gstreamer/libs/bytestream/gstbytestream.c

/* GStreamer
 * Copyright (C) 2001 Erik Walthinsen <omega@temple-baptist.com>
 *
 * gstbytestream.c: adds a convenient bytestream based API to a pad.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 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
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#include <gst/gstinfo.h>
#include "gstbytestream.h"

//#define BS_DEBUG

#ifdef BS_DEBUG
# define bs_print(format,args...)	GST_DEBUG (GST_CAT_BUFFER,  format, ## args)
# define bs_status(bs)			gst_bytestream_print_status(bs)
#else
# define bs_print(format,args...)
# define bs_status(bs)
#endif

guint8 *gst_bytestream_assemble (GstByteStream * bs, guint32 len);

/**
 * gst_bytestream_new:
 * @pad: the pad to attach the bytestream to
 *
 * creates a bytestream from the given pad
 *
 * Returns: a new #GstByteStream object
 */
GstByteStream *
gst_bytestream_new (GstPad * pad)
{
  GstByteStream *bs = g_new (GstByteStream, 1);

  bs->pad = pad;

  bs->buflist = NULL;
  bs->headbufavail = 0;
  bs->listavail = 0;

  return bs;
}

void
gst_bytestream_destroy (GstByteStream * bs)
{
  GSList *walk;

  walk = bs->buflist;
  while (walk) {
    gst_buffer_unref (GST_BUFFER (walk->data));
    walk = g_slist_next (walk);
  }
  g_slist_free (bs->buflist);
  g_free (bs);
}

// HOW THIS WORKS:
//
// The fundamental structure is a singly-linked list of buffers.  The
// buffer on the front is the oldest, and thus the first to read data
// from.  The number of bytes left to be read in this buffer is stored
// in bs->headbufavail.  The number of bytes available in the entire
// list (including the head buffer) is in bs->listavail.
//
// When a request is made for data (peek), _fill_bytes is called with
// the number of bytes needed, but only if the listavail indicates
// that there aren't already enough.  This calls _get_next_buf until
// the listavail is sufficient to satisfy the demand.
//
// _get_next_buf pulls a buffer from the pad the bytestream is attached
// to, and shoves it in the list.  There are actually two things it can
// do.  If there's already a buffer in the list, and the _is_span_fast()
// test returns true, it will merge it with that last buffer.  Otherwise
// it will simply tack it onto the end of the list.
//
// The _peek itself first checks the simple case of the request fitting
// within the head buffer, and if so creates a subbuffer and returns.
// Otherwise, it creates a new buffer and allocates space for the request
// and calls _assemble to fill it.  We know we have to copy because this
// case only happens when the _merge wasn't feasible during _get_next_buf.
//
// The _flush method repeatedly inspects the head buffer and flushes as
// much data from it as it needs to, up to the size of the buffer.  If
// the flush decimates the buffer, it's stripped, unref'd, and removed.


// get the next buffer
// if the buffer can be merged with the head buffer, do so
// else add it onto the head of the 
static gboolean
gst_bytestream_get_next_buf (GstByteStream * bs)
{
  GstBuffer *nextbuf, *lastbuf;
  GSList *end;

  bs_print ("get_next_buf: pulling buffer\n");
  nextbuf = gst_pad_pull (bs->pad);
  bs_print ("get_next_buf: got buffer of %d bytes\n", GST_BUFFER_SIZE (nextbuf));

  // first see if there are any buffers in the list at all
  if (bs->buflist) {
    bs_print ("gst_next_buf: there is at least one buffer in the list\n");
    // now find the end of the list
    end = g_slist_last (bs->buflist);
    // get the buffer that's there
    lastbuf = GST_BUFFER (end->data);

    // see if we can marge cheaply
    if (gst_buffer_is_span_fast (lastbuf, nextbuf)) {
      bs_print ("get_next_buf: merging new buffer with last buf on list\n");
      // it is, let's merge them (this is really an append, but...)
      end->data = gst_buffer_merge (lastbuf, nextbuf);
      // add to the length of the list
      bs->listavail += GST_BUFFER_SIZE (nextbuf);

      // have to check to see if we merged with the head buffer
      if (end == bs->buflist) {
	bs->headbufavail += GST_BUFFER_SIZE (nextbuf);
      }

      gst_buffer_unref (lastbuf);
      gst_buffer_unref (nextbuf);

      // if we can't, we just append this buffer
    }
    else {
      bs_print ("get_next_buf: adding new buffer to the end of the list\n");
      end = g_slist_append (end, nextbuf);
      // also need to increment length of list and buffer count
      bs->listavail += GST_BUFFER_SIZE (nextbuf);
    }

    // if there are no buffers in the list
  }
  else {
    bs_print ("get_next_buf: buflist is empty, adding new buffer to list\n");
    // put this on the end of the list
    bs->buflist = g_slist_append (bs->buflist, nextbuf);
    // and increment the number of bytes in the list
    bs->listavail = GST_BUFFER_SIZE (nextbuf);
    // set the head buffer avail to the size
    bs->headbufavail = GST_BUFFER_SIZE (nextbuf);
  }

  return TRUE;
}


static gboolean
gst_bytestream_fill_bytes (GstByteStream * bs, guint32 len)
{
  // as long as we don't have enough, we get more buffers
  while (bs->listavail < len) {
    bs_print ("fill_bytes: there are %d bytes in the list, we need %d\n", bs->listavail, len);
    gst_bytestream_get_next_buf (bs);
  }

  return TRUE;
}


GstBuffer *
gst_bytestream_peek (GstByteStream * bs, guint32 len)
{
  GstBuffer *headbuf, *retbuf = NULL;

  g_return_val_if_fail (bs != NULL, NULL);
  g_return_val_if_fail (len > 0, NULL);

  bs_print ("peek: asking for %d bytes\n", len);

  // make sure we have enough
  bs_print ("peek: there are %d bytes in the list\n", bs->listavail);
  if (len > bs->listavail) {
    gst_bytestream_fill_bytes (bs, len);
    bs_print ("peek: there are now %d bytes in the list\n", bs->listavail);
  }
  bs_status (bs)

  // extract the head buffer
  headbuf = GST_BUFFER (bs->buflist->data);

  // if the requested bytes are in the current buffer
  bs_print ("peek: headbufavail is %d\n", bs->headbufavail);
  if (len <= bs->headbufavail) {
    bs_print ("peek: there are enough bytes in headbuf (need %d, have %d)\n", len, bs->headbufavail);
    // create a sub-buffer of the headbuf
    retbuf = gst_buffer_create_sub (headbuf, GST_BUFFER_SIZE (headbuf) - bs->headbufavail, len);

    // otherwise we need to figure out how to assemble one
  }
  else {
    bs_print ("peek: current buffer is not big enough for len %d\n", len);

    retbuf = gst_buffer_new ();
    GST_BUFFER_SIZE (retbuf) = len;
    GST_BUFFER_DATA (retbuf) = gst_bytestream_assemble (bs, len);
    if (GST_BUFFER_OFFSET (headbuf) != -1)
      GST_BUFFER_OFFSET (retbuf) = GST_BUFFER_OFFSET (headbuf) + (GST_BUFFER_SIZE (headbuf) - bs->headbufavail);
  }

  return retbuf;
}

guint8 *
gst_bytestream_peek_bytes (GstByteStream * bs, guint32 len)
{
  GstBuffer *headbuf;
  guint8 *data = NULL;

  g_return_val_if_fail (bs != NULL, NULL);
  g_return_val_if_fail (len > 0, NULL);

  bs_print ("peek_bytes: asking for %d bytes\n", len);

  // make sure we have enough
  bs_print ("peek_bytes: there are %d bytes in the list\n", bs->listavail);
  if (len > bs->listavail) {
    gst_bytestream_fill_bytes (bs, len);
    bs_print ("peek_bytes: there are now %d bytes in the list\n", bs->listavail);
  }
  bs_status (bs)

  // extract the head buffer
  headbuf = GST_BUFFER (bs->buflist->data);

  // if the requested bytes are in the current buffer
  bs_print ("peek_bytes: headbufavail is %d\n", bs->headbufavail);
  if (len <= bs->headbufavail) {
    bs_print ("peek_bytes: there are enough bytes in headbuf (need %d, have %d)\n", len, bs->headbufavail);
    // create a sub-buffer of the headbuf
    data = GST_BUFFER_DATA (headbuf) + (GST_BUFFER_SIZE (headbuf) - bs->headbufavail);

    // otherwise we need to figure out how to assemble one
  }
  else {
    bs_print ("peek_bytes: current buffer is not big enough for len %d\n", len);

    data = gst_bytestream_assemble (bs, len);
  }

  return data;
}

guint8 *
gst_bytestream_assemble (GstByteStream * bs, guint32 len)
{
  guint8 *data = g_malloc (len);
  GSList *walk;
  guint32 copied = 0;
  GstBuffer *buf;

  // copy the data from the curbuf
  buf = GST_BUFFER (bs->buflist->data);
  bs_print ("assemble: copying %d bytes from curbuf at %d to *data\n", bs->headbufavail,
	    GST_BUFFER_SIZE (buf) - bs->headbufavail);
  memcpy (data, GST_BUFFER_DATA (buf) + GST_BUFFER_SIZE (buf) - bs->headbufavail, bs->headbufavail);
  copied += bs->headbufavail;

  // asumption is made that the buffers all exist in the list
  walk = g_slist_next (bs->buflist);
  while (copied < len) {
    buf = GST_BUFFER (walk->data);
    if (GST_BUFFER_SIZE (buf) < (len - copied)) {
      bs_print ("assemble: copying %d bytes from buf to output offset %d\n", GST_BUFFER_SIZE (buf), copied);
      memcpy (data + copied, GST_BUFFER_DATA (buf), GST_BUFFER_SIZE (buf));
      copied += GST_BUFFER_SIZE (buf);
    }
    else {
      bs_print ("assemble: copying %d bytes from buf to output offset %d\n", len - copied, copied);
      memcpy (data + copied, GST_BUFFER_DATA (buf), len - copied);
      copied = len;
    }
    walk = g_slist_next (walk);
  }

  return data;
}

gboolean
gst_bytestream_flush (GstByteStream * bs, guint32 len)
{
  GstBuffer *headbuf;

  bs_print ("flush: flushing %d bytes\n", len);

  // make sure we have enough
  bs_print ("flush: there are %d bytes in the list\n", bs->listavail);
  if (len > bs->listavail) {
    gst_bytestream_fill_bytes (bs, len);
    bs_print ("flush: there are now %d bytes in the list\n", bs->listavail);
  }

  // repeat until we've flushed enough data
  while (len > 0) {
    headbuf = GST_BUFFER (bs->buflist->data);

    bs_print ("flush: analyzing buffer that's %d bytes long, offset %d\n", GST_BUFFER_SIZE (headbuf),
	      GST_BUFFER_OFFSET (headbuf));

    // if there's enough to complete the flush
    if (bs->headbufavail > len) {
      // just trim it off
      bs_print ("flush: trimming %d bytes off end of headbuf\n", len);
      bs->headbufavail -= len;
      bs->listavail -= len;
      len = 0;

      // otherwise we have to trim the whole buffer
    }
    else {
      bs_print ("flush: removing head buffer completely\n");
      // remove it from the list
      bs->buflist = g_slist_delete_link (bs->buflist, bs->buflist);
      // trim it from the avail size
      bs->listavail -= bs->headbufavail;
      // record that we've trimmed this many bytes
      len -= bs->headbufavail;
      // unref it
      gst_buffer_unref (headbuf);

      // record the new headbufavail
      if (bs->buflist) {
	bs->headbufavail = GST_BUFFER_SIZE (GST_BUFFER (bs->buflist->data));
	bs_print ("flush: next headbuf is %d bytes\n", bs->headbufavail);
      }
      else {
	bs_print ("flush: no more bytes at all\n");
      }
    }

    bs_print ("flush: bottom of while(), len is now %d\n", len);
  }

  return TRUE;
}

GstBuffer *
gst_bytestream_read (GstByteStream * bs, guint32 len)
{
  GstBuffer *buf = gst_bytestream_peek (bs, len);
  gst_bytestream_flush (bs, len);
  return buf;
}

void
gst_bytestream_print_status (GstByteStream * bs)
{
  GSList *walk;
  GstBuffer *buf;

  bs_print ("STATUS: head buffer has %d bytes available\n", bs->headbufavail);
  bs_print ("STATUS: list has %d bytes available\n", bs->listavail);
  walk = bs->buflist;
  while (walk) {
    buf = GST_BUFFER (walk->data);
    walk = g_slist_next (walk);

    bs_print ("STATUS: buffer starts at %d and is %d bytes long\n", GST_BUFFER_OFFSET (buf), GST_BUFFER_SIZE (buf));
  }
}