network_utils.py
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network_utils.py
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	# -- coding: utf-8 --

	# -------------------------------------------------------------
	# Salt — Network execution module
	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
	# Project: Nasqueron
	# License: BSD-2-Clause
	# -------------------------------------------------------------


	import re


	# -------------------------------------------------------------
	# CIDR netmask and prefixes
	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


	def is_valid_netmask(netmask):
	# "255.255.255.240" → "11111111111111111111111111110000"
	bits = "".join([format(int(octet), "b") for octet in netmask.split(".")])

	# A netmask is valid if the suite of bits:
	# - starts by contiguous 1, e.g. here 1111111111111111111111111111
	# - ends by contiguous 0, e.g. here 0000
	#
	# Also, as 0.0.0.0 is invalid, netmask must starts by 1.
	return re.compile("^1+0*$").match(bits) is not None


	def netmask_to_cidr_prefix(netmask):
	"""
	Convert a netmask like 255.255.255.240 into a CIDR prefix like 24.

	This can be useful for RHEL network scripts requiring PREFIX information.
	"""

	if not is_valid_netmask(netmask):
	raise ValueError("Netmask is invalid.")

	# The CIDR prefix is the count of 1 bits in each octet.
	# e.g. 255.255.255.240 can be split in octets [255, 255, 255, 240],
	# then becomes ['0b11111111', '0b11111111', '0b11111111', '0b11110000'].
	#
	# There is 24 "1" in this expression, that's 24 is our CIDR prefix.
	return sum([bin(int(octet)).count("1") for octet in netmask.split(".")])