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avformat/mpjpegdec: make sure we seek back to the ensured buffer

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It was possible for the old code to seek back before the most recently read
data if start of a new multipart was across read boundaries. Now we read some
small sections multiple times to avoid this, but that is OK.

Signed-off-by: Marton Balint <cus@passwd.hu>
This commit is contained in:
Marton Balint 2020-09-26 20:36:25 +02:00
parent 2933ee8ff0
commit 1490a682dc
1 changed files with 6 additions and 5 deletions
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11
libavformat/mpjpegdec.c
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@ -328,18 +328,18 @@ static int mpjpeg_read_packet(AVFormatContext *s, AVPacket *pkt)
ret = av_get_packet(s->pb, pkt, size);
} else {
/* no size was given -- we read until the next boundary or end-of-file */
int remaining = 0, len;
int len;
const int read_chunk = 2048;
pkt->pos = avio_tell(s->pb);
while ((ret = ffio_ensure_seekback(s->pb, read_chunk - remaining)) >= 0 && /* we may need to return as much as all we've read back to the buffer */
(ret = av_append_packet(s->pb, pkt, read_chunk - remaining)) >= 0) {
while ((ret = ffio_ensure_seekback(s->pb, read_chunk)) >= 0 && /* we may need to return as much as all we've read back to the buffer */
(ret = av_append_packet(s->pb, pkt, read_chunk)) >= 0) {
/* scan the new data */
char *start;
len = ret + remaining;
len = ret;
start = pkt->data + pkt->size - len;
do {
if (!memcmp(start, mpjpeg->searchstr, mpjpeg->searchstr_len)) {
@ -351,7 +351,8 @@ static int mpjpeg_read_packet(AVFormatContext *s, AVPacket *pkt)
len--;
start++;
} while (len >= mpjpeg->searchstr_len);
remaining = len;
avio_seek(s->pb, -len, SEEK_CUR);
pkt->size -= len;
}
/* error or EOF occurred */