Usage: ./fixmeta.py --input $path_to_input_json --output $path_to_output_json

fixmeta.py

#!/usr/bin/python3
import os, hashlib, urllib.request, optparse, json

def get_remote_info(url):
  remote = urllib.request.urlopen(url)
  #Hash types
  hash1 = hashlib.sha1()
  hash256 = hashlib.sha256()
  #Download data into buffer
  data = remote.read()
  #Get size
  filesize = data.__len__()
  #Get hashes
  hash1.update(data)
  hash256.update(data)
  #Return dictionary
  info = {
    'sha1' : hash1.hexdigest(),
    'sha256' : hash256.hexdigest(),
    'size' : filesize
  }
  return info

def fixjson(input_file,output_file):
  #Load JSON meta file
  with open(input_file) as f:
    data = json.load(f)
  #Iterate through libraries
  for library in data['libraries']:
    try:
      #Replace URL
      library['downloads']['artifact']['url'] = library['downloads']['artifact']['url'].replace('libraries.minecraft.net', 'jjtech0130.github.io/natives')
      #Get hash and size of new URL
      remote_info = get_remote_info(library['downloads']['artifact']['url'])
      #Insert new hash and size
      library['downloads']['artifact']['sha1'] = remote_info['sha1']
      library['downloads']['artifact']['size'] = remote_info['size']
    except KeyError:
      pass

    try:
      #We don't need OSX and Windows natives
      del library['downloads']['classifiers']['natives-osx']
      del library['downloads']['classifiers']['natives-windows']
      #Replace URL
      library['downloads']['classifiers']['natives-linux']['url'] = library['downloads']['classifiers']['natives-linux']['url'].replace('libraries.minecraft.net', 'jjtech0130.github.io/natives')
      #Get hash and size of new URL
      remote_info = get_remote_info(library['downloads']['classifiers']['natives-linux']['url'])
      #Insert new hash and size
      library['downloads']['classifiers']['natives-linux']['sha1'] = remote_info['sha1']
      library['downloads']['classifiers']['natives-linux']['size'] = remote_info['size']
      #Delete references to the OSX and Windows natives
      del library['natives']['osx']
      del library['natives']['windows']
    except KeyError:
      pass
  #Output modified JSON
  with open(output_file, 'w') as f:
    json.dump(data, f, indent=4)

if __name__ == '__main__':
  opt = optparse.OptionParser()
  opt.add_option('--input', '-i')
  opt.add_option('--output', '-o')

  options, args = opt.parse_args()
  fixjson(options.input, options.output)