Testing tool: corrupt a file

corrupt.py

#!/usr/bin/env python -u

# Read from stdin, corrupt/remove random bytes, write to standard out.

import optparse
import random
import sys

def main():
  parser = optparse.OptionParser(usage="%prog [options]")
  parser.add_option("--n", dest="n", type="int", default=1,
                    help="how many single-byte errors to introduce")
  parser.add_option("--r", dest="remove", type="int", default=0,
                    help="how many bytes to erase")
  parser.add_option("--verbose", dest="verbose", action="store_true",
                    help="be verbose")
  (options, args) = parser.parse_args()

  data = bytearray(sys.stdin.read())

  for i in range(0, options.n):
    position = random.randrange(0, len(data))
    oldbyte = data[position]
    newbyte = (oldbyte+random.randrange(1,256))%256
    data[position] = newbyte
    if options.verbose:
      print >> sys.stderr, "Replaced byte %d with %d at position %d"%(oldbyte,newbyte,position)

  for i in range(0, options.remove):
    position = random.randrange(0, len(data))
    oldbyte = data[position]
    del data[position]
    if options.verbose:
      print >> sys.stderr, "Deleted byte at position %d"%(position)

  sys.stdout.write(data)

if __name__ == '__main__':
  main()