[Spice-devel] RFC: remove Adler checksum and zlib header/trailer from zlib compressed images

[Yaniv Kaul]

On 01/29/2012 11:29 AM, Alon Levy wrote:
> On Sun, Jan 29, 2012 at 09:28:34AM +0200, Yaniv Kaul wrote:
>> These small changes to server and (gtk) client seem to work, and
>> remove both the zlib header/trailer from the deflate stream as well
>> as the Adler checksum, which removes several bytes from the stream
>> as well as speedup (unnoticeable) of the compression/decompression
>> due to the removal of the checksum calculation.
>>
>> Problem is - not sure how to test it - don't know how to get an
>> image once with and once without the patch - and ensure it's the
>> same image.
>> The fact that the first image is never zlib compressed complicates
>> things. I could not reliably get a 2nd image sent to the client
>> which looks the same as one in a different connection.
>>
>> Nevertheless it does no harm - and images pass well - verified by
>> connecting with a modified Spice GTK client to a modified Spice
>> server, as well as looking at the network capture via wireshark.
>>
>> It's of course missing the display channel specific capability
>> negotiation for this change.

I'm afraid I could not really find where to perform the display channel 
specific capability negotiation. :(
Anyone?

TIA,
Y.

>> Comments are welcome.
> Other then that adding a link to the docs page of
> inlateInit2/deflateInit2 in the commit message would be nice for those
> seeking to find the explanation for the magic numbers, no comment,
> thanks for doing this!
>
> If you want a repeatable test you can write one or use one of the
> existing artificial tests in server/tests.
>
>> Client change:
>> diff --git a/gtk/decode-zlib.c b/gtk/decode-zlib.c
>> index a692020..997f350 100644
>> --- a/gtk/decode-zlib.c
>> +++ b/gtk/decode-zlib.c
>> @@ -63,7 +63,7 @@ SpiceZlibDecoder *zlib_decoder_new(void)
>>       d->_z_strm.opaque = Z_NULL;
>>       d->_z_strm.next_in = Z_NULL;
>>       d->_z_strm.avail_in = 0;
>> -    z_ret = inflateInit(&d->_z_strm);
>> +    z_ret = inflateInit2(&d->_z_strm, -15);
>>       if (z_ret != Z_OK) {
>>           g_warning("zlib decoder init failed, error %d", z_ret);
>>           goto fail;
>>
>>
>> server change:
>> diff --git a/server/zlib_encoder.c b/server/zlib_encoder.c
>> index c51466b..66a039a 100644
>> --- a/server/zlib_encoder.c
>> +++ b/server/zlib_encoder.c
>> @@ -47,7 +47,7 @@ ZlibEncoder*
>> zlib_encoder_create(ZlibEncoderUsrContext *usr, int level)
>>       enc->strm.zfree = Z_NULL;
>>       enc->strm.opaque = Z_NULL;
>>
>> -    z_ret = deflateInit(&enc->strm, level);
>> +    z_ret = deflateInit2(&enc->strm, level, Z_DEFLATED, -15, 8,
>> Z_DEFAULT_STRATEGY);
>>       enc->last_level = level;
>>       if (z_ret != Z_OK) {
>>           red_printf("zlib error");
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