[FFmpeg-devel] [PATCH] avcodec/bsf: switch to av_get_token to parse bsf list string

[James Almer]

On 7/3/2021 12:48 PM, Gyan Doshi wrote:
> 
> 
> On 2021-07-03 19:47, James Almer wrote:
>> On 7/3/2021 8:42 AM, Gyan Doshi wrote:
>>> The recently added setts bsf makes use of the eval API whose
>>> expressions can contain commas. The existing parsing in
>>> av_bsf_list_parse_str() uses av_strtok to naively split
>>> the string at commas, thus preventing the use of setts filter
>>> with expressions containing commas.
>>> ---
>>>   libavcodec/bsf.c | 13 +++++++------
>>>   1 file changed, 7 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/libavcodec/bsf.c b/libavcodec/bsf.c
>>> index 9d67ea5395..726911785d 100644
>>> --- a/libavcodec/bsf.c
>>> +++ b/libavcodec/bsf.c
>>> @@ -520,7 +520,8 @@ static int bsf_parse_single(char *str, AVBSFList 
>>> *bsf_lst)
>>>   int av_bsf_list_parse_str(const char *str, AVBSFContext **bsf_lst)
>>>   {
>>>       AVBSFList *lst;
>>> -    char *bsf_str, *buf, *dup, *saveptr;
>>> +    char *bsf_str, *dup;
>>> +    const char *buf;
>>>       int ret;
>>>         if (!str)
>>> @@ -530,18 +531,18 @@ int av_bsf_list_parse_str(const char *str, 
>>> AVBSFContext **bsf_lst)
>>>       if (!lst)
>>>           return AVERROR(ENOMEM);
>>>   -    if (!(dup = buf = av_strdup(str))) {
>>> +    if (!(buf = dup = av_strdup(str))) {
>>
>> Is this av_strdup() even necessary? You could let av_get_token() 
>> update str just fine and remove both buf and dup. Or maybe just use a 
>> copy of the pointer in buf.
>>
>>>           ret = AVERROR(ENOMEM);
>>>           goto end;
>>>       }
>>>   -    while (bsf_str = av_strtok(buf, ",", &saveptr)) {
>>> +    do {
>>> +        bsf_str = av_get_token(&buf, ",");
>>
>> You can reduce the scope of bsf_str now, so declare it here.
>>
>>>           ret = bsf_parse_single(bsf_str, lst);
>>> +        av_free(bsf_str);
>>>           if (ret < 0)
>>>               goto end;
>>> -
>>> -        buf = NULL;
>>> -    }
>>> +    } while (*buf == ',' && buf++);
>>
>> You can simplify this into while (*++buf) or (*++str) if you remove 
>> the av_strdup().
> 
> Won't this go out of bounds at the end?

Yeah, good catch. Change it to while (*buf && *++buf) then, which will 
also preserve the existing behavior.

> 
> 
>> It will also preserve the existing behavior of discarding the last 
>> comma in the string if it's the last character, instead of aborting 
>> with EINVAL.
>>
>>>         ret = av_bsf_list_finalize(&lst, bsf_lst);
>>>   end:
>>>
>>
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