gstreamer/libs/bytestream/gstbytestream.c

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/* 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_print(format,args...) g_print(format, ## args)
#define bs_print(format,args...)
//static void gst_bytestream_print_status(GstByteStream *bs);
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; // need to refcnt?
bs->buflist = NULL;
bs->headbufavail = 0;
bs->listavail = 0;
return bs;
}
void
gst_bytestream_destroy (GstByteStream * bs)
{
GSList *walk;
// release bs->pad ??
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);
if (!nextbuf)
return FALSE;
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);
if (!gst_bytestream_get_next_buf (bs))
return FALSE;
}
return TRUE;
}
GstBuffer *
gst_bytestream_peek_loc (GST_WHERE_ARGS_ 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) {
if (!gst_bytestream_fill_bytes (bs, len))
return NULL;
bs_print ("peek: there are now %d bytes in the list\n", bs->listavail);
}
gst_bytestream_print_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_loc (GST_WHERE_VARS_ 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_loc (GST_WHERE_VARS);
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) {
if (!gst_bytestream_fill_bytes (bs, len))
return NULL;
bs_print ("peek_bytes: there are now %d bytes in the list\n", bs->listavail);
}
gst_bytestream_print_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;
g_assert (len <= bs->listavail);
// 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) {
g_assert (walk);
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) {
if (!gst_bytestream_fill_bytes (bs, len))
return FALSE;
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_loc (GST_WHERE_ARGS_ GstByteStream * bs, guint32 len)
{
GstBuffer *buf = gst_bytestream_peek_loc (GST_WHERE_VARS_ 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));
}
}