1package cidr
2
3import (
4	"fmt"
5	"net"
6
7	"github.com/zclconf/go-cty/cty"
8	"github.com/zclconf/go-cty/cty/function"
9)
10
11// NetmaskFunc is a function that converts an IPv4 address prefix given in CIDR
12// notation into a subnet mask address.
13var NetmaskFunc = function.New(&function.Spec{
14	Params: []function.Parameter{
15		{
16			Name: "prefix",
17			Type: cty.String,
18		},
19	},
20	Type: function.StaticReturnType(cty.String),
21	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
22		_, network, err := net.ParseCIDR(args[0].AsString())
23		if err != nil {
24			return cty.UnknownVal(cty.String), fmt.Errorf("invalid CIDR expression: %s", err)
25		}
26
27		return cty.StringVal(net.IP(network.Mask).String()), nil
28	},
29})
30
31// Netmask converts an IPv4 address prefix given in CIDR notation into a subnet mask address.
32func Netmask(prefix cty.Value) (cty.Value, error) {
33	return NetmaskFunc.Call([]cty.Value{prefix})
34}
35