dhcp_active_leases.py

#!/usr/bin/python
import datetime
from pprint import pprint

def parse_leases(lease_file):
	leases = {}
	lease = {}
	in_lease = False
	for line in lease_file:
		if line.lstrip().startswith('#'):

			continue
		tokens = line.split()

		if len(tokens) == 0:
			continue
		key = tokens[0].lower()

		if key == 'lease':
			if in_lease:
				raise Exception('Parsing error')
			else:
				in_lease = True
				lease = {'id' : tokens[1]}

		elif key == 'starts' or key == 'ends':
			if not in_lease:
				raise Exception('Parsing error')
			else:
				lease[key] = datetime.datetime.strptime(tokens[2]+' '+tokens[3].rstrip(';'), '%Y/%m/%d %H:%M:%S')

		elif key == '}':
			in_lease = False
			leases[lease['id']] = lease
			lease = {}

	return leases

def count_active_leases(all_leases, now):
	count = 0
	for lease in all_leases.itervalues():
		if timestamp_inbetween(now, lease['starts'], lease['ends']):
			count += 1
	return count

def timestamp_inbetween(now, start, end):
	return start < now < end

myfile = open('/var/lib/dhcp/dhcpd.leases', 'r')
all_leases = parse_leases(myfile)
count = count_active_leases(all_leases, datetime.datetime.utcnow())
print count