haiku/docs/user/support/BufferIO.dox

/*
 * Copyright 2007, Haiku, Inc. All Rights Reserved.
 * Distributed under the terms of the MIT License.
 *
 * Documentation by: 
 *   Niels Sascha Reedijk <niels.reedijk@gmail.com>
 *   Stefano Ceccherini (burton666@libero.it) 
 * Corresponds to:
 *   /trunk/headers/os/support/BufferIO.h  rev 19972
 *   /trunk/src/kits/support/BufferIO.cpp  rev 20510
 */

/*!
  \file BufferIO.h
  \brief Provides the BBufferIO class.
*/

/*!
  \class BBufferIO
  \ingroup support
  \ingroup libbe
  \brief A buffered adapter for BPositionIO objects.
  \author Stefano Ceccherini \<burton666@freemail.it\>

  This class differs from other classes derived from BPositionIO in a sense that
  it does not actually provide an actual entity to be read or written to, but
  rather acts like a "frontend" to a stream. This class especially comes in
  handy when working with files that are constantly written and rewritten and
  where you want do this writing buffered so that the hard disk or the network
  will not have to be accessed so frequently.

  This class works as follows. After constructing a BBufferIO object that you
  want to be buffered, you can create this object. The constructor takes a 
  \a stream parameter that points to the object to be buffered. You then use
  this object as a proxy to the resource you want to read of or write to. As
  soon as you use ReadAt(), the buffer will be initialised to the contents
  of the original stream,
  and subsequent calls to the positions within the buffer will not be
  routed to the original stream. In the same way WriteAt() will change
  the data in the buffer, but not in the actual stream. In order to flush
  the changes to the original stream, use the Flush() method. Deleting
  the object when you are done with it will also flush the stream and
  update the original stream.

  \note This class is not meant to be used in cases where the 
  original stream requires to be in a consistent state. Neither should this
  class be used as a way to perform 'atomic' writes, because the object 
  might need to do partial writes if it needs to 'move' the buffer. This 
  happens for instance if the original stream is bigger than the buffer. 
*/

/*!
  \fn BBufferIO::BBufferIO(BPositionIO *stream, size_t bufferSize, bool ownsStream)
  \brief Initialize a BBufferIO object.
    
  The constructor will create a buffer of the given size
  and associate the object with the given BPositionIO stream.

  \param stream A pointer to a BPositionIO object.
  \param bufferSize The size of the buffer that the object will allocate and 
    use.
  \param ownsStream Specifies if the object will delete the stream on 
    destruction.
*/

/*!
  \fn BBufferIO::~BBufferIO()
  \brief Free the resources allocated by the object

  Flush pending changes to the stream and free the allocated memory.
  If the \c owns_stream property is \c true, the destructor also
  deletes the stream associated with the BBufferIO object.
*/


/*! 
  \fn ssize_t BBufferIO::ReadAt(off_t pos, void *buffer, size_t size)
  \brief Read the specified amount of bytes at the given position.
  \param pos The offset into the stream where to read.
  \param buffer A pointer to a buffer where to copy the read data.
  \param size The amount of bytes to read.
  \return The amount of bytes actually read, or an error code.
  \retval B_NO_INIT The object is not associated with a valid BPositionIO
    stream.
  \retval B_BAD_VALUE The \c buffer parameter is not valid.
*/

/*! 
  \fn ssize_t BBufferIO::WriteAt(off_t pos, const void *buffer, size_t size)
  \brief Write the specified amount of bytes at the given position.
  \param pos The offset into the stream where to write.
  \param buffer A pointer to a buffer which contains the data to write.
  \param size The amount of bytes to write.
  \return The amount of bytes actually written, or an error code.
  \retval B_NO_INIT The object is not associated with a valid BPositionIO
    stream.
  \retval B_BAD_VALUE The \c buffer parameter is not valid.
*/

/*! 
  \fn off_t BBufferIO::Seek(off_t position, uint32 seekMode)
  \brief Set the position in the stream.
    
   Set the position in the stream where the Read() and Write() functions
   (inherited from BPositionIO) begin reading and writing.
   How the position argument is understood depends on the seek_mode flag.
   
   \param position The position where you want to seek.
   \param seekMode Can have three values:
   - \c SEEK_SET. The position passed is an offset from the beginning of the
     stream; in other words, the current position is set to position.
    For this mode, position should be a positive value. 
   - \c SEEK_CUR. The position argument is an offset from the current position;
    the value of the argument is added to the current position.
   - \c SEEK_END. The position argument is an offset from the end of the
     stream. In this mode the position argument should be negative (or zero).

   \return The current position as an offset in bytes from the beginning of
     the stream.
    
    \retval B_NO_INIT The object is not associated with a valid BPositionIO
      stream.
*/

/*! 
  \fn off_t BBufferIO::Position() const
  \brief Return the current position in the stream.
  \return The current position as an offset in bytes
    from the beginning of the stream.
  \retval B_NO_INIT The object is not associated with a valid BPositionIO
    stream.
*/

/*! 
  \fn status_t BBufferIO::SetSize(off_t size)
  \brief Call the SetSize() function of the assigned BPositionIO stream.
  \param size The new size of the BPositionIO object.
  \retval B_OK The stream is resized.
  \retval B_NO_INIT The object is not associated with a valid BPositionIO
    stream.
*/

/*!
  \fn status_t BBufferIO::Flush()
  \brief Write pending modifications to the stream.
  \return The amount of bytes written, or if it failed it will return an error
    code.
*/


/*! 
  \fn BPositionIO *BBufferIO::Stream() const
  \brief Return a pointer to the stream specified on construction.
  \return A pointer to the BPositionIO stream specified on construction.
*/


/*! 
  \fn size_t BBufferIO::BufferSize() const
  \brief Return the size of the internal buffer.
  \return The size of the buffer allocated by the object.
*/

/*! 
  \fn bool BBufferIO::OwnsStream() const
  \brief Tell if the BBufferIO object "owns" the specified stream.
  \retval true The object "owns" the stream and will destroy it upon
    destruction.
  \retval false The object does not own the stream.
  \see SetOwnsStream()
*/

/*! 
  \fn void BBufferIO::SetOwnsStream(bool owns_stream)
  \brief Set the \c owns_stream property of the object.
  \param owns_stream If you pass \c true, the object will delete the stream
    upon destruction, if you pass \c false it will not.
*/


/*! 
  \fn void BBufferIO::PrintToStream() const
  \brief Print the object to stdout.
*/