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: attempting 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
48typedef GSeekableIface GSeekableInterface;
49G_DEFINE_INTERFACE (GSeekable, g_seekable, G_TYPE_OBJECT)
50
51static void
52g_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 **/
64goffset
65g_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 **/
84gboolean
85g_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 **/
124gboolean
125g_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 **/
149gboolean
150g_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 * previously 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 **/
183gboolean
184g_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}
197

source code of gtk/subprojects/glib/gio/gseekable.c