GNUTLS compression

Handi Ajimasta hajimasta at
Tue Nov 10 11:40:20 CET 2009

Hi all,

I installed gnutls 2.5.5 in Windows XP, and gnutls 2.8.4 in Windows 7
Release Candidate from .

I thought that 'DEFLATE' compression algorithm is enabled by default in
all gnutls releases. However, when I force my TLS client to use DEFLATE
algorithm (and not the NULL) by:

int pPriorities[3] = {GNUTLS_COMP_DEFLATE, 0};
gnutls_compression_set_priority(session, pPriorities);

My TLS client is not able to handshake with the server, because the
compression algorithm is not available.

When I did a 'gnutls-cli -l' in command prompt in both Windows XP and
Windows 7, what I saw was: "COMPRESSION: NULL" only, without DEFLATE nor
LZO algorithm.

I successfully installed gnutls in an Ubuntu machine though, and when I
did 'gnutls-cli -l' I could see that it has both DEFLATE algorithm and
NULL there without me configuring anything at all.

My questions are:
1) Is compression available for gnutls in Windows?
2) If it's yes.. how do I enable it?
3) If it's not available.. is there any way that I could enable it?
4) Is there any performance gain from enabling the compression? I
understand that we might save some bandwidth with the compression, but
with increased lag time, is there any noticeable difference?

Thanks in advance for any help given.


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