httpdate.py

#!/usr/bin/env python

# Copyright (c) 2017,2019,2020 Mikolaj Kucharski <mikolaj@kucharski.name>
#
# Permission to use, copy, modify, and/or distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

from datetime import datetime
try:
	from httplib import HTTPConnection
except ImportError:
	from http.client import HTTPConnection
from subprocess import Popen, PIPE
from sys import exit

def main():
	conn = HTTPConnection("www.google.com")
	conn.request("HEAD", "/")
	res = conn.getresponse()

	if res.status not in [200, 301, 302, 303, 307, 308]:
		raise Exception("Wrong HTTP status code: {}".format(res.status))

	for name, dh in res.getheaders():
		if name.lower() != 'date':
			continue
		if not dh.endswith(' GMT'):
			raise Exception('Date not in GMT timezone')

		print("Time from HTTP header is {}".format(dh))
		dt = datetime.strptime(dh, '%a, %d %b %Y %H:%M:%S %Z')

		# current time
		ct = datetime.utcnow().replace(microsecond=0)

		print("Remote datetime is {}".format(dt))
		print("Local datatime is {}".format(ct))

		delta = int(round(abs((ct - dt).total_seconds())))

		print("Timedelta is {} seconds".format(delta))

		if delta < 60 * 10:	# minutes
			exit(0)

		nt = dt.strftime('%Y%m%d%H%M.%S')
		cmd = ['date', '-u', '-s', nt]
		print("Executing command {}".format(" ".join(cmd)))
		p = Popen(cmd, stdout=PIPE, stderr=PIPE)
		stdoutdata, stderrdata = p.communicate()

		print("stdout={}".format(stdoutdata.strip()))
		print("stderr={}".format(stderrdata.strip()))
		print("code={}".format(p.returncode))

		exit(p.returncode)

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