Re: [FFmpeg-devel] [PATCH 01/21] avformat/avio: Don't use incompatible function pointer type for call

[Marton Balint <cus@passwd.hu>]

On Thu, 7 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).
>
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
> libavformat/avio.c | 25 ++++++++++++++++---------
> 1 file changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/libavformat/avio.c b/libavformat/avio.c
> index ab1c19a58d..d53da5cb0c 100644
> --- a/libavformat/avio.c
> +++ b/libavformat/avio.c
> @@ -354,10 +354,15 @@ 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_func)(URLContext *h,
> +                                                          uint8_t *buf,
> +                                                          int size),
> +                                         int (*write_func)(URLContext *h,
> +                                                           const uint8_t *buf,
> +                                                           int size),
> +                                         int read)

These extra parameters are very ugly, can't we think of another way to 
properly support this?

One idea is putting retry_transfer_wrapper in a template file and include 
it twice with proper defines-s for the read and write flavours.

Regards,
Marton


> {
>     int ret, len;
>     int fast_retries = 5;
> @@ -367,7 +372,8 @@ 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 ? read_func (h,  buf + len, size - len)
> +                   : write_func(h, cbuf + len, size - len);
>         if (ret == AVERROR(EINTR))
>             continue;
>         if (h->flags & AVIO_FLAG_NONBLOCK)
> @@ -402,14 +408,16 @@ int ffurl_read(URLContext *h, unsigned char *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,
> +                                  h->prot->url_read, NULL, 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,
> +                                  h->prot->url_read, NULL, 1);
> }
>
> int ffurl_write(URLContext *h, const unsigned char *buf, int size)
> @@ -420,9 +428,8 @@ int ffurl_write(URLContext *h, const unsigned char *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,
> +                                  NULL, h->prot->url_write, 0);
> }
>
> int64_t ffurl_seek(URLContext *h, int64_t pos, int whence)
> -- 
> 2.34.1
>
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