Add value migrations to config options

config/option.go

@@ -66,6 +66,9 @@ type PossibleValue struct {
 // Format: <vendor/package>:<scope>:<identifier> //.
 type Annotations map[string]interface{}
 
+// MigrationFunc is a function that migrates a config option value.
+type MigrationFunc func(option *Option, value any) any
+
 // Well known annotations defined by this package.
 const (
 	// DisplayHintAnnotation provides a hint for the user
@@ -259,6 +262,9 @@ type Option struct {
 	// Annotations is considered mutable and setting/reading annotation keys
 	// must be performed while the option is locked.
 	Annotations Annotations
+	// Migrations holds migration functions that are given the raw option value
+	// before any validation is run. The returned value is then used.
+	Migrations []MigrationFunc `json:"-"`
 
 	activeValue         *valueCache // runtime value (loaded from config file or set by user)
 	activeDefaultValue  *valueCache // runtime default value (may be set internally)
@@ -361,6 +367,7 @@ func (option *Option) ValidateValue(value any) error {
 	option.Lock()
 	defer option.Unlock()
 
+	value = migrateValue(option, value)
 	if _, err := validateValue(option, value); err != nil {
 		return err
 	}

config/perspective.go

@@ -35,6 +35,8 @@ optionsLoop:
 		if !ok {
 			continue
 		}
+		// migrate value
+		configValue = migrateValue(option, configValue)
 		// validate value
 		valueCache, err := validateValue(option, configValue)
 		if err != nil {

config/set.go

@@ -56,6 +56,7 @@ func ValidateConfig(newValues map[string]interface{}) (validationErrors []*Valid
 				option.Lock()
 				defer option.Unlock()
 
+				newValue = migrateValue(option, newValue)
 				_, err := validateValue(option, newValue)
 				if err != nil {
 					validationErrors = append(validationErrors, err)
@@ -88,6 +89,7 @@ func ReplaceConfig(newValues map[string]interface{}) (validationErrors []*Valida
 
 			option.activeValue = nil
 			if ok {
+				newValue = migrateValue(option, newValue)
 				valueCache, err := validateValue(option, newValue)
 				if err == nil {
 					option.activeValue = valueCache
@@ -125,6 +127,7 @@ func ReplaceDefaultConfig(newValues map[string]interface{}) (validationErrors []
 
 			option.activeDefaultValue = nil
 			if ok {
+				newValue = migrateValue(option, newValue)
 				valueCache, err := validateValue(option, newValue)
 				if err == nil {
 					option.activeDefaultValue = valueCache
@@ -160,6 +163,7 @@ func setConfigOption(key string, value any, push bool) (err error) {
 	if value == nil {
 		option.activeValue = nil
 	} else {
+		value = migrateValue(option, value)
 		valueCache, vErr := validateValue(option, value)
 		if vErr == nil {
 			option.activeValue = valueCache
@@ -201,6 +205,7 @@ func setDefaultConfigOption(key string, value interface{}, push bool) (err error
 	if value == nil {
 		option.activeDefaultValue = nil
 	} else {
+		value = migrateValue(option, value)
 		valueCache, vErr := validateValue(option, value)
 		if vErr == nil {
 			option.activeDefaultValue = valueCache

config/validate.go

@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"math"
 	"reflect"
+
+	"github.com/safing/portbase/log"
 )
 
 type valueCache struct {
@@ -64,6 +66,18 @@ func isAllowedPossibleValue(opt *Option, value interface{}) error {
 	return errors.New("value is not allowed")
 }
 
+// migrateValue runs all value migrations.
+func migrateValue(option *Option, value any) any {
+	for _, migration := range option.Migrations {
+		newValue := migration(option, value)
+		if newValue != value {
+			log.Debugf("config: migrated %s value from %v to %v", option.Key, value, newValue)
+		}
+		value = newValue
+	}
+	return value
+}
+
 // validateValue ensures that value matches the expected type of option.
 // It does not create a copy of the value!
 func validateValue(option *Option, value interface{}) (*valueCache, *ValidationError) { //nolint:gocyclo
@@ -76,8 +90,6 @@ func validateValue(option *Option, value interface{}) (*valueCache, *ValidationE
 		}
 	}
 
-	reflect.TypeOf(value).ConvertibleTo(reflect.TypeOf(""))
-
 	var validated *valueCache
 	switch v := value.(type) {
 	case string: