Are zlib.compress on Python and Deflater.deflate on Java (Android) compatible?

Question

I am porting a Python application to Android and, at some point, this application has to communicate with a Web Service, sending it compressed data.

In order to do t

Answer 1

compress and deflate are different compression algorithms so the answer is they will not be compatible. As an example of the difference here is 'a' compressed using the two algorithms via Tcl:

% binary encode hex [zlib compress a]
789c4b040000620062
% binary encode hex [zlib deflate a]
4b0400

Your python code is indeed doing compress. And the android code is doing deflate, however you are also getting the UTF-8 byte order mark prepended to the android version (\xef\xbf\xbf)

You can emit deflate data using python:

def deflate(data):
    zobj = zlib.compressobj(6,zlib.DEFLATED,-zlib.MAX_WBITS,zlib.DEF_MEM_LEVEL,0)
    zdata = zobj.compress(data)
    zdata += zobj.flush()
    return zdata

>>> deflate("a")
'K\x04\x00'

Answer 2

Does byte[] input = stringToCompress.getBytes("utf-8"); help? In case your platform's default encoding is not UTF-8, this will force the encoding String -> bytes to use UTF-8. Also, the same goes for the last line of your code where you create a new String - you may want to explicitly specify UTF-8 as the decoding Charset.

Answer 3

Although they are not exactly the same algorithms, it seems that they are totally compatible (meaning that if you compress, for example, an String using Deflater.deflate you can correctly uncompress it using zlib).

What caused my problem was that all form variables in a POST need to be percent escaped, and the Android application was not doing that. Encoding the data to Base64 before sending it, and modifying the server to decode it using Base64 before uncompressing it using zlib solved the problem.