This adds some code to zlib to provide in-memory unzip capability.

From the zlib[1] home page, zlib is designed to be a free, general-purpose, legally unencumbered -- that is, not covered by any patents -- lossless data-compression library for use on virtually any computer hardware and operating system.

At minizip[2], I found a reference to Justin Fletcher who "wrote a very simple implementation of a memory access method for the ioapi code". I made a few edits to handle 64 bit builds.

ioapi_mem.h and ioapi_mem.c are placed into the main zlib build directory. I use the following to build a custom zlib (I could probably build a separate library, but it simplifies some stuff for me to include this code):

wget http://zlib.net/zlib-1.2.8.tar.gz
tar zxvf zlib-1.2.8.tar.gz
cd zlib-1.2.8

git clone https://github.com/rburkholder/ioapi_mem.git

ln -s ioapi_mem/ioapi_mem.c ioapi_mem.c
ln -s ioapi_mem/ioapi_mem.h ioapi_mem.h

ln -s contrib/minizip/unzip.c unzip.c
ln -s contrib/minizip/unzip.h unzip.h
ln -s contrib/minizip/ioapi.c ioapi.c
ln -s contrib/minizip/ioapi.h ioapi.h

cp Makefile.in Makefile.in.original
sed -i "s/zutil.o$/zutil.o ioapi.o ioapi_mem.o unzip.o/" Makefile.in
sed -i "s/zutil.lo$/zutil.lo ioapi.lo ioapi_mem.lo unzip.lo/" Makefile.in

./configure --64 --prefix=/usr/local --includedir=/usr/local/include/zlib

make
sudo make install

sudo cp ioapi.h /usr/local/include/zlib
sudo cp ioapi_mem.h /usr/local/include/zlib
sudo cp unzip.h /usr/local/include/zlib

Some additional background info can be found at my blog[3] for some build info for visual studio (possibly out of date).

[1] http://www.zlib.net/
[2] http://www.winimage.com/zLibDll/minizip.html
[3] http://blog.raymond.burkholder.net/index.php?/archives/598-Build-zlib-v1.2.8-with-Visual-Studio-2012.html