New function cidrnet_to_addr_mask().

This new function tries to convert a network specification in CIDR
notation (<address> "/" <prefix_length>) into an old-style address
plus mask pair.  It supports this for both IPv4 and IPv6.  It is
intended to be used when generating config files for programs that
does not support CIDR notation, and needs a network mask instead,
e.g. the ntp.org NTP daemon, or ISC dhcpd.

lib/puppet/parser/functions/cidrnet_to_addr_mask.rb

+# Copyright (C) 2020 Thomas Bellman.
+# Licensed under the GNU LGPL v3+; see the README file for more information.
+
+
+module Puppet::Parser::Functions
+    newfunction(:cidrnet_to_addr_mask, :type => :rvalue, :doc => '
+	Parse a network specification on the form "ipaddr/netmask" into a
+	pair "ipaddr" and "netmask".  The netmask can be either a prefix
+	length in bits, or a full netmask in (dotted quad for IPv4, hex
+	mask with colons for IPv6).  In the former case it is converted to
+	a full netmask.	 If no netmask is specified, nil is returned for
+	the mask, unless the optional second argument is true, in which
+	case a mask specifying a host is returned for the mask.
+
+	This is useful when generating configuration files for programs
+	needing network masks instead of prefix lengths, e.g. ISC dhcpd
+	or the ntp.org NTP daemon.
+
+	The address part of the network specification does not need to be
+	a valid IP address.  This can be used e.g. to specify a hostname
+	instead of a numeric address, which can be useful somtimes.  In
+	that case, the function cannot determine if the netmask / prefix
+	length is for IPv4 or IPv6, and the mask will be returned without
+	any changes.  You should really not specify a mask in that case,
+	and the fillmask flag is not used.
+
+	If an invalid mask / prefix length is specified, it will currently
+	be returned unchanged, without any error being raised.  This might
+	change in the future.
+    ') \
+    do |args|
+        if args.length < 1 or args.length > 2
+            raise(ArgumentError, #Puppet::ParseError,
+                  "cidrnet_to_addr_mask(): Bad number of arguments, #{args.length}")
+        end
+        netspec = args[0]
+        fillmask = args[1] or false
+	ipv6_re = /^[0-9a-f:]+$/i
+	ipv4_re = /^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$/
+        addr,mask = netspec.split('/', 2)
+        if ipv6_re =~ addr  and  mask == nil
+            # IPv6 without mask
+            mask = "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff"  if fillmask
+        elsif ipv4_re =~ addr  and  mask == nil
+            # IPv4 without mask
+            mask = "255.255.255.255"  if fillmask
+        elsif ipv6_re =~ addr  and  /^[0-9]+$/ =~ mask
+            # IPv6 with prefix length
+            bits = mask.to_i
+            m = 0xffffffffffffffffffffffffffffffff >> (128-bits) << (128-bits)
+            mask = sprintf("%032x", m).gsub(/....(?!$)/, '\&:')
+            mask.sub!(/(:0000)+$/, '::')
+        elsif ipv4_re =~ addr  and  /^[0-9]+$/ =~ mask
+            # IPv4 with prefix length
+            bits = mask.to_i
+            m = 0xffffffff >> (32-bits) << (32-bits)
+            mask = sprintf("%d.%d.%d.%d",
+                           m>>24 & 0xff, m>>16 & 0xff, m>>8 & 0xff, m & 0xff)
+        else
+            # Assume proper mask according to address family
+        end
+        return addr,mask
+    end
+end