Marc Mason wrote:
> avio.h defines AVSEEK_SIZE.
>
> #define AVSEEK_SIZE 0x10000
>
> """
> Passing AVSEEK_SIZE as the "whence" parameter to a seek function causes
> it to return the filesize without seeking anywhere. Supporting this is
> optional. If it is not supported then the seek function will return <0.
> """
>
> typedef struct URLProtocol {
> const char *name;
> int (*url_open)(URLContext *h, const char *filename, int flags);
> int (*url_read)(URLContext *h, unsigned char *buf, int size);
> int (*url_write)(URLContext *h, unsigned char *buf, int size);
> int64_t (*url_seek)(URLContext *h, int64_t pos, int whence);
> int (*url_close)(URLContext *h);
> struct URLProtocol *next;
> int (*url_read_pause)(URLContext *h, int pause);
> int64_t (*url_read_seek)(URLContext *h, int stream_index,
> int64_t timestamp, int flags);
> } URLProtocol;
>
> """
> int64_t (*url_seek)(URLContext *h, int64_t pos, int whence);
> """
>
> http://www.opengroup.org/onlinepubs/000095399/functions/lseek.html
>
> Consider the following implementation of a url_seek() callback.
>
> static int64_t file_seek(URLContext *h, int64_t pos, int whence)
> {
> ...
> switch(whence)
> {
> case SEEK_SET : FFMPEG_Seek=FS_SEEK_SET; break;
> case SEEK_CUR : FFMPEG_Seek=FS_SEEK_CUR; break;
> case SEEK_END : FFMPEG_Seek=FS_SEEK_END; break;
> default : FFMPEG_Seek=FS_SEEK_SET; break;
> }
> ...
> }
>
> i.e. treat AVSEEK_SIZE like a SEEK_SET request.
>
> $ grep -r AVSEEK_SIZE .
> ./libavformat/avio.c: size= url_seek(h, 0, AVSEEK_SIZE);
> ./libavformat/avio.h:#define AVSEEK_SIZE 0x10000
> ./libavformat/aviobuf.c: size = s->seek(s->opaque, 0, AVSEEK_SIZE);
> ./libavformat/http.c: if (whence == AVSEEK_SIZE)
>
> i.e. pos=0 every time whence=AVSEEK_SIZE
>
> thus file_seek(h, 0, AVSEEK_SIZE) will return 0 (instead of the file
> size or -1)
>
> As far as I understand, this behavior is incorrect. Either the function
> should return the file size or it should return an error.
>
> Is that correct ?
>
> Something else seems wrong in the implementation of file_seek()
>
> if (whence == SEEK_END)
> {
> pos = 0;
> }
>
> file_seek() will ignore whatever offset from the end is requested, seek
> to the end of the file, and return the file size.
>
> This behavior seems incorrect too. Do you agree ?
Would anyone care to comment ?
--
Regards.
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