Compress in Java, decompress in Python?

Question

I am trying to compress a string in my Android app (Java) and then decompress it on the server with Python. I tried using the Inflater class, but then I get an "error: Error -3 while decompressing data: incorrect header check" on the python side. On the python side, I'm using zlib to decompress:

data_string = zlib.decompress(compressed_string)

On the Android side, we are using Deflater to compress:

String stringData = commentData == null ? sleepData.toString() : sleepData.toString() + commentData.toString();

byte[] bytes = stringData.getBytes("UTF-8");
int length = bytes.length;
Deflater deflater = new Deflater();
deflater.setInput(bytes);
deflater.finish();
byte[] compressedBytes = new byte[length];
deflater.deflate(compressedBytes);
deflater.end();

How can I decompress in python the string that the app is sending?

Thanks!

EDITS: This is what we are sending from Android and are feeding into the decompress command: (the dots represent just more of the same - there are a lot of zeros and then some "0b's" in the end: "78efbfbdefbfbdefbfbdefbfbd6e1b2....efbfbd190000000.....0000‌​000000000b0b0b0b0b0b‌​0b0b0b0b0b

Things we have tried:

-- data_string = zlib.decompress(decrypted,-zlib.MAX_WBITS), which gives a new error: "Error -3 while decompressing data: invalid stored block lengths"

-- data_string = zlib.decompressobj(decrypted,15+32) and data_string = zlib.decompress(compressed_string, 16+zlib.MAX_WBITS) which both give the initial error "invalid header check".

Answer 1

Add 16+zlib.MAX_WBITS or 15 + 32 as the second [optional] wbits arg in decompress: https://docs.python.org/2/library/zlib.html#zlib.decompress

data_string = zlib.decompress(compressed_string, 16+zlib.MAX_WBITS)

EDIT: Depending on how you're passing the compressed bytes to Python, it's likely your issue is with how Python is reading your compressed bytes.

I recommend using Base64 encoding on the compressed bytes in Java, then decoding the base64 in Python then decompressing those bytes in this vein...

Java:

String inputString = "blahblahblah";
byte[] input = inputString.getBytes("UTF-8");

// Compress the bytes
byte[] output = new byte[100];
Deflater compresser = new Deflater();
compresser.setInput(input);
compresser.finish();
int compressedDataLength = compresser.deflate(output);
compresser.end();
System.out.println(Base64.getEncoder().encodeToString(output)); 

Python:

import base64
import zlib
base64_binary = b"eJxLyknMSIJiAB8CBMYAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=="
deflate_bytes=base64.decodebytes(base64_binary)
zlib.decompress(deflate_bytes)
# b'blahblahblah'

Related:

How can I decompress a gzip stream with zlib?

Python decompressing gzip chunk-by-chunk

Byte Array in Python