feat(vpn): auto detection of IPv6 support

- `OPENVPN_IPV6` removed
- Affects OpenVPN
- Use the same mechanism for OpenVPN and Wireguard
- Check only once at program start since this is unlikely to change at runtime
- Log if IPv6 is supported
- Remove `IPv6` boolean from settings structs
- Move IPv6 detection as a method on NetLinker

internal/provider/custom/openvpnconf.go

@@ -15,7 +15,7 @@ import (
 var ErrExtractData = errors.New("failed extracting information from custom configuration file")
 
 func (p *Provider) OpenVPNConfig(connection models.Connection,
-	settings settings.OpenVPN) (lines []string) {
+	settings settings.OpenVPN, ipv6Supported bool) (lines []string) {
 	lines, _, err := p.extractor.Data(*settings.ConfFile)
 	if err != nil {
 		// Configuration file is already validated in settings validation in
@@ -24,13 +24,13 @@ func (p *Provider) OpenVPNConfig(connection models.Connection,
 		panic(fmt.Sprintf("failed extracting information from custom configuration file: %s", err))
 	}
 
-	lines = modifyConfig(lines, connection, settings)
+	lines = modifyConfig(lines, connection, settings, ipv6Supported)
 
 	return lines
 }
 
 func modifyConfig(lines []string, connection models.Connection,
-	settings settings.OpenVPN) (modified []string) {
+	settings settings.OpenVPN, ipv6Supported bool) (modified []string) {
 	// Remove some lines
 	for _, line := range lines {
 		switch {
@@ -57,7 +57,7 @@ func modifyConfig(lines []string, connection models.Connection,
 				"cipher ", "ncp-ciphers ", "data-ciphers ", "data-ciphers-fallback "),
 			*settings.Auth != "" && strings.HasPrefix(line, "auth "),
 			*settings.MSSFix > 0 && strings.HasPrefix(line, "mssfix "),
-			!*settings.IPv6 && hasPrefixOneOf(line, "tun-ipv6",
+			!ipv6Supported && hasPrefixOneOf(line, "tun-ipv6",
 				`pull-filter ignore "route-ipv6"`,
 				`pull-filter ignore "ifconfig-ipv6"`):
 		default:
@@ -87,7 +87,7 @@ func modifyConfig(lines []string, connection models.Connection,
 	if *settings.MSSFix > 0 {
 		modified = append(modified, "mssfix "+strconv.Itoa(int(*settings.MSSFix)))
 	}
-	if !*settings.IPv6 {
+	if !ipv6Supported {
 		modified = append(modified, `pull-filter ignore "route-ipv6"`)
 		modified = append(modified, `pull-filter ignore "ifconfig-ipv6"`)
 	}

internal/provider/custom/openvpnconf_test.go

@@ -19,10 +19,11 @@ func Test_modifyConfig(t *testing.T) {
 	t.Parallel()
 
 	testCases := map[string]struct {
-		lines      []string
-		settings   settings.OpenVPN
-		connection models.Connection
-		modified   []string
+		lines         []string
+		settings      settings.OpenVPN
+		connection    models.Connection
+		ipv6Supported bool
+		modified      []string
 	}{
 		"mixed": {
 			lines: []string{
@@ -49,6 +50,7 @@ func Test_modifyConfig(t *testing.T) {
 				Port:     1194,
 				Protocol: constants.UDP,
 			},
+			ipv6Supported: false,
 			modified: []string{
 				"up bla",
 				"keep me here",
@@ -82,7 +84,7 @@ func Test_modifyConfig(t *testing.T) {
 			t.Parallel()
 
 			modified := modifyConfig(testCase.lines,
-				testCase.connection, testCase.settings)
+				testCase.connection, testCase.settings, testCase.ipv6Supported)
 
 			assert.Equal(t, testCase.modified, modified)
 		})