chore(settings): refactor settings processing (#756)

- Better settings tree structure logged using `qdm12/gotree`
- Read settings from environment variables, then files, then secret files
- Settings methods to default them, merge them and override them
- `DNS_PLAINTEXT_ADDRESS` default changed to `127.0.0.1` to use DoT. Warning added if set to something else.
- `HTTPPROXY_LISTENING_ADDRESS` instead of `HTTPPROXY_PORT` (with retro-compatibility)

internal/configuration/settings/wireguard.go

@@ -0,0 +1,138 @@
+package settings
+
+import (
+	"fmt"
+	"net"
+	"regexp"
+
+	"github.com/qdm12/gluetun/internal/configuration/settings/helpers"
+	"github.com/qdm12/gluetun/internal/constants"
+	"github.com/qdm12/gotree"
+	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
+)
+
+// Wireguard contains settings to configure the Wireguard client.
+type Wireguard struct {
+	// PrivateKey is the Wireguard client peer private key.
+	// It cannot be nil in the internal state.
+	PrivateKey *string
+	// PreSharedKey is the Wireguard pre-shared key.
+	// It can be the empty string to indicate there
+	// is no pre-shared key.
+	// It cannot be nil in the internal state.
+	PreSharedKey *string
+	// Addresses are the Wireguard interface addresses.
+	Addresses []net.IPNet
+	// Interface is the name of the Wireguard interface
+	// to create. It cannot be the empty string in the
+	// internal state.
+	Interface string
+}
+
+var regexpInterfaceName = regexp.MustCompile(`^[a-zA-Z0-9_]+$`)
+
+// Validate validates Wireguard settings.
+// It should only be ran if the VPN type chosen is Wireguard.
+func (w Wireguard) validate(vpnProvider string) (err error) {
+	if !helpers.IsOneOf(vpnProvider,
+		constants.Custom,
+		constants.Ivpn,
+		constants.Mullvad,
+		constants.Windscribe,
+	) {
+		// do not validate for VPN provider not supporting Wireguard
+		return nil
+	}
+
+	// Validate PrivateKey
+	if *w.PrivateKey == "" {
+		return ErrWireguardPrivateKeyNotSet
+	}
+	_, err = wgtypes.ParseKey(*w.PrivateKey)
+	if err != nil {
+		return fmt.Errorf("%w: %s", ErrWireguardPrivateKeyNotValid, err)
+	}
+
+	// Validate PreSharedKey
+	if *w.PreSharedKey != "" { // Note: this is optional
+		_, err = wgtypes.ParseKey(*w.PreSharedKey)
+		if err != nil {
+			return fmt.Errorf("%w: %s", ErrWireguardPreSharedKeyNotValid, err)
+		}
+	}
+
+	// Validate Addresses
+	if len(w.Addresses) == 0 {
+		return ErrWireguardInterfaceAddressNotSet
+	}
+	for i, ipNet := range w.Addresses {
+		if ipNet.IP == nil || ipNet.Mask == nil {
+			return fmt.Errorf("%w: for address at index %d: %s",
+				ErrWireguardInterfaceAddressNotSet, i, ipNet.String())
+		}
+	}
+
+	// Validate interface
+	if !regexpInterfaceName.MatchString(w.Interface) {
+		return fmt.Errorf("%w: '%s' does not match regex '%s'",
+			ErrWireguardInterfaceNotValid, w.Interface, regexpInterfaceName)
+	}
+
+	return nil
+}
+
+func (w *Wireguard) copy() (copied Wireguard) {
+	return Wireguard{
+		PrivateKey:   helpers.CopyStringPtr(w.PrivateKey),
+		PreSharedKey: helpers.CopyStringPtr(w.PreSharedKey),
+		Addresses:    helpers.CopyIPNetSlice(w.Addresses),
+		Interface:    w.Interface,
+	}
+}
+
+func (w *Wireguard) mergeWith(other Wireguard) {
+	w.PrivateKey = helpers.MergeWithStringPtr(w.PrivateKey, other.PrivateKey)
+	w.PreSharedKey = helpers.MergeWithStringPtr(w.PreSharedKey, other.PreSharedKey)
+	w.Addresses = helpers.MergeIPNetsSlices(w.Addresses, other.Addresses)
+	w.Interface = helpers.MergeWithString(w.Interface, other.Interface)
+}
+
+func (w *Wireguard) overrideWith(other Wireguard) {
+	w.PrivateKey = helpers.OverrideWithStringPtr(w.PrivateKey, other.PrivateKey)
+	w.PreSharedKey = helpers.OverrideWithStringPtr(w.PreSharedKey, other.PreSharedKey)
+	w.Addresses = helpers.OverrideWithIPNetsSlice(w.Addresses, other.Addresses)
+	w.Interface = helpers.OverrideWithString(w.Interface, other.Interface)
+}
+
+func (w *Wireguard) setDefaults() {
+	w.PrivateKey = helpers.DefaultStringPtr(w.PrivateKey, "")
+	w.PreSharedKey = helpers.DefaultStringPtr(w.PreSharedKey, "")
+	w.Interface = helpers.DefaultString(w.Interface, "wg0")
+}
+
+func (w Wireguard) String() string {
+	return w.toLinesNode().String()
+}
+
+func (w Wireguard) toLinesNode() (node *gotree.Node) {
+	node = gotree.New("Wireguard settings:")
+
+	if *w.PrivateKey != "" {
+		s := helpers.ObfuscateWireguardKey(*w.PrivateKey)
+		node.Appendf("Private key: %s", s)
+	}
+
+	if *w.PreSharedKey != "" {
+		s := helpers.ObfuscateWireguardKey(*w.PreSharedKey)
+		node.Appendf("Pre-shared key: %s", s)
+	}
+
+	addressesNode := node.Appendf("Interface addresses:")
+	for _, address := range w.Addresses {
+		addressesNode.Appendf(address.String())
+	}
+
+	node.Appendf("Network interface: %s", w.Interface)
+
+	return node
+}