This has been completed.

I've added stream support to the zip compress method.  There is a 
limitation however - all data passed in must be converted at some 
point to an in-memory stream before passing through gzdeflate() - I 
can't get zlib stream filtering to work, although I have a hunch it is 
directly related to http://bugs.php.net/?id=48725

I guess the question for me is how widely available the pecl 
extensions are. Except for bugs, using our PHP code vs. PEAR or 
someone else's PHP code is kind of a wash to me - control vs. bugs vs. 
flexibility, etc.

(A bit broader goal:) I personally would like to see us get out of 
compression data generation all together - meaning removing PHP code 
and instead exclusively using the other solutions available (PEAR/PECL 
libraries).  pear has evolved to the point that requiring a pear/pecl 
package is not difficult/prohibitive that we need a entirely local, 
PHP-based fallback IMHO.

Moving to Framework queue for Horde 4 since this should be implemented 
in Horde_Compress

Code for inspiration or adaptation, from 
http://pablotron.org/software/zipstream-php

from chuck:



and probably changing our zip generation code to stream, instead of 
just hitting the heck out of server memory