fix(config): keep the category cache in the memory cache when available

A cache belongs in Nextcloud's memory cache rather than in the app
config. Use the distributed cache (e.g. Redis) with a one-week TTL when
one is available; Nextcloud falls back to the local cache (APCu) when
only that is configured. Without any memory cache the lazy app config
value stays as the fallback. A leftover app config value is removed
when the categories are stored in the memory cache, and saving the
settings clears both.

lib/Service/CategoryRepository.php

@@ -6,6 +6,8 @@ use OC\App\AppStore\Fetcher\CategoryFetcher;
 use OCA\SideMenu\AppInfo\Application;
 use OCP\AppFramework\Utility\ITimeFactory;
 use OCP\IAppConfig;
+use OCP\ICache;
+use OCP\ICacheFactory;
 use OCP\IConfig;
 use OCP\IUserSession;
 use OCP\L10N\IFactory;
@@ -33,6 +35,7 @@ class CategoryRepository
         protected IAppConfig $appConfig,
         protected ITimeFactory $timeFactory,
         protected LangRepository $langRepository,
+        protected ICacheFactory $cacheFactory,
     ) {
     }
 
@@ -94,6 +97,7 @@ class CategoryRepository
 
     public function clearCache(): void
     {
+        $this->getDistributedCache()?->remove(self::CACHE_KEY);
         $this->appConfig->deleteKey(Application::APP_ID, self::CACHE_KEY);
     }
 
@@ -117,18 +121,52 @@ class CategoryRepository
     }
 
     /**
-     * Returns the app store categories with only their names, from a
-     * cache that is stored lazily: it holds the names in every language,
-     * so it must not be loaded on every request with the other settings.
+     * Returns the app store categories with only their names. They are
+     * cached in the distributed cache (e.g. Redis) when one is configured,
+     * otherwise in a lazy app config value, so they are not loaded on
+     * every request with the other settings.
      */
     protected function getCategories(): array
     {
-        $cache = $this->appConfig->getValueArray(Application::APP_ID, self::CACHE_KEY, [], lazy: true);
+        $cache = $this->getDistributedCache();
 
-        if (isset($cache['expires'], $cache['categories']) && $cache['expires'] > $this->timeFactory->getTime()) {
-            return $cache['categories'];
+        if ($cache !== null) {
+            $categories = $cache->get(self::CACHE_KEY);
+
+            if (is_array($categories)) {
+                return $categories;
+            }
+        } else {
+            $stored = $this->appConfig->getValueArray(Application::APP_ID, self::CACHE_KEY, [], lazy: true);
+
+            if (isset($stored['expires'], $stored['categories']) && $stored['expires'] > $this->timeFactory->getTime()) {
+                return $stored['categories'];
+            }
         }
 
+        $categories = $this->fetchCategories();
+
+        // Don't cache an empty list, e.g. when the app store is unreachable
+        if (empty($categories)) {
+            return $categories;
+        }
+
+        $this->clearCache();
+
+        if ($cache !== null) {
+            $cache->set(self::CACHE_KEY, $categories, self::CACHE_TTL);
+        } else {
+            $this->appConfig->setValueArray(Application::APP_ID, self::CACHE_KEY, [
+                'expires' => $this->timeFactory->getTime() + self::CACHE_TTL,
+                'categories' => $categories,
+            ], lazy: true);
+        }
+
+        return $categories;
+    }
+
+    protected function fetchCategories(): array
+    {
         $langs = $this->getCachedLangs();
         $categories = [];
 
@@ -147,15 +185,13 @@ class CategoryRepository
             ];
         }
 
-        // Don't cache an empty list, e.g. when the app store is unreachable
-        if (!empty($categories)) {
-            $this->clearCache();
-            $this->appConfig->setValueArray(Application::APP_ID, self::CACHE_KEY, [
-                'expires' => $this->timeFactory->getTime() + self::CACHE_TTL,
-                'categories' => $categories,
-            ], lazy: true);
-        }
-
         return $categories;
     }
+
+    protected function getDistributedCache(): ?ICache
+    {
+        return $this->cacheFactory->isAvailable()
+            ? $this->cacheFactory->createDistributed(Application::APP_ID)
+            : null;
+    }
 }