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/configuration/settings/openvpn.go

@@ -65,10 +65,6 @@ type OpenVPN struct {
 	// Private Internet Access. It can be set to an
 	// empty string for other providers.
 	PIAEncPreset *string
-	// IPv6 is set to true if IPv6 routing should be
-	// set to be tunnel in OpenVPN, and false otherwise.
-	// It cannot be nil in the internal state.
-	IPv6 *bool // TODO automate like with Wireguard
 	// MSSFix is the value (1 to 10000) to set for the
 	// mssfix option for OpenVPN. It is ignored if set to 0.
 	// It cannot be nil in the internal state.
@@ -253,7 +249,6 @@ func (o *OpenVPN) copy() (copied OpenVPN) {
 		EncryptedKey:  helpers.CopyStringPtr(o.EncryptedKey),
 		KeyPassphrase: helpers.CopyStringPtr(o.KeyPassphrase),
 		PIAEncPreset:  helpers.CopyStringPtr(o.PIAEncPreset),
-		IPv6:          helpers.CopyBoolPtr(o.IPv6),
 		MSSFix:        helpers.CopyUint16Ptr(o.MSSFix),
 		Interface:     o.Interface,
 		ProcessUser:   o.ProcessUser,
@@ -276,7 +271,6 @@ func (o *OpenVPN) mergeWith(other OpenVPN) {
 	o.EncryptedKey = helpers.MergeWithStringPtr(o.EncryptedKey, other.EncryptedKey)
 	o.KeyPassphrase = helpers.MergeWithStringPtr(o.KeyPassphrase, other.KeyPassphrase)
 	o.PIAEncPreset = helpers.MergeWithStringPtr(o.PIAEncPreset, other.PIAEncPreset)
-	o.IPv6 = helpers.MergeWithBool(o.IPv6, other.IPv6)
 	o.MSSFix = helpers.MergeWithUint16(o.MSSFix, other.MSSFix)
 	o.Interface = helpers.MergeWithString(o.Interface, other.Interface)
 	o.ProcessUser = helpers.MergeWithString(o.ProcessUser, other.ProcessUser)
@@ -299,7 +293,6 @@ func (o *OpenVPN) overrideWith(other OpenVPN) {
 	o.EncryptedKey = helpers.OverrideWithStringPtr(o.EncryptedKey, other.EncryptedKey)
 	o.KeyPassphrase = helpers.OverrideWithStringPtr(o.KeyPassphrase, other.KeyPassphrase)
 	o.PIAEncPreset = helpers.OverrideWithStringPtr(o.PIAEncPreset, other.PIAEncPreset)
-	o.IPv6 = helpers.OverrideWithBool(o.IPv6, other.IPv6)
 	o.MSSFix = helpers.OverrideWithUint16(o.MSSFix, other.MSSFix)
 	o.Interface = helpers.OverrideWithString(o.Interface, other.Interface)
 	o.ProcessUser = helpers.OverrideWithString(o.ProcessUser, other.ProcessUser)
@@ -328,8 +321,6 @@ func (o *OpenVPN) setDefaults(vpnProvider string) {
 		defaultEncPreset = presets.Strong
 	}
 	o.PIAEncPreset = helpers.DefaultStringPtr(o.PIAEncPreset, defaultEncPreset)
-
-	o.IPv6 = helpers.DefaultBool(o.IPv6, false)
 	o.MSSFix = helpers.DefaultUint16(o.MSSFix, 0)
 	o.Interface = helpers.DefaultString(o.Interface, "tun0")
 	o.ProcessUser = helpers.DefaultString(o.ProcessUser, "root")
@@ -375,8 +366,6 @@ func (o OpenVPN) toLinesNode() (node *gotree.Node) {
 		node.Appendf("Private Internet Access encryption preset: %s", *o.PIAEncPreset)
 	}
 
-	node.Appendf("Tunnel IPv6: %s", helpers.BoolPtrToYesNo(o.IPv6))
-
 	if *o.MSSFix > 0 {
 		node.Appendf("MSS Fix: %d", *o.MSSFix)
 	}

internal/configuration/settings/settings_test.go

@@ -34,7 +34,6 @@ func Test_Settings_String(t *testing.T) {
 |       ├── User: [not set]
 |       ├── Password: [not set]
 |       ├── Private Internet Access encryption preset: strong
-|       ├── Tunnel IPv6: no
 |       ├── Network interface: tun0
 |       ├── Run OpenVPN as: root
 |       └── Verbosity level: 1

internal/configuration/sources/env/openvpn.go

@@ -39,11 +39,6 @@ func (s *Source) readOpenVPN() (
 
 	openVPN.PIAEncPreset = s.readPIAEncryptionPreset()
 
-	openVPN.IPv6, err = envToBoolPtr("OPENVPN_IPV6")
-	if err != nil {
-		return openVPN, fmt.Errorf("environment variable OPENVPN_IPV6: %w", err)
-	}
-
 	openVPN.MSSFix, err = envToUint16Ptr("OPENVPN_MSSFIX")
 	if err != nil {
 		return openVPN, fmt.Errorf("environment variable OPENVPN_MSSFIX: %w", err)