fix: Correctly filter users when the backend does not implement ISearchKnownUsersBackend

Signed-off-by: Côme Chilliet <come.chilliet@nextcloud.com>

Author: come-nc

lib/private/User/Manager.php

@@ -8,6 +8,7 @@
 namespace OC\User;
 
 use OC\Hooks\PublicEmitter;
+use OC\KnownUser\KnownUserService;
 use OC\Memcache\WithLocalCache;
 use OCP\Config\IUserConfig;
 use OCP\DB\QueryBuilder\IQueryBuilder;
@@ -69,6 +70,9 @@ class Manager extends PublicEmitter implements IUserManager {
 
 	private DisplayNameCache $displayNameCache;
 
+	// These services cannot be injected through DI because user manager is used early in install process
+	private ?KnownUserService $knownUserService = null;
+
 	// This constructor can't autoload any class requiring a DB connection.
 	public function __construct(
 		private IConfig $config,
@@ -83,6 +87,10 @@ public function __construct(
 		$this->displayNameCache = new DisplayNameCache($cacheFactory, $this);
 	}
 
+	private function getKnownUserService(): KnownUserService {
+		return $this->knownUserService ??= Server::get(KnownUserService::class);
+	}
+
 	/**
 	 * Get the active backends
 	 * @return UserInterface[]
@@ -362,7 +370,12 @@ public function searchKnownUsersByDisplayName(string $searcher, string $pattern,
 				$backendUsers = $backend->searchKnownUsersByDisplayName($searcher, $pattern, $limit, $offset);
 			} else {
 				// Better than nothing, but filtering after pagination can remove lots of results.
-				$backendUsers = $backend->getDisplayNames($pattern, $limit, $offset);
+				$backendUsers = array_filter(
+					$backend->getDisplayNames($pattern, $limit, $offset),
+					fn (string $uid): bool => $this->getKnownUserService()->isKnownToUser($searcher, $uid),
+					ARRAY_FILTER_USE_KEY,
+				);
+
 			}
 			if (is_array($backendUsers)) {
 				foreach ($backendUsers as $uid => $displayName) {