Compression

In wowm both messages and individual arrays can have the compressed tag.

Before the compressed data there is a u32 with the size of the data after decompression. This is present both for entire messages that are compressed and for individual arrays.

Both variables and messages can be decompressed with zlib.

In order to verify, the following bytes:

0x78, 0x9c, 0x75, 0xcc, 0xbd, 0x0e, 0xc2, 0x30, 0x0c,
0x04, 0xe0, 0xf2, 0x1e, 0xbc, 0x0c, 0x61, 0x40, 0x95,
0xc8, 0x42, 0xc3, 0x8c, 0x4c, 0xe2, 0x22, 0x0b, 0xc7,
0xa9, 0x8c, 0xcb, 0x4f, 0x9f, 0x1e, 0x16, 0x24, 0x06,
0x73, 0xeb, 0x77, 0x77, 0x81, 0x69, 0x59, 0x40, 0xcb,
0x69, 0x33, 0x67, 0xa3, 0x26, 0xc7, 0xbe, 0x5b, 0xd5,
0xc7, 0x7a, 0xdf, 0x7d, 0x12, 0xbe, 0x16, 0xc0, 0x8c,
0x71, 0x24, 0xe4, 0x12, 0x49, 0xa8, 0xc2, 0xe4, 0x95,
0x48, 0x0a, 0xc9, 0xc5, 0x3d, 0xd8, 0xb6, 0x7a, 0x06,
0x4b, 0xf8, 0x34, 0x0f, 0x15, 0x46, 0x73, 0x67, 0xbb,
0x38, 0xcc, 0x7a, 0xc7, 0x97, 0x8b, 0xbd, 0xdc, 0x26,
0xcc, 0xfe, 0x30, 0x42, 0xd6, 0xe6, 0xca, 0x01, 0xa8,
0xb8, 0x90, 0x80, 0x51, 0xfc, 0xb7, 0xa4, 0x50, 0x70,
0xb8, 0x12, 0xf3, 0x3f, 0x26, 0x41, 0xfd, 0xb5, 0x37,
0x90, 0x19, 0x66, 0x8f

Should decompress to the following bytes:

66, 108, 105, 122, 122, 97, 114, 100, 95, 65, 117, 99, 116, 105, 111, 110, 85, 73, 0, // [0].AddonInfo.addon_name: CString
1, // [0].AddonInfo.addon_has_signature: u8
109, 119, 28, 76, // [0].AddonInfo.addon_crc: u32
0, 0, 0, 0, // [0].AddonInfo.addon_extra_crc: u32
66, 108, 105, 122, 122, 97, 114, 100, 95, 66, 97, 116, 116, 108, 101, 102, 105, 101, 108, 100, 77, 105, 110, 105, 109, 97, 112, 0, // [1].AddonInfo.addon_name: CString
1, // [1].AddonInfo.addon_has_signature: u8
109, 119, 28, 76, // [1].AddonInfo.addon_crc: u32
0, 0, 0, 0, // [1].AddonInfo.addon_extra_crc: u32
66, 108, 105, 122, 122, 97, 114, 100, 95, 66, 105, 110, 100, 105, 110, 103, 85, 73, 0, // [2].AddonInfo.addon_name: CString
1, // [2].AddonInfo.addon_has_signature: u8
109, 119, 28, 76, // [2].AddonInfo.addon_crc: u32
0, 0, 0, 0, // [2].AddonInfo.addon_extra_crc: u32
66, 108, 105, 122, 122, 97, 114, 100, 95, 67, 111, 109, 98, 97, 116, 84, 101, 120, 116, 0, // [3].AddonInfo.addon_name: CString
1, // [3].AddonInfo.addon_has_signature: u8
109, 119, 28, 76, // [3].AddonInfo.addon_crc: u32
0, 0, 0, 0, // [3].AddonInfo.addon_extra_crc: u32
66, 108, 105, 122, 122, 97, 114, 100, 95, 67, 114, 97, 102, 116, 85, 73, 0, // [4].AddonInfo.addon_name: CString
1, // [4].AddonInfo.addon_has_signature: u8
109, 119, 28, 76, // [4].AddonInfo.addon_crc: u32
0, 0, 0, 0, // [4].AddonInfo.addon_extra_crc: u32
66, 108, 105, 122, 122, 97, 114, 100, 95, 71, 77, 83, 117, 114, 118, 101, 121, 85, 73, 0, // [5].AddonInfo.addon_name: CString
1, // [5].AddonInfo.addon_has_signature: u8
109, 119, 28, 76, // [5].AddonInfo.addon_crc: u32
0, 0, 0, 0, // [5].AddonInfo.addon_extra_crc: u32
66, 108, 105, 122, 122, 97, 114, 100, 95, 73, 110, 115, 112, 101, 99, 116, 85, 73, 0, // [6].AddonInfo.addon_name: CString
1, // [6].AddonInfo.addon_has_signature: u8
109, 119, 28, 76, // [6].AddonInfo.addon_crc: u32
0, 0, 0, 0, // [6].AddonInfo.addon_extra_crc: u32
66, 108, 105, 122, 122, 97, 114, 100, 95, 77, 97, 99, 114, 111, 85, 73, 0, // [7].AddonInfo.addon_name: CString
1, // [7].AddonInfo.addon_has_signature: u8
109, 119, 28, 76, // [7].AddonInfo.addon_crc: u32
0, 0, 0, 0, // [7].AddonInfo.addon_extra_crc: u32
66, 108, 105, 122, 122, 97, 114, 100, 95, 82, 97, 105, 100, 85, 73, 0, // [8].AddonInfo.addon_name: CString
1, // [8].AddonInfo.addon_has_signature: u8
109, 119, 28, 76, // [8].AddonInfo.addon_crc: u32
0, 0, 0, 0, // [8].AddonInfo.addon_extra_crc: u32
66, 108, 105, 122, 122, 97, 114, 100, 95, 84, 97, 108, 101, 110, 116, 85, 73, 0, // [9].AddonInfo.addon_name: CString
1, // [9].AddonInfo.addon_has_signature: u8
109, 119, 28, 76, // [9].AddonInfo.addon_crc: u32
0, 0, 0, 0, // [9].AddonInfo.addon_extra_crc: u32
66, 108, 105, 122, 122, 97, 114, 100, 95, 84, 114, 97, 100, 101, 83, 107, 105, 108, 108, 85, 73, 0, // [10].AddonInfo.addon_name: CString
1, // [10].AddonInfo.addon_has_signature: u8
109, 119, 28, 76, // [10].AddonInfo.addon_crc: u32
0, 0, 0, 0, // [10].AddonInfo.addon_extra_crc: u32
66, 108, 105, 122, 122, 97, 114, 100, 95, 84, 114, 97, 105, 110, 101, 114, 85, 73, 0, // [11].AddonInfo.addon_name: CString
1, // [11].AddonInfo.addon_has_signature: u8
109, 119, 28, 76, // [11].AddonInfo.addon_crc: u32
0, 0, 0, 0, // [11].AddonInfo.addon_extra_crc: u32

The Python standard library has a zlib module which can be used for this:

import zlib
data = bytes([0x78, 0x9c, 0x75, 0xcc, 0xbd, 0x0e, 0xc2, 0x30, 0x0c, 0x04, 0xe0, 0xf2, 0x1e, 0xbc, 0x0c, 0x61, 0x40, 0x95, 0xc8, 0x42, 0xc3, 0x8c, 0x4c, 0xe2, 0x22, 0x0b, 0xc7, 0xa9, 0x8c, 0xcb, 0x4f, 0x9f, 0x1e, 0x16, 0x24, 0x06, 0x73, 0xeb, 0x77, 0x77, 0x81, 0x69, 0x59, 0x40, 0xcb, 0x69, 0x33, 0x67, 0xa3, 0x26, 0xc7, 0xbe, 0x5b, 0xd5, 0xc7, 0x7a, 0xdf, 0x7d, 0x12, 0xbe, 0x16, 0xc0, 0x8c, 0x71, 0x24, 0xe4, 0x12, 0x49, 0xa8, 0xc2, 0xe4, 0x95, 0x48, 0x0a, 0xc9, 0xc5, 0x3d, 0xd8, 0xb6, 0x7a, 0x06, 0x4b, 0xf8, 0x34, 0x0f, 0x15, 0x46, 0x73, 0x67, 0xbb, 0x38, 0xcc, 0x7a, 0xc7, 0x97, 0x8b, 0xbd, 0xdc, 0x26, 0xcc, 0xfe, 0x30, 0x42, 0xd6, 0xe6, 0xca, 0x01, 0xa8, 0xb8, 0x90, 0x80, 0x51, 0xfc, 0xb7, 0xa4, 0x50, 0x70, 0xb8, 0x12, 0xf3, 0x3f, 0x26, 0x41, 0xfd, 0xb5, 0x37, 0x90, 0x19, 0x66, 0x8f])

decompressed_data = zlib.decompress(data)

compressed_data = zlib.compress(decompressed_data)

In order to create an uncompressed zlib stream, the following python code can be used:

def adler32(data: bytes) -> int:
    MOD_ADLER = 65521
    a = 1
    b = 0

    for i in range(0, len(data)):
        a = (a + data[i]) % MOD_ADLER
        b = (b + a) % MOD_ADLER

    return b << 16 | a

def create_zlib_stream(data: bytes) -> bytes:
    b = bytearray([
        0x78, 0x01, # zlib header
        0x01, # BFINAL and no compression
    ])
    length = len(data)
    b.append(length & 0xff)
    b.append((length & 0xff00) >> 8)

    nlength = length ^ 0xffff
    b.append(nlength & 0xff)
    b.append((nlength & 0xff00) >> 8)

    b += (data)

    b += (adler32(data).to_bytes(4, "big"))

    return b

print(create_zlib_stream(data))

This can be used instead of a library for compressing, although decompression will probably still require a library.

Wowm Language

Compression