feat: add a way to filter list of IPs for the machine

This will be used to filter out SideroLink IPs on Talos side.

Signed-off-by: Andrey Smirnov <andrey.smirnov@talos-systems.com>

net.go

@@ -41,6 +41,35 @@ func IPAddrs() (ips []net.IP, err error) {
 	return ips, nil
 }
 
+// IPFilterFunc filters IP addresses.
+//
+// List of IPFilterFuncs is applied with AND logic: all filters should return true
+// for the IP address to be included in the response.
+type IPFilterFunc func(ip net.IP) bool
+
+// IPFilter filters list of IP addresses by applying sequence of filters.
+//
+// If any of the filters returns false, address is skipped.
+func IPFilter(addrs []net.IP, filters ...IPFilterFunc) (result []net.IP) {
+	for _, addr := range addrs {
+		skip := false
+
+		for _, filter := range filters {
+			if !filter(addr) {
+				skip = true
+
+				break
+			}
+		}
+
+		if !skip {
+			result = append(result, addr)
+		}
+	}
+
+	return result
+}
+
 // FormatAddress checks that the address has a consistent format.
 func FormatAddress(addr string) string {
 	addr = strings.Trim(addr, "[]")

net_test.go

@@ -272,3 +272,69 @@ func TestFilterIPs(t *testing.T) {
 		})
 	}
 }
+
+func TestIPFilter(t *testing.T) {
+	t.Parallel()
+
+	for _, tt := range []struct { //nolint:govet
+		name     string
+		ips      []string
+		filters  []talosnet.IPFilterFunc
+		expected string
+	}{
+		{
+			name: "no filters",
+			ips: []string{
+				"10.3.4.6",
+				"2001:db8::1",
+			},
+			expected: "[10.3.4.6 2001:db8::1]",
+		},
+		{
+			name: "even",
+			ips: []string{
+				"10.3.4.6",
+				"10.3.4.1",
+				"172.20.0.1",
+				"2001:db8::1",
+				"2001:db8::2",
+			},
+			filters: []talosnet.IPFilterFunc{
+				func(addr net.IP) bool { return addr[len(addr)-1]%2 == 0 },
+			},
+			expected: "[10.3.4.6 2001:db8::2]",
+		},
+		{
+			name: "even and not v6",
+			ips: []string{
+				"10.3.4.6",
+				"10.3.4.1",
+				"172.20.0.1",
+				"2001:db8::2",
+			},
+			filters: []talosnet.IPFilterFunc{
+				func(addr net.IP) bool { return addr[len(addr)-1]%2 == 0 },
+				func(addr net.IP) bool { return addr.To4() != nil },
+			},
+			expected: "[10.3.4.6]",
+		},
+	} {
+		tt := tt
+
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			ips := make([]net.IP, len(tt.ips))
+
+			for i := range ips {
+				ips[i] = net.ParseIP(tt.ips[i])
+
+				require.NotNil(t, ips[i])
+			}
+
+			result := talosnet.IPFilter(ips, tt.filters...)
+
+			assert.Equal(t, tt.expected, fmt.Sprintf("%s", result))
+		})
+	}
+}