written to it.
   *
   * @param ex The I/O executor that the file will use, by default, to
   * dispatch handlers for any asynchronous operations performed on the file.
   */
  explicit basic_random_access_file(const executor_type& ex)
    : basic_file<Executor>(ex)
  {
  }

  /// Construct a basic_random_access_file without opening it.
  /**
   * This constructor initialises a file without opening it. The file needs to
   * be opened before data can be read from or or written to it.
   *
   * @param context An execution context which provides the I/O executor that
   * the file will use, by default, to dispatch handlers for any asynchronous
   * operations performed on the file.
   */
  template <typename ExecutionContext>
  explicit basic_random_access_file(ExecutionContext& context,
      typename constraint<
        is_convertible<ExecutionContext&, execution_context&>::value,
        defaulted_constraint
      >::type = defaulted_constraint())
    : basic_file<Executor>(context)
  {
  }

  /// Construct and open a basic_random_access_file.
  /**
   * This constructor initialises and opens a file.
   *
   * @param ex The I/O executor that the file will use, by default, to
   * dispatch handlers for any asynchronous operations performed on the file.
   *
   * @param path The path name identifying the file to be opened.
   *
   * @param open_flags A set of flags that determine how the file should be
   * opened.
   *
   * @throws boost::system::system_error Thrown on failure.
   */
  basic_random_access_file(const executor_type& ex,
      const char* path, file_base::flags open_flags)
    : basic_file<Executor>(ex, path, open_flags)
  {
  }

  /// Construct and open a basic_random_access_file.
  /**
   * This constructor initialises and opens a file.
   *
   * @param context An execution context which provides the I/O executor that
   * the file will use, by default, to dispatch handlers for any asynchronous
   * operations performed on the file.
   *
   * @param path The path name identifying the file to be opened.
   *
   * @param open_flags A set of flags that determine how the file should be
   * opened.
   *
   * @throws boost::system::system_error Thrown on failure.
   */
  template <typename ExecutionContext>
  basic_random_access_file(ExecutionContext& context,
      const char* path, file_base::flags open_flags,
      typename constraint<
        is_convertible<ExecutionContext&, execution_context&>::value,
        defaulted_constraint
      >::type = defaulted_constraint())
    : basic_file<Executor>(context, path, open_flags)
  {
  }

  /// Construct and open a basic_random_access_file.
  /**
   * This constructor initialises and opens a file.
   *
   * @param ex The I/O executor that the file will use, by default, to
   * dispatch handlers for any asynchronous operations performed on the file.
   *
   * @param path The path name identifying the file to be opened.
   *
   * @param open_flags A set of flags that determine how the file should be
   * opened.
   *
   * @throws boost::system::system_error Thrown on failure.
   */
  basic_random_access_file(const executor_type& ex,
      const std::string& path, file_base::flags open_flags)
    : basic_file<Executor>(ex, path, open_flags)
  {
  }

  /// Construct and open a basic_random_access_file.
  /**
   * This constructor initialises and opens a file.
   *
   * @param context An execution context which provides the I/O executor that
   * the file will use, by default, to dispatch handlers for any asynchronous
   * operations performed on the file.
   *
   * @param path The path name identifying the file to be opened.
   *
   * @param open_flags A set of flags that determine how the file should be
   * opened.
   *
   * @throws boost::system::system_error Thrown on failure.
   */
  template <typename ExecutionContext>
  basic_random_access_file(ExecutionContext& context,
      const std::string& path, file_base::flags open_flags,
      typename constraint<
        is_convertible<ExecutionContext&, execution_context&>::value,
        defaulted_constraint
      >::type = defaulted_constraint())
    : basic_file<Executor>(context, path, open_flags)
  {
  }

  /// Construct a basic_random_access_file on an existing native file.
  /**
   * This constructor initialises a random-access file object to hold an
   * existing native file.
   *
   * @param ex The I/O executor that the file will use, by default, to
   * dispatch handlers for any asynchronous operations performed on the file.
   *
   * @param native_file The new underlying file implementation.
   *
   * @throws boost::system::system_error Thrown on failure.
   */
  basic_random_access_file(const executor_type& ex,
      const native_handle_type& native_file)
    : basic_file<Executor>(ex, native_file)
  {
  }

  /// Construct a basic_random_access_file on an existing native file.
  /**
   * This constructor initialises a random-access file object to hold an
   * existing native file.
   *
   * @param context An execution context which provides the I/O executor that
   * the file will use, by default, to dispatch handlers for any asynchronous
   * operations performed on the file.
   *
   * @param native_file The new underlying file implementation.
   *
   * @throws boost::system::system_error Thrown on failure.
   */
  template <typename ExecutionContext>
  basic_random_access_file(ExecutionContext& context,
      const native_handle_type& native_file,
      typename constraint<
        is_convertible<ExecutionContext&, execution_context&>::value,
        defaulted_constraint
      >::type = defaulted_constraint())
    : basic_file<Executor>(context, native_file)
  {
  }

#if defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
  /// Move-construct a basic_random_access_file from another.
  /**
   * This constructor moves a random-access file from one object to another.
   *
   * @param other The other basic_random_access_file object from which the move
   * will occur.
   *
   * @note Following the move, the moved-from object is in the same state as if
   * constructed using the @c basic_random_access_file(const executor_type&)
   * constructor.
   */
  basic_random_access_file(basic_random_access_file&& other) BOOST_ASIO_NOEXCEPT
    : basic_file<Executor>(std::move(other))
  {
  }

  /// Move-assign a basic_random_access_file from another.
  /**
   * This assignment operator moves a random-access file from one object to
   * another.
   *
   * @param other The other basic_random_access_file object from which the move
   * will occur.
   *
   * @note Following the move, the moved-from object is in the same state as if
   * constructed using the @c basic_random_access_file(const executor_type&)
   * constructor.
   */
  basic_random_access_file& operator=(basic_random_access_file&& other)
  {
    basic_file<Executor>::operator=(std::move(other));
    return *this;
  }

  /// Move-construct a basic_random_access_file from a file of another executor
  /// type.
  /**
   * This constructor moves a random-access file from one object to another.
   *
   * @param other The other basic_random_access_file object from which the move
   * will occur.
   *
   * @note Following the move, the moved-from object is in the same state as if
   * constructed using the @c basic_random_access_file(const executor_type&)
   * constructor.
   */
  template <typename Executor1>
  basic_random_access_file(basic_random_access_file<Executor1>&& other,
      typename constraint<
        is_convertible<Executor1, Executor>::value,
        defaulted_constraint
      >::type = defaulted_constraint())
    : basic_file<Executor>(std::move(other))
  {
  }

  /// Move-assign a basic_random_access_file from a file of another executor
  /// type.
  /**
   * This assignment operator moves a random-access file from one object to
   * another.
   *
   * @param other The other basic_random_access_file object from which the move
   * will occur.
   *
   * @note Following the move, the moved-from object is in the same state as if
   * constructed using the @c basic_random_access_file(const executor_type&)
   * constructor.
   */
  template <typename Executor1>
  typename constraint<
    is_convertible<Executor1, Executor>::value,
    basic_random_access_file&
  >::type operator=(basic_random_access_file<Executor1>&& other)
  {
    basic_file<Executor>::operator=(std::move(other));
    return *this;
  }
#endif // defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)

  /// Destroys the file.
  /**
   * This function destroys the file, cancelling any outstanding asynchronous
   * operations associated with the file as if by calling @c cancel.
   */
  ~basic_random_access_file()
  {
  }

  /// Write some data to the handle at the specified offset.
  /**
   * This function is used to write data to the random-access handle. The
   * function call will block until one or more bytes of the data has been
   * written successfully, or until an error occurs.
   *
   * @param offset The offset at which the data will be written.
   *
   * @param buffers One or more data buffers to be written to the handle.
   *
   * @returns The number of bytes written.
   *
   * @throws boost::system::system_error Thrown on failure. An error code of
   * boost::asio::error::eof indicates that the end of the file was reached.
   *
   * @note The write_some_at operation may not write all of the data. Consider
   * using the @ref write_at function if you need to ensure that all data is
   * written before the blocking operation completes.
   *
   * @par Example
   * To write a single data buffer use the @ref buffer function as follows:
   * @code
   * handle.write_some_at(42, boost::asio::buffer(data, size));
   * @endcode
   * See the @ref buffer documentation for information on writing multiple
   * buffers in one go, and how to use it with arrays, boost::array or
   * std::vector.
   */
  template <typename ConstBufferSequence>
  std::size_t write_some_at(uint64_t offset,
      const ConstBufferSequence& buffers)
  {
    boost::system::error_code ec;
    std::size_t s = this->impl_.get_service().write_some_at(
        this->impl_.get_implementation(), offset, buffers, ec);
    boost::asio::detail::throw_error(ec, "write_some_at");
    return s;
  }

  /// Write some data to the handle at the specified offset.
  /**
   * This function is used to write data to the random-access handle. The
   * function call will block until one or more bytes of the data has been
   * written successfully, or until an error occurs.
   *
   * @param offset The offset at which the data will be written.
   *
   * @param buffers One or more data buffers to be written to the handle.
   *
   * @param ec Set to indicate what error occurred, if any.
   *
   * @returns The number of bytes written. Returns 0 if an error occurred.
   *
   * @note The write_some operation may not write all of the data to the
   * file. Consider using the @ref write_at function if you need to ensure that
   * all data is written before the blocking operation completes.
   */
  template <typename ConstBufferSequence>
  std::size_t write_some_at(uint64_t offset,
      const ConstBufferSequence& buffers, boost::system::error_code& ec)
  {
    return this->impl_.get_service().write_some_at(
        this->impl_.get_implementation(), offset, buffers, ec);
  }

  /// Start an asynchronous write at the specified offset.
  /**
   * This function is used to asynchronously write data to the random-access
   * handle. It is an initiating function for an @ref asynchronous_operation,
   * and always returns immediately.
   *
   * @param offset The offset at which the data will be written.
   *
   * @param buffers One or more data buffers to be written to the handle.
   * 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 write 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(
   *   const boost::system::error_code& error, // Result of operation.
   *   std::size_t bytes_transferred // Number of bytes written.
   * ); @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::post().
   *
   * @par Completion Signature
   * @code void(boost::system::error_code, std::size_t) @endcode
   *
   * @note The write operation may not write all of the data to the file.
   * Consider using the @ref async_write_at function if you need to ensure that
   * all data is written before the asynchronous operation completes.
   *
   * @par Example
   * To write a single data buffer use the @ref buffer function as follows:
   * @code
   * handle.async_write_some_at(42, boost::asio::buffer(data, size), handler);
   * @endcode
   * See the @ref buffer documentation for information on writing 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
   *
   * @li @c cancellation_type::total
   */
  template <typename ConstBufferSequence,
      BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
        std::size_t)) WriteToken
          BOOST_ASIO_DEFAULT_COMPLETION_TOKEN_TYPE(executor_type)>
  BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(WriteToken,
      void (boost::system::error_code, std::size_t))
  async_write_some_at(uint64_t offset,
      const ConstBufferSequence& buffers,
      BOOST_ASIO_MOVE_ARG(WriteToken) token
        BOOST_ASIO_DEFAULT_COMPLETION_TOKEN(executor_type))
  {
    return async_initiate<WriteToken,
      void (boost::system::error_code, std::size_t)>(
        initiate_async_write_some_at(this), token, offset, buffers);
  }

  /// Read some data from the handle at the specified offset.
  /**
   * This function is used to read data from the random-access handle. The
   * function call will block until one or more bytes of data has been read
   * successfully, or until an error occurs.
   *
   * @param offset The offset at which the data will be read.
   *
   * @param buffers One or more buffers into which the data will be read.
   *
   * @returns The number of bytes read.
   *
   * @throws boost::system::system_error Thrown on failure. An error code of
   * boost::asio::error::eof indicates that the end of the file was reached.
   *
   * @note The read_some operation may not read all of the requested number of
   * bytes. Consider using the @ref read_at function if you need to ensure that
   * the requested amount of data is read before the blocking operation
   * completes.
   *
   * @par Example
   * To read into a single data buffer use the @ref buffer function as follows:
   * @code
   * handle.read_some_at(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.
   */
  template <typename MutableBufferSequence>
  std::size_t read_some_at(uint64_t offset,
      const MutableBufferSequence& buffers)
  {
    boost::system::error_code ec;
    std::size_t s = this->impl_.get_service().read_some_at(
        this->impl_.get_implementation(), offset, buffers, ec);
    boost::asio::detail::throw_error(ec, "read_some_at");
    return s;
  }

  /// Read some data from the handle at the specified offset.
  /**
   * This function is used to read data from the random-access handle. The
   * function call will block until one or more bytes of data has been read
   * successfully, or until an error occurs.
   *
   * @param offset The offset at which the data will be read.
   *
   * @param buffers One or more buffers into which the data will be read.
   *
   * @param ec Set to indicate what error occurred, if any.
   *
   * @returns The number of bytes read. Returns 0 if an error occurred.
   *
   * @note The read_some operation may not read all of the requested number of
   * bytes. Consider using the @ref read_at function if you need to ensure that
   * the requested amount of data is read before the blocking operation
   * completes.
   */
  template <typename MutableBufferSequence>
  std::size_t read_some_at(uint64_t offset,
      const MutableBufferSequence& buffers, boost::system::error_code& ec)
  {
    return this->impl_.get_service().read_some_at(
        this->impl_.get_implementation(), offset, buffers, ec);
  }

  /// Start an asynchronous read at the specified offset.
  /**
   * This function is used to asynchronously read data from the random-access
   * handle. It is an initiating function for an @ref asynchronous_operation,
   * and always returns immediately.
   *
   * @param offset The offset at which the data will be read.
   *
   * @param buffers One or more buffers into which the data will be read.
   * 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(
   *   const boost::system::error_code& error, // Result of operation.
   *   std::size_t bytes_transferred // Number of bytes read.
   * ); @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::post().
   *
   * @par Completion Signature
   * @code void(boost::system::error_code, std::size_t) @endcode
   *
   * @note The read operation may not read all of the requested number of bytes.
   * Consider using the @ref async_read_at function if you need to ensure that
   * the requested amount of data is read before the asynchronous operation
   * completes.
   *
   * @par Example
   * To read into a single data buffer use the @ref buffer function as follows:
   * @code
   * handle.async_read_some_at(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.
   *
   * @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
   *
   * @li @c cancellation_type::total
   */
  template <typename MutableBufferSequence,
      BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
        std::size_t)) ReadToken
          BOOST_ASIO_DEFAULT_COMPLETION_TOKEN_TYPE(executor_type)>
  BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(ReadToken,
      void (boost::system::error_code, std::size_t))
  async_read_some_at(uint64_t offset,
      const MutableBufferSequence& buffers,
      BOOST_ASIO_MOVE_ARG(ReadToken) token
        BOOST_ASIO_DEFAULT_COMPLETION_TOKEN(executor_type))
  {
    return async_initiate<ReadToken,
      void (boost::system::error_code, std::size_t)>(
        initiate_async_read_some_at(this), token, offset, buffers);
  }

private:
  // Disallow copying and assignment.
  basic_random_access_file(const basic_random_access_file&) BOOST_ASIO_DELETED;
  basic_random_access_file& operator=(
      const basic_random_access_file&) BOOST_ASIO_DELETED;

  class initiate_async_write_some_at
  {
  public:
    typedef Executor executor_type;

    explicit initiate_async_write_some_at(basic_random_access_file* self)
      : self_(self)
    {
    }

    executor_type get_executor() const BOOST_ASIO_NOEXCEPT
    {
      return self_->get_executor();
    }

    template <typename WriteHandler, typename ConstBufferSequence>
    void operator()(BOOST_ASIO_MOVE_ARG(WriteHandler) handler,
        uint64_t offset, const ConstBufferSequence& buffers) const
    {
      // If you get an error on the following line it means that your handler
      // does not meet the documented type requirements for a WriteHandler.
      BOOST_ASIO_WRITE_HANDLER_CHECK(WriteHandler, handler) type_check;

      detail::non_const_lvalue<WriteHandler> handler2(handler);
      self_->impl_.get_service().async_write_some_at(
          self_->impl_.get_implementation(), offset, buffers,
          handler2.value, self_->impl_.get_executor());
    }

  private:
    basic_random_access_file* self_;
  };

  class initiate_async_read_some_at
  {
  public:
    typedef Executor executor_type;

    explicit initiate_async_read_some_at(basic_random_access_file* self)
      : self_(self)
    {
    }

    executor_type get_executor() const BOOST_ASIO_NOEXCEPT
    {
      return self_->get_executor();
    }

    template <typename ReadHandler, typename MutableBufferSequence>
    void operator()(BOOST_ASIO_MOVE_ARG(ReadHandler) handler,
        uint64_t offset, const MutableBufferSequence& buffers) const
    {
      // If you get an error on the following line it means that your handler
      // does not meet the documented type requirements for a ReadHandler.
      BOOST_ASIO_READ_HANDLER_CHECK(ReadHandler, handler) type_check;

      detail::non_const_lvalue<ReadHandler> handler2(handler);
      self_->impl_.get_service().async_read_some_at(
          self_->impl_.get_implementation(), offset, buffers,
          handler2.value, self_->impl_.get_executor());
    }

  private:
    basic_random_access_file* self_;
  };
};

} // namespace asio
} // namespace boost

#include <boost/asio/detail/pop_options.hpp>

#endif // defined(BOOST_ASIO_HAS_FILE)
       //   || defined(GENERATING_DOCUMENTATION)

#endif // BOOST_ASIO_BASIC_RANDOM_ACCESS_FILE_HPP