env/utils/openbsd/pf-martians/iana-ip-special-registry-parser.py

#!/usr/bin/env python3
import argparse
from enum import Enum
import sys
import xml.sax


class ParserState(Enum):
	NOOP = 0
	DISCARD = 1
	CAPTURE = 2


class IPDisallowedHandler(xml.sax.ContentHandler):
	TRANSITIONS = {
		"address": ParserState.CAPTURE,
		"source": ParserState.CAPTURE,
		"destination": ParserState.CAPTURE,
		"global": ParserState.CAPTURE,
	}

	def __init__(self):
		self._reset()

	def _reset(self):
		self._state = ParserState.NOOP
		self._address = None
		self._source = None
		self._destination = None
		self._global = None
		self._content = ""

	def _processElement(self, name):
		pass

	def startElement(self, name, attrs):
		if name == "record":
			self._state = ParserState.DISCARD
			return
		if self._state == ParserState.NOOP:
			return

		self._state = self.TRANSITIONS.get(name, ParserState.DISCARD)

	def endElement(self, name):
		if name == "record":
			if self._address is not None:
				self._processElement()
			self._reset()
		if self._state == ParserState.NOOP:
			return

		if self._content == "":
			return
		self._content = self._content.strip()
		if name == "address":
			self._address = self._content.split(", ")
		if name == "source":
			self._source = self._content == "True"
		if name == "destination":
			self._destination = self._content == "True"
		if name == "global":
			self._global = self._content == "True"
		self._content = ""
		self._state = ParserState.DISCARD

	def characters(self, content):
		if self._state != ParserState.CAPTURE:
			return
		self._content += content


class IPDisallowedInboundHandler(IPDisallowedHandler):
	def _processElement(self):
		if not self._source:
			for address in self._address:
				print(address)


class IPDisallowedOutboundHandler(IPDisallowedHandler):
	def _processElement(self):
		# Document states:
		# > If the value of "Destination" is FALSE, the values of
		# > "Forwardable" and "Globally Reachable" must also be false.
		# So, `self._destination == False` implies `self._global ==
		# False.` For this reason, it's enough to test for
		# `self._global == False`.
		if not self._global:
			for address in self._address:
				print(address)

if __name__ == "__main__":
	parser = argparse.ArgumentParser()
	parser.add_argument("direction", choices=["inbound", "outbound"])
	args = parser.parse_args()

	if args.direction == "inbound":
		handler = IPDisallowedInboundHandler()
	else:
		handler = IPDisallowedOutboundHandler()
	xml.sax.parse(sys.stdin, handler)