1 files changed, 84 insertions, 0 deletions
diff --git a/lib/private/User/DisplayNameCache.php b/lib/private/User/DisplayNameCache.php
new file mode 100644
index 00000000000..4321d95f88e
--- /dev/null
+++ b/lib/private/User/DisplayNameCache.php
@@ -0,0 +1,84 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2022 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+namespace OC\User;
+
+use OCP\EventDispatcher\Event;
+use OCP\EventDispatcher\IEventListener;
+use OCP\ICache;
+use OCP\ICacheFactory;
+use OCP\IUser;
+use OCP\IUserManager;
+use OCP\User\Events\UserChangedEvent;
+use OCP\User\Events\UserDeletedEvent;
+
+/**
+ * Class that cache the relation UserId -> Display name
+ *
+ * This saves fetching the user from a user backend and later on fetching
+ * their preferences. It's generally not an issue if this data is slightly
+ * outdated.
+ * @template-implements IEventListener<UserChangedEvent|UserDeletedEvent>
+ */
+class DisplayNameCache implements IEventListener {
+	private const CACHE_TTL = 24 * 60 * 60; // 1 day
+
+	private array $cache = [];
+	private ICache $memCache;
+	private IUserManager $userManager;
+
+	public function __construct(ICacheFactory $cacheFactory, IUserManager $userManager) {
+		$this->memCache = $cacheFactory->createDistributed('displayNameMappingCache');
+		$this->userManager = $userManager;
+	}
+
+	public function getDisplayName(string $userId): ?string {
+		if (isset($this->cache[$userId])) {
+			return $this->cache[$userId];
+		}
+
+		if (strlen($userId) > IUser::MAX_USERID_LENGTH) {
+			return null;
+		}
+
+		$displayName = $this->memCache->get($userId);
+		if ($displayName) {
+			$this->cache[$userId] = $displayName;
+			return $displayName;
+		}
+
+		$user = $this->userManager->get($userId);
+		if ($user) {
+			$displayName = $user->getDisplayName();
+		} else {
+			$displayName = null;
+		}
+		$this->cache[$userId] = $displayName;
+		$this->memCache->set($userId, $displayName, self::CACHE_TTL);
+
+		return $displayName;
+	}
+
+	public function clear(): void {
+		$this->cache = [];
+		$this->memCache->clear();
+	}
+
+	public function handle(Event $event): void {
+		if ($event instanceof UserChangedEvent && $event->getFeature() === 'displayName') {
+			$userId = $event->getUser()->getUID();
+			$newDisplayName = $event->getValue();
+			$this->cache[$userId] = $newDisplayName;
+			$this->memCache->set($userId, $newDisplayName, self::CACHE_TTL);
+		}
+		if ($event instanceof UserDeletedEvent) {
+			$userId = $event->getUser()->getUID();
+			unset($this->cache[$userId]);
+			$this->memCache->remove($userId);
+		}
+	}
+}