tcpdump_context_manager.py

from datetime import datetime
import logging
import os
import subprocess

logger = logging.getLogger(__name__)

class TcpDump:
    def __enter__(self):
        now = int(datetime.now().timestamp())
        self.pcap_name = '{}_pid{}.pcap'.format(now, os.getpid())
        try:
            self.proc = subprocess.Popen(
                                         ['tcpdump', '-w', self.pcap_name],
                                         stderr=subprocess.DEVNULL
                                         )
            while now == int(datetime.now().timestamp()) and \
                    not os.path.isfile(self.pcap_name):
                pass
            logger.info("Running tcpdump")
        except FileNotFoundError:
            logger.warn("tcpdump is not available")
            self.proc = lambda: None
            self.proc.terminate = lambda: None

    def __exit__(self, exc_type, *args):
        self.proc.terminate()
        if exc_type is None:
            try:
                os.remove(self.pcap_name)
            except FileNotFoundError:
                logger.warn("tcpdump pcap file does not exist")
        else:
            logger.warn("tcpdump pcap captured")