Re: [FFmpeg-devel] [PATCH 1/3] avutil/dict: add av_dict_pop

[Marvin Scholz <epirat07@gmail.com>]

On 22 May 2023, at 1:52, Stefano Sabatini wrote:

> On date Monday 2023-05-01 13:44:54 +0200, Marvin Scholz wrote:
>> This new API allows to remove an entry and obtain ownership of the
>> key/value that was associated with the removed entry.

Thanks for the review!

>> ---
>>  doc/APIchanges         |  4 ++++
>>  libavutil/dict.c       | 27 +++++++++++++++++++++++++++
>>  libavutil/dict.h       | 20 ++++++++++++++++++++
>>  libavutil/tests/dict.c | 34 ++++++++++++++++++++++++++++++++++
>>  libavutil/version.h    |  2 +-
>>  tests/ref/fate/dict    | 12 ++++++++++++
>>  6 files changed, 98 insertions(+), 1 deletion(-)
>>
>> diff --git a/doc/APIchanges b/doc/APIchanges
>> index 0b609e3d3b..5b807873b7 100644
>> --- a/doc/APIchanges
>> +++ b/doc/APIchanges
>> @@ -2,6 +2,10 @@ The last version increases of all libraries were on 2023-02-09
>>
>>  API changes, most recent first:
>>
>> +2023-04-29 - xxxxxxxxxx - lavu 58.7.100 - dict.c
>> +  Add av_dict_pop() to remove an entry from a dict
>> +  and get ownership of the removed key/value.
>> +
>>  2023-04-10 - xxxxxxxxxx - lavu 58.6.100 - frame.h
>>    av_frame_get_plane_buffer() now accepts const AVFrame*.
>>
>> diff --git a/libavutil/dict.c b/libavutil/dict.c
>> index f673977a98..ac41771994 100644
>> --- a/libavutil/dict.c
>> +++ b/libavutil/dict.c
>> @@ -173,6 +173,33 @@ int av_dict_set_int(AVDictionary **pm, const char *key, int64_t value,
>>      return av_dict_set(pm, key, valuestr, flags);
>>  }
>>
>> +int av_dict_pop(AVDictionary **pm, const char *key,
>> +                char **out_key, char **out_value, int flags)
>> +{
>> +    AVDictionary *m = *pm;
>> +    AVDictionaryEntry *entry = NULL;
>> +    entry = (AVDictionaryEntry *)av_dict_get(m, key, NULL, flags);
>> +    if (!entry)
>> +        return AVERROR(ENOENT);
>> +
>> +    if (out_key)
>> +        *out_key = entry->key;
>> +    else
>> +        av_free(entry->key);
>> +
>> +    if (out_value)
>> +        *out_value = entry->value;
>> +    else
>> +        av_free(entry->value);
>> +
>> +    *entry = m->elems[--m->count];
>
>> +    if (m && !m->count) {
>> +        av_freep(&m->elems);
>> +        av_freep(pm);
>> +    }
>
> I'm not sure this is the right behavior. Should we clear the
> dictionary when it is empty? What if you need to refill it later?
>

Thats the same behaviour as if you use av_dict_set to remove all items
and IMO this should be consistent.
Additionally NULL means an empty AVDictionary, suddenly
having a non-NULL but empty dictionary seems like a very bad idea.

>> +    return 0;
>> +}
>> +
>>  static int parse_key_value_pair(AVDictionary **pm, const char **buf,
>>                                  const char *key_val_sep, const char *pairs_sep,
>>                                  int flags)
>> diff --git a/libavutil/dict.h b/libavutil/dict.h
>> index 713c9e361a..b2ab55a026 100644
>> --- a/libavutil/dict.h
>> +++ b/libavutil/dict.h
>> @@ -172,6 +172,26 @@ int av_dict_set(AVDictionary **pm, const char *key, const char *value, int flags
>>   */
>>  int av_dict_set_int(AVDictionary **pm, const char *key, int64_t value, int flags);
>>
>> +/**
>> + * Remove the entry with the given key from the dictionary.
>> + *
>
>> + * Search for an entry matching `key` and remove it, if found. Optionally
>
> Not sure the `foo` syntax is supported by doxygen (and probably we
> should eschew it for consistency with the other doxys).
>

I tested it locally and it works fine and its much more readable than the
alternatives.

However if you feel it should be removed I am happy to do that, I have no
strong opinions there.

>> + * the found key and/or value can be returned using the `out_key`/`out_value`
>> + * arguments.
>
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