IMAPClient hangs without timeout

select_folder_and_shutdown.py

#!/usr/bin/env python3

# Standard libraries.
import logging
import socket
import sys
import threading

# External libraries.
import imapclient  # type: ignore[import]


_logger = logging.getLogger(__name__)


HOST = "imap.example.com"
USERNAME = "user@example.com"
PASSWORD = "Tr0ub4dor&3"
FOLDER = "INBOX"
TIMEOUT_SECONDS = None


def run() -> int:
    _logger.info("Connecting to %s.", HOST)
    try:
        server = imapclient.IMAPClient(HOST, timeout=TIMEOUT_SECONDS)
    except socket.gaierror as error:
        _logger.error(error)
        return 1
    with server as server:
        _logger.info("Logging in as %s.", USERNAME)
        server.login(USERNAME, PASSWORD)
        print("Waiting for SIGINT before selecing folder.")
        try:
            lock = threading.Lock()
            # Deliberately double lock to wait indefinitely.
            with lock, lock:
                pass
        except KeyboardInterrupt:
            _logger.info("SIGINT received.")
        if TIMEOUT_SECONDS is None:
            _logger.info("No timeout set in TIMEOUT_SECONDS.")
        else:
            _logger.info(
                "Time out is set to %s seconds.", TIMEOUT_SECONDS
            )
        _logger.info("Selecting folder %s.", FOLDER)
        try:
            server.select_folder("INBOX", readonly=True)
        # TODO(Python version 3.10): Catch TimeoutError instead.
        except socket.error:
            _logger.error("Timed out selecting folder.")
    return 0


def main() -> int:
    formatter = logging.Formatter(
        "[%(asctime)s] [%(levelno)03s] %(name)s: %(message)s",
    )
    handler = logging.StreamHandler(sys.stderr)
    handler.setFormatter(formatter)
    _logger.addHandler(handler)
    _logger.setLevel(logging.DEBUG)

    logger = logging.getLogger("imapclient.imapclient")
    logger.addHandler(handler)
    logger.setLevel(logging.DEBUG)
    try:
        return run()
    except KeyboardInterrupt:
        _logger.info("SIGINT received. Exiting.")
    return 1


if __name__ == "__main__":
    sys.exit(main())