# Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
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# Use of this source code is governed by a BSD-style license that can be
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# found in the LICENSE file.
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import logging
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import os
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import subprocess
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from autotest_lib.client.bin import utils
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class Tcpdump(object):
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"""tcpdump capture process wrapper."""
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def __init__(self, iface, dumpfilename):
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"""Launches a tcpdump process on the background.
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@param iface: The name of the interface to listen on.
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@param dumpfilename: The filename of the destination dump file.
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@raise utils.TimeoutError if tcpdump fails to start after 10 seconds.
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"""
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logging.debug('Recording %s traffic to %s.', iface, dumpfilename)
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# Force to run tcpdump as root, since the dump file is created *after*
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# the process drops to a unprivileged user, meaning that it can't create
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# the passed dumpfilename file.
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self._tcpdump_proc = subprocess.Popen(
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['tcpdump', '-i', iface, '-w', dumpfilename, '-Z', 'root'],
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stdout=open('/dev/null', 'w'),
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stderr=subprocess.STDOUT)
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# Wait for tcpdump to initialize and create the dump file.
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utils.poll_for_condition(
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lambda: os.path.exists(dumpfilename),
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desc='tcpdump creates the dump file.',
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sleep_interval=1,
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timeout=10.)
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def stop(self, timeout=10.):
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"""Stop the dump process and wait for it to return.
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This method stops the tcpdump process running in background and waits
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for it to finish for a given timeout.
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@param timeout: The time to wait for the tcpdump to finish in seconds.
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None means no timeout.
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@return whether the tcpdump is not running.
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"""
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if not self._tcpdump_proc:
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return True
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# Send SIGTERM to tcpdump.
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try:
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self._tcpdump_proc.terminate()
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except OSError, e:
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# If the process exits before we can send it a SIGTERM, an
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# OSError exception is raised here which we can ignore since the
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# process already finished.
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logging.error('Trying to kill tcpdump (%d): %s',
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self._tcpdump_proc.pid, e.strerror)
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logging.debug('Waiting for pid %d to finish.', self._tcpdump_proc.pid)
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if timeout is None:
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self._tcpdump_proc.wait()
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else:
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try:
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utils.poll_for_condition(
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lambda: not self._tcpdump_proc.poll() is None,
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sleep_interval=1,
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timeout=timeout)
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except utils.TimeoutError:
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logging.error('tcpdump failed to finish after %f seconds. Dump '
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'file can be truncated.', timeout)
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return False
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self._tcpdump_proc = None
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return True
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def __del__(self):
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self.stop()
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