haiku/docs/user/support/BufferIO.dox

/*
 * Copyright 2007,Haiku, Inc. All rights reserved.
 * Distributed under the terms of the MIT License.
 *
 * Authors:
 *		Stefano Ceccherini, burton666@libero.it
 *		Niels Sascha Reedijk, niels.reedijk@gmail.com
 *
 * Corresponds to:
 *		headers/os/support/BufferIO.h	rev 19972
 *		src/kits/support/BufferIO.cpp	rev 20510
 */


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


/*!
	\class BBufferIO
	\ingroup support
	\ingroup libroot
	\brief A buffered adapter for BPositionIO objects.

	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
	initialized 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.

	\returns A status code.
	\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.
*/