options refactor (#1088)

* refactor config loading

* wip

* move autocert to its own config source

* refactor options updaters

* fix stuttering

* fix autocert validate check

config/config_source.go

@@ -0,0 +1,103 @@
+package config
+
+import (
+	"reflect"
+	"sync"
+
+	"github.com/fsnotify/fsnotify"
+	"github.com/mitchellh/copystructure"
+	"github.com/spf13/viper"
+)
+
+// Config holds pomerium configuration options.
+type Config struct {
+	Options *Options
+}
+
+// Clone creates a deep clone of the config.
+func (cfg *Config) Clone() *Config {
+	return copystructure.Must(copystructure.Config{
+		Copiers: map[reflect.Type]copystructure.CopierFunc{
+			reflect.TypeOf((*viper.Viper)(nil)): func(i interface{}) (interface{}, error) {
+				return i, nil
+			},
+		},
+	}.Copy(cfg)).(*Config)
+}
+
+// A ChangeListener is called when configuration changes.
+type ChangeListener = func(*Config)
+
+// A ChangeDispatcher manages listeners on config changes.
+type ChangeDispatcher struct {
+	sync.Mutex
+	onConfigChangeListeners []ChangeListener
+}
+
+// Trigger triggers a change.
+func (dispatcher *ChangeDispatcher) Trigger(cfg *Config) {
+	dispatcher.Lock()
+	defer dispatcher.Unlock()
+
+	for _, li := range dispatcher.onConfigChangeListeners {
+		li(cfg)
+	}
+}
+
+// OnConfigChange adds a listener.
+func (dispatcher *ChangeDispatcher) OnConfigChange(li ChangeListener) {
+	dispatcher.Lock()
+	defer dispatcher.Unlock()
+	dispatcher.onConfigChangeListeners = append(dispatcher.onConfigChangeListeners, li)
+}
+
+// A Source gets configuration.
+type Source interface {
+	GetConfig() *Config
+	OnConfigChange(ChangeListener)
+}
+
+// A FileOrEnvironmentSource retrieves config options from a file or the environment.
+type FileOrEnvironmentSource struct {
+	configFile string
+
+	mu     sync.RWMutex
+	config *Config
+
+	ChangeDispatcher
+}
+
+// NewFileOrEnvironmentSource creates a new FileOrEnvironmentSource.
+func NewFileOrEnvironmentSource(configFile string) (*FileOrEnvironmentSource, error) {
+	options, err := newOptionsFromConfig(configFile)
+	if err != nil {
+		return nil, err
+	}
+
+	src := &FileOrEnvironmentSource{
+		configFile: configFile,
+		config:     &Config{Options: options},
+	}
+	options.viper.OnConfigChange(src.onConfigChange)
+	go options.viper.WatchConfig()
+
+	return src, nil
+}
+
+func (src *FileOrEnvironmentSource) onConfigChange(evt fsnotify.Event) {
+	src.mu.Lock()
+	newOptions := handleConfigUpdate(src.configFile, src.config.Options)
+	cfg := &Config{Options: newOptions}
+	src.config = cfg
+	src.mu.Unlock()
+
+	src.Trigger(cfg)
+}
+
+// GetConfig gets the config.
+func (src *FileOrEnvironmentSource) GetConfig() *Config {
+	src.mu.RLock()
+	defer src.mu.RUnlock()
+
+	return src.config
+}