compress_json.py

#!/usr/bin/env python

import json
import struct
import sys
import zlib

try:
    xrange          # Python 2
    PY2 = True
except NameError:
    PY2 = False
    xrange = range  # Python 3


if __name__ == '__main__':
  with open(sys.argv[1]) as fp:
    obj = json.load(fp)
  text = json.dumps(obj, separators=(',', ':')).encode('utf-8')
  data = zlib.compress(text, zlib.Z_BEST_COMPRESSION)

  # To make decompression a little easier, we prepend the compressed data
  # with the size of the uncompressed data as a 24 bits BE unsigned integer.
  assert len(text) < 1 << 24, 'Uncompressed JSON must be < 16 MB.'
  data = struct.pack('>I', len(text))[1:4] + data

  step = 20
  slices = (data[i:i+step] for i in xrange(0, len(data), step))
  slices = [','.join(str(ord(c) if PY2 else c) for c in s) for s in slices]
  text = ',\n'.join(slices)

  with open(sys.argv[2], 'w') as fp:
    fp.write(text)