feat(netlink): detect IPv6 using query to address

- If a default IPv6 route is found, query the ip:port defined by `IPV6_CHECK_ADDRESS` to check for internet access

internal/configuration/settings/ipv6.go

@@ -0,0 +1,51 @@
+package settings
+
+import (
+	"net/netip"
+
+	"github.com/qdm12/gosettings"
+	"github.com/qdm12/gosettings/reader"
+	"github.com/qdm12/gotree"
+)
+
+// IPv6 contains settings regarding IPv6 configuration.
+type IPv6 struct {
+	// CheckAddress is the TCP ip:port address to dial to check
+	// IPv6 is supported, in case a default IPv6 route is found.
+	// It defaults to cloudflare.com address [2606:4700::6810:84e5]:443
+	CheckAddress netip.AddrPort
+}
+
+func (i IPv6) validate() (err error) {
+	return nil
+}
+
+func (i *IPv6) copy() (copied IPv6) {
+	return IPv6{
+		CheckAddress: i.CheckAddress,
+	}
+}
+
+func (i *IPv6) overrideWith(other IPv6) {
+	i.CheckAddress = gosettings.OverrideWithValidator(i.CheckAddress, other.CheckAddress)
+}
+
+func (i *IPv6) setDefaults() {
+	defaultCheckAddress := netip.MustParseAddrPort("[2606:4700::6810:84e5]:443")
+	i.CheckAddress = gosettings.DefaultComparable(i.CheckAddress, defaultCheckAddress)
+}
+
+func (i IPv6) String() string {
+	return i.toLinesNode().String()
+}
+
+func (i IPv6) toLinesNode() (node *gotree.Node) {
+	node = gotree.New("IPv6 settings:")
+	node.Appendf("Check address: %s", i.CheckAddress)
+	return node
+}
+
+func (i *IPv6) read(r *reader.Reader) (err error) {
+	i.CheckAddress, err = r.NetipAddrPort("IPV6_CHECK_ADDRESS")
+	return err
+}

internal/configuration/settings/settings.go

@@ -27,6 +27,7 @@ type Settings struct {
 	Updater       Updater
 	Version       Version
 	VPN           VPN
+	IPv6          IPv6
 	Pprof         pprof.Settings
 }
 
@@ -53,6 +54,7 @@ func (s *Settings) Validate(filterChoicesGetter FilterChoicesGetter, ipv6Support
 		"system":          s.System.validate,
 		"updater":         s.Updater.Validate,
 		"version":         s.Version.validate,
+		"ipv6":            s.IPv6.validate,
 		// Pprof validation done in pprof constructor
 		"VPN": func() error {
 			return s.VPN.Validate(filterChoicesGetter, ipv6Supported, warner)
@@ -85,6 +87,7 @@ func (s *Settings) copy() (copied Settings) {
 		Version:       s.Version.copy(),
 		VPN:           s.VPN.Copy(),
 		Pprof:         s.Pprof.Copy(),
+		IPv6:          s.IPv6.copy(),
 	}
 }
 
@@ -106,6 +109,7 @@ func (s *Settings) OverrideWith(other Settings,
 	patchedSettings.Version.overrideWith(other.Version)
 	patchedSettings.VPN.OverrideWith(other.VPN)
 	patchedSettings.Pprof.OverrideWith(other.Pprof)
+	patchedSettings.IPv6.overrideWith(other.IPv6)
 	err = patchedSettings.Validate(filterChoicesGetter, ipv6Supported, warner)
 	if err != nil {
 		return err
@@ -121,6 +125,7 @@ func (s *Settings) SetDefaults() {
 	s.Health.SetDefaults()
 	s.HTTPProxy.setDefaults()
 	s.Log.setDefaults()
+	s.IPv6.setDefaults()
 	s.PublicIP.setDefaults()
 	s.Shadowsocks.setDefaults()
 	s.Storage.setDefaults()
@@ -142,6 +147,7 @@ func (s Settings) toLinesNode() (node *gotree.Node) {
 	node.AppendNode(s.DNS.toLinesNode())
 	node.AppendNode(s.Firewall.toLinesNode())
 	node.AppendNode(s.Log.toLinesNode())
+	node.AppendNode(s.IPv6.toLinesNode())
 	node.AppendNode(s.Health.toLinesNode())
 	node.AppendNode(s.Shadowsocks.toLinesNode())
 	node.AppendNode(s.HTTPProxy.toLinesNode())
@@ -208,6 +214,7 @@ func (s *Settings) Read(r *reader.Reader, warner Warner) (err error) {
 		"updater":     s.Updater.read,
 		"version":     s.Version.read,
 		"VPN":         s.VPN.read,
+		"IPv6":        s.IPv6.read,
 		"profiling":   s.Pprof.Read,
 	}
 

internal/configuration/settings/settings_test.go

@@ -55,6 +55,8 @@ func Test_Settings_String(t *testing.T) {
 |   └── Enabled: yes
 ├── Log settings:
 |   └── Log level: INFO
+├── IPv6 settings:
+|   └── Check address: [2606:4700::6810:84e5]:443
 ├── Health settings:
 |   ├── Server listening address: 127.0.0.1:9999
 |   ├── Target address: cloudflare.com:443