text: # Authors: 
  #   Trevor Perrin
  #   Moxie Marlinspike
  #
  # See the LICENSE file for legal information regarding use of this file.
  
  from tack.compat import a2b_base64
  
  class PEMDecoder:
  
      def __init__(self, data):
          self.data = data
  
      def containsEncoded(self, name):
          searchStr = "-----BEGIN %s-----" % name
          return searchStr in self.data
  
      def decode(self, name):
          """Decode a PEM string into a bytearray of its payload.
  
          The input must contain an appropriate PEM prefix and postfix
          based on the input name string, e.g. for name="CERTIFICATE":
  
          -----BEGIN CERTIFICATE-----
          MIIBXDCCAUSgAwIBAgIBADANBgkqhkiG9w0BAQUFADAPMQ0wCwYDVQQDEwRUQUNL
          ...
          KoZIhvcNAQEFBQADAwA5kw==
          -----END CERTIFICATE-----
  
          The first such PEM block in the input will be found, and its
          payload will be base64 decoded and returned.
          """
          prefix  = "-----BEGIN %s-----" % name
          postfix = "-----END %s-----" % name
          start = self.data.find(prefix)
          if start == -1:
              raise SyntaxError("Missing PEM prefix")
          end = self.data.find(postfix, start+len(prefix))
          if end == -1:
              raise SyntaxError("Missing PEM postfix")
          if end < start:
              raise SyntaxError("PEM postfix before prefix")
          s = self.data[start+len(prefix) : end]
          retBytes = a2b_base64(s)
          return retBytes
  
  
      def decodeList(self, name):
          """Decode a sequence of PEM blocks into a list of bytearrays.
  
             The input must contain any number of PEM blocks, each with the appropriate
             PEM prefix and postfix based on the input name string, e.g. for
             name="TACK BREAK SIG".  Arbitrary text can appear between and before and
             after the PEM blocks.  For example:
  
             " Created by tack.py 0.9.3 Created at 2012-02-01T00:30:10Z -----BEGIN TACK
             BREAK SIG-----
             ATKhrz5C6JHJW8BF5fLVrnQss6JnWVyEaC0p89LNhKPswvcC9/s6+vWLd9snYTUv
             YMEBdw69PUP8JB4AdqA3K6Ap0Fgd9SSTOECeAKOUAym8zcYaXUwpk0+WuPYa7Zmm
             SkbOlK4ywqt+amhWbg9txSGUwFO5tWUHT3QrnRlE/e3PeNFXLx5Bckg= -----END TACK
             BREAK SIG----- Created by tack.py 0.9.3 Created at 2012-02-01T00:30:11Z
             -----BEGIN TACK BREAK SIG-----
             ATKhrz5C6JHJW8BF5fLVrnQss6JnWVyEaC0p89LNhKPswvcC9/s6+vWLd9snYTUv
             YMEBdw69PUP8JB4AdqA3K6BVCWfcjN36lx6JwxmZQncS6sww7DecFO/qjSePCxwM
             +kdDqX/9/183nmjx6bf0ewhPXkA0nVXsDYZaydN8rJU1GaMlnjcIYxY= -----END TACK
             BREAK SIG----- "
  
             All such PEM blocks will be found, decoded, and return in an ordered list
             of bytearrays, which may have zero elements if not PEM blocks are found.
          """
          bList = []
          prefix  = "-----BEGIN %s-----" % name
          postfix = "-----END %s-----" % name
  
          s = self.data
  
          while 1:
              start = s.find(prefix)
              if start == -1:
                  return bList
              end = s.find(postfix, start+len(prefix))
              if end == -1:
                  raise SyntaxError("Missing PEM postfix")
              s2 = s[start+len(prefix) : end]
              retBytes = a2b_base64(s2) # May raise SyntaxError
              bList.append(retBytes)
              s = s[end+len(postfix) : ]
  