Instance-wide (global) info banner and maintenance mode (#36571)

The banner allows site operators to communicate important announcements
(e.g., maintenance windows, policy updates, service notices) directly
within the UI.

The maintenance mode only allows admin to access the web UI.

* Fix #2345
* Fix #9618

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/admin/config.go

@@ -5,9 +5,9 @@
 package admin
 
 import (
+	"errors"
 	"net/http"
 	"net/url"
-	"strconv"
 	"strings"
 
 	system_model "code.gitea.io/gitea/models/system"
@@ -145,7 +145,6 @@ func Config(ctx *context.Context) {
 	ctx.Data["Service"] = setting.Service
 	ctx.Data["DbCfg"] = setting.Database
 	ctx.Data["Webhook"] = setting.Webhook
-
 	ctx.Data["MailerEnabled"] = false
 	if setting.MailService != nil {
 		ctx.Data["MailerEnabled"] = true
@@ -191,52 +190,27 @@ func ConfigSettings(ctx *context.Context) {
 	ctx.Data["Title"] = ctx.Tr("admin.config_settings")
 	ctx.Data["PageIsAdminConfig"] = true
 	ctx.Data["PageIsAdminConfigSettings"] = true
-	ctx.Data["DefaultOpenWithEditorAppsString"] = setting.DefaultOpenWithEditorApps().ToTextareaString()
 	ctx.HTML(http.StatusOK, tplConfigSettings)
 }
 
+func validateConfigKeyValue(dynKey, input string) error {
+	opt := config.GetConfigOption(dynKey)
+	if opt == nil {
+		return util.NewInvalidArgumentErrorf("unknown config key: %s", dynKey)
+	}
+
+	const limit = 64 * 1024
+	if len(input) > limit {
+		return util.NewInvalidArgumentErrorf("value length exceeds limit of %d", limit)
+	}
+
+	if !json.Valid([]byte(input)) {
+		return util.NewInvalidArgumentErrorf("invalid json value for key: %s", dynKey)
+	}
+	return nil
+}
+
 func ChangeConfig(ctx *context.Context) {
-	cfg := setting.Config()
-
-	marshalBool := func(v string) ([]byte, error) {
-		b, _ := strconv.ParseBool(v)
-		return json.Marshal(b)
-	}
-
-	marshalString := func(emptyDefault string) func(v string) ([]byte, error) {
-		return func(v string) ([]byte, error) {
-			return json.Marshal(util.IfZero(v, emptyDefault))
-		}
-	}
-
-	marshalOpenWithApps := func(value string) ([]byte, error) {
-		// TODO: move the block alongside OpenWithEditorAppsType.ToTextareaString
-		lines := strings.Split(value, "\n")
-		var openWithEditorApps setting.OpenWithEditorAppsType
-		for _, line := range lines {
-			line = strings.TrimSpace(line)
-			if line == "" {
-				continue
-			}
-			displayName, openURL, ok := strings.Cut(line, "=")
-			displayName, openURL = strings.TrimSpace(displayName), strings.TrimSpace(openURL)
-			if !ok || displayName == "" || openURL == "" {
-				continue
-			}
-			openWithEditorApps = append(openWithEditorApps, setting.OpenWithEditorApp{
-				DisplayName: strings.TrimSpace(displayName),
-				OpenURL:     strings.TrimSpace(openURL),
-			})
-		}
-		return json.Marshal(openWithEditorApps)
-	}
-	marshallers := map[string]func(string) ([]byte, error){
-		cfg.Picture.DisableGravatar.DynKey():       marshalBool,
-		cfg.Picture.EnableFederatedAvatar.DynKey(): marshalBool,
-		cfg.Repository.OpenWithEditorApps.DynKey(): marshalOpenWithApps,
-		cfg.Repository.GitGuideRemoteName.DynKey(): marshalString(cfg.Repository.GitGuideRemoteName.DefaultValue()),
-	}
-
 	_ = ctx.Req.ParseForm()
 	configKeys := ctx.Req.Form["key"]
 	configValues := ctx.Req.Form["value"]
@@ -249,18 +223,16 @@ loop:
 		}
 		value := configValues[i]
 
-		marshaller, hasMarshaller := marshallers[key]
-		if !hasMarshaller {
-			ctx.JSONError(ctx.Tr("admin.config.set_setting_failed", key))
-			break loop
-		}
-
-		marshaledValue, err := marshaller(value)
+		err := validateConfigKeyValue(key, value)
 		if err != nil {
-			ctx.JSONError(ctx.Tr("admin.config.set_setting_failed", key))
+			if errors.Is(err, util.ErrInvalidArgument) {
+				ctx.JSONError(err.Error())
+			} else {
+				ctx.JSONError(ctx.Tr("admin.config.set_setting_failed", key))
+			}
 			break loop
 		}
-		configSettings[key] = string(marshaledValue)
+		configSettings[key] = value
 	}
 	if ctx.Written() {
 		return