gio/gmemoryoutputstream.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 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, write to the
  17  * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  18  * Boston, MA 02111-1307, USA.
  19  *
  20  * Authors:
  21  *   Christian Kellner <gicmo@gnome.org>
  22  *   Krzysztof Kosiński <tweenk.pl@gmail.com>
  23  */
  24
  25 #include "config.h"
  26 #include "gmemoryoutputstream.h"
  27 #include "goutputstream.h"
  28 #include "gpollableoutputstream.h"
  29 #include "gseekable.h"
  30 #include "gsimpleasyncresult.h"
  31 #include "gioerror.h"
  32 #include "string.h"
  33 #include "glibintl.h"
  34
  35
  36 /**
  37  * SECTION:gmemoryoutputstream
  38  * @short_description: Streaming output operations on memory chunks
  39  * @include: gio/gio.h
  40  * @see_also: #GMemoryInputStream
  41  *
  42  * #GMemoryOutputStream is a class for using arbitrary
  43  * memory chunks as output for GIO streaming output operations.
  44  *
  45  * As of GLib 2.34, #GMemoryOutputStream implements
  46  * #GPollableOutputStream.
  47  */
  48
  49 #define MIN_ARRAY_SIZE  16
  50
  51 enum {
  52   PROP_0,
  53   PROP_DATA,
  54   PROP_SIZE,
  55   PROP_DATA_SIZE,
  56   PROP_REALLOC_FUNCTION,
  57   PROP_DESTROY_FUNCTION
  58 };
  59
  60 struct _GMemoryOutputStreamPrivate {
  61
  62   gpointer       data; /* Write buffer */
  63   gsize          len; /* Current length of the data buffer. Can change with resizing. */
  64   gsize          valid_len; /* The part of data that has been written to */
  65   gsize          pos; /* Current position in the stream. Distinct from valid_len,
  66                          because the stream is seekable. */
  67
  68   GReallocFunc   realloc_fn;
  69   GDestroyNotify destroy;
  70 };
  71
  72 static void     g_memory_output_stream_set_property (GObject      *object,
  73                                                      guint         prop_id,
  74                                                      const GValue *value,
  75                                                      GParamSpec   *pspec);
  76 static void     g_memory_output_stream_get_property (GObject      *object,
  77                                                      guint         prop_id,
  78                                                      GValue       *value,
  79                                                      GParamSpec   *pspec);
  80 static void     g_memory_output_stream_finalize     (GObject      *object);
  81
  82 static gssize   g_memory_output_stream_write       (GOutputStream *stream,
  83                                                     const void    *buffer,
  84                                                     gsize          count,
  85                                                     GCancellable  *cancellable,
  86                                                     GError       **error);
  87
  88 static gboolean g_memory_output_stream_close       (GOutputStream  *stream,
  89                                                     GCancellable   *cancellable,
  90                                                     GError        **error);
  91
  92 static void     g_memory_output_stream_close_async  (GOutputStream        *stream,
  93                                                      int                   io_priority,
  94                                                      GCancellable         *cancellable,
  95                                                      GAsyncReadyCallback   callback,
  96                                                      gpointer              data);
  97 static gboolean g_memory_output_stream_close_finish (GOutputStream        *stream,
  98                                                      GAsyncResult         *result,
  99                                                      GError              **error);
 100
 101 static void     g_memory_output_stream_seekable_iface_init (GSeekableIface  *iface);
 102 static goffset  g_memory_output_stream_tell                (GSeekable       *seekable);
 103 static gboolean g_memory_output_stream_can_seek            (GSeekable       *seekable);
 104 static gboolean g_memory_output_stream_seek                (GSeekable       *seekable,
 105                                                            goffset          offset,
 106                                                            GSeekType        type,
 107                                                            GCancellable    *cancellable,
 108                                                            GError         **error);
 109 static gboolean g_memory_output_stream_can_truncate        (GSeekable       *seekable);
 110 static gboolean g_memory_output_stream_truncate            (GSeekable       *seekable,
 111                                                            goffset          offset,
 112                                                            GCancellable    *cancellable,
 113                                                            GError         **error);
 114
 115 static gboolean g_memory_output_stream_is_writable       (GPollableOutputStream *stream);
 116 static GSource *g_memory_output_stream_create_source     (GPollableOutputStream *stream,
 117                                                           GCancellable          *cancellable);
 118
 119 static void g_memory_output_stream_pollable_iface_init (GPollableOutputStreamInterface *iface);
 120
 121 G_DEFINE_TYPE_WITH_CODE (GMemoryOutputStream, g_memory_output_stream, G_TYPE_OUTPUT_STREAM,
 122                          G_IMPLEMENT_INTERFACE (G_TYPE_SEEKABLE,
 123                                                 g_memory_output_stream_seekable_iface_init);
 124                          G_IMPLEMENT_INTERFACE (G_TYPE_POLLABLE_OUTPUT_STREAM,
 125                                                 g_memory_output_stream_pollable_iface_init))
 126
 127
 128 static void
 129 g_memory_output_stream_class_init (GMemoryOutputStreamClass *klass)
 130 {
 131   GOutputStreamClass *ostream_class;
 132   GObjectClass *gobject_class;
 133
 134   g_type_class_add_private (klass, sizeof (GMemoryOutputStreamPrivate));
 135
 136   gobject_class = G_OBJECT_CLASS (klass);
 137   gobject_class->set_property = g_memory_output_stream_set_property;
 138   gobject_class->get_property = g_memory_output_stream_get_property;
 139   gobject_class->finalize     = g_memory_output_stream_finalize;
 140
 141   ostream_class = G_OUTPUT_STREAM_CLASS (klass);
 142
 143   ostream_class->write_fn = g_memory_output_stream_write;
 144   ostream_class->close_fn = g_memory_output_stream_close;
 145   ostream_class->close_async  = g_memory_output_stream_close_async;
 146   ostream_class->close_finish = g_memory_output_stream_close_finish;
 147
 148   /**
 149    * GMemoryOutputStream:data:
 150    *
 151    * Pointer to buffer where data will be written.
 152    *
 153    * Since: 2.24
 154    **/
 155   g_object_class_install_property (gobject_class,
 156                                    PROP_DATA,
 157                                    g_param_spec_pointer ("data",
 158                                                          P_("Data Buffer"),
 159                                                          P_("Pointer to buffer where data will be written."),
 160                                                          G_PARAM_READWRITE | G_PARAM_CONSTRUCT_ONLY |
 161                                                          G_PARAM_STATIC_STRINGS));
 162
 163   /**
 164    * GMemoryOutputStream:size:
 165    *
 166    * Current size of the data buffer.
 167    *
 168    * Since: 2.24
 169    **/
 170   g_object_class_install_property (gobject_class,
 171                                    PROP_SIZE,
 172                                    g_param_spec_ulong ("size",
 173                                                        P_("Data Buffer Size"),
 174                                                        P_("Current size of the data buffer."),
 175                                                        0, G_MAXULONG, 0,
 176                                                        G_PARAM_READWRITE | G_PARAM_CONSTRUCT_ONLY |
 177                                                        G_PARAM_STATIC_STRINGS));
 178
 179   /**
 180    * GMemoryOutputStream:data-size:
 181    *
 182    * Size of data written to the buffer.
 183    *
 184    * Since: 2.24
 185    **/
 186   g_object_class_install_property (gobject_class,
 187                                    PROP_DATA_SIZE,
 188                                    g_param_spec_ulong ("data-size",
 189                                                        P_("Data Size"),
 190                                                        P_("Size of data written to the buffer."),
 191                                                        0, G_MAXULONG, 0,
 192                                                        G_PARAM_READABLE |
 193                                                        G_PARAM_STATIC_STRINGS));
 194
 195   /**
 196    * GMemoryOutputStream:realloc-function: (skip)
 197    *
 198    * Function with realloc semantics called to enlarge the buffer.
 199    *
 200    * Since: 2.24
 201    **/
 202   g_object_class_install_property (gobject_class,
 203                                    PROP_REALLOC_FUNCTION,
 204                                    g_param_spec_pointer ("realloc-function",
 205                                                          P_("Memory Reallocation Function"),
 206                                                          P_("Function with realloc semantics called to enlarge the buffer."),
 207                                                          G_PARAM_READWRITE | G_PARAM_CONSTRUCT_ONLY |
 208                                                          G_PARAM_STATIC_STRINGS));
 209
 210   /**
 211    * GMemoryOutputStream:destroy-function: (skip)
 212    *
 213    * Function called with the buffer as argument when the stream is destroyed.
 214    *
 215    * Since: 2.24
 216    **/
 217   g_object_class_install_property (gobject_class,
 218                                    PROP_DESTROY_FUNCTION,
 219                                    g_param_spec_pointer ("destroy-function",
 220                                                          P_("Destroy Notification Function"),
 221                                                          P_("Function called with the buffer as argument when the stream is destroyed."),
 222                                                          G_PARAM_READWRITE | G_PARAM_CONSTRUCT_ONLY |
 223                                                          G_PARAM_STATIC_STRINGS));
 224 }
 225
 226 static void
 227 g_memory_output_stream_pollable_iface_init (GPollableOutputStreamInterface *iface)
 228 {
 229   iface->is_writable = g_memory_output_stream_is_writable;
 230   iface->create_source = g_memory_output_stream_create_source;
 231 }
 232
 233 static void
 234 g_memory_output_stream_set_property (GObject      *object,
 235                                      guint         prop_id,
 236                                      const GValue *value,
 237                                      GParamSpec   *pspec)
 238 {
 239   GMemoryOutputStream        *stream;
 240   GMemoryOutputStreamPrivate *priv;
 241
 242   stream = G_MEMORY_OUTPUT_STREAM (object);
 243   priv = stream->priv;
 244
 245   switch (prop_id)
 246     {
 247     case PROP_DATA:
 248       priv->data = g_value_get_pointer (value);
 249       break;
 250     case PROP_SIZE:
 251       priv->len = g_value_get_ulong (value);
 252       break;
 253     case PROP_REALLOC_FUNCTION:
 254       priv->realloc_fn = g_value_get_pointer (value);
 255       break;
 256     case PROP_DESTROY_FUNCTION:
 257       priv->destroy = g_value_get_pointer (value);
 258       break;
 259     default:
 260       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
 261       break;
 262     }
 263 }
 264
 265 static void
 266 g_memory_output_stream_get_property (GObject      *object,
 267                                      guint         prop_id,
 268                                      GValue       *value,
 269                                      GParamSpec   *pspec)
 270 {
 271   GMemoryOutputStream        *stream;
 272   GMemoryOutputStreamPrivate *priv;
 273
 274   stream = G_MEMORY_OUTPUT_STREAM (object);
 275   priv = stream->priv;
 276
 277   switch (prop_id)
 278     {
 279     case PROP_DATA:
 280       g_value_set_pointer (value, priv->data);
 281       break;
 282     case PROP_SIZE:
 283       g_value_set_ulong (value, priv->len);
 284       break;
 285     case PROP_DATA_SIZE:
 286       g_value_set_ulong (value, priv->valid_len);
 287       break;
 288     case PROP_REALLOC_FUNCTION:
 289       g_value_set_pointer (value, priv->realloc_fn);
 290       break;
 291     case PROP_DESTROY_FUNCTION:
 292       g_value_set_pointer (value, priv->destroy);
 293       break;
 294     default:
 295       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
 296       break;
 297     }
 298 }
 299
 300 static void
 301 g_memory_output_stream_finalize (GObject *object)
 302 {
 303   GMemoryOutputStream        *stream;
 304   GMemoryOutputStreamPrivate *priv;
 305
 306   stream = G_MEMORY_OUTPUT_STREAM (object);
 307   priv = stream->priv;
 308
 309   if (priv->destroy)
 310     priv->destroy (priv->data);
 311
 312   G_OBJECT_CLASS (g_memory_output_stream_parent_class)->finalize (object);
 313 }
 314
 315 static void
 316 g_memory_output_stream_seekable_iface_init (GSeekableIface *iface)
 317 {
 318   iface->tell         = g_memory_output_stream_tell;
 319   iface->can_seek     = g_memory_output_stream_can_seek;
 320   iface->seek         = g_memory_output_stream_seek;
 321   iface->can_truncate = g_memory_output_stream_can_truncate;
 322   iface->truncate_fn  = g_memory_output_stream_truncate;
 323 }
 324
 325
 326 static void
 327 g_memory_output_stream_init (GMemoryOutputStream *stream)
 328 {
 329   stream->priv = G_TYPE_INSTANCE_GET_PRIVATE (stream,
 330                                               G_TYPE_MEMORY_OUTPUT_STREAM,
 331                                               GMemoryOutputStreamPrivate);
 332   stream->priv->pos = 0;
 333   stream->priv->valid_len = 0;
 334 }
 335
 336 /**
 337  * g_memory_output_stream_new: (skip)
 338  * @data: (allow-none): pointer to a chunk of memory to use, or %NULL
 339  * @size: the size of @data
 340  * @realloc_function: (allow-none): a function with realloc() semantics (like g_realloc())
 341  *     to be called when @data needs to be grown, or %NULL
 342  * @destroy_function: (allow-none): a function to be called on @data when the stream is
 343  *     finalized, or %NULL
 344  *
 345  * Creates a new #GMemoryOutputStream.
 346  *
 347  * If @data is non-%NULL, the stream  will use that for its internal storage.
 348  * If @realloc_fn is non-%NULL, it will be used for resizing the internal
 349  * storage when necessary. To construct a fixed-size output stream,
 350  * pass %NULL as @realloc_fn.
 351  *
 352  * |[
 353  * /&ast; a stream that can grow &ast;/
 354  * stream = g_memory_output_stream_new (NULL, 0, realloc, free);
 355  *
 356  * /&ast; another stream that can grow &ast;/
 357  * stream2 = g_memory_output_stream_new (NULL, 0, g_realloc, g_free);
 358  *
 359  * /&ast; a fixed-size stream &ast;/
 360  * data = malloc (200);
 361  * stream3 = g_memory_output_stream_new (data, 200, NULL, free);
 362  * ]|
 363  *
 364  * Return value: A newly created #GMemoryOutputStream object.
 365  **/
 366 GOutputStream *
 367 g_memory_output_stream_new (gpointer       data,
 368                             gsize          size,
 369                             GReallocFunc   realloc_function,
 370                             GDestroyNotify destroy_function)
 371 {
 372   GOutputStream *stream;
 373
 374   stream = g_object_new (G_TYPE_MEMORY_OUTPUT_STREAM,
 375                          "data", data,
 376                          "size", size,
 377                          "realloc-function", realloc_function,
 378                          "destroy-function", destroy_function,
 379                          NULL);
 380
 381   return stream;
 382 }
 383
 384 /**
 385  * g_memory_output_stream_get_data:
 386  * @ostream: a #GMemoryOutputStream
 387  *
 388  * Gets any loaded data from the @ostream.
 389  *
 390  * Note that the returned pointer may become invalid on the next
 391  * write or truncate operation on the stream.
 392  *
 393  * Returns: (transfer none): pointer to the stream's data
 394  **/
 395 gpointer
 396 g_memory_output_stream_get_data (GMemoryOutputStream *ostream)
 397 {
 398   g_return_val_if_fail (G_IS_MEMORY_OUTPUT_STREAM (ostream), NULL);
 399
 400   return ostream->priv->data;
 401 }
 402
 403 /**
 404  * g_memory_output_stream_get_size:
 405  * @ostream: a #GMemoryOutputStream
 406  *
 407  * Gets the size of the currently allocated data area (available from
 408  * g_memory_output_stream_get_data()). If the stream isn't
 409  * growable (no realloc was passed to g_memory_output_stream_new()) then
 410  * this is the maximum size of the stream and further writes
 411  * will return %G_IO_ERROR_NO_SPACE.
 412  *
 413  * Note that for growable streams the returned size may become invalid on
 414  * the next write or truncate operation on the stream.
 415  *
 416  * If you want the number of bytes currently written to the stream, use
 417  * g_memory_output_stream_get_data_size().
 418  *
 419  * Returns: the number of bytes allocated for the data buffer
 420  */
 421 gsize
 422 g_memory_output_stream_get_size (GMemoryOutputStream *ostream)
 423 {
 424   g_return_val_if_fail (G_IS_MEMORY_OUTPUT_STREAM (ostream), 0);
 425
 426   return ostream->priv->len;
 427 }
 428
 429 /**
 430  * g_memory_output_stream_get_data_size:
 431  * @ostream: a #GMemoryOutputStream
 432  *
 433  * Returns the number of bytes from the start up
 434  * to including the last byte written in the stream
 435  * that has not been truncated away.
 436  *
 437  * Returns: the number of bytes written to the stream
 438  *
 439  * Since: 2.18
 440  */
 441 gsize
 442 g_memory_output_stream_get_data_size (GMemoryOutputStream *ostream)
 443 {
 444   g_return_val_if_fail (G_IS_MEMORY_OUTPUT_STREAM (ostream), 0);
 445
 446   return ostream->priv->valid_len;
 447 }
 448
 449 /**
 450  * g_memory_output_stream_steal_data:
 451  * @ostream: a #GMemoryOutputStream
 452  *
 453  * Gets any loaded data from the @ostream. Ownership of the data
 454  * is transferred to the caller; when no longer needed it must be
 455  * freed using the free function set in @ostream's
 456  * #GMemoryOutputStream:destroy-function property.
 457  *
 458  * @ostream must be closed before calling this function.
 459  *
 460  * Returns: (transfer full): the stream's data
 461  *
 462  * Since: 2.26
 463  **/
 464 gpointer
 465 g_memory_output_stream_steal_data (GMemoryOutputStream *ostream)
 466 {
 467   gpointer data;
 468
 469   g_return_val_if_fail (G_IS_MEMORY_OUTPUT_STREAM (ostream), NULL);
 470   g_return_val_if_fail (g_output_stream_is_closed (G_OUTPUT_STREAM (ostream)), NULL);
 471
 472   data = ostream->priv->data;
 473   ostream->priv->data = NULL;
 474
 475   return data;
 476 }
 477
 478 static gboolean
 479 array_resize (GMemoryOutputStream  *ostream,
 480               gsize                 size,
 481               gboolean              allow_partial,
 482               GError              **error)
 483 {
 484   GMemoryOutputStreamPrivate *priv;
 485   gpointer data;
 486   gsize len;
 487
 488   priv = ostream->priv;
 489
 490   if (priv->len == size)
 491     return TRUE;
 492
 493   if (!priv->realloc_fn)
 494     {
 495       if (allow_partial &&
 496           priv->pos < priv->len)
 497         return TRUE; /* Short write */
 498
 499       g_set_error_literal (error,
 500                            G_IO_ERROR,
 501                            G_IO_ERROR_NO_SPACE,
 502                            _("Memory output stream not resizable"));
 503       return FALSE;
 504     }
 505
 506   len = priv->len;
 507   data = priv->realloc_fn (priv->data, size);
 508
 509   if (size > 0 && !data)
 510     {
 511       if (allow_partial &&
 512           priv->pos < priv->len)
 513         return TRUE; /* Short write */
 514
 515       g_set_error_literal (error,
 516                            G_IO_ERROR,
 517                            G_IO_ERROR_NO_SPACE,
 518                            _("Failed to resize memory output stream"));
 519       return FALSE;
 520     }
 521
 522   if (size > len)
 523     memset ((guint8 *)data + len, 0, size - len);
 524
 525   priv->data = data;
 526   priv->len = size;
 527
 528   if (priv->len < priv->valid_len)
 529     priv->valid_len = priv->len;
 530
 531   return TRUE;
 532 }
 533
 534 static gint
 535 g_nearest_pow (gint num)
 536 {
 537   gint n = 1;
 538
 539   while (n < num)
 540     n <<= 1;
 541
 542   return n;
 543 }
 544
 545 static gssize
 546 g_memory_output_stream_write (GOutputStream  *stream,
 547                               const void     *buffer,
 548                               gsize           count,
 549                               GCancellable   *cancellable,
 550                               GError        **error)
 551 {
 552   GMemoryOutputStream        *ostream;
 553   GMemoryOutputStreamPrivate *priv;
 554   guint8   *dest;
 555   gsize new_size;
 556
 557   ostream = G_MEMORY_OUTPUT_STREAM (stream);
 558   priv = ostream->priv;
 559
 560   if (count == 0)
 561     return 0;
 562
 563   /* Check for address space overflow, but only if the buffer is resizable.
 564      Otherwise we just do a short write and don't worry. */
 565   if (priv->realloc_fn && priv->pos + count < priv->pos)
 566     goto overflow;
 567
 568   if (priv->pos + count > priv->len)
 569     {
 570       /* At least enought to fit the write, rounded up
 571              for greater than linear growth.
 572          TODO: This wastes a lot of memory at large stream sizes.
 573                Figure out a more rational allocation strategy. */
 574       new_size = g_nearest_pow (priv->pos + count);
 575       /* Check for overflow again. We have only checked if
 576          pos + count > G_MAXSIZE, but it only catches the case of writing
 577          more than 4GiB total on a 32-bit system. There's still the problem
 578          of g_nearest_pow overflowing above 0x7fffffff, so we're
 579          effectively limited to 2GiB. */
 580       if (new_size < priv->len)
 581         goto overflow;
 582
 583       new_size = MAX (new_size, MIN_ARRAY_SIZE);
 584       if (!array_resize (ostream, new_size, TRUE, error))
 585         return -1;
 586     }
 587
 588   /* Make sure we handle short writes if the array_resize
 589      only added part of the required memory */
 590   count = MIN (count, priv->len - priv->pos);
 591
 592   dest = (guint8 *)priv->data + priv->pos;
 593   memcpy (dest, buffer, count);
 594   priv->pos += count;
 595
 596   if (priv->pos > priv->valid_len)
 597     priv->valid_len = priv->pos;
 598
 599   return count;
 600
 601  overflow:
 602   /* Overflow: buffer size would need to be bigger than G_MAXSIZE. */
 603   g_set_error_literal (error,
 604                        G_IO_ERROR,
 605                        G_IO_ERROR_NO_SPACE,
 606                        _("Amount of memory required to process the write is "
 607                          "larger than available address space"));
 608   return -1;
 609 }
 610
 611 static gboolean
 612 g_memory_output_stream_close (GOutputStream  *stream,
 613                               GCancellable   *cancellable,
 614                               GError        **error)
 615 {
 616   return TRUE;
 617 }
 618
 619 static void
 620 g_memory_output_stream_close_async (GOutputStream       *stream,
 621                                     int                  io_priority,
 622                                     GCancellable        *cancellable,
 623                                     GAsyncReadyCallback  callback,
 624                                     gpointer             data)
 625 {
 626   GSimpleAsyncResult *simple;
 627
 628   simple = g_simple_async_result_new (G_OBJECT (stream),
 629                                       callback,
 630                                       data,
 631                                       g_memory_output_stream_close_async);
 632
 633
 634   /* will always return TRUE */
 635   g_memory_output_stream_close (stream, cancellable, NULL);
 636
 637   g_simple_async_result_complete_in_idle (simple);
 638   g_object_unref (simple);
 639 }
 640
 641 static gboolean
 642 g_memory_output_stream_close_finish (GOutputStream  *stream,
 643                                      GAsyncResult   *result,
 644                                      GError        **error)
 645 {
 646   GSimpleAsyncResult *simple;
 647
 648   simple = G_SIMPLE_ASYNC_RESULT (result);
 649
 650   g_warn_if_fail (g_simple_async_result_get_source_tag (simple) ==
 651                   g_memory_output_stream_close_async);
 652
 653   return TRUE;
 654 }
 655
 656 static goffset
 657 g_memory_output_stream_tell (GSeekable *seekable)
 658 {
 659   GMemoryOutputStream *stream;
 660   GMemoryOutputStreamPrivate *priv;
 661
 662   stream = G_MEMORY_OUTPUT_STREAM (seekable);
 663   priv = stream->priv;
 664
 665   return priv->pos;
 666 }
 667
 668 static gboolean
 669 g_memory_output_stream_can_seek (GSeekable *seekable)
 670 {
 671   return TRUE;
 672 }
 673
 674 static gboolean
 675 g_memory_output_stream_seek (GSeekable    *seekable,
 676                             goffset        offset,
 677                             GSeekType      type,
 678                             GCancellable  *cancellable,
 679                             GError       **error)
 680 {
 681   GMemoryOutputStream        *stream;
 682   GMemoryOutputStreamPrivate *priv;
 683   goffset absolute;
 684
 685   stream = G_MEMORY_OUTPUT_STREAM (seekable);
 686   priv = stream->priv;
 687
 688   switch (type)
 689     {
 690     case G_SEEK_CUR:
 691       absolute = priv->pos + offset;
 692       break;
 693
 694     case G_SEEK_SET:
 695       absolute = offset;
 696       break;
 697
 698     case G_SEEK_END:
 699       absolute = priv->len + offset;
 700       break;
 701
 702     default:
 703       g_set_error_literal (error,
 704                            G_IO_ERROR,
 705                            G_IO_ERROR_INVALID_ARGUMENT,
 706                            _("Invalid GSeekType supplied"));
 707
 708       return FALSE;
 709     }
 710
 711   if (absolute < 0)
 712     {
 713       g_set_error_literal (error,
 714                            G_IO_ERROR,
 715                            G_IO_ERROR_INVALID_ARGUMENT,
 716                            _("Requested seek before the beginning of the stream"));
 717       return FALSE;
 718     }
 719
 720   if (absolute > priv->len)
 721     {
 722       g_set_error_literal (error,
 723                            G_IO_ERROR,
 724                            G_IO_ERROR_INVALID_ARGUMENT,
 725                            _("Requested seek beyond the end of the stream"));
 726       return FALSE;
 727     }
 728
 729   priv->pos = absolute;
 730
 731   return TRUE;
 732 }
 733
 734 static gboolean
 735 g_memory_output_stream_can_truncate (GSeekable *seekable)
 736 {
 737   GMemoryOutputStream *ostream;
 738   GMemoryOutputStreamPrivate *priv;
 739
 740   ostream = G_MEMORY_OUTPUT_STREAM (seekable);
 741   priv = ostream->priv;
 742
 743   return priv->realloc_fn != NULL;
 744 }
 745
 746 static gboolean
 747 g_memory_output_stream_truncate (GSeekable     *seekable,
 748                                  goffset        offset,
 749                                  GCancellable  *cancellable,
 750                                  GError       **error)
 751 {
 752   GMemoryOutputStream *ostream = G_MEMORY_OUTPUT_STREAM (seekable);
 753
 754   if (!array_resize (ostream, offset, FALSE, error))
 755     return FALSE;
 756
 757   return TRUE;
 758 }
 759
 760 static gboolean
 761 g_memory_output_stream_is_writable (GPollableOutputStream *stream)
 762 {
 763   return TRUE;
 764 }
 765
 766 static GSource *
 767 g_memory_output_stream_create_source (GPollableOutputStream *stream,
 768                                       GCancellable          *cancellable)
 769 {
 770   GSource *base_source, *pollable_source;
 771
 772   base_source = g_timeout_source_new (0);
 773   pollable_source = g_pollable_source_new_full (stream, base_source,
 774                                                 cancellable);
 775   g_source_unref (base_source);
 776
 777   return pollable_source;
 778 }