#!/usr/bin/env python
# A script to verify the email of type multipart signed
# passed in from stdin
# Want to handle pgp signatures attached to messages from evolution
# (cf. RFC 2015, application/pgp-signature)

from pprint import pprint
import sys, re, mimetools, cStringIO, multifile

# (1) read in entire message for safekeeping and then turn back into
# file object with cStringIO

inputbuf  =sys.stdin.read()   
strfp = cStringIO.StringIO(inputbuf)

# use mimetools to parse mime headers

msg = mimetools.Message(strfp)


email_type = msg.getmaintype()

if  email_type == 'multipart' and msg.getsubtype()=='signed':
    sys.stdout.write("This is a multipart/signed message.  Let get busy\n")
    # plist = msg.getplist()
    # pprint(plist)

    # assume that it's protocol is correct for now
    boundary = msg.getparam('boundary')
    # print "boundary is %s" % boundary
    # now split message at boundaries
    mfile = multifile.MultiFile(strfp)
    mfile.push(msg.getparam("boundary"))
    while mfile.next():
        submsg = mimetools.Message(mfile)
        try:
            data = cStringIO.StringIO()
            mimetools.decode(mfile, data, submsg.getencoding())
        except ValueError:
            continue
        if submsg.gettype() == 'application/pgp-signature':
            print "This is the signature: "
            sys.stdout.write(data.getvalue() )
            open("/tmp/body.asc", "wb").write(data.getvalue())
        else:
            print "This is part of the body"
            sys.stdout.write(data.getvalue() )
            open("/tmp/body.decoded", "wb").write(data.getvalue() )
            mfile.seek(0)
            open("/home/clee/body", "wb").write(mfile.read())
            
    mfile.pop()
else:
    sys.stdout.write("Not a multipart/signed message\n")
    sys.stdout.write("The actual mime type is:\n")
    sys.stdout.write("getmaintype(): %s\n" % msg.getmaintype())
    sys.stdout.write("getsubtype(): %s\n" % msg.getsubtype())
    sys.stdout.write("getplist(): %s\n" % msg.getplist())
    

# [From RFC 2015]
#
# When the PGP digital signature is generated:

# (1) The data to be signed must first be converted to its type/subtype
#     specific canonical form. For text/plain, this means conversion to an
#     appropriate character set and conversion of line endings to the
#     canonical <CR><LF> sequence.

# (2) An appropriate Content-Transfer-Encoding is then applied. Each line of
#     the encoded data MUST end with the canonical <CR><LF> sequence.

# (3) MIME content headers are then added to the body, each ending with the
#     canonical <CR><LF> sequence.

# (4) As described in [1], the digital signature MUST be calculated over both
#     the data to be signed and its set of content headers.

# (5) The signature MUST be generated detached from the signed data so that
#     the process does not alter the signed data in any way.