Re: [RFC] CryptoAPI & Compression

["Artem B. Bityuckiy" <dedekind@yandex.ru>]

Herbert Xu wrote:
> You might be right.  But I'm not sure yet.
> 
> If we use the current code and supply zlib_deflate with 1048576-12 bytes
> of (incompressible) input and 1048576 bytes of output buffer, wouldn't
> zlib keep writing incompressible blocks and return when it can't do that
> anymore because the output buffer has been exhausted?
It must not. Look at the algoritm closer.

stream->next_in = (u8 *)src;
stream->next_out = dst;

while (stream->total_in < *slen
        && stream->total_out < *dlen - DEFLATE_PCOMPR_RESERVE) {

         stream->avail_out = *dlen - DEFLATE_PCOMPR_RESERVE - 
stream->total_out;
         stream->avail_in = min((unsigned int)(*slen - 
stream->total_in), stream->avail_out);

         ret = zlib_deflate(stream, Z_SYNC_FLUSH);
         if (ret != Z_OK)
                 return -EINVAL;
}

stream->avail_out += DEFLATE_PCOMPR_RESERVE;
stream->avail_in = 0; /* <------ no more input ! ---------- */

ret = zlib_deflate(stream, Z_FINISH);
if (ret != Z_STREAM_END)
         return -EINVAL;



> 
> When it does return it has to finish writing the last block it's on.
No, it must only put EOB and adler32, we won't give it more input.

-- 
Best Regards,
Artem B. Bityuckiy,
St.-Petersburg, Russia.