A python script to decode the hello games no man's sky save files. (The newer compressed kind)

decode.py

#!/usr/bin/python3
import io
import os
import lz4.block
from glob import glob

FILE_PATH = os.path.dirname(os.path.realpath(__file__))

def uint32(data):
  """Convert 4 bytes to a little endian unsigned integer."""
  return int.from_bytes(data, byteorder='little', signed=False)

def decompress(data):
  """Decompresses the given save bytes. If your groking this file for the important bit, this is it."""
  size = len(data)
  din = io.BytesIO(data)
  out = bytearray()
  while din.tell() < size:
    magic = uint32(din.read(4))
    if magic != 0xfeeda1e5:
      print("Invalid Block, bad file")
      return bytes() # some unsupported format
    compressedSize = uint32(din.read(4))
    uncompressedSize = uint32(din.read(4))
    din.seek(4, 1) # skip 4 bytes
    out += lz4.block.decompress(din.read(compressedSize), uncompressed_size=uncompressedSize)
  return out

def findSaveGames():
  """Finds all saves on windows."""
  return glob("C:\\Users\\*\\AppData\\Roaming\\HelloGames\\NMS\\*\\save*.hg")

def decodeSave(src, dst):
  print("Decoding save: %s" % os.path.basename(src))
  fin = open(src, "rb")
  data = fin.read(2)
  if data[0] != 0x7B and data[1] != 0x22:
    print("Decompressing file.")
    fin.seek(0,0) # seek to start
    data = decompress(fin.read())
  else:
    fin.seek(0,0)
    data = fin.read()
  fin.close()
  print("Saving to: %s" % os.path.basename(dst))
  fout = open(dst, "wb")
  fout.write(data)
  fout.close()

for file in findSaveGames():
  dst = os.path.join(FILE_PATH, "d_" + os.path.basename(file))
  decodeSave(file, dst)

Interested to ask a question or two. Just a fellow coder and mod developer for NMS. I'm BigBuffaloBill on discord if you have a minute sometime.

This was a bit ago I didn't really remember the details.

Hi, thanks for responding! I'm just wondering what your approach was to finding the format of the files? I want to do that same in python for the latest versions of the game files. Do you recall how you determined the file formats? I mean...if you did that just by looking at the binary you have more skill than I do. I would assume there was some source defining the format used? Thanks again!

There is a lot you can tell just looking at the binary files. But I think I got the information off from a discord chat.