[Project Solar / Phase 1 / Engineering Follow-ups] Add localStorage parsing validation

packages/components/src/services/hds-theming.ts

@@ -65,6 +65,42 @@ export const HDS_THEMING_LOCALSTORAGE_DATA = 'hds-theming-data';
 export const DEFAULT_THEMING_OPTION_LIGHT_THEME = HdsModesLightValues.CdsG0;
 export const DEFAULT_THEMING_OPTION_DARK_THEME = HdsModesDarkValues.CdsG100;
 
+type StoredThemingData = {
+  theme: HdsThemes | undefined;
+  options: HdsThemingOptions;
+};
+
+// We use this guard function to check if the data parsed from `localStorage` conforms to the `StoredThemingData` type and so is safe to use.
+// This prevents the application from using corrupted, malformed or malicious data, by validating the object structure, theme, and mode values.
+
+function isSafeStoredThemingData(data: unknown): data is StoredThemingData {
+  if (typeof data !== 'object' || data === null) return false;
+
+  const d = data as Record<string, unknown>;
+
+  const isSafeThemeData =
+    // there is no stored `theme` key in the object (eg. the `default` theme was selected)
+    !('theme' in d) ||
+    // there is a `theme` value and is one of the valid `HdsThemes`
+    d['theme'] === undefined ||
+    THEMES.includes(d['theme'] as HdsThemes);
+
+  const options = d['options'] as Record<string, unknown> | undefined;
+
+  const isSafeOptionsData =
+    // there is no stored `options` key in the object (eg. it's the first run of the application)
+    !('options' in d) ||
+    // there is an `options` value and has valid entries
+    (typeof options === 'object' &&
+      options !== null &&
+      'lightTheme' in options &&
+      MODES_LIGHT.includes(options['lightTheme'] as HdsModesLight) &&
+      'darkTheme' in options &&
+      MODES_DARK.includes(options['darkTheme'] as HdsModesDark));
+
+  return isSafeThemeData && isSafeOptionsData;
+}
+
 export default class HdsThemingService extends Service {
   @tracked _currentTheme: HdsThemes | undefined = undefined;
   @tracked _currentMode: HdsModes | undefined = undefined;
@@ -77,6 +113,7 @@ export default class HdsThemingService extends Service {
     const rawStoredThemingData = localStorage.getItem(
       HDS_THEMING_LOCALSTORAGE_DATA
     );
+
     if (rawStoredThemingData !== null) {
       let storedThemingData: unknown;
       try {
@@ -87,16 +124,18 @@ export default class HdsThemingService extends Service {
           `Error while reading local storage '${HDS_THEMING_LOCALSTORAGE_DATA}' for theming`,
           error
         );
-        storedThemingData = undefined;
       }
-      if (storedThemingData) {
-        const { theme, options } = storedThemingData as {
-          theme: HdsThemes | undefined;
-          options: HdsThemingOptions;
-        };
+
+      if (isSafeStoredThemingData(storedThemingData)) {
+        this.setTheme({
+          theme: storedThemingData.theme,
+          options: storedThemingData.options,
+        });
+      } else {
+        // if data is not safe or malformed, reset theming to its defaults
         this.setTheme({
-          theme,
-          options,
+          theme: undefined,
+          options: undefined,
         });
       }
     }

showcase/app/services/shw-theming.ts

@@ -9,11 +9,14 @@ import HdsThemingService from '@hashicorp/design-system-components/services/hds-
 //   HdsOnSetThemeCallbackArgs,
 // } from '@hashicorp/design-system-components/services/hds-theming';
 
-export type ShwStylesheets =
-  | 'standard'
-  | 'css-selectors'
-  | 'css-selectors--migration'
-  | 'css-selectors--advanced';
+const STYLESHEETS = [
+  'standard',
+  'css-selectors',
+  'css-selectors--migration',
+  'css-selectors--advanced',
+] as const;
+
+export type ShwStylesheets = (typeof STYLESHEETS)[number];
 
 const ALL_STYLESHEETS_IDS: string[] = [
   'hds-components-stylesheet-default',
@@ -41,6 +44,10 @@ const STYLESHEETS_MAPPING: Record<ShwStylesheets, string[]> = {
 
 const LOCALSTORAGE_CURRENT_STYLESHEET = 'shw-theming-current-stylesheet';
 
+function isSafeStylesheetData(data: string): data is ShwStylesheets {
+  return STYLESHEETS.includes(data as ShwStylesheets);
+}
+
 export default class ShwThemingService extends HdsThemingService {
   @service declare readonly hdsTheming: HdsThemingService;
 
@@ -52,8 +59,11 @@ export default class ShwThemingService extends HdsThemingService {
     const storedStylesheet = localStorage.getItem(
       LOCALSTORAGE_CURRENT_STYLESHEET,
     ) as ShwStylesheets;
-    if (storedStylesheet) {
+    if (storedStylesheet && isSafeStylesheetData(storedStylesheet)) {
       this.setStylesheet(storedStylesheet);
+    } else {
+      // if data is not safe or malformed, reset stylesheet to its default
+      this.setStylesheet('standard');
     }
   }