1/* 2 * Copyright 2007, Haiku, Inc. All Rights Reserved. 3 * Distributed under the terms of the MIT License. 4 * 5 * Documentation by: 6 * Niels Sascha Reedijk <niels.reedijk@gmail.com> 7 * Stefano Ceccherini (burton666@libero.it) 8 * Corresponds to: 9 * /trunk/headers/os/support/BufferIO.h rev 19972 10 * /trunk/src/kits/support/BufferIO.cpp rev 20510 11 */ 12 13/*! 14 \file BufferIO.h 15 \brief Provides the BBufferIO class. 16*/ 17 18/*! 19 \class BBufferIO 20 \ingroup support 21 \ingroup libbe 22 \brief A buffered adapter for BPositionIO objects. 23 \author Stefano Ceccherini \<burton666@freemail.it\> 24 25 This class differs from other classes derived from BPositionIO in a sense that 26 it does not actually provide an actual entity to be read or written to, but 27 rather acts like a "frontend" to a stream. This class especially comes in 28 handy when working with files that are constantly written and rewritten and 29 where you want do this writing buffered so that the hard disk or the network 30 will not have to be accessed so frequently. 31 32 This class works as follows. After constructing a BBufferIO object that you 33 want to be buffered, you can create this object. The constructor takes a 34 \a stream parameter that points to the object to be buffered. You then use 35 this object as a proxy to the resource you want to read of or write to. As 36 soon as you use ReadAt(), the buffer will be initialised to the contents 37 of the original stream, 38 and subsequent calls to the positions within the buffer will not be 39 routed to the original stream. In the same way WriteAt() will change 40 the data in the buffer, but not in the actual stream. In order to flush 41 the changes to the original stream, use the Flush() method. Deleting 42 the object when you are done with it will also flush the stream and 43 update the original stream. 44 45 \note This class is not meant to be used in cases where the 46 original stream requires to be in a consistent state. Neither should this 47 class be used as a way to perform 'atomic' writes, because the object 48 might need to do partial writes if it needs to 'move' the buffer. This 49 happens for instance if the original stream is bigger than the buffer. 50*/ 51 52/*! 53 \fn BBufferIO::BBufferIO(BPositionIO *stream, size_t bufferSize, bool ownsStream) 54 \brief Initialize a BBufferIO object. 55 56 The constructor will create a buffer of the given size 57 and associate the object with the given BPositionIO stream. 58 59 \param stream A pointer to a BPositionIO object. 60 \param bufferSize The size of the buffer that the object will allocate and 61 use. 62 \param ownsStream Specifies if the object will delete the stream on 63 destruction. 64*/ 65 66/*! 67 \fn BBufferIO::~BBufferIO() 68 \brief Free the resources allocated by the object 69 70 Flush pending changes to the stream and free the allocated memory. 71 If the \c owns_stream property is \c true, the destructor also 72 deletes the stream associated with the BBufferIO object. 73*/ 74 75 76/*! 77 \fn ssize_t BBufferIO::ReadAt(off_t pos, void *buffer, size_t size) 78 \brief Read the specified amount of bytes at the given position. 79 \param pos The offset into the stream where to read. 80 \param buffer A pointer to a buffer where to copy the read data. 81 \param size The amount of bytes to read. 82 \return The amount of bytes actually read, or an error code. 83 \retval B_NO_INIT The object is not associated with a valid BPositionIO 84 stream. 85 \retval B_BAD_VALUE The \c buffer parameter is not valid. 86*/ 87 88/*! 89 \fn ssize_t BBufferIO::WriteAt(off_t pos, const void *buffer, size_t size) 90 \brief Write the specified amount of bytes at the given position. 91 \param pos The offset into the stream where to write. 92 \param buffer A pointer to a buffer which contains the data to write. 93 \param size The amount of bytes to write. 94 \return The amount of bytes actually written, or an error code. 95 \retval B_NO_INIT The object is not associated with a valid BPositionIO 96 stream. 97 \retval B_BAD_VALUE The \c buffer parameter is not valid. 98*/ 99 100/*! 101 \fn off_t BBufferIO::Seek(off_t position, uint32 seekMode) 102 \brief Set the position in the stream. 103 104 Set the position in the stream where the Read() and Write() functions 105 (inherited from BPositionIO) begin reading and writing. 106 How the position argument is understood depends on the seek_mode flag. 107 108 \param position The position where you want to seek. 109 \param seekMode Can have three values: 110 - \c SEEK_SET. The position passed is an offset from the beginning of the 111 stream; in other words, the current position is set to position. 112 For this mode, position should be a positive value. 113 - \c SEEK_CUR. The position argument is an offset from the current position; 114 the value of the argument is added to the current position. 115 - \c SEEK_END. The position argument is an offset from the end of the 116 stream. In this mode the position argument should be negative (or zero). 117 118 \return The current position as an offset in bytes from the beginning of 119 the stream. 120 121 \retval B_NO_INIT The object is not associated with a valid BPositionIO 122 stream. 123*/ 124 125/*! 126 \fn off_t BBufferIO::Position() const 127 \brief Return the current position in the stream. 128 \return The current position as an offset in bytes 129 from the beginning of the stream. 130 \retval B_NO_INIT The object is not associated with a valid BPositionIO 131 stream. 132*/ 133 134/*! 135 \fn status_t BBufferIO::SetSize(off_t size) 136 \brief Call the SetSize() function of the assigned BPositionIO stream. 137 \param size The new size of the BPositionIO object. 138 \retval B_OK The stream is resized. 139 \retval B_NO_INIT The object is not associated with a valid BPositionIO 140 stream. 141*/ 142 143/*! 144 \fn status_t BBufferIO::Flush() 145 \brief Write pending modifications to the stream. 146 \return The amount of bytes written, or if it failed it will return an error 147 code. 148*/ 149 150 151/*! 152 \fn BPositionIO *BBufferIO::Stream() const 153 \brief Return a pointer to the stream specified on construction. 154 \return A pointer to the BPositionIO stream specified on construction. 155*/ 156 157 158/*! 159 \fn size_t BBufferIO::BufferSize() const 160 \brief Return the size of the internal buffer. 161 \return The size of the buffer allocated by the object. 162*/ 163 164/*! 165 \fn bool BBufferIO::OwnsStream() const 166 \brief Tell if the BBufferIO object "owns" the specified stream. 167 \retval true The object "owns" the stream and will destroy it upon 168 destruction. 169 \retval false The object does not own the stream. 170 \see SetOwnsStream() 171*/ 172 173/*! 174 \fn void BBufferIO::SetOwnsStream(bool owns_stream) 175 \brief Set the \c owns_stream property of the object. 176 \param owns_stream If you pass \c true, the object will delete the stream 177 upon destruction, if you pass \c false it will not. 178*/ 179 180 181/*! 182 \fn void BBufferIO::PrintToStream() const 183 \brief Print the object to stdout. 184*/ 185