[FFmpeg-trac] #8385(avformat:new): libavformat/aviobuf: A part of conditional expression is always true: whence != 2

[FFmpeg]

#8385: libavformat/aviobuf: A part of conditional expression is always true:
whence != 2
----------------------------------+--------------------------------------
             Reporter:  Balling   |                     Type:  defect
               Status:  new       |                 Priority:  normal
            Component:  avformat  |                  Version:  git-master
             Keywords:            |               Blocked By:
             Blocking:            |  Reproduced by developer:  0
Analyzed by developer:  0         |
----------------------------------+--------------------------------------
 If you look here
 https://github.com/FFmpeg/FFmpeg/blob/b741a84a15aed8afa01800dbc4b8b0e344e5d2da/libavformat/aviobuf.c#L297
 you will see that on line 265 we would have already returned if whence
 were SEEK_END (2). It is not changed in between.

 This change was done in commit:
 https://github.com/FFmpeg/FFmpeg/commit/7a6fe01f99cb95797ba59134f44b6666b1a5e792

 whence != SEEK_END is always true, so short circuiting and force will not
 be checked.
 Also see #8156
 https://trac.ffmpeg.org/attachment/ticket/8156/project2019.tasks

 Dunno how to fix it.

 The code is like this ():

 {{{
     if (whence != SEEK_CUR && whence != SEEK_SET)
         return AVERROR(EINVAL);

     if (whence == SEEK_CUR) {
         offset1 = pos + (s->buf_ptr - s->buffer);
         if (offset == 0)
             return offset1;
         if (offset > INT64_MAX - offset1)
             return AVERROR(EINVAL);
         offset += offset1;
     }
     if (offset < 0)
         return AVERROR(EINVAL);

     if (s->short_seek_get) {
         short_seek = s->short_seek_get(s->opaque);
         /* fallback to default short seek */
         if (short_seek <= 0)
             short_seek = s->short_seek_threshold;
     } else
         short_seek = s->short_seek_threshold;

     offset1 = offset - pos; // "offset1" is the relative offset from the
 beginning of s->buffer
     s->buf_ptr_max = FFMAX(s->buf_ptr_max, s->buf_ptr);
     if ((!s->direct || !s->seek) &&
         offset1 >= 0 && offset1 <= (s->write_flag ? s->buf_ptr_max -
 s->buffer : buffer_size)) {
         /* can do the seek inside the buffer */
         s->buf_ptr = s->buffer + offset1;
     } else if ((!(s->seekable & AVIO_SEEKABLE_NORMAL) ||
                offset1 <= buffer_size + short_seek) &&
                !s->write_flag && offset1 >= 0 &&
                (!s->direct || !s->seek) &&
               (whence != SEEK_END || force)) {
 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/8385>
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