Accessing a compressed file in an apk from native code (read a zip from inside a zip)

Question

The background:

In trying to make the codebase (C/C++) for my app more portable, I would like to minimize my use of android's native AAssetManager and switch to libzip for loading assets from the APK. I had a look at libzip; merged it into the project and - lo and behold - I can read my files directly from the APK using libzip.

Now, I would like to obfuscate my assets (or at least make access to them non-trivial), so I thought I'd package them into an encrypted zip archive and include that archive in the APK (basically, a zip in a zip).

My question:

What would be the easiest/most effective way to access the files in the archive directly from within the APK using native code?

I was hoping for a similar approach as with libzip, where I can simply specify a filename and then get a buffer with uncompressed data.

I have tried opening the compressed archive directly from within the APK using libzip, but I'm coming up empty... it appears libzip will only open a zip file using a directory and not from a buffer in memory (which is as far as I got).

I suppose zlib would be an obvious choice, but I admit I have no clue how to go about it.

I also thought about copying the archive out of the APK, but I would like to waste as little space as possible (lots of assets == big archive). Delivery of the assets as a separate download is also something I'd like to avoid.

Helpful suggestions or pointers are welcome.

Answer 1

From your question it sounds like you've already got past getting to the asset stream in your APK, so I'll jump right to this: As you say, zlib is an obvious choice. There are tons and tons of examples online to process in-memory streams. For example, In Memory Decompression: GZIP . With zlib you also have the benefit that it's already available via the NDK (eg you don't need to build and link in your own).