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Filename : clean_exim.py
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#!/usr/lib/rads/venv/bin/python3
"""Python exim cleanup script to reduce the urge to run hacky oneliners"""

import argparse
import re
import subprocess
import sys
from collections import defaultdict

# compile regex once and recycle them throughout the script for efficiency
EXIM_BP_RE = re.compile(
    r'\s*(?P<age>[0-9]+[mhd])\s+[0-9\.]+[M|K]? '  # 5m 15K
    r'(?P<id>[a-zA-Z0-9\-]+)\s+'  # 1XEhho-0006AU-Tx
    r'\<(?P<sender>.*)\>'  # <emailuser@domain>
)


def run(command: list[str] | str, shell=False) -> subprocess.CompletedProcess:
    """
    Run a process with arguments.
    Optionally, as a shell command
    returns CompletedProcess.
    """
    args = command

    result = subprocess.run(
        args,
        capture_output=True,
        shell=shell,
        errors="surrogateescape",
        encoding="utf-8",
        check=False,
    )
    return result


def get_queue(exclude_bounces=False, bounces_only=False):
    """Get current exim queue as a list of dicts, each dict
    containing a single message, with keys 'age', 'id', and 'sender'"""
    queue = []
    out = run(["exim", "-bp"])
    queue_lines = out.stdout.splitlines()
    for line in queue_lines:
        match = EXIM_BP_RE.match(line)
        if match is None:
            continue
        groupdict = match.groupdict()
        if exclude_bounces and groupdict['sender'] == '':
            continue
        if bounces_only and groupdict['sender'] != '':
            continue
        groupdict['age'] = exim_age_to_secs(groupdict['age'])
        if groupdict['age'] > 3600:
            queue.append(groupdict)
    return queue


def exim_age_to_secs(age):
    """convert exim age to seconds"""
    conversions = {'m': 60, 'h': 3600, 'd': 86400}
    # find the multiplier based on above conversions
    multiplier = conversions[age[-1]]
    # typecast to int and use multiplier above
    return int(age.rstrip('mhd')) * multiplier


def is_boxtrapper(msg_id):
    """Determine if a message ID is a boxtrapper msg in queue"""
    try:
        out = run(['exim', '-Mvh', msg_id])
        out.check_returncode()
        head = out.stdout.strip()
    except subprocess.CalledProcessError:
        return False  # likely no longer in queue
    return 'Subject: Your email requires verification verify#' in head


def remove_msg(msg_id):
    """Here, msg_id may be a list or just one string"""
    if isinstance(msg_id, list):
        msg_id = ' '.join(msg_id)
    try:
        run(['exim', '-Mrm', msg_id]).check_returncode()
    except subprocess.CalledProcessError:
        pass  # may have already been removed from queue or sent


def print_removed(removed):
    """Given a dict of user:count mappings, print removed"""
    if len(list(removed.keys())) == 0:
        print('None to remove')
    else:
        print('Removed:')
        for user, count in removed.items():
            print(' %s: %d' % (user, count))


def clean_boxtrapper():
    """Remove old boxtrapper messages from queue. The theory is that if
    still stuck in queue after min_age_secs, they were likely sent from
    an illigitimate email address and will never clear from queue normally"""
    print('Removing old boxtrapper messages...')
    removed = defaultdict(int)
    queue = get_queue(exclude_bounces=True)
    queue = [x for x in queue if is_boxtrapper(x['id'])]
    for msg in queue:
        remove_msg(msg['id'])
        removed[msg['sender']] += 1
    print_removed(removed)


def get_full_quota_user(msg_id):
    """Get the user for a message which is at full quota, or None"""
    try:
        out = run(['exim', '-Mvb', msg_id])
        out.check_returncode()
        body = out.stdout.strip()
    except subprocess.CalledProcessError:
        return None
    if not '    Mailbox quota exceeded' in body:
        return None
    body = body.splitlines()
    addr_line = -1
    for line_num, line in enumerate(body):
        if '    Mailbox quota exceeded' in line:
            addr_line = line_num - 1
            break
    if addr_line >= 0:
        return body[addr_line].strip()
    return None


def clean_full_inbox_bounces():
    """Remove "mailbox quota exceeded" bounces from queue"""
    print('Removing old full inbox bounces...')
    removed = defaultdict(int)
    queue = get_queue(bounces_only=True)
    for msg in queue:
        user = get_full_quota_user(msg['id'])
        if user is None:
            continue
        remove_msg(msg['id'])
        removed[user] += 1
    print_removed(removed)


def clean_autoresponders():
    """Remove old auto-responder emails from queue which are
    likely responses to spam if they have been stuck in queue"""
    print('Removing old auto-responses...')
    removed = defaultdict(int)
    queue = get_queue(exclude_bounces=True)
    for msg in queue:
        try:
            out = run(['exim', '-Mvh', msg['id']])
            out.check_returncode()
            headers = out.stdout.strip()
        except subprocess.CalledProcessError:
            continue
        if 'X-Autorespond:' in headers and 'auto_reply' in headers:
            remove_msg(msg['id'])
            removed[msg['sender']] += 1
    print_removed(removed)


def _parse_args():
    """Parse commandline arguments"""
    parser = argparse.ArgumentParser(
        description="Exim cleanup tool",
        epilog="One and only one option is allowed",
    )
    parser.add_argument(
        '-a', '--all', action='store_true', help='Do all cleanup procedures'
    )
    parser.add_argument(
        '-b',
        '--boxtrapper',
        action='store_true',
        help='Remove old boxtrapper messages',
    )
    parser.add_argument(
        '-r',
        '--autorespond',
        action='store_true',
        help='Remove old auto-responder messages',
    )
    parser.add_argument(
        '-f',
        '--full',
        action='store_true',
        help='Remove old bounces for full inbox',
    )
    args = parser.parse_args()
    chosen = [key for key, value in vars(args).items() if value is True]
    if len(chosen) != 1:
        parser.print_help()
        sys.exit(1)
    return args


def main():
    """Main logic"""
    args = _parse_args()
    if args.boxtrapper or args.all:
        clean_boxtrapper()
    if args.full or args.all:
        clean_full_inbox_bounces()
    if args.autorespond or args.all:
        clean_autoresponders()


if __name__ == '__main__':
    main()