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/sources/files/health.go

@@ -0,0 +1,5 @@
+package files
+
+import "github.com/qdm12/gluetun/internal/configuration/settings"
+
+func (r *Reader) ReadHealth() (settings settings.Health, err error) { return settings, nil }

internal/configuration/sources/files/helpers.go

@@ -0,0 +1,31 @@
+package files
+
+import (
+	"io"
+	"os"
+)
+
+// ReadFromFile reads the content of the file as a string.
+// It returns a nil string pointer if the file does not exist.
+func ReadFromFile(filepath string) (s *string, err error) {
+	file, err := os.Open(filepath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil //nolint:nilnil
+		}
+		return nil, err
+	}
+
+	b, err := io.ReadAll(file)
+	if err != nil {
+		_ = file.Close()
+		return nil, err
+	}
+
+	if err := file.Close(); err != nil {
+		return nil, err
+	}
+
+	content := string(b)
+	return &content, nil
+}

internal/configuration/sources/files/openvpn.go

@@ -0,0 +1,22 @@
+package files
+
+import (
+	"fmt"
+
+	"github.com/qdm12/gluetun/internal/configuration/settings"
+	"github.com/qdm12/gluetun/internal/constants"
+)
+
+func (r *Reader) readOpenVPN() (settings settings.OpenVPN, err error) {
+	settings.ClientKey, err = ReadFromFile(constants.ClientKey)
+	if err != nil {
+		return settings, fmt.Errorf("cannot read client key: %w", err)
+	}
+
+	settings.ClientCrt, err = ReadFromFile(constants.ClientCertificate)
+	if err != nil {
+		return settings, fmt.Errorf("cannot read client certificate: %w", err)
+	}
+
+	return settings, nil
+}

internal/configuration/sources/files/reader.go

@@ -0,0 +1,28 @@
+package files
+
+import (
+	"github.com/qdm12/gluetun/internal/configuration/settings"
+	"github.com/qdm12/gluetun/internal/configuration/sources"
+)
+
+var _ sources.Source = (*Reader)(nil)
+
+type Reader struct{}
+
+func New() *Reader {
+	return &Reader{}
+}
+
+func (r *Reader) Read() (settings settings.Settings, err error) {
+	settings.VPN, err = r.readVPN()
+	if err != nil {
+		return settings, err
+	}
+
+	settings.System, err = r.readSystem()
+	if err != nil {
+		return settings, err
+	}
+
+	return settings, nil
+}

internal/configuration/sources/files/system.go

@@ -0,0 +1,10 @@
+package files
+
+import (
+	"github.com/qdm12/gluetun/internal/configuration/settings"
+)
+
+func (r *Reader) readSystem() (system settings.System, err error) {
+	// TODO timezone from /etc/localtime
+	return system, nil
+}

internal/configuration/sources/files/vpn.go

@@ -0,0 +1,16 @@
+package files
+
+import (
+	"fmt"
+
+	"github.com/qdm12/gluetun/internal/configuration/settings"
+)
+
+func (r *Reader) readVPN() (vpn settings.VPN, err error) {
+	vpn.OpenVPN, err = r.readOpenVPN()
+	if err != nil {
+		return vpn, fmt.Errorf("cannot read OpenVPN settings: %w", err)
+	}
+
+	return vpn, nil
+}