/* GIO - GLib Input, Output and Streaming Library

 *

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

 * Copyright (C) 2007 Jürg Billeter

 *

 * SPDX-License-Identifier: LGPL-2.1-or-later

 *

 * 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/>.

 *

 * Author: Christian Kellner <gicmo@gnome.org>

 */

#include "config.h"

#include "gbufferedinputstream.h"

#include "ginputstream.h"

#include "gcancellable.h"

#include "gasyncresult.h"

#include "gtask.h"

#include "gseekable.h"

#include "gioerror.h"

#include <string.h>

#include "glibintl.h"

/**

 * SECTION:gbufferedinputstream

 * @short_description: Buffered Input Stream

 * @include: gio/gio.h

 * @see_also: #GFilterInputStream, #GInputStream

 *

 * Buffered input stream implements #GFilterInputStream and provides

 * for buffered reads.

 *

 * By default, #GBufferedInputStream's buffer size is set at 4 kilobytes.

 *

 * To create a buffered input stream, use g_buffered_input_stream_new(),

 * or g_buffered_input_stream_new_sized() to specify the buffer's size at

 * construction.

 *

 * To get the size of a buffer within a buffered input stream, use

 * g_buffered_input_stream_get_buffer_size(). To change the size of a

 * buffered input stream's buffer, use

 * g_buffered_input_stream_set_buffer_size(). Note that the buffer's size

 * cannot be reduced below the size of the data within the buffer.

 */

#define DEFAULT_BUFFER_SIZE 4096

struct _GBufferedInputStreamPrivate {

  guint8 *buffer;

  gsize   len;

  gsize   pos;

  gsize   end;

  GAsyncReadyCallback outstanding_callback;

};

enum {

  PROP_0,

  PROP_BUFSIZE

};

static void g_buffered_input_stream_set_property  (GObject      *object,

                                                   guint         prop_id,

                                                   const GValue *value,

                                                   GParamSpec   *pspec);

static void g_buffered_input_stream_get_property  (GObject      *object,

                                                   guint         prop_id,

                                                   GValue       *value,

                                                   GParamSpec   *pspec);

static void g_buffered_input_stream_finalize      (GObject *object);

static gssize g_buffered_input_stream_skip             (GInputStream          *stream,

                                                        gsize                  count,

                                                        GCancellable          *cancellable,

                                                        GError               **error);

static void   g_buffered_input_stream_skip_async       (GInputStream          *stream,

                                                        gsize                  count,

                                                        int                    io_priority,

                                                        GCancellable          *cancellable,

                                                        GAsyncReadyCallback    callback,

                                                        gpointer               user_data);

static gssize g_buffered_input_stream_skip_finish      (GInputStream          *stream,

                                                        GAsyncResult          *result,

                                                        GError               **error);

static gssize g_buffered_input_stream_read             (GInputStream          *stream,

                                                        void                  *buffer,

                                                        gsize                  count,

                                                        GCancellable          *cancellable,

                                                        GError               **error);

static gssize g_buffered_input_stream_real_fill        (GBufferedInputStream  *stream,

                                                        gssize                 count,

                                                        GCancellable          *cancellable,

                                                        GError               **error);

static void   g_buffered_input_stream_real_fill_async  (GBufferedInputStream  *stream,

                                                        gssize                 count,

                                                        int                    io_priority,

                                                        GCancellable          *cancellable,

                                                        GAsyncReadyCallback    callback,

                                                        gpointer               user_data);

static gssize g_buffered_input_stream_real_fill_finish (GBufferedInputStream  *stream,

                                                        GAsyncResult          *result,

                                                        GError               **error);

static void     g_buffered_input_stream_seekable_iface_init (GSeekableIface  *iface);

static goffset  g_buffered_input_stream_tell                (GSeekable       *seekable);

static gboolean g_buffered_input_stream_can_seek            (GSeekable       *seekable);

static gboolean g_buffered_input_stream_seek                (GSeekable       *seekable,

                   goffset          offset,

                   GSeekType        type,

                   GCancellable    *cancellable,

                   GError         **error);

static gboolean g_buffered_input_stream_can_truncate        (GSeekable       *seekable);

static gboolean g_buffered_input_stream_truncate            (GSeekable       *seekable,

                   goffset          offset,

                   GCancellable    *cancellable,

                   GError         **error);

static void compact_buffer (GBufferedInputStream *stream);

G_DEFINE_TYPE_WITH_CODE (GBufferedInputStream,

       g_buffered_input_stream,

       G_TYPE_FILTER_INPUT_STREAM,

                         G_ADD_PRIVATE (GBufferedInputStream)

       G_IMPLEMENT_INTERFACE (G_TYPE_SEEKABLE,

            g_buffered_input_stream_seekable_iface_init))

static void

g_buffered_input_stream_class_init (GBufferedInputStreamClass *klass)

{

  GObjectClass *object_class;

  GInputStreamClass *istream_class;

  GBufferedInputStreamClass *bstream_class;

  object_class = G_OBJECT_CLASS (klass);

  object_class->get_property = g_buffered_input_stream_get_property;

  object_class->set_property = g_buffered_input_stream_set_property;

  object_class->finalize     = g_buffered_input_stream_finalize;

  istream_class = G_INPUT_STREAM_CLASS (klass);

  istream_class->skip = g_buffered_input_stream_skip;

  istream_class->skip_async  = g_buffered_input_stream_skip_async;

  istream_class->skip_finish = g_buffered_input_stream_skip_finish;

  istream_class->read_fn = g_buffered_input_stream_read;

  bstream_class = G_BUFFERED_INPUT_STREAM_CLASS (klass);

  bstream_class->fill = g_buffered_input_stream_real_fill;

  bstream_class->fill_async = g_buffered_input_stream_real_fill_async;

  bstream_class->fill_finish = g_buffered_input_stream_real_fill_finish;

  g_object_class_install_property (object_class,

                                   PROP_BUFSIZE,

                                   g_param_spec_uint ("buffer-size",

                                                      P_("Buffer Size"),

                                                      P_("The size of the backend buffer"),

                                                      1,

                                                      G_MAXUINT,

                                                      DEFAULT_BUFFER_SIZE,

                                                      G_PARAM_READWRITE | G_PARAM_CONSTRUCT |

                                                      G_PARAM_STATIC_NAME|G_PARAM_STATIC_NICK|G_PARAM_STATIC_BLURB));

}

/**

 * g_buffered_input_stream_get_buffer_size:

 * @stream: a #GBufferedInputStream

 *

 * Gets the size of the input buffer.

 *

 * Returns: the current buffer size.

 */

gsize

g_buffered_input_stream_get_buffer_size (GBufferedInputStream  *stream)

{

  g_return_val_if_fail (G_IS_BUFFERED_INPUT_STREAM (stream), 0);

  return stream->priv->len;

}

/**

 * g_buffered_input_stream_set_buffer_size:

 * @stream: a #GBufferedInputStream

 * @size: a #gsize

 *

 * Sets the size of the internal buffer of @stream to @size, or to the

 * size of the contents of the buffer. The buffer can never be resized

 * smaller than its current contents.

 */

void

g_buffered_input_stream_set_buffer_size (GBufferedInputStream *stream,

                                         gsize                 size)

{

  GBufferedInputStreamPrivate *priv;

  gsize in_buffer;

  guint8 *buffer;

  g_return_if_fail (G_IS_BUFFERED_INPUT_STREAM (stream));

  priv = stream->priv;

  if (priv->len == size)

    return;

  if (priv->buffer)

    {

      in_buffer = priv->end - priv->pos;

      /* Never resize smaller than current buffer contents */

      size = MAX (size, in_buffer);

      buffer = g_malloc (size);

      memcpy (buffer, priv->buffer + priv->pos, in_buffer);

      priv->len = size;

      priv->pos = 0;

      priv->end = in_buffer;

      g_free (priv->buffer);

      priv->buffer = buffer;

    }

  else

    {

      priv->len = size;

      priv->pos = 0;

      priv->end = 0;

      priv->buffer = g_malloc (size);

    }

  g_object_notify (G_OBJECT (stream), "buffer-size");

}

static void

g_buffered_input_stream_set_property (GObject      *object,

                                      guint         prop_id,

                                      const GValue *value,

                                      GParamSpec   *pspec)

{

  GBufferedInputStream        *bstream;

  bstream = G_BUFFERED_INPUT_STREAM (object);

  switch (prop_id)

    {

    case PROP_BUFSIZE:

      g_buffered_input_stream_set_buffer_size (bstream, g_value_get_uint (value));

      break;

    default:

      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);

      break;

    }

}

static void

g_buffered_input_stream_get_property (GObject    *object,

                                      guint       prop_id,

                                      GValue     *value,

                                      GParamSpec *pspec)

{

  GBufferedInputStreamPrivate *priv;

  GBufferedInputStream        *bstream;

  bstream = G_BUFFERED_INPUT_STREAM (object);

  priv = bstream->priv;

  switch (prop_id)

    {

    case PROP_BUFSIZE:

      g_value_set_uint (value, priv->len);

      break;

    default:

      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);

      break;

    }

}

static void

g_buffered_input_stream_finalize (GObject *object)

{

  GBufferedInputStreamPrivate *priv;

  GBufferedInputStream        *stream;

  stream = G_BUFFERED_INPUT_STREAM (object);

  priv = stream->priv;

  g_free (priv->buffer);

  G_OBJECT_CLASS (g_buffered_input_stream_parent_class)->finalize (object);

}

static void

g_buffered_input_stream_seekable_iface_init (GSeekableIface *iface)

{

  iface->tell         = g_buffered_input_stream_tell;

  iface->can_seek     = g_buffered_input_stream_can_seek;

  iface->seek         = g_buffered_input_stream_seek;

  iface->can_truncate = g_buffered_input_stream_can_truncate;

  iface->truncate_fn  = g_buffered_input_stream_truncate;

}

static void

g_buffered_input_stream_init (GBufferedInputStream *stream)

{

  stream->priv = g_buffered_input_stream_get_instance_private (stream);

}

/**

 * g_buffered_input_stream_new:

 * @base_stream: a #GInputStream

 *

 * Creates a new #GInputStream from the given @base_stream, with

 * a buffer set to the default size (4 kilobytes).

 *

 * Returns: a #GInputStream for the given @base_stream.

 */

GInputStream *

g_buffered_input_stream_new (GInputStream *base_stream)

{

  GInputStream *stream;

  g_return_val_if_fail (G_IS_INPUT_STREAM (base_stream), NULL);

  stream = g_object_new (G_TYPE_BUFFERED_INPUT_STREAM,

                         "base-stream", base_stream,

                         NULL);

  return stream;

}

/**

 * g_buffered_input_stream_new_sized:

 * @base_stream: a #GInputStream

 * @size: a #gsize

 *

 * Creates a new #GBufferedInputStream from the given @base_stream,

 * with a buffer set to @size.

 *

 * Returns: a #GInputStream.

 */

GInputStream *

g_buffered_input_stream_new_sized (GInputStream *base_stream,

                                   gsize         size)

{

  GInputStream *stream;

  g_return_val_if_fail (G_IS_INPUT_STREAM (base_stream), NULL);

  stream = g_object_new (G_TYPE_BUFFERED_INPUT_STREAM,

                         "base-stream", base_stream,

                         "buffer-size", (guint)size,

                         NULL);

  return stream;

}

/**

 * g_buffered_input_stream_fill:

 * @stream: a #GBufferedInputStream

 * @count: the number of bytes that will be read from the stream

 * @cancellable: (nullable): optional #GCancellable object, %NULL to ignore

 * @error: location to store the error occurring, or %NULL to ignore

 *

 * Tries to read @count bytes from the stream into the buffer.

 * Will block during this read.

 *

 * If @count is zero, returns zero and does nothing. A value of @count

 * larger than %G_MAXSSIZE will cause a %G_IO_ERROR_INVALID_ARGUMENT error.

 *

 * On success, the number of bytes read into the buffer is returned.

 * It is not an error if this is not the same as the requested size, as it

 * can happen e.g. near the end of a file. Zero is returned on end of file

 * (or if @count is zero),  but never otherwise.

 *

 * If @count is -1 then the attempted read size is equal to the number of

 * bytes that are required to fill the buffer.

 *

 * If @cancellable is not %NULL, then the operation can be cancelled by

 * triggering the cancellable object from another thread. If the operation

 * was cancelled, the error %G_IO_ERROR_CANCELLED will be returned. If an

 * operation was partially finished when the operation was cancelled the

 * partial result will be returned, without an error.

 *

 * On error -1 is returned and @error is set accordingly.

 *

 * For the asynchronous, non-blocking, version of this function, see

 * g_buffered_input_stream_fill_async().

 *

 * Returns: the number of bytes read into @stream's buffer, up to @count,

 *     or -1 on error.

 */

gssize

g_buffered_input_stream_fill (GBufferedInputStream  *stream,

                              gssize                 count,

                              GCancellable          *cancellable,

                              GError               **error)

{

  GBufferedInputStreamClass *class;

  GInputStream *input_stream;

  gssize res;

  g_return_val_if_fail (G_IS_BUFFERED_INPUT_STREAM (stream), -1);

  input_stream = G_INPUT_STREAM (stream);

  if (count < -1)

    {

      g_set_error (error, G_IO_ERROR, G_IO_ERROR_INVALID_ARGUMENT,

                   _("Too large count value passed to %s"), G_STRFUNC);

      return -1;

    }

  if (!g_input_stream_set_pending (input_stream, error))

    return -1;

  if (cancellable)

    g_cancellable_push_current (cancellable);

  class = G_BUFFERED_INPUT_STREAM_GET_CLASS (stream);

  res = class->fill (stream, count, cancellable, error);

  if (cancellable)

    g_cancellable_pop_current (cancellable);

  g_input_stream_clear_pending (input_stream);

  return res;

}

static void

async_fill_callback_wrapper (GObject      *source_object,

                             GAsyncResult *res,

                             gpointer      user_data)

{

  GBufferedInputStream *stream = G_BUFFERED_INPUT_STREAM (source_object);

  g_input_stream_clear_pending (G_INPUT_STREAM (stream));

  (*stream->priv->outstanding_callback) (source_object, res, user_data);

  g_object_unref (stream);

}

/**

 * g_buffered_input_stream_fill_async:

 * @stream: a #GBufferedInputStream

 * @count: the number of bytes that will be read from the stream

 * @io_priority: the [I/O priority][io-priority] of the request

 * @cancellable: (nullable): optional #GCancellable object

 * @callback: (scope async) (closure user_data): a #GAsyncReadyCallback

 * @user_data: a #gpointer

 *

 * Reads data into @stream's buffer asynchronously, up to @count size.

 * @io_priority can be used to prioritize reads. For the synchronous

 * version of this function, see g_buffered_input_stream_fill().

 *

 * If @count is -1 then the attempted read size is equal to the number

 * of bytes that are required to fill the buffer.

 */

void

g_buffered_input_stream_fill_async (GBufferedInputStream *stream,

                                    gssize                count,

                                    int                   io_priority,

                                    GCancellable         *cancellable,

                                    GAsyncReadyCallback   callback,

                                    gpointer              user_data)

{

  GBufferedInputStreamClass *class;

  GError *error = NULL;

  g_return_if_fail (G_IS_BUFFERED_INPUT_STREAM (stream));

  if (count == 0)

    {

      GTask *task;

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

      g_task_set_source_tag (task, g_buffered_input_stream_fill_async);

      g_task_return_int (task, 0);

      g_object_unref (task);

      return;

    }

  if (count < -1)

    {

      g_task_report_new_error (stream, callback, user_data,

                               g_buffered_input_stream_fill_async,

                               G_IO_ERROR, G_IO_ERROR_INVALID_ARGUMENT,

             _("Too large count value passed to %s"),

             G_STRFUNC);

      return;

    }

  if (!g_input_stream_set_pending (G_INPUT_STREAM (stream), &error))

    {

      g_task_report_error (stream, callback, user_data,

                           g_buffered_input_stream_fill_async,

                           error);

      return;

    }

  class = G_BUFFERED_INPUT_STREAM_GET_CLASS (stream);

  stream->priv->outstanding_callback = callback;

  g_object_ref (stream);

  class->fill_async (stream, count, io_priority, cancellable,

                     async_fill_callback_wrapper, user_data);

}

/**

 * g_buffered_input_stream_fill_finish:

 * @stream: a #GBufferedInputStream

 * @result: a #GAsyncResult

 * @error: a #GError

 *

 * Finishes an asynchronous read.

 *

 * Returns: a #gssize of the read stream, or `-1` on an error.

 */

gssize

g_buffered_input_stream_fill_finish (GBufferedInputStream  *stream,

                                     GAsyncResult          *result,

                                     GError               **error)

{

  GBufferedInputStreamClass *class;

  g_return_val_if_fail (G_IS_BUFFERED_INPUT_STREAM (stream), -1);

  g_return_val_if_fail (G_IS_ASYNC_RESULT (result), -1);

  if (g_async_result_legacy_propagate_error (result, error))

    return -1;

  else if (g_async_result_is_tagged (result, g_buffered_input_stream_fill_async))

    return g_task_propagate_int (G_TASK (result), error);

  class = G_BUFFERED_INPUT_STREAM_GET_CLASS (stream);

  return class->fill_finish (stream, result, error);

}

/**

 * g_buffered_input_stream_get_available:

 * @stream: #GBufferedInputStream

 *

 * Gets the size of the available data within the stream.

 *

 * Returns: size of the available stream.

 */

gsize

g_buffered_input_stream_get_available (GBufferedInputStream *stream)

{

  g_return_val_if_fail (G_IS_BUFFERED_INPUT_STREAM (stream), -1);

  return stream->priv->end - stream->priv->pos;

}

/**

 * g_buffered_input_stream_peek:

 * @stream: a #GBufferedInputStream

 * @buffer: (array length=count) (element-type guint8): a pointer to

 *   an allocated chunk of memory

 * @offset: a #gsize

 * @count: a #gsize

 *

 * Peeks in the buffer, copying data of size @count into @buffer,

 * offset @offset bytes.

 *

 * Returns: a #gsize of the number of bytes peeked, or -1 on error.

 */

gsize

g_buffered_input_stream_peek (GBufferedInputStream *stream,

                              void                 *buffer,

                              gsize                 offset,

                              gsize                 count)

{

  gsize available;

  gsize end;

  g_return_val_if_fail (G_IS_BUFFERED_INPUT_STREAM (stream), -1);

  g_return_val_if_fail (buffer != NULL, -1);

  available = g_buffered_input_stream_get_available (stream);

  if (offset > available)

    return 0;

  end = MIN (offset + count, available);

  count = end - offset;

  memcpy (buffer, stream->priv->buffer + stream->priv->pos + offset, count);

  return count;

}

/**

 * g_buffered_input_stream_peek_buffer:

 * @stream: a #GBufferedInputStream

 * @count: (out): a #gsize to get the number of bytes available in the buffer

 *

 * Returns the buffer with the currently available bytes. The returned

 * buffer must not be modified and will become invalid when reading from

 * the stream or filling the buffer.

 *

 * Returns: (array length=count) (element-type guint8) (transfer none):

 *          read-only buffer

 */

const void*

g_buffered_input_stream_peek_buffer (GBufferedInputStream *stream,

                                     gsize                *count)

{

  GBufferedInputStreamPrivate *priv;

  g_return_val_if_fail (G_IS_BUFFERED_INPUT_STREAM (stream), NULL);

  priv = stream->priv;

  if (count)

    *count = priv->end - priv->pos;

  return priv->buffer + priv->pos;

}

static void

compact_buffer (GBufferedInputStream *stream)

{

  GBufferedInputStreamPrivate *priv;

  gsize current_size;

  priv = stream->priv;

  current_size = priv->end - priv->pos;

  memmove (priv->buffer, priv->buffer + priv->pos, current_size);

  priv->pos = 0;

  priv->end = current_size;

}

static gssize

g_buffered_input_stream_real_fill (GBufferedInputStream  *stream,

                                   gssize                 count,

                                   GCancellable          *cancellable,

                                   GError               **error)

{

  GBufferedInputStreamPrivate *priv;

  GInputStream *base_stream;

  gssize nread;

  gsize in_buffer;

  priv = stream->priv;

  if (count == -1)

    count = priv->len;

  in_buffer = priv->end - priv->pos;

  /* Never fill more than can fit in the buffer */

  count = MIN ((gsize) count, priv->len - in_buffer);

  /* If requested length does not fit at end, compact */

  if (priv->len - priv->end < (gsize) count)

    compact_buffer (stream);

  base_stream = G_FILTER_INPUT_STREAM (stream)->base_stream;

  nread = g_input_stream_read (base_stream,

                               priv->buffer + priv->end,

                               count,

                               cancellable,

                               error);

  if (nread > 0)

    priv->end += nread;

  return nread;

}

static gssize

g_buffered_input_stream_skip (GInputStream  *stream,

                              gsize          count,

                              GCancellable  *cancellable,

                              GError       **error)

{

  GBufferedInputStream        *bstream;

  GBufferedInputStreamPrivate *priv;

  GBufferedInputStreamClass *class;

  GInputStream *base_stream;

  gsize available, bytes_skipped;

  gssize nread;

  bstream = G_BUFFERED_INPUT_STREAM (stream);

  priv = bstream->priv;

  available = priv->end - priv->pos;

  if (count <= available)

    {

      priv->pos += count;

      return count;

    }

  /* Full request not available, skip all currently available and

   * request refill for more

   */

  priv->pos = 0;

  priv->end = 0;

  bytes_skipped = available;

  count -= available;

  if (bytes_skipped > 0)

    error = NULL; /* Ignore further errors if we already read some data */

  if (count > priv->len)

    {

      /* Large request, shortcut buffer */

      base_stream = G_FILTER_INPUT_STREAM (stream)->base_stream;

      nread = g_input_stream_skip (base_stream,

                                   count,

                                   cancellable,

                                   error);

      if (nread < 0 && bytes_skipped == 0)

        return -1;

      if (nread > 0)

        bytes_skipped += nread;

      return bytes_skipped;

    }

  class = G_BUFFERED_INPUT_STREAM_GET_CLASS (stream);

  nread = class->fill (bstream, priv->len, cancellable, error);

  if (nread < 0)

    {

      if (bytes_skipped == 0)

        return -1;

      else

        return bytes_skipped;

    }

  available = priv->end - priv->pos;

  count = MIN (count, available);

  bytes_skipped += count;

  priv->pos += count;

  return bytes_skipped;

}

static gssize

g_buffered_input_stream_read (GInputStream *stream,

                              void         *buffer,

                              gsize         count,

                              GCancellable *cancellable,

                              GError      **error)

{

  GBufferedInputStream        *bstream;

  GBufferedInputStreamPrivate *priv;

  GBufferedInputStreamClass *class;

  GInputStream *base_stream;

  gsize available, bytes_read;

  gssize nread;

  bstream = G_BUFFERED_INPUT_STREAM (stream);

  priv = bstream->priv;

  available = priv->end - priv->pos;

  if (count <= available)

    {

      memcpy (buffer, priv->buffer + priv->pos, count);

      priv->pos += count;

      return count;

    }

  /* Full request not available, read all currently available and

   * request refill for more

   */

  memcpy (buffer, priv->buffer + priv->pos, available);

  priv->pos = 0;

  priv->end = 0;

  bytes_read = available;

  count -= available;

  if (bytes_read > 0)

    error = NULL; /* Ignore further errors if we already read some data */

  if (count > priv->len)

    {

      /* Large request, shortcut buffer */

      base_stream = G_FILTER_INPUT_STREAM (stream)->base_stream;

      nread = g_input_stream_read (base_stream,

                                   (char *)buffer + bytes_read,

                                   count,

                                   cancellable,

                                   error);

      if (nread < 0 && bytes_read == 0)

        return -1;

      if (nread > 0)

        bytes_read += nread;

      return bytes_read;

    }

  class = G_BUFFERED_INPUT_STREAM_GET_CLASS (stream);

  nread = class->fill (bstream, priv->len, cancellable, error);

  if (nread < 0)

    {

      if (bytes_read == 0)

        return -1;

      else

        return bytes_read;

    }

  available = priv->end - priv->pos;

  count = MIN (count, available);

  memcpy ((char *)buffer + bytes_read, (char *)priv->buffer + priv->pos, count);

  bytes_read += count;

  priv->pos += count;

  return bytes_read;

}

static goffset

g_buffered_input_stream_tell (GSeekable *seekable)

{

  GBufferedInputStream        *bstream;

  GBufferedInputStreamPrivate *priv;

  GInputStream *base_stream;

  GSeekable    *base_stream_seekable;

  gsize available;

  goffset base_offset;

  bstream = G_BUFFERED_INPUT_STREAM (seekable);

  priv = bstream->priv;

  base_stream = G_FILTER_INPUT_STREAM (seekable)->base_stream;

  if (!G_IS_SEEKABLE (base_stream))

    return 0;

  base_stream_seekable = G_SEEKABLE (base_stream);

  available = priv->end - priv->pos;

  base_offset = g_seekable_tell (base_stream_seekable);

  return base_offset - available;

}

static gboolean

g_buffered_input_stream_can_seek (GSeekable *seekable)

{

  GInputStream *base_stream;

  base_stream = G_FILTER_INPUT_STREAM (seekable)->base_stream;

  return G_IS_SEEKABLE (base_stream) && g_seekable_can_seek (G_SEEKABLE (base_stream));

}

static gboolean

g_buffered_input_stream_seek (GSeekable     *seekable,

            goffset        offset,

            GSeekType      type,

            GCancellable  *cancellable,

            GError       **error)

{

  GBufferedInputStream        *bstream;

  GBufferedInputStreamPrivate *priv;

  GInputStream *base_stream;

  GSeekable *base_stream_seekable;

  bstream = G_BUFFERED_INPUT_STREAM (seekable);

  priv = bstream->priv;

  base_stream = G_FILTER_INPUT_STREAM (seekable)->base_stream;

  if (!G_IS_SEEKABLE (base_stream))

    {

      g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED,

                           _("Seek not supported on base stream"));

      return FALSE;

    }

  base_stream_seekable = G_SEEKABLE (base_stream);

  if (type == G_SEEK_CUR)

    {

      if (offset <= (goffset) (priv->end - priv->pos) &&

          offset >= (goffset) -priv->pos)

  {

    priv->pos += offset;

    return TRUE;

  }

      else

  {

    offset -= priv->end - priv->pos;

  }

    }

  if (g_seekable_seek (base_stream_seekable, offset, type, cancellable, error))

    {

      priv->pos = 0;

      priv->end = 0;

      return TRUE;

    }

  else

    {

      return FALSE;

    }

}

static gboolean

g_buffered_input_stream_can_truncate (GSeekable *seekable)

{

  return FALSE;

}

static gboolean

g_buffered_input_stream_truncate (GSeekable     *seekable,

          goffset        offset,

          GCancellable  *cancellable,

          GError       **error)

{

  g_set_error_literal (error,

           G_IO_ERROR,

           G_IO_ERROR_NOT_SUPPORTED,

           _("Cannot truncate GBufferedInputStream"));

  return FALSE;

}

/**

 * g_buffered_input_stream_read_byte:

 * @stream: a #GBufferedInputStream

 * @cancellable: (nullable): optional #GCancellable object, %NULL to ignore

 * @error: location to store the error occurring, or %NULL to ignore

 *

 * Tries to read a single byte from the stream or the buffer. Will block

 * during this read.

 *

 * On success, the byte read from the stream is returned. On end of stream

 * -1 is returned but it's not an exceptional error and @error is not set.

 *

 * If @cancellable is not %NULL, then the operation can be cancelled by

 * triggering the cancellable object from another thread. If the operation

 * was cancelled, the error %G_IO_ERROR_CANCELLED will be returned. If an

 * operation was partially finished when the operation was cancelled the

 * partial result will be returned, without an error.

 *

 * On error -1 is returned and @error is set accordingly.

 *