interfaces.py

#!/usr/bin/env python3

# Copyright (c) 2016, Troy Telford
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import ipaddress
import logging
import netifaces
import sys

"""
This module gets the current IPv4 and/or IPv6 addresses of the network
interfaces provided.

While we could get the full set of interface information using
netifaces, for this module, we are only interested in one IPv4 and one
IPv6 address, each having been provided by the configuration

See [netifaces documentation](https://pypi.python.org/pypi/netifaces)

netifaces provides a somewhat standardized method of getting interface
information, such as IP addresses.

Technically, interfaces can have multiple IP addresses, but multiple
addresses is not often the case with home users.
* This chooses the first address for the interface, which covers the use
  case of many users who only use one ip address per interface.

Also handles the case where an address family isn't used:
* Not everybody has IPv6.
* Maybe a user is behind a NAT on IPv4, and is only updating their IPv6
  address in DNS.
"""
class interfaces():

    def __init__(self,configured_interfaces):
        self.addresses = self.get_if_addresses(configured_interfaces)

    def get_if_addresses(self, interfaces):
        """Get IP addresses from configured interfaces"""

        addresses = []
        for addr_type in interfaces:
            address_retrieved = True
            # Netifaces has a lookup for address families. The index
            # number is os-dependent, so we look up the index using the
            # method provided by netifaces.
            if addr_type == "AF_INET6":
                address_family = netifaces.AF_INET6
            elif addr_type == "AF_INET":
                address_family = netifaces.AF_INET
            interface_addresses = netifaces.ifaddresses(interfaces[addr_type])
            try:
                if addr_type == "AF_INET6":
                    # I'm not counting on IPv6 to only have one address;
                    # mulitple is common as there's always link-local in
                    # addition to an internet-routable address.
                    # Make sure we don't get a link-local IPv6 Address.
                    # These are in the subnet fe80:://10
                    for address in interface_addresses[address_family]:
                        address_retrieved = True
                        if address["addr"].split(':')[0] != "fe80":
                            new_address = address["addr"]
                            break
                        # We haven't found a non-link-local IPv6 Address
                        address_retrieved = False
                else:
                    new_address = interface_addresses[address_family][0]["addr"]
            except ValueError as exception:
                # Interface doesn't have an address we could report.
                logging.warning("Could not get %s address from interface %s."
                                % (addr_type, interfaces[addr_type]))
                logging.warning("Exception: %s" % (exception))
                address_retrieved = False
            except KeyError as index:
                # Most likely, there is no IP address for the address family
                # (ie. no IPv4 or IPv6 address on the interface)
                if str(index) == str(address_family):
                    logging.warning("No %s address is assigned to interface %s." 
                                    % (addr_type, interfaces[addr_type]))
                else:
                    logging.error("Unknown KeyError %s in finding %s address"
                                  % (index, addr_type))
                address_retrieved = False
            if address_retrieved:
                new_address = ipaddress.ip_address(new_address)
                addresses.append(new_address)
                logging.info("The current %s Address on %s is: %s"
                             % (addr_type, interfaces[addr_type], new_address))
        return addresses

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