MM-13893: introduce file store (#10243)

* config file store

Introduce an interface and concrete implementation for accessing the config.

This mostly maps 1:1 with the exiting usage in `App`, except for internalizing the watcher. A future change will likely eliminate `App.PersistConfig()` and make this implicit on `Set` or `Patch`

* experimental file test changes

* emoji: move file driver checks from api4 to app

It is no longer possible to app.UpdateConfig and provide an invalid configuration, making it hard to test this case. This check doesn't really belong in the api anyway, since it's a configuration validity check and not a permissions check. Either way, the check now occurs at the App level.

* api4: generate valid public link salts for test

* TestStartServerRateLimiterCriticalError: use mock store to test invalid config

* remove config_test.go

* remove needsSave, and have Load() save to the backing store as necessary

* restore README.md

* move ldap UserFilter check to model isValid checks

* remove databaseStore until ready

* remove unimplemented Patch

* simplify unlockOnce implementation

* revert forgetting to set s.Ldap

* config/file.go: rename ReadOnlyConfigurationError to ErrReadOnlyConfiguration

* config: export FileStore

* add TestFileStoreSave

* improved config/utils test coverage

* restore config/README.md copy

* tweaks

* file store: acquire a write lock on Save/Close to safely close watcher

* fix unmarshal_test.go

app/server.go

@@ -35,7 +35,6 @@ import (
 	"github.com/mattermost/mattermost-server/services/timezones"
 	"github.com/mattermost/mattermost-server/store"
 	"github.com/mattermost/mattermost-server/utils"
-	"github.com/mattermost/mattermost-server/utils/fileutils"
 )
 
 var MaxNotificationsPerChannelDefault int64 = 1000000
@@ -75,10 +74,6 @@ type Server struct {
 	runjobs bool
 	Jobs    *jobs.JobServer
 
-	config                 atomic.Value
-	envConfig              map[string]interface{}
-	configFile             string
-	configListeners        map[string]func(*model.Config, *model.Config)
 	clusterLeaderListeners sync.Map
 
 	licenseValue       atomic.Value
@@ -96,8 +91,7 @@ type Server struct {
 	licenseListenerId       string
 	logListenerId           string
 	clusterLeaderListenerId string
-	disableConfigWatch      bool
-	configWatcher           *config.ConfigWatcher
+	configStore             config.Store
 	asymmetricSigningKey    *ecdsa.PrivateKey
 
 	pluginCommands     []*PluginCommand
@@ -137,8 +131,6 @@ func NewServer(options ...Option) (*Server, error) {
 	s := &Server{
 		goroutineExitSignal:     make(chan struct{}, 1),
 		RootRouter:              rootRouter,
-		configFile:              "config.json",
-		configListeners:         make(map[string]func(*model.Config, *model.Config)),
 		licenseListeners:        map[string]func(){},
 		sessionCache:            utils.NewLru(model.SESSION_CACHE_SIZE),
 		seenPendingPostIdsCache: utils.NewLru(PENDING_POST_IDS_CACHE_SIZE),
@@ -150,11 +142,14 @@ func NewServer(options ...Option) (*Server, error) {
 		}
 	}
 
-	if err := s.LoadConfig(s.configFile); err != nil {
-		return nil, err
-	}
+	if s.configStore == nil {
+		configStore, err := config.NewFileStore("config.json", true)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to load config")
+		}
 
-	s.EnableConfigWatch()
+		s.configStore = configStore
+	}
 
 	// Initalize logging
 	s.Log = mlog.NewLogger(utils.MloggerConfigFromLoggerConfig(&s.Config().LogSettings))
@@ -198,7 +193,7 @@ func NewServer(options ...Option) (*Server, error) {
 	mlog.Info(fmt.Sprintf("Enterprise Enabled: %v", model.BuildEnterpriseReady))
 	pwd, _ := os.Getwd()
 	mlog.Info(fmt.Sprintf("Current working directory is %v", pwd))
-	mlog.Info(fmt.Sprintf("Loaded config file from %v", fileutils.FindConfigFile(s.configFile)))
+	mlog.Info("Loaded config", mlog.String("source", s.configStore.String()))
 
 	license := s.License()
 
@@ -323,7 +318,7 @@ func (s *Server) Shutdown() error {
 	s.RemoveConfigListener(s.configListenerId)
 	s.RemoveConfigListener(s.logListenerId)
 
-	s.DisableConfigWatch()
+	s.configStore.Close()
 
 	if s.Cluster != nil {
 		s.Cluster.StopInterNodeCommunication()