fs/skeleton/bin/dnsck

#!/usr/bin/python
"""DNS service check.

Prints a one line summary of whether DNS servers are functioning.
Supports IPv4 and IPv6.

$ dnsck 2001:4860:4860::8888 2001:4860:4860::8844 8.8.8.8 8.8.4.4
2001:4860:4860::8888(OK),13.2ms 2001:4860:4860::8844(TIMEOUT),3000.0ms \
8.8.8.8(OK),13.7ms 8.8.4.4(OK),15.8ms
"""

import dns.resolver
import sys
import time

try:
  import monotime  # gpylint disable=unused-import,g-import-not-at-top
except ImportError:
  pass


_time = getattr(time, 'monotime', time.time)


def GetDefaultNameservers():
  s = dns.resolver.Resolver(configure=True)
  return s.nameservers


def DnsCheck(server, qname):
  """Resolve qname using server, return status."""
  s = dns.resolver.Resolver(configure=False)
  s.timeout = s.lifetime = 3  # in seconds
  s.nameservers.append(server)
  start = _time()
  result = 'UNKNOWN'
  try:
    answer = s.query(qname=qname)
    result = 'OK'
  except dns.exception.Timeout:
    result = 'TIMEOUT'
  except dns.exception.DNSException:
    result = 'DNSERR'
  end = _time()
  msec = '%.1fms' % ((end - start) * 1000)
  return '%s(%s),%s' % (server, result, msec)


def main():
  servers = set(GetDefaultNameservers())
  if (len(sys.argv) > 1):
    servers |= set(sys.argv[1:])
  output = []
  for server in servers:
    output.append(DnsCheck(server, qname='gstatic.com'))
  print ' '.join(output)


if __name__ == '__main__':
  main()