clearmime.py

   1 #!/usr/bin/python
   2
   3 # Copyright 2008 Lenny Domnitser <http://domnit.org/>
   4 #
   5 # This program is free software; you can redistribute it and/or modify
   6 # it under the terms of the GNU General Public License as published by
   7 # the Free Software Foundation; either version 3 of the License, or (at
   8 # your option) any later version.
   9 #
  10 # This program is distributed in the hope that it will be useful, but
  11 # WITHOUT ANY WARRANTY; without even the implied warranty of
  12 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 # General Public License for more details.
  14 #
  15 # You should have received a copy of the GNU General Public License
  16 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17
  18 __all__ = 'clarify',
  19 __author__ = 'Lenny Domnitser'
  20 __version__ = '0.1'
  21
  22 import email
  23 import re
  24
  25 TEMPLATE = '''-----BEGIN PGP SIGNED MESSAGE-----
  26 Hash: %(hashname)s
  27 NotDashEscaped: You need GnuPG to verify this message
  28
  29 %(text)s%(sig)s'''
  30
  31
  32 def _clarify(message, messagetext):
  33     if message.get_content_type() == 'multipart/signed':
  34         if message.get_param('protocol') == 'application/pgp-signature':
  35             hashname = message.get_param('micalg').upper()
  36             assert hashname.startswith('PGP-')
  37             hashname = hashname.replace('PGP-', '', 1)
  38             textmess, sigmess = message.get_payload()
  39             assert sigmess.get_content_type() == 'application/pgp-signature'
  40             #text = textmess.as_string() - not byte-for-byte accurate
  41             text = messagetext.split('\n--%s\n' % message.get_boundary(), 2)[1]
  42             sig = sigmess.get_payload()
  43             assert isinstance(sig, str)
  44             # Setting content-type to application/octet instead of text/plain
  45             # to maintain CRLF endings. Using replace_header instead of
  46             # set_type because replace_header clears parameters.
  47             message.replace_header('Content-Type', 'application/octet')
  48             clearsign = TEMPLATE % locals()
  49             clearsign = clearsign.replace(
  50                 '\r\n', '\n').replace('\r', '\n').replace('\n', '\r\n')
  51             message.set_payload(clearsign)
  52     elif message.is_multipart():
  53         for message in message.get_payload():
  54             _clarify(message, messagetext)
  55
  56
  57 def clarify(messagetext):
  58     '''given a string containing a MIME message, returns a string
  59     where PGP/MIME messages are replaced with clearsigned messages.'''
  60
  61     message = email.message_from_string(messagetext)
  62     _clarify(message, messagetext)
  63     return message.as_string()
  64
  65
  66 if __name__ == '__main__':
  67     import sys
  68     sys.stdout.write(clarify(sys.stdin.read()))
  69