decodemail.py

#!/usr/bin/env python

# Decode From and Subject lines spammers encode in other charsets
# to try to hide them from spam filters. (RFC 2047 encoding.)
# Use in conjunction with programs like procmail or spamassassin,
# instead of something like formail

import sys, os
import email
import email.utils

progname = os.path.basename(sys.argv[0])
Usage = """Usage: %s [-a] headername [filename]

Find a line matching the given header name (Subject:, From:, etc.)
and decode it according to RFC 2047.
Without a filemame, will read standard input.
Adding -a will print all matches within the given file, not just the first.

Example: %s -a Subject: /var/mail/yourname""" % (progname, progname)

def decode_piece(piece):
    ret = ''
    for part in email.Header.decode_header(piece) :
        ret += part[0]

        # Special case: the header itself comes out with charset None
        # and decode doesn't add a space between it and the next part,
        # even though there was a space in the original. So add one.
        # I'm taking a wild guess that the relevant factor here is
        # the None charset rather than the fact that it matched
        # the header, but keep an eye open for counterexamples.
        if not part[1] :
            ret += ' '

    return ret

def decode_file(filename, header_wanted) :
    if filename == '-' :
        fil = sys.stdin
    else :
        fil = open(filename)

    output = ''
    found_something = False
    for line in fil :
        # If it matches the header we seek, or if we've already started
        # matching the header and we're looking for continuation lines,
        # build up our string:
        if (not output and line.startswith(header_wanted)) \
          or (output and (line.startswith(' ') or line.startswith('\t'))) :
            # We have a match! But we may need to read multiple lines,
            # since one header can be split over several lines.
            found_something = True

            # Strip output because we don't want the final newline.
            # But add a space if this is a continuation.
            if output:
                output += ' '
            output += decode_piece(line.strip())

        elif output :
            # if we've already matched the header, and this isn't a
            # continuation line, then we're done. Print and exit.

            # If the header is an address, we have to split it into parts
            # before we can decode it. If it's another header such as Subject,
            # we can't do that.
            if header_wanted.startswith("From") \
                    or header_wanted.startswith("To") \
                    or header_wanted.startswith("Cc") \
                    or header_wanted.startswith("Bcc"):
                pieces = email.utils.parseaddr(output)
                if pieces[0] or pieces[1]:
                    output = header_wanted + ' ' + \
                             email.utils.formataddr(map(decode_piece, pieces))
                else:
                    output += line
                    print "parseaddr failed on", line,


            #sys.stdout.write("<<" + part[0] + '>>')
            print output.strip()
            if all :
                output = ''
            else :
                sys.exit(0)

    # If we get here, we never matched a header,
    # or ended with a continuation line.
    if not found_something :
        print "No such header", header_wanted, "in", filename
        return

if sys.argv[1] == '-h' or sys.argv[1] == '--help' :
    print Usage
    sys.exit(1)

# A -a argument means don't stop at the first header,
# decode all matching headers in the file.
if sys.argv[1] == '-a' :
    all = True
    sys.argv = sys.argv[1:]
else :
    all = False

header_wanted = sys.argv[1]

try :
    if len(sys.argv) > 2 :
        for filename in sys.argv[2:] :
            decode_file(filename, sys.argv[1])
    else :
        fil = sys.stdin
        decode_file('-', sys.argv[1])
except KeyboardInterrupt :
    sys.exit(1)