At work I recently was given the task to support gzip-based HTTP response compression in a C++ MFC application. For a while I was convinced that there was no way to support in-memory decompression of gzip-compressed data using zlib, and so I wrote the gzipped data to a temporary file and then used the gzopen()/gzread()-family of functions in zlib to read it back (as described in the zlib manual).
I spent a lot of time looking at the zlib code to try to see why the in-memory streaming decompression function inflate() wasn’t working for gzip-compressed data and determined that zlib wasn’t recognizing the gzip headers. The inflate() function had code which purported to understand the headers, but it wasn’t being enabled due to reasons unknown. After some more sleuthing, I noticed the gzopen()/gzread() functions implemented their own gzip header detection and passed only the raw data to inflate(). Once I noticed this, I threw my hands up in disgust and said it couldn’t be done.