gio/gseekable.c

   1 /* GIO - GLib Input, Output and Streaming Library
   2  *
   3  * Copyright (C) 2006-2007 Red Hat, Inc.
   4  *
   5  * This library is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU Lesser General Public
   7  * License as published by the Free Software Foundation; either
   8  * version 2.1 of the License, or (at your option) any later version.
   9  *
  10  * This library is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * Lesser General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General
  16  * Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
  17  *
  18  * Author: Alexander Larsson <alexl@redhat.com>
  19  */
  20
  21 #include "config.h"
  22 #include "gseekable.h"
  23 #include "glibintl.h"
  24
  25
  26 /**
  27  * SECTION:gseekable
  28  * @short_description: Stream seeking interface
  29  * @include: gio/gio.h
  30  * @see_also: #GInputStream, #GOutputStream
  31  *
  32  * #GSeekable is implemented by streams (implementations of
  33  * #GInputStream or #GOutputStream) that support seeking.
  34  *
  35  * Seekable streams largely fall into two categories: resizable and
  36  * fixed-size.
  37  *
  38  * #GSeekable on fixed-sized streams is approximately the same as POSIX
  39  * lseek() on a block device (for example: attmepting to seek past the
  40  * end of the device is an error).  Fixed streams typically cannot be
  41  * truncated.
  42  *
  43  * #GSeekable on resizable streams is approximately the same as POSIX
  44  * lseek() on a normal file.  Seeking past the end and writing data will
  45  * usually cause the stream to resize by introducing zero bytes.
  46  **/
  47
  48 typedef GSeekableIface GSeekableInterface;
  49 G_DEFINE_INTERFACE (GSeekable, g_seekable, G_TYPE_OBJECT)
  50
  51 static void
  52 g_seekable_default_init (GSeekableInterface *iface)
  53 {
  54 }
  55
  56 /**
  57  * g_seekable_tell:
  58  * @seekable: a #GSeekable.
  59  *
  60  * Tells the current position within the stream.
  61  *
  62  * Returns: the offset from the beginning of the buffer.
  63  **/
  64 goffset
  65 g_seekable_tell (GSeekable *seekable)
  66 {
  67   GSeekableIface *iface;
  68
  69   g_return_val_if_fail (G_IS_SEEKABLE (seekable), 0);
  70
  71   iface = G_SEEKABLE_GET_IFACE (seekable);
  72
  73   return (* iface->tell) (seekable);
  74 }
  75
  76 /**
  77  * g_seekable_can_seek:
  78  * @seekable: a #GSeekable.
  79  *
  80  * Tests if the stream supports the #GSeekableIface.
  81  *
  82  * Returns: %TRUE if @seekable can be seeked. %FALSE otherwise.
  83  **/
  84 gboolean
  85 g_seekable_can_seek (GSeekable *seekable)
  86 {
  87   GSeekableIface *iface;
  88
  89   g_return_val_if_fail (G_IS_SEEKABLE (seekable), FALSE);
  90
  91   iface = G_SEEKABLE_GET_IFACE (seekable);
  92
  93   return (* iface->can_seek) (seekable);
  94 }
  95
  96 /**
  97  * g_seekable_seek:
  98  * @seekable: a #GSeekable.
  99  * @offset: a #goffset.
 100  * @type: a #GSeekType.
 101  * @cancellable: (nullable): optional #GCancellable object, %NULL to ignore.
 102  * @error: a #GError location to store the error occurring, or %NULL to
 103  * ignore.
 104  *
 105  * Seeks in the stream by the given @offset, modified by @type.
 106  *
 107  * Attempting to seek past the end of the stream will have different
 108  * results depending on if the stream is fixed-sized or resizable.  If
 109  * the stream is resizable then seeking past the end and then writing
 110  * will result in zeros filling the empty space.  Seeking past the end
 111  * of a resizable stream and reading will result in EOF.  Seeking past
 112  * the end of a fixed-sized stream will fail.
 113  *
 114  * Any operation that would result in a negative offset will fail.
 115  *
 116  * If @cancellable is not %NULL, then the operation can be cancelled by
 117  * triggering the cancellable object from another thread. If the operation
 118  * was cancelled, the error %G_IO_ERROR_CANCELLED will be returned.
 119  *
 120  * Returns: %TRUE if successful. If an error
 121  *     has occurred, this function will return %FALSE and set @error
 122  *     appropriately if present.
 123  **/
 124 gboolean
 125 g_seekable_seek (GSeekable     *seekable,
 126                  goffset        offset,
 127                  GSeekType      type,
 128                  GCancellable  *cancellable,
 129                  GError       **error)
 130 {
 131   GSeekableIface *iface;
 132
 133   g_return_val_if_fail (G_IS_SEEKABLE (seekable), FALSE);
 134
 135   iface = G_SEEKABLE_GET_IFACE (seekable);
 136
 137   return (* iface->seek) (seekable, offset, type, cancellable, error);
 138 }
 139
 140 /**
 141  * g_seekable_can_truncate:
 142  * @seekable: a #GSeekable.
 143  *
 144  * Tests if the length of the stream can be adjusted with
 145  * g_seekable_truncate().
 146  *
 147  * Returns: %TRUE if the stream can be truncated, %FALSE otherwise.
 148  **/
 149 gboolean
 150 g_seekable_can_truncate (GSeekable *seekable)
 151 {
 152   GSeekableIface *iface;
 153
 154   g_return_val_if_fail (G_IS_SEEKABLE (seekable), FALSE);
 155
 156   iface = G_SEEKABLE_GET_IFACE (seekable);
 157
 158   return (* iface->can_truncate) (seekable);
 159 }
 160
 161 /**
 162  * g_seekable_truncate: (virtual truncate_fn)
 163  * @seekable: a #GSeekable.
 164  * @offset: new length for @seekable, in bytes.
 165  * @cancellable: (nullable): optional #GCancellable object, %NULL to ignore.
 166  * @error: a #GError location to store the error occurring, or %NULL to
 167  * ignore.
 168  *
 169  * Sets the length of the stream to @offset. If the stream was previously
 170  * larger than @offset, the extra data is discarded. If the stream was
 171  * previouly shorter than @offset, it is extended with NUL ('\0') bytes.
 172  *
 173  * If @cancellable is not %NULL, then the operation can be cancelled by
 174  * triggering the cancellable object from another thread. If the operation
 175  * was cancelled, the error %G_IO_ERROR_CANCELLED will be returned. If an
 176  * operation was partially finished when the operation was cancelled the
 177  * partial result will be returned, without an error.
 178  *
 179  * Returns: %TRUE if successful. If an error
 180  *     has occurred, this function will return %FALSE and set @error
 181  *     appropriately if present.
 182  **/
 183 gboolean
 184 g_seekable_truncate (GSeekable     *seekable,
 185                      goffset        offset,
 186                      GCancellable  *cancellable,
 187                      GError       **error)
 188 {
 189   GSeekableIface *iface;
 190
 191   g_return_val_if_fail (G_IS_SEEKABLE (seekable), FALSE);
 192
 193   iface = G_SEEKABLE_GET_IFACE (seekable);
 194
 195   return (* iface->truncate_fn) (seekable, offset, cancellable, error);
 196 }