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/vpn.go

@@ -0,0 +1,98 @@
+package settings
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/qdm12/gluetun/internal/configuration/settings/helpers"
+	"github.com/qdm12/gluetun/internal/constants"
+	"github.com/qdm12/gluetun/internal/models"
+	"github.com/qdm12/gotree"
+)
+
+type VPN struct {
+	// Type is the VPN type and can only be
+	// 'openvpn' or 'wireguard'. It cannot be the
+	// empty string in the internal state.
+	Type      string
+	Provider  Provider
+	OpenVPN   OpenVPN
+	Wireguard Wireguard
+}
+
+// Validate validates VPN settings.
+func (v VPN) validate(allServers models.AllServers) (err error) {
+	// Validate Type
+	validVPNTypes := []string{constants.OpenVPN, constants.Wireguard}
+	if !helpers.IsOneOf(v.Type, validVPNTypes...) {
+		return fmt.Errorf("%w: %q and can only be one of %s",
+			ErrVPNTypeNotValid, v.Type, strings.Join(validVPNTypes, ", "))
+	}
+
+	err = v.Provider.validate(v.Type, allServers)
+	if err != nil {
+		return fmt.Errorf("provider settings validation failed: %w", err)
+	}
+
+	if v.Type == constants.OpenVPN {
+		err := v.OpenVPN.validate(*v.Provider.Name)
+		if err != nil {
+			return fmt.Errorf("OpenVPN settings validation failed: %w", err)
+		}
+	} else {
+		err := v.Wireguard.validate(*v.Provider.Name)
+		if err != nil {
+			return fmt.Errorf("Wireguard settings validation failed: %w", err)
+		}
+	}
+
+	return nil
+}
+
+func (v *VPN) copy() (copied VPN) {
+	return VPN{
+		Type:      v.Type,
+		Provider:  v.Provider.copy(),
+		OpenVPN:   v.OpenVPN.copy(),
+		Wireguard: v.Wireguard.copy(),
+	}
+}
+
+func (v *VPN) mergeWith(other VPN) {
+	v.Type = helpers.MergeWithString(v.Type, other.Type)
+	v.Provider.mergeWith(other.Provider)
+	v.OpenVPN.mergeWith(other.OpenVPN)
+	v.Wireguard.mergeWith(other.Wireguard)
+}
+
+func (v *VPN) overrideWith(other VPN) {
+	v.Type = helpers.OverrideWithString(v.Type, other.Type)
+	v.Provider.overrideWith(other.Provider)
+	v.OpenVPN.overrideWith(other.OpenVPN)
+	v.Wireguard.overrideWith(other.Wireguard)
+}
+
+func (v *VPN) setDefaults() {
+	v.Type = helpers.DefaultString(v.Type, constants.OpenVPN)
+	v.Provider.setDefaults()
+	v.OpenVPN.setDefaults(*v.Provider.Name)
+	v.Wireguard.setDefaults()
+}
+
+func (v VPN) String() string {
+	return v.toLinesNode().String()
+}
+
+func (v VPN) toLinesNode() (node *gotree.Node) {
+	node = gotree.New("VPN settings:")
+
+	node.AppendNode(v.Provider.toLinesNode())
+
+	if v.Type == constants.OpenVPN {
+		node.AppendNode(v.OpenVPN.toLinesNode())
+	} else {
+		node.AppendNode(v.Wireguard.toLinesNode())
+	}
+
+	return node
+}