/* GIO - GLib Input, Output and Streaming Library

 * 

 * Copyright (C) 2006-2007 Red Hat, Inc.

 *

 * This library is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Lesser General Public

 * License as published by the Free Software Foundation; either

 * version 2.1 of the License, or (at your option) any later version.

 *

 * This library is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General

 * Public License along with this library; if not, see <http://www.gnu.org/licenses/>.

 *

 * Authors:

 *   Christian Kellner <gicmo@gnome.org>

 *   Krzysztof Kosiński <tweenk.pl@gmail.com>

 */

#include "config.h"

#include "gmemoryoutputstream.h"

#include "goutputstream.h"

#include "gpollableoutputstream.h"

#include "gseekable.h"

#include "gtask.h"

#include "gioerror.h"

#include "string.h"

#include "glibintl.h"

/**

 * SECTION:gmemoryoutputstream

 * @short_description: Streaming output operations on memory chunks

 * @include: gio/gio.h

 * @see_also: #GMemoryInputStream

 *

 * #GMemoryOutputStream is a class for using arbitrary

 * memory chunks as output for GIO streaming output operations.

 *

 * As of GLib 2.34, #GMemoryOutputStream trivially implements

 * #GPollableOutputStream: it always polls as ready.

 */

#define MIN_ARRAY_SIZE  16

enum {

  PROP_0,

  PROP_DATA,

  PROP_SIZE,

  PROP_DATA_SIZE,

  PROP_REALLOC_FUNCTION,

  PROP_DESTROY_FUNCTION

};

struct _GMemoryOutputStreamPrivate

{

  gpointer       data; /* Write buffer */

  gsize          len; /* Current length of the data buffer. Can change with resizing. */

  gsize          valid_len; /* The part of data that has been written to */

  gsize          pos; /* Current position in the stream. Distinct from valid_len,

                         because the stream is seekable. */

  GReallocFunc   realloc_fn;

  GDestroyNotify destroy;

};

static void     g_memory_output_stream_set_property (GObject      *object,

                                                     guint         prop_id,

                                                     const GValue *value,

                                                     GParamSpec   *pspec);

static void     g_memory_output_stream_get_property (GObject      *object,

                                                     guint         prop_id,

                                                     GValue       *value,

                                                     GParamSpec   *pspec);

static void     g_memory_output_stream_finalize     (GObject      *object);

static gssize   g_memory_output_stream_write       (GOutputStream *stream,

                                                    const void    *buffer,

                                                    gsize          count,

                                                    GCancellable  *cancellable,

                                                    GError       **error);

static gboolean g_memory_output_stream_close       (GOutputStream  *stream,

                                                    GCancellable   *cancellable,

                                                    GError        **error);

static void     g_memory_output_stream_close_async  (GOutputStream        *stream,

                                                     int                   io_priority,

                                                     GCancellable         *cancellable,

                                                     GAsyncReadyCallback   callback,

                                                     gpointer              data);

static gboolean g_memory_output_stream_close_finish (GOutputStream        *stream,

                                                     GAsyncResult         *result,

                                                     GError              **error);

static void     g_memory_output_stream_seekable_iface_init (GSeekableIface  *iface);

static goffset  g_memory_output_stream_tell                (GSeekable       *seekable);

static gboolean g_memory_output_stream_can_seek            (GSeekable       *seekable);

static gboolean g_memory_output_stream_seek                (GSeekable       *seekable,

                                                           goffset          offset,

                                                           GSeekType        type,

                                                           GCancellable    *cancellable,

                                                           GError         **error);

static gboolean g_memory_output_stream_can_truncate        (GSeekable       *seekable);

static gboolean g_memory_output_stream_truncate            (GSeekable       *seekable,

                                                           goffset          offset,

                                                           GCancellable    *cancellable,

                                                           GError         **error);

static gboolean g_memory_output_stream_is_writable       (GPollableOutputStream *stream);

static GSource *g_memory_output_stream_create_source     (GPollableOutputStream *stream,

                                                          GCancellable          *cancellable);

static void g_memory_output_stream_pollable_iface_init (GPollableOutputStreamInterface *iface);

G_DEFINE_TYPE_WITH_CODE (GMemoryOutputStream, g_memory_output_stream, G_TYPE_OUTPUT_STREAM,

                         G_ADD_PRIVATE (GMemoryOutputStream)

                         G_IMPLEMENT_INTERFACE (G_TYPE_SEEKABLE,

                                                g_memory_output_stream_seekable_iface_init);

                         G_IMPLEMENT_INTERFACE (G_TYPE_POLLABLE_OUTPUT_STREAM,

                                                g_memory_output_stream_pollable_iface_init))

static void

g_memory_output_stream_class_init (GMemoryOutputStreamClass *klass)

{

  GOutputStreamClass *ostream_class;

  GObjectClass *gobject_class;

  gobject_class = G_OBJECT_CLASS (klass);

  gobject_class->set_property = g_memory_output_stream_set_property;

  gobject_class->get_property = g_memory_output_stream_get_property;

  gobject_class->finalize     = g_memory_output_stream_finalize;

  ostream_class = G_OUTPUT_STREAM_CLASS (klass);

  ostream_class->write_fn = g_memory_output_stream_write;

  ostream_class->close_fn = g_memory_output_stream_close;

  ostream_class->close_async  = g_memory_output_stream_close_async;

  ostream_class->close_finish = g_memory_output_stream_close_finish;

  /**

   * GMemoryOutputStream:data:

   *

   * Pointer to buffer where data will be written.

   *

   * Since: 2.24

   **/

  g_object_class_install_property (gobject_class,

                                   PROP_DATA,

                                   g_param_spec_pointer ("data",

                                                         P_("Data Buffer"),

                                                         P_("Pointer to buffer where data will be written."),

                                                         G_PARAM_READWRITE | G_PARAM_CONSTRUCT_ONLY |

                                                         G_PARAM_STATIC_STRINGS));

  /**

   * GMemoryOutputStream:size:

   *

   * Current size of the data buffer.

   *

   * Since: 2.24

   **/

  g_object_class_install_property (gobject_class,

                                   PROP_SIZE,

                                   g_param_spec_ulong ("size",

                                                       P_("Data Buffer Size"),

                                                       P_("Current size of the data buffer."),

                                                       0, G_MAXULONG, 0,

                                                       G_PARAM_READWRITE | G_PARAM_CONSTRUCT_ONLY |

                                                       G_PARAM_STATIC_STRINGS));

  /**

   * GMemoryOutputStream:data-size:

   *

   * Size of data written to the buffer.

   *

   * Since: 2.24

   **/

  g_object_class_install_property (gobject_class,

                                   PROP_DATA_SIZE,

                                   g_param_spec_ulong ("data-size",

                                                       P_("Data Size"),

                                                       P_("Size of data written to the buffer."),

                                                       0, G_MAXULONG, 0,

                                                       G_PARAM_READABLE |

                                                       G_PARAM_STATIC_STRINGS));

  /**

   * GMemoryOutputStream:realloc-function: (skip)

   *

   * Function with realloc semantics called to enlarge the buffer.

   *

   * Since: 2.24

   **/

  g_object_class_install_property (gobject_class,

                                   PROP_REALLOC_FUNCTION,

                                   g_param_spec_pointer ("realloc-function",

                                                         P_("Memory Reallocation Function"),

                                                         P_("Function with realloc semantics called to enlarge the buffer."),

                                                         G_PARAM_READWRITE | G_PARAM_CONSTRUCT_ONLY |

                                                         G_PARAM_STATIC_STRINGS));

  /**

   * GMemoryOutputStream:destroy-function: (skip)

   *

   * Function called with the buffer as argument when the stream is destroyed.

   *

   * Since: 2.24

   **/

  g_object_class_install_property (gobject_class,

                                   PROP_DESTROY_FUNCTION,

                                   g_param_spec_pointer ("destroy-function",

                                                         P_("Destroy Notification Function"),

                                                         P_("Function called with the buffer as argument when the stream is destroyed."),

                                                         G_PARAM_READWRITE | G_PARAM_CONSTRUCT_ONLY |

                                                         G_PARAM_STATIC_STRINGS));

}

static void

g_memory_output_stream_pollable_iface_init (GPollableOutputStreamInterface *iface)

{

  iface->is_writable = g_memory_output_stream_is_writable;

  iface->create_source = g_memory_output_stream_create_source;

}

static void

g_memory_output_stream_set_property (GObject      *object,

                                     guint         prop_id,

                                     const GValue *value,

                                     GParamSpec   *pspec)

{

  GMemoryOutputStream        *stream;

  GMemoryOutputStreamPrivate *priv;

  stream = G_MEMORY_OUTPUT_STREAM (object);

  priv = stream->priv;

  switch (prop_id)

    {

    case PROP_DATA:

      priv->data = g_value_get_pointer (value);

      break;

    case PROP_SIZE:

      priv->len = g_value_get_ulong (value);

      break;

    case PROP_REALLOC_FUNCTION:

      priv->realloc_fn = g_value_get_pointer (value);

      break;

    case PROP_DESTROY_FUNCTION:

      priv->destroy = g_value_get_pointer (value);

      break;

    default:

      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);

      break;

    }

}

static void

g_memory_output_stream_get_property (GObject      *object,

                                     guint         prop_id,

                                     GValue       *value,

                                     GParamSpec   *pspec)

{

  GMemoryOutputStream        *stream;

  GMemoryOutputStreamPrivate *priv;

  stream = G_MEMORY_OUTPUT_STREAM (object);

  priv = stream->priv;

  switch (prop_id)

    {

    case PROP_DATA:

      g_value_set_pointer (value, priv->data);

      break;

    case PROP_SIZE:

      g_value_set_ulong (value, priv->len);

      break;

    case PROP_DATA_SIZE:

      g_value_set_ulong (value, priv->valid_len);

      break;

    case PROP_REALLOC_FUNCTION:

      g_value_set_pointer (value, priv->realloc_fn);

      break;

    case PROP_DESTROY_FUNCTION:

      g_value_set_pointer (value, priv->destroy);

      break;

    default:

      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);

      break;

    }

}

static void

g_memory_output_stream_finalize (GObject *object)

{

  GMemoryOutputStream        *stream;

  GMemoryOutputStreamPrivate *priv;

  stream = G_MEMORY_OUTPUT_STREAM (object);

  priv = stream->priv;

  if (priv->destroy)

    priv->destroy (priv->data);

  G_OBJECT_CLASS (g_memory_output_stream_parent_class)->finalize (object);

}

static void

g_memory_output_stream_seekable_iface_init (GSeekableIface *iface)

{

  iface->tell         = g_memory_output_stream_tell;

  iface->can_seek     = g_memory_output_stream_can_seek;

  iface->seek         = g_memory_output_stream_seek;

  iface->can_truncate = g_memory_output_stream_can_truncate;

  iface->truncate_fn  = g_memory_output_stream_truncate;

}

static void

g_memory_output_stream_init (GMemoryOutputStream *stream)

{

  stream->priv = g_memory_output_stream_get_instance_private (stream);

  stream->priv->pos = 0;

  stream->priv->valid_len = 0;

}

/**

 * g_memory_output_stream_new: (skip)

 * @data: (nullable): pointer to a chunk of memory to use, or %NULL

 * @size: the size of @data

 * @realloc_function: (nullable): a function with realloc() semantics (like g_realloc())

 *     to be called when @data needs to be grown, or %NULL

 * @destroy_function: (nullable): a function to be called on @data when the stream is

 *     finalized, or %NULL

 *

 * Creates a new #GMemoryOutputStream.

 *

 * In most cases this is not the function you want.  See

 * g_memory_output_stream_new_resizable() instead.

 *

 * If @data is non-%NULL, the stream will use that for its internal storage.

 *

 * If @realloc_fn is non-%NULL, it will be used for resizing the internal

 * storage when necessary and the stream will be considered resizable.

 * In that case, the stream will start out being (conceptually) empty.

 * @size is used only as a hint for how big @data is.  Specifically,

 * seeking to the end of a newly-created stream will seek to zero, not

 * @size.  Seeking past the end of the stream and then writing will

 * introduce a zero-filled gap.

 *

 * If @realloc_fn is %NULL then the stream is fixed-sized.  Seeking to

 * the end will seek to @size exactly.  Writing past the end will give

 * an 'out of space' error.  Attempting to seek past the end will fail.

 * Unlike the resizable case, seeking to an offset within the stream and

 * writing will preserve the bytes passed in as @data before that point

 * and will return them as part of g_memory_output_stream_steal_data().

 * If you intend to seek you should probably therefore ensure that @data

 * is properly initialised.

 *

 * It is probably only meaningful to provide @data and @size in the case

 * that you want a fixed-sized stream.  Put another way: if @realloc_fn

 * is non-%NULL then it makes most sense to give @data as %NULL and

 * @size as 0 (allowing #GMemoryOutputStream to do the initial

 * allocation for itself).

 *

 * |[

 * // a stream that can grow

 * stream = g_memory_output_stream_new (NULL, 0, realloc, free);

 *

 * // another stream that can grow

 * stream2 = g_memory_output_stream_new (NULL, 0, g_realloc, g_free);

 *

 * // a fixed-size stream

 * data = malloc (200);

 * stream3 = g_memory_output_stream_new (data, 200, NULL, free);

 * ]|

 *

 * Returns: A newly created #GMemoryOutputStream object.

 **/

GOutputStream *

g_memory_output_stream_new (gpointer       data,

                            gsize          size,

                            GReallocFunc   realloc_function,

                            GDestroyNotify destroy_function)

{

  GOutputStream *stream;

  stream = g_object_new (G_TYPE_MEMORY_OUTPUT_STREAM,

                         "data", data,

                         "size", size,

                         "realloc-function", realloc_function,

                         "destroy-function", destroy_function,

                         NULL);

  return stream;

}

/**

 * g_memory_output_stream_new_resizable:

 *

 * Creates a new #GMemoryOutputStream, using g_realloc() and g_free()

 * for memory allocation.

 *

 * Since: 2.36

 */

GOutputStream *

g_memory_output_stream_new_resizable (void)

{

  return g_memory_output_stream_new (NULL, 0, g_realloc, g_free);

}

/**

 * g_memory_output_stream_get_data:

 * @ostream: a #GMemoryOutputStream

 *

 * Gets any loaded data from the @ostream.

 *

 * Note that the returned pointer may become invalid on the next

 * write or truncate operation on the stream.

 *

 * Returns: (transfer none): pointer to the stream's data, or %NULL if the data

 *    has been stolen

 **/

gpointer

g_memory_output_stream_get_data (GMemoryOutputStream *ostream)

{

  g_return_val_if_fail (G_IS_MEMORY_OUTPUT_STREAM (ostream), NULL);

  return ostream->priv->data;

}

/**

 * g_memory_output_stream_get_size:

 * @ostream: a #GMemoryOutputStream

 *

 * Gets the size of the currently allocated data area (available from

 * g_memory_output_stream_get_data()).

 *

 * You probably don't want to use this function on resizable streams.

 * See g_memory_output_stream_get_data_size() instead.  For resizable

 * streams the size returned by this function is an implementation

 * detail and may be change at any time in response to operations on the

 * stream.

 *

 * If the stream is fixed-sized (ie: no realloc was passed to

 * g_memory_output_stream_new()) then this is the maximum size of the

 * stream and further writes will return %G_IO_ERROR_NO_SPACE.

 *

 * In any case, if you want the number of bytes currently written to the

 * stream, use g_memory_output_stream_get_data_size().

 *

 * Returns: the number of bytes allocated for the data buffer

 */

gsize

g_memory_output_stream_get_size (GMemoryOutputStream *ostream)

{

  g_return_val_if_fail (G_IS_MEMORY_OUTPUT_STREAM (ostream), 0);

  return ostream->priv->len;

}

/**

 * g_memory_output_stream_get_data_size:

 * @ostream: a #GMemoryOutputStream

 *

 * Returns the number of bytes from the start up to including the last

 * byte written in the stream that has not been truncated away.

 *

 * Returns: the number of bytes written to the stream

 *

 * Since: 2.18

 */

gsize

g_memory_output_stream_get_data_size (GMemoryOutputStream *ostream)

{

  g_return_val_if_fail (G_IS_MEMORY_OUTPUT_STREAM (ostream), 0);

  return ostream->priv->valid_len;

}

/**

 * g_memory_output_stream_steal_data:

 * @ostream: a #GMemoryOutputStream

 *

 * Gets any loaded data from the @ostream. Ownership of the data

 * is transferred to the caller; when no longer needed it must be

 * freed using the free function set in @ostream's

 * #GMemoryOutputStream:destroy-function property.

 *

 * @ostream must be closed before calling this function.

 *

 * Returns: (transfer full): the stream's data, or %NULL if it has previously

 *    been stolen

 *

 * Since: 2.26

 **/

gpointer

g_memory_output_stream_steal_data (GMemoryOutputStream *ostream)

{

  gpointer data;

  g_return_val_if_fail (G_IS_MEMORY_OUTPUT_STREAM (ostream), NULL);

  g_return_val_if_fail (g_output_stream_is_closed (G_OUTPUT_STREAM (ostream)), NULL);

  data = ostream->priv->data;

  ostream->priv->data = NULL;

  return data;

}

/**

 * g_memory_output_stream_steal_as_bytes:

 * @ostream: a #GMemoryOutputStream

 *

 * Returns data from the @ostream as a #GBytes. @ostream must be

 * closed before calling this function.

 *

 * Returns: (transfer full): the stream's data

 *

 * Since: 2.34

 **/

GBytes *

g_memory_output_stream_steal_as_bytes (GMemoryOutputStream *ostream)

{

  GBytes *result;

  g_return_val_if_fail (G_IS_MEMORY_OUTPUT_STREAM (ostream), NULL);

  g_return_val_if_fail (g_output_stream_is_closed (G_OUTPUT_STREAM (ostream)), NULL);

  result = g_bytes_new_with_free_func (ostream->priv->data,

                                       ostream->priv->valid_len,

                                       ostream->priv->destroy,

                                       ostream->priv->data);

  ostream->priv->data = NULL;

  return result;

}

static gboolean

array_resize (GMemoryOutputStream  *ostream,

              gsize                 size,

              gboolean              allow_partial,

              GError              **error)

{

  GMemoryOutputStreamPrivate *priv;

  gpointer data;

  gsize len;

  priv = ostream->priv;

  if (priv->len == size)

    return TRUE;

  if (!priv->realloc_fn)

    {

      if (allow_partial &&

          priv->pos < priv->len)

        return TRUE; /* Short write */

      g_set_error_literal (error,

                           G_IO_ERROR,

                           G_IO_ERROR_NO_SPACE,

                           _("Memory output stream not resizable"));

      return FALSE;

    }

  len = priv->len;

  data = priv->realloc_fn (priv->data, size);

  if (size > 0 && !data)

    {

      if (allow_partial &&

          priv->pos < priv->len)

        return TRUE; /* Short write */

      g_set_error_literal (error,

                           G_IO_ERROR,

                           G_IO_ERROR_NO_SPACE,

                           _("Failed to resize memory output stream"));

      return FALSE;

    }

  if (size > len)

    memset ((guint8 *)data + len, 0, size - len);

  priv->data = data;

  priv->len = size;

  if (priv->len < priv->valid_len)

    priv->valid_len = priv->len;

  return TRUE;

}

static gsize

g_nearest_pow (gsize num)

{

  gsize n = 1;

  while (n < num && n > 0)

    n <<= 1;

  return n;

}

static gssize

g_memory_output_stream_write (GOutputStream  *stream,

                              const void     *buffer,

                              gsize           count,

                              GCancellable   *cancellable,

                              GError        **error)

{

  GMemoryOutputStream        *ostream;

  GMemoryOutputStreamPrivate *priv;

  guint8   *dest;

  gsize new_size;

  ostream = G_MEMORY_OUTPUT_STREAM (stream);

  priv = ostream->priv;

  if (count == 0)

    return 0;

  /* Check for address space overflow, but only if the buffer is resizable.

     Otherwise we just do a short write and don't worry. */

  if (priv->realloc_fn && priv->pos + count < priv->pos)

    goto overflow;

  if (priv->pos + count > priv->len)

    {

      /* At least enough to fit the write, rounded up for greater than

       * linear growth.

       *

       * Assuming that we're using something like realloc(), the kernel

       * will overcommit memory to us, so doubling the size each time

       * will keep the number of realloc calls low without wasting too

       * much memory.

       */

      new_size = g_nearest_pow (priv->pos + count);

      /* Check for overflow again. We have checked if

         pos + count > G_MAXSIZE, but now check if g_nearest_pow () has

         overflowed */

      if (new_size == 0)

        goto overflow;

      new_size = MAX (new_size, MIN_ARRAY_SIZE);

      if (!array_resize (ostream, new_size, TRUE, error))

        return -1;

    }

  /* Make sure we handle short writes if the array_resize

     only added part of the required memory */

  count = MIN (count, priv->len - priv->pos);

  dest = (guint8 *)priv->data + priv->pos;

  memcpy (dest, buffer, count);

  priv->pos += count;

  if (priv->pos > priv->valid_len)

    priv->valid_len = priv->pos;

  return count;

 overflow:

  /* Overflow: buffer size would need to be bigger than G_MAXSIZE. */

  g_set_error_literal (error,

                       G_IO_ERROR,

                       G_IO_ERROR_NO_SPACE,

                       _("Amount of memory required to process the write is "

                         "larger than available address space"));

  return -1;

}

static gboolean

g_memory_output_stream_close (GOutputStream  *stream,

                              GCancellable   *cancellable,

                              GError        **error)

{

  return TRUE;

}

static void

g_memory_output_stream_close_async (GOutputStream       *stream,

                                    int                  io_priority,

                                    GCancellable        *cancellable,

                                    GAsyncReadyCallback  callback,

                                    gpointer             data)

{

  GTask *task;

  task = g_task_new (stream, cancellable, callback, data);

  g_task_set_source_tag (task, g_memory_output_stream_close_async);

  /* will always return TRUE */

  g_memory_output_stream_close (stream, cancellable, NULL);

  g_task_return_boolean (task, TRUE);

  g_object_unref (task);

}

static gboolean

g_memory_output_stream_close_finish (GOutputStream  *stream,

                                     GAsyncResult   *result,

                                     GError        **error)

{

  g_return_val_if_fail (g_task_is_valid (result, stream), FALSE);

  return g_task_propagate_boolean (G_TASK (result), error);

}

static goffset

g_memory_output_stream_tell (GSeekable *seekable)

{

  GMemoryOutputStream *stream;

  GMemoryOutputStreamPrivate *priv;

  stream = G_MEMORY_OUTPUT_STREAM (seekable);

  priv = stream->priv;

  return priv->pos;

}

static gboolean

g_memory_output_stream_can_seek (GSeekable *seekable)

{

  return TRUE;

}

static gboolean

g_memory_output_stream_seek (GSeekable    *seekable,

                             goffset        offset,

                             GSeekType      type,

                             GCancellable  *cancellable,

                             GError       **error)

{

  GMemoryOutputStream        *stream;

  GMemoryOutputStreamPrivate *priv;

  goffset absolute;

  stream = G_MEMORY_OUTPUT_STREAM (seekable);

  priv = stream->priv;

  switch (type)

    {

    case G_SEEK_CUR:

      absolute = priv->pos + offset;

      break;

    case G_SEEK_SET:

      absolute = offset;

      break;

    case G_SEEK_END:

      /* For resizable streams, we consider the end to be the data

       * length.  For fixed-sized streams, we consider the end to be the

       * size of the buffer.

       */

      if (priv->realloc_fn)

        absolute = priv->valid_len + offset;

      else

        absolute = priv->len + offset;

      break;

    default:

      g_set_error_literal (error,

                           G_IO_ERROR,

                           G_IO_ERROR_INVALID_ARGUMENT,

                           _("Invalid GSeekType supplied"));

      return FALSE;

    }

  if (absolute < 0)

    {

      g_set_error_literal (error,

                           G_IO_ERROR,

                           G_IO_ERROR_INVALID_ARGUMENT,

                           _("Requested seek before the beginning of the stream"));

      return FALSE;

    }

  /* Can't seek past the end of a fixed-size stream.

   *

   * Note: seeking to the non-existent byte at the end of a fixed-sized

   * stream is valid (eg: a 1-byte fixed sized stream can have position

   * 0 or 1).  Therefore '>' is what we want.

   * */

  if (priv->realloc_fn == NULL && absolute > priv->len)

    {

      g_set_error_literal (error,

                           G_IO_ERROR,

                           G_IO_ERROR_INVALID_ARGUMENT,

                           _("Requested seek beyond the end of the stream"));

      return FALSE;

    }

  priv->pos = absolute;

  return TRUE;

}

static gboolean

g_memory_output_stream_can_truncate (GSeekable *seekable)

{

  GMemoryOutputStream *ostream;

  GMemoryOutputStreamPrivate *priv;

  ostream = G_MEMORY_OUTPUT_STREAM (seekable);

  priv = ostream->priv;

  /* We do not allow truncation of fixed-sized streams */

  return priv->realloc_fn != NULL;

}

static gboolean

g_memory_output_stream_truncate (GSeekable     *seekable,

                                 goffset        offset,

                                 GCancellable  *cancellable,

                                 GError       **error)

{

  GMemoryOutputStream *ostream = G_MEMORY_OUTPUT_STREAM (seekable);

  if (!array_resize (ostream, offset, FALSE, error))

    return FALSE;

  ostream->priv->valid_len = offset;

  return TRUE;

}

static gboolean

g_memory_output_stream_is_writable (GPollableOutputStream *stream)

{

  return TRUE;

}

static GSource *

g_memory_output_stream_create_source (GPollableOutputStream *stream,

                                      GCancellable          *cancellable)

{

  GSource *base_source, *pollable_source;

  base_source = g_timeout_source_new (0);

  pollable_source = g_pollable_source_new_full (stream, base_source, cancellable);

  g_source_unref (base_source);

  return pollable_source;

}