filter-reportlogger.py

#!/usr/bin/env python3
#
# OpenSMTPD filter (smtpd-filters(7)) to log reporting information.

import logging
import sys
import tempfile
from argparse import ArgumentParser

logging.basicConfig(
    level=logging.DEBUG,
    format="%(levelname)s: %(message)s",
)

REGISTER_LINES = [
    "register|report|smtp-in|link-connect",
    "register|report|smtp-in|link-identify",
    "register|report|smtp-in|link-disconnect",
    "register|report|smtp-in|link-auth",
    "register|report|smtp-in|timeout",
]
REGISTER_READY_LINE = "register|ready"


def process_stream_to_output(fp):
    """Process input event stream and write to specified output file

    fp: writable output file object
    """
    logging.info("writing events from stdin to %s", fp.name)
    for in_line in sys.stdin:
        fp.write(in_line.encode())
        in_line = in_line.strip()
        logging.info("received line >>%s<<", in_line)
        if in_line == "config|ready":
            logging.info(
                "configuration received from smtpd (ready to process events)"
            )
            for out_line in REGISTER_LINES:
                sys.stdout.write(f"{out_line}\n")
                logging.debug("wrote the %s line to smtpd on stdout", out_line)
            sys.stdout.write(f"{REGISTER_READY_LINE}")
            logging.debug(
                "wrote the %s line to smtpd on stdout", REGISTER_READY_LINE
            )
            sys.stdout.flush()
            logging.debug("flushed stdout")


def main():
    parser = ArgumentParser(description="log events from smtpd(8)")
    parser.add_argument(
        "-o",
        "--outfile",
        help="output file to which to write received events",
    )
    parser.add_argument(
        "-t",
        "--temp-outfile",
        action="store_true",
        help="write received events to an autogenerated temporary file",
    )
    args = parser.parse_args()

    if args.temp_outfile:
        with tempfile.NamedTemporaryFile(
            delete=False, buffering=0, prefix="filter-bruteforce-"
        ) as fp:
            process_stream_to_output(fp)
    elif args.outfile:
        with open(args.outfile, "ab", buffering=0) as fp:
            process_stream_to_output(fp)


if __name__ == "__main__":
    try:
        main()
    except KeyboardInterrupt:
        pass