decode-base64

#!/usr/bin/env python3

# SPDX-FileCopyrightText: 2022 sudorook <daemon@nullcodon.com>
#
# SPDX-License-Identifier: GPL-3.0-or-later
#
# This program is free software: you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the Free
# Software Foundation, either version 3 of the License, or (at your option)
# any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
# or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
# for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program. If not, see <https://www.gnu.org/licenses/>.

"""Detect base64-encoded text in emails and convert to UTF-8."""

import base64
import os
import sys
import re

INFILE = sys.argv[1]


def parse_input(raw_data):
    """Parse lines of raw data, and convert any detetcted base64 to UTF-8."""
    base64_flag = False
    chunks = []
    chunk = ""
    for line in raw_data:
        if base64_flag is False:
            if re.match(r"^Content-Transfer-Encoding: base64", line):
                base64_flag = True
                chunks.append(chunk)
                chunk = ""
            else:
                chunk += line
        else:
            if re.match("^--", line):
                base64_flag = False
                chunk = base64.b64decode(chunk).decode("utf-8")
                chunk += "\n" + line
                chunks.append(chunk)
                chunk = ""
            else:
                chunk += line
    chunks.append(chunk)
    return "\n".join(chunks)


def make_output_name(input_file):
    """Generate output file name by adding '_parsed' before the extension."""
    [base, ext] = os.path.splitext(input_file)
    base += "_parsed"
    return base + ext


if __name__ == "__main__":
    if not os.path.isfile(INFILE):
        sys.exit(f"'{INFILE}' not a file. Exiting")
    with open(INFILE, "r", encoding="utf-8") as f:
        DATA = f.readlines()
    PARSED_DATA = parse_input(DATA)
    OUTFILE = make_output_name(INFILE)
    with open(OUTFILE, "w", encoding="utf-8") as f:
        f.write(PARSED_DATA)