I've been trying to write some Java code to read .mca files, based on the information at http://wiki.vg/Map_Format and http://wiki.vg/User:Sprenger120 . I am at the point where I can read in the header correctly, and read the header for each section, telling me its compression mode and size. I am now trying to inflate the NBT blob that is the actual section, but it's not working at all. I just get "java.io.IOException: Not in GZIP format".
I'm starting the deflation stream five bytes into the memory segment specified by the header, and given that I am consistently getting sane section sizes and compression types, it seems like I'm managing to parse correctly up to this point, but now I'm stuck.
The code is at: https://github.com/Zarkonnen/Ager/tree/master/src/ager
I don't know if this is the correct forum to ask this kind of question - if it isn't, I apologise and would be very thankful if someone could direct me to a good place to ask it.