[FFmpeg-devel] [PATCH 1/2] avformat/aviobuf: add ff_read_line_to_bprint and ff_read_line_to_bprint_overwrite functions

[Marton Balint]

On Sun, 11 Feb 2018, Nicolas George wrote:

> Marton Balint (2018-02-10):
>> To be able to read lines longer than a static buffer size.
>>
>> Signed-off-by: Marton Balint <cus at passwd.hu>
>> ---
>>  libavformat/aviobuf.c  | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>>  libavformat/internal.h | 26 ++++++++++++++++++++++++++
>>  2 files changed, 72 insertions(+)
>>
>> diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
>> index 86eb6579f4..12cd73745d 100644
>> --- a/libavformat/aviobuf.c
>> +++ b/libavformat/aviobuf.c
>> @@ -821,6 +821,52 @@ int ff_get_line(AVIOContext *s, char *buf, int maxlen)
>>      return i;
>>  }
>>
>> +int64_t ff_read_line_to_bprint(AVIOContext *s, AVBPrint *bp)
>> +{
>> +    int len, end;
>> +    int64_t read = 0;
>> +    char tmp[1024];
>> +    char c;
>> +
>
>> +    do {
>> +        len = 0;
>> +        do {
>> +            c = avio_r8(s);
>> +            end = (c == '\r' || c == '\n' || c == '\0');
>> +            if (!end)
>> +                tmp[len++] = c;
>> +        } while (!end && len < sizeof(tmp));
>> +        av_bprint_append_data(bp, tmp, len);
>> +        read += len;
>> +    } while (!end);
>
> I think the code would be much simpler if you just call
> av_bprint_chars() for each read character. The loop-within-loop makes
> the logic a little hard to understand.
>
> If speed is critic, then you could read directly into the bprint buffer,
> but I do not think this is necessary.

It is a 500% speed improvement on a 260 MB line compared to using 
av_bprint_chars, so I'd rather leave it as is. I can add a comment saying 
"for performance reasons we fill a temporary buffer, and use av_bprint 
functions on chunks of data".

Regards,
Marton