Re: [FFmpeg-devel] [PATCH v3] avformat/avio: Don't use incompatible function pointer type for call

[Marton Balint <cus@passwd.hu>]

On Mon, 11 Sep 2023, Andreas Rheinhardt wrote:

> It is undefined behaviour even in cases where it works
> (it works because it is only a const uint8_t* vs. uint8_t* difference).
>
> Instead add a cbuf parameter to pass a const buffer (for writing)
> as well as a parameter indicating whether we are reading or writing;
> retry_transfer_wrapper() itself then uses the correct function
> based upon this information.
>
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
> Another approach; IMO the best of the three. What do you think?

OK for me, thanks.

Marton

>
> libavformat/avio.c | 16 +++++++---------
> 1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/libavformat/avio.c b/libavformat/avio.c
> index b6a192892a..b793a7546c 100644
> --- a/libavformat/avio.c
> +++ b/libavformat/avio.c
> @@ -348,10 +348,9 @@ fail:
> }
>
> static inline int retry_transfer_wrapper(URLContext *h, uint8_t *buf,
> +                                         const uint8_t *cbuf,
>                                          int size, int size_min,
> -                                         int (*transfer_func)(URLContext *h,
> -                                                              uint8_t *buf,
> -                                                              int size))
> +                                         int read)
> {
>     int ret, len;
>     int fast_retries = 5;
> @@ -361,7 +360,8 @@ static inline int retry_transfer_wrapper(URLContext *h, uint8_t *buf,
>     while (len < size_min) {
>         if (ff_check_interrupt(&h->interrupt_callback))
>             return AVERROR_EXIT;
> -        ret = transfer_func(h, buf + len, size - len);
> +        ret = read ? h->prot->url_read (h, buf + len, size - len):
> +                     h->prot->url_write(h, cbuf + len, size - len);
>         if (ret == AVERROR(EINTR))
>             continue;
>         if (h->flags & AVIO_FLAG_NONBLOCK)
> @@ -398,14 +398,14 @@ int ffurl_read2(void *urlcontext, uint8_t *buf, int size)
>
>     if (!(h->flags & AVIO_FLAG_READ))
>         return AVERROR(EIO);
> -    return retry_transfer_wrapper(h, buf, size, 1, h->prot->url_read);
> +    return retry_transfer_wrapper(h, buf, NULL, size, 1, 1);
> }
>
> int ffurl_read_complete(URLContext *h, unsigned char *buf, int size)
> {
>     if (!(h->flags & AVIO_FLAG_READ))
>         return AVERROR(EIO);
> -    return retry_transfer_wrapper(h, buf, size, size, h->prot->url_read);
> +    return retry_transfer_wrapper(h, buf, NULL, size, size, 1);
> }
>
> #if FF_API_AVIO_WRITE_NONCONST
> @@ -422,9 +422,7 @@ int ffurl_write2(void *urlcontext, const uint8_t *buf, int size)
>     if (h->max_packet_size && size > h->max_packet_size)
>         return AVERROR(EIO);
>
> -    return retry_transfer_wrapper(h, (unsigned char *)buf, size, size,
> -                                  (int (*)(struct URLContext *, uint8_t *, int))
> -                                  h->prot->url_write);
> +    return retry_transfer_wrapper(h, NULL, buf, size, size, 0);
> }
>
> int64_t ffurl_seek2(void *urlcontext, int64_t pos, int whence)
> -- 
> 2.34.1
>
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