Remove global config watcher (#8080)

* remove global config watcher

* keep config watcher disabled for tests

* compile fix

* fix resource leak

app/config.go

@@ -0,0 +1,73 @@
+// Copyright (c) 2016-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package app
+
+import (
+	"crypto/md5"
+	"encoding/json"
+	"fmt"
+	"runtime/debug"
+
+	l4g "github.com/alecthomas/log4go"
+
+	"github.com/mattermost/mattermost-server/model"
+	"github.com/mattermost/mattermost-server/utils"
+)
+
+func (a *App) Config() *model.Config {
+	return utils.Cfg
+}
+
+func (a *App) UpdateConfig(f func(*model.Config)) {
+	old := utils.Cfg.Clone()
+	f(utils.Cfg)
+	utils.InvokeGlobalConfigListeners(old, utils.Cfg)
+}
+
+func (a *App) PersistConfig() {
+	utils.SaveConfig(a.ConfigFileName(), a.Config())
+}
+
+func (a *App) ReloadConfig() {
+	debug.FreeOSMemory()
+	utils.LoadGlobalConfig(a.ConfigFileName())
+
+	// start/restart email batching job if necessary
+	a.InitEmailBatching()
+}
+
+func (a *App) ConfigFileName() string {
+	return utils.CfgFileName
+}
+
+func (a *App) ClientConfig() map[string]string {
+	return a.clientConfig
+}
+
+func (a *App) ClientConfigHash() string {
+	return a.clientConfigHash
+}
+
+func (a *App) EnableConfigWatch() {
+	if a.configWatcher == nil && !a.disableConfigWatch {
+		configWatcher, err := utils.NewConfigWatcher(utils.CfgFileName)
+		if err != nil {
+			l4g.Error(err)
+		}
+		a.configWatcher = configWatcher
+	}
+}
+
+func (a *App) DisableConfigWatch() {
+	if a.configWatcher != nil {
+		a.configWatcher.Close()
+		a.configWatcher = nil
+	}
+}
+
+func (a *App) regenerateClientConfig() {
+	a.clientConfig = utils.GenerateClientConfig(a.Config(), a.DiagnosticId())
+	clientConfigJSON, _ := json.Marshal(a.clientConfig)
+	a.clientConfigHash = fmt.Sprintf("%x", md5.Sum(clientConfigJSON))
+}