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manager.go
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manager.go
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// SPDX-License-Identifier: BSD-3-Clause
// Copyright (c) 2022, Unikraft GmbH and The KraftKit Authors.
// Licensed under the BSD-3-Clause License (the "License").
// You may not use this file except in compliance with the License.
package config
import (
"fmt"
"os"
"os/signal"
"reflect"
"strings"
"syscall"
)
// ConfigManager uses the package facilities, there should be at least one
// instance of it. It holds the configuration feeders and structs.
type ConfigManager[C any] struct {
Config *C
ConfigFile string
Feeders []Feeder
}
type ConfigManagerOption[C any] func(cm *ConfigManager[C]) error
func WithFeeder[C any](feeder Feeder) ConfigManagerOption[C] {
return func(cm *ConfigManager[C]) error {
cm.AddFeeder(feeder)
return nil
}
}
func WithFile[C any](file string, forceCreate bool) ConfigManagerOption[C] {
return func(cm *ConfigManager[C]) error {
ext := strings.Split(file, ".")
if len(ext) == 1 {
return fmt.Errorf("unknown file extension for config file: %s", file)
}
_, err := os.Stat(file)
switch ext[len(ext)-1] {
case "yaml", "yml":
yml := YamlFeeder{
File: file,
}
if os.IsNotExist(err) {
err := yml.Write(cm.Config, forceCreate)
if err != nil {
return fmt.Errorf("could not write initial config: %v", err)
}
}
return WithFeeder[C](yml)(cm)
default:
return fmt.Errorf("unsupported file extension: %s", file)
}
}
}
func WithDefaultConfigFile[C any]() ConfigManagerOption[C] {
return func(cm *ConfigManager[C]) error {
return WithFile[C](DefaultConfigFile(), true)(cm)
}
}
func NewConfigManager[C any](c *C, opts ...ConfigManagerOption[C]) (*ConfigManager[C], error) {
if c == nil {
return nil, fmt.Errorf("cannot instantiate ConfigManager without Config")
}
cm := &ConfigManager[C]{
Config: c,
}
for _, o := range opts {
if err := o(cm); err != nil {
return nil, fmt.Errorf("could not apply config manager option: %v", err)
}
}
// Feed the config, pass the manager anyway if this fails, we still have
// defaults
if err := cm.Feed(); err != nil {
return cm, fmt.Errorf("could not feed config: %v", err)
}
return cm, nil
}
// AddFeeder adds a feeder that provides configuration data.
func (cm *ConfigManager[C]) AddFeeder(f Feeder) *ConfigManager[C] {
if f == nil {
return cm
}
cm.Feeders = append(cm.Feeders, f)
return cm
}
// Feed binds configuration data from added feeders to the added structs.
func (cm *ConfigManager[C]) Feed() error {
for _, f := range cm.Feeders {
if err := cm.feedStruct(f, cm.Config); err != nil {
return err
}
}
return nil
}
func (cm *ConfigManager[C]) Write(merge bool) error {
for _, f := range cm.Feeders {
if err := f.Write(cm.Config, merge); err != nil {
return err
}
}
return nil
}
// SetupListener adds an OS signal listener to the Config instance. The listener
// listens to the `SIGHUP` signal and refreshes the Config instance. It would
// call the provided fallback if the refresh process failed.
func (cm *ConfigManager[C]) SetupListener(fallback func(err error)) *ConfigManager[C] {
s := make(chan os.Signal, 1)
signal.Notify(s, syscall.SIGHUP)
go func() {
for {
<-s
if err := cm.Feed(); err != nil {
fallback(err)
}
}
}()
return cm
}
// feedStruct feeds a struct using given feeder.
func (cm *ConfigManager[C]) feedStruct(f Feeder, s interface{}) error {
if err := f.Feed(s); err != nil {
return fmt.Errorf("failed to feed config: %v", err)
}
return nil
}
func AllowedValues(key string) []string {
for _, details := range ConfigDetails() {
if details.Key == key {
return details.AllowedValues
}
}
return []string{}
}
// FetchConfigDirFromArgs returns the path to the alternate config directory
// that can be set via the --config-dir flag. This needs to be fetched before flags
// are populated with AttributeFlags to ensure that the function is called only once.
func FetchConfigDirFromArgs(args []string) (path string) {
for idx, arg := range args {
if !strings.HasPrefix(arg, "--config-dir") {
continue
}
if strings.Contains(arg, "=") {
if split := strings.Split(arg, "="); len(split) == 2 {
path = split[1]
}
} else {
if !strings.HasPrefix(args[idx+1], "-") {
path = args[idx+1]
}
}
break
}
return
}
func Default[C any](key string) string {
found, _, def, _, err := findConfigDefault[C](key, "", "", reflect.ValueOf(new([0]C)))
if err != nil || found != key {
return def
}
return ""
}
func findConfigDefault[C any](needle, offset, def string, v reflect.Value) (string, string, string, reflect.Value, error) {
if v.Kind() != reflect.Ptr {
return needle, offset, def, v, fmt.Errorf("not a pointer value")
}
if needle == offset {
return needle, offset, def, v, nil
}
v = reflect.Indirect(v)
switch v.Kind() {
case reflect.Struct:
for i := 0; i < v.NumField(); i++ {
name := v.Type().Field(i).Tag.Get("json")
if len(name) == 0 {
continue
}
check := name
if len(offset) > 0 {
check = offset + "." + name
}
dNeedle, dOffset, dDef, dv, dErr := findConfigDefault[C](
needle,
check,
v.Type().Field(i).Tag.Get("default"),
v.Field(i).Addr(),
)
if dOffset == needle {
return dNeedle, dOffset, dDef, dv, dErr
}
}
}
return needle, offset, def, v, fmt.Errorf("could not find default for: %s", needle)
}