while-telnet

#!/usr/bin/python3

import socket
import logging
import argparse
import subprocess
import time
import sys


DEFAULT_PORT = 59468
DEFAULT_HOST = "localhost"


class Spinner:
    chars = "-\|/"

    def __init__(self):
        self._idx = 0

    def spin(self):
        self._idx = (self._idx + 1) % len(self.chars)

    def print(self, out):
        out.write("\r")
        out.write(self.chars[self._idx])
        out.write(" ")

    def reset(self):
        self._idx = 0


def parse_arguments():
    parser = argparse.ArgumentParser(description="telnet wait loop")
    parser.add_argument(
        "port",
        type=int,
        help="port number (default %(default)s)",
        metavar="PORT",
        default=DEFAULT_PORT,
        nargs="?",
    )
    parser.add_argument(
        "-k", "--keep", help="keep reconnecting after telnet exits", action="store_true"
    )

    return parser.parse_args()


def main(opts):
    logging.debug("connect to %s:%s...", DEFAULT_HOST, opts.port)
    spinner = Spinner()
    try:
        while True:
            try:
                with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
                    s.connect((DEFAULT_HOST, opts.port))
                    logging.info("connected, port is open")
            except OSError:
                # logging.debug("connect failed... waiting")
                spinner.spin()
                spinner.print(sys.stderr)
                time.sleep(1)
                continue

            spinner.reset()
            logging.debug("host is live at port %s, trying telnet", opts.port)
            try:
                subprocess.check_call(["telnet", DEFAULT_HOST, "{}".format(opts.port)])
                if opts.keep:
                    logging.warning("retrying connection as requested")
                    continue
            except subprocess.CalledProcessError as cpe:
                logging.debug(
                    "telnet exited with status %s, retrying...", cpe.returncode
                )
                continue
            break
    except KeyboardInterrupt:
        logging.debug("interrupted")


if __name__ == "__main__":
    opts = parse_arguments()
    logging.basicConfig(level=logging.DEBUG)
    main(opts)