[MM-30436] Add support for configuration custom defaults (#16265)

* [MM-30436] Add support for configuration custom defaults

* Addressing review comments

* Addressing PR comments

* Soft fail if the configuration defaults cannot be read

* Directly print error in log message

* Fix linter

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

cmd/mattermost/commands/config.go

@@ -145,7 +145,7 @@ func getConfigStore(command *cobra.Command) (*config.Store, error) {
 		return nil, errors.Wrap(err, "failed to initialize i18n")
 	}
 
-	configStore, err := config.NewStore(getConfigDSN(command, config.GetEnvironment()), false)
+	configStore, err := config.NewStore(getConfigDSN(command, config.GetEnvironment()), false, nil)
 	if err != nil {
 		return nil, errors.Wrap(err, "failed to initialize config store")
 	}

cmd/mattermost/commands/config_test.go

@@ -543,9 +543,9 @@ func TestConfigMigrate(t *testing.T) {
 	sqlDSN := getDsn(*sqlSettings.DriverName, *sqlSettings.DataSource)
 	fileDSN := "config.json"
 
-	ds, err := config.NewStore(sqlDSN, false)
+	ds, err := config.NewStore(sqlDSN, false, nil)
 	require.NoError(t, err)
-	fs, err := config.NewStore(fileDSN, false)
+	fs, err := config.NewStore(fileDSN, false, nil)
 	require.NoError(t, err)
 
 	defer ds.Close()

cmd/mattermost/commands/init.go

@@ -32,7 +32,7 @@ func InitDBCommandContext(configDSN string) (*app.App, error) {
 	model.AppErrorInit(utils.T)
 
 	s, err := app.NewServer(
-		app.Config(configDSN, false),
+		app.Config(configDSN, false, nil),
 		app.StartSearchEngine,
 	)
 	if err != nil {

cmd/mattermost/commands/plugin_test.go

@@ -37,7 +37,7 @@ func TestPlugin(t *testing.T) {
 
 	fs, err := config.NewFileStore(th.ConfigPath(), false)
 	require.Nil(t, err)
-	cfsStore, err := config.NewStoreFromBacking(fs)
+	cfsStore, err := config.NewStoreFromBacking(fs, nil)
 	require.Nil(t, err)
 	require.NotNil(t, cfsStore.Get().PluginSettings.PluginStates["testplugin"])
 	assert.True(t, cfsStore.Get().PluginSettings.PluginStates["testplugin"].Enable)
@@ -47,7 +47,7 @@ func TestPlugin(t *testing.T) {
 	assert.Contains(t, output, "Disabled plugin: testplugin")
 	fs, err = config.NewFileStore(th.ConfigPath(), false)
 	require.Nil(t, err)
-	cfsStore, err = config.NewStoreFromBacking(fs)
+	cfsStore, err = config.NewStoreFromBacking(fs, nil)
 	require.Nil(t, err)
 	require.NotNil(t, cfsStore.Get().PluginSettings.PluginStates["testplugin"])
 	assert.False(t, cfsStore.Get().PluginSettings.PluginStates["testplugin"].Enable)

cmd/mattermost/commands/server.go

@@ -4,6 +4,7 @@
 package commands
 
 import (
+	"encoding/json"
 	"net"
 	"os"
 	"os/signal"
@@ -15,6 +16,7 @@ import (
 	"github.com/mattermost/mattermost-server/v5/config"
 	"github.com/mattermost/mattermost-server/v5/manualtesting"
 	"github.com/mattermost/mattermost-server/v5/mlog"
+	"github.com/mattermost/mattermost-server/v5/model"
 	"github.com/mattermost/mattermost-server/v5/utils"
 	"github.com/mattermost/mattermost-server/v5/web"
 	"github.com/mattermost/mattermost-server/v5/wsapi"
@@ -22,6 +24,8 @@ import (
 	"github.com/spf13/cobra"
 )
 
+const CUSTOM_DEFAULTS_ENV_VAR = "MM_CUSTOM_DEFAULTS_PATH"
+
 var serverCmd = &cobra.Command{
 	Use:          "server",
 	Short:        "Run the Mattermost server",
@@ -34,6 +38,27 @@ func init() {
 	RootCmd.RunE = serverCmdF
 }
 
+func loadCustomDefaults() (*model.Config, error) {
+	customDefaultsPath := os.Getenv(CUSTOM_DEFAULTS_ENV_VAR)
+	if customDefaultsPath == "" {
+		return nil, nil
+	}
+
+	file, err := os.Open(customDefaultsPath)
+	if err != nil {
+		return nil, errors.Wrapf(err, "unable to open custom defaults file at %q", customDefaultsPath)
+	}
+	defer file.Close()
+
+	var customDefaults *model.Config
+	err = json.NewDecoder(file).Decode(&customDefaults)
+	if err != nil {
+		return nil, errors.Wrap(err, "unable to decode custom defaults configuration")
+	}
+
+	return customDefaults, nil
+}
+
 func serverCmdF(command *cobra.Command, args []string) error {
 	disableConfigWatch, _ := command.Flags().GetBool("disableconfigwatch")
 	usedPlatform, _ := command.Flags().GetBool("platform")
@@ -41,9 +66,15 @@ func serverCmdF(command *cobra.Command, args []string) error {
 	interruptChan := make(chan os.Signal, 1)
 
 	if err := utils.TranslationsPreInit(); err != nil {
-		return errors.Wrapf(err, "unable to load Mattermost translation files")
+		return errors.Wrap(err, "unable to load Mattermost translation files")
 	}
-	configStore, err := config.NewStore(getConfigDSN(command, config.GetEnvironment()), !disableConfigWatch)
+
+	customDefaults, err := loadCustomDefaults()
+	if err != nil {
+		mlog.Error("Error loading custom configuration defaults: " + err.Error())
+	}
+
+	configStore, err := config.NewStore(getConfigDSN(command, config.GetEnvironment()), !disableConfigWatch, customDefaults)
 	if err != nil {
 		return errors.Wrap(err, "failed to load configuration")
 	}