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Date: Thu, 9 Mar 2023 00:37:51 +0100 (CET)
From: Marton Balint <cus@passwd.hu>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
In-Reply-To: <tencent_5FEB93A291A4AB1D5FCD5042F2AA4AC5E306@qq.com>
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MIME-Version: 1.0
Subject: Re: [FFmpeg-devel] [PATCH] libavformat/img2dec: fix unable to find
 svg format when the svg resources start with "<svg"
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On Tue, 7 Mar 2023, 1035567130@qq.com wrote:

> From: Wang Yaqiang <wangyaqiang03@kuaishou.com>
>
> svg is xml, but <?xml is not required,
> it can start with <svg and can have multiple empty lines.
>
> Signed-off-by: Wang Yaqiang <wangyaqiang03@kuaishou.com>
> ---
> libavformat/img2dec.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/libavformat/img2dec.c b/libavformat/img2dec.c
> index 5a63d7c81d..448a574b59 100644
> --- a/libavformat/img2dec.c
> +++ b/libavformat/img2dec.c
> @@ -25,6 +25,7 @@
> #define _DEFAULT_SOURCE
> #define _BSD_SOURCE
> #include <sys/stat.h>
> +#include <ctype.h>

Please no, use libavutil/avstring.h for av_isspace() instead.

> #include "libavutil/avstring.h"
> #include "libavutil/log.h"
> #include "libavutil/opt.h"
> @@ -964,18 +965,19 @@ static int svg_probe(const AVProbeData *p)
> {
>     const uint8_t *b = p->buf;
>     const uint8_t *end = p->buf + p->buf_size;
> -
> -    if (memcmp(p->buf, "<?xml", 5))
> +    while (b && b < end && isspace(*b)) b++;

av_isspace()

> +    if (b >= end - 5) return 0;

line break before return

> +    if (memcmp(p->buf, "<?xml", 5) && memcmp(b, "<svg", 4))
>         return 0;

Why not simply return AVPROBE_SCORE_EXTENSION + 1 here for the <svg case? 
You don't have to change the rest that way which skips the first line 
which supposed to contain <?xml

Regards,
Marton

>     while (b < end) {
>         int inc = ff_subtitles_next_line(b);
>         if (!inc)
>             break;
> +        if (!memcmp(b, "<svg", 4))
> +            return AVPROBE_SCORE_EXTENSION + 1;
>         b += inc;
>         if (b >= end - 4)
>             return 0;
> -        if (!memcmp(b, "<svg", 4))
> -            return AVPROBE_SCORE_EXTENSION + 1;
>     }
>     return 0;
> }
> -- 
> 2.39.2
>
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