nextcloud / server

apps/user_ldap/lib/Access.php

Indentation +2028 added lines, -2028 removed lines

@@ -63,1779 +63,1779 @@ 
  * @package OCA\User_LDAP
  */
 class Access extends LDAPUtility {
-	const UUID_ATTRIBUTES = ['entryuuid', 'nsuniqueid', 'objectguid', 'guid', 'ipauniqueid'];
-
-	/** @var \OCA\User_LDAP\Connection */
-	public $connection;
-	/** @var Manager */
-	public $userManager;
-	//never ever check this var directly, always use getPagedSearchResultState
-	protected $pagedSearchedSuccessful;
-
-	/**
-	 * @var string[] $cookies an array of returned Paged Result cookies
-	 */
-	protected $cookies = array();
-
-	/**
-	 * @var string $lastCookie the last cookie returned from a Paged Results
-	 * operation, defaults to an empty string
-	 */
-	protected $lastCookie = '';
-
-	/**
-	 * @var AbstractMapping $userMapper
-	 */
-	protected $userMapper;
-
-	/**
-	* @var AbstractMapping $userMapper
-	*/
-	protected $groupMapper;
-
-	/**
-	 * @var \OCA\User_LDAP\Helper
-	 */
-	private $helper;
-	/** @var IConfig */
-	private $config;
-	/** @var IUserManager */
-	private $ncUserManager;
-
-	public function __construct(
-		Connection $connection,
-		ILDAPWrapper $ldap,
-		Manager $userManager,
-		Helper $helper,
-		IConfig $config,
-		IUserManager $ncUserManager
-	) {
-		parent::__construct($ldap);
-		$this->connection = $connection;
-		$this->userManager = $userManager;
-		$this->userManager->setLdapAccess($this);
-		$this->helper = $helper;
-		$this->config = $config;
-		$this->ncUserManager = $ncUserManager;
-	}
-
-	/**
-	 * sets the User Mapper
-	 * @param AbstractMapping $mapper
-	 */
-	public function setUserMapper(AbstractMapping $mapper) {
-		$this->userMapper = $mapper;
-	}
-
-	/**
-	 * returns the User Mapper
-	 * @throws \Exception
-	 * @return AbstractMapping
-	 */
-	public function getUserMapper() {
-		if(is_null($this->userMapper)) {
-			throw new \Exception('UserMapper was not assigned to this Access instance.');
-		}
-		return $this->userMapper;
-	}
-
-	/**
-	 * sets the Group Mapper
-	 * @param AbstractMapping $mapper
-	 */
-	public function setGroupMapper(AbstractMapping $mapper) {
-		$this->groupMapper = $mapper;
-	}
-
-	/**
-	 * returns the Group Mapper
-	 * @throws \Exception
-	 * @return AbstractMapping
-	 */
-	public function getGroupMapper() {
-		if(is_null($this->groupMapper)) {
-			throw new \Exception('GroupMapper was not assigned to this Access instance.');
-		}
-		return $this->groupMapper;
-	}
-
-	/**
-	 * @return bool
-	 */
-	private function checkConnection() {
-		return ($this->connection instanceof Connection);
-	}
-
-	/**
-	 * returns the Connection instance
-	 * @return \OCA\User_LDAP\Connection
-	 */
-	public function getConnection() {
-		return $this->connection;
-	}
-
-	/**
-	 * reads a given attribute for an LDAP record identified by a DN
-	 *
-	 * @param string $dn the record in question
-	 * @param string $attr the attribute that shall be retrieved
-	 *        if empty, just check the record's existence
-	 * @param string $filter
-	 * @return array|false an array of values on success or an empty
-	 *          array if $attr is empty, false otherwise
-	 * @throws ServerNotAvailableException
-	 */
-	public function readAttribute($dn, $attr, $filter = 'objectClass=*') {
-		if(!$this->checkConnection()) {
-			\OCP\Util::writeLog('user_ldap',
-				'No LDAP Connector assigned, access impossible for readAttribute.',
-				ILogger::WARN);
-			return false;
-		}
-		$cr = $this->connection->getConnectionResource();
-		if(!$this->ldap->isResource($cr)) {
-			//LDAP not available
-			\OCP\Util::writeLog('user_ldap', 'LDAP resource not available.', ILogger::DEBUG);
-			return false;
-		}
-		//Cancel possibly running Paged Results operation, otherwise we run in
-		//LDAP protocol errors
-		$this->abandonPagedSearch();
-		// openLDAP requires that we init a new Paged Search. Not needed by AD,
-		// but does not hurt either.
-		$pagingSize = (int)$this->connection->ldapPagingSize;
-		// 0 won't result in replies, small numbers may leave out groups
-		// (cf. #12306), 500 is default for paging and should work everywhere.
-		$maxResults = $pagingSize > 20 ? $pagingSize : 500;
-		$attr = mb_strtolower($attr, 'UTF-8');
-		// the actual read attribute later may contain parameters on a ranged
-		// request, e.g. member;range=99-199. Depends on server reply.
-		$attrToRead = $attr;
-
-		$values = [];
-		$isRangeRequest = false;
-		do {
-			$result = $this->executeRead($cr, $dn, $attrToRead, $filter, $maxResults);
-			if(is_bool($result)) {
-				// when an exists request was run and it was successful, an empty
-				// array must be returned
-				return $result ? [] : false;
-			}
-
-			if (!$isRangeRequest) {
-				$values = $this->extractAttributeValuesFromResult($result, $attr);
-				if (!empty($values)) {
-					return $values;
-				}
-			}
-
-			$isRangeRequest = false;
-			$result = $this->extractRangeData($result, $attr);
-			if (!empty($result)) {
-				$normalizedResult = $this->extractAttributeValuesFromResult(
-					[ $attr => $result['values'] ],
-					$attr
-				);
-				$values = array_merge($values, $normalizedResult);
-
-				if($result['rangeHigh'] === '*') {
-					// when server replies with * as high range value, there are
-					// no more results left
-					return $values;
-				} else {
-					$low  = $result['rangeHigh'] + 1;
-					$attrToRead = $result['attributeName'] . ';range=' . $low . '-*';
-					$isRangeRequest = true;
-				}
-			}
-		} while($isRangeRequest);
-
-		\OCP\Util::writeLog('user_ldap', 'Requested attribute '.$attr.' not found for '.$dn, ILogger::DEBUG);
-		return false;
-	}
-
-	/**
-	 * Runs an read operation against LDAP
-	 *
-	 * @param resource $cr the LDAP connection
-	 * @param string $dn
-	 * @param string $attribute
-	 * @param string $filter
-	 * @param int $maxResults
-	 * @return array|bool false if there was any error, true if an exists check
-	 *                    was performed and the requested DN found, array with the
-	 *                    returned data on a successful usual operation
-	 * @throws ServerNotAvailableException
-	 */
-	public function executeRead($cr, $dn, $attribute, $filter, $maxResults) {
-		$this->initPagedSearch($filter, array($dn), array($attribute), $maxResults, 0);
-		$dn = $this->helper->DNasBaseParameter($dn);
-		$rr = @$this->invokeLDAPMethod('read', $cr, $dn, $filter, array($attribute));
-		if (!$this->ldap->isResource($rr)) {
-			if ($attribute !== '') {
-				//do not throw this message on userExists check, irritates
-				\OCP\Util::writeLog('user_ldap', 'readAttribute failed for DN ' . $dn, ILogger::DEBUG);
-			}
-			//in case an error occurs , e.g. object does not exist
-			return false;
-		}
-		if ($attribute === '' && ($filter === 'objectclass=*' || $this->invokeLDAPMethod('countEntries', $cr, $rr) === 1)) {
-			\OCP\Util::writeLog('user_ldap', 'readAttribute: ' . $dn . ' found', ILogger::DEBUG);
-			return true;
-		}
-		$er = $this->invokeLDAPMethod('firstEntry', $cr, $rr);
-		if (!$this->ldap->isResource($er)) {
-			//did not match the filter, return false
-			return false;
-		}
-		//LDAP attributes are not case sensitive
-		$result = \OCP\Util::mb_array_change_key_case(
-			$this->invokeLDAPMethod('getAttributes', $cr, $er), MB_CASE_LOWER, 'UTF-8');
-
-		return $result;
-	}
-
-	/**
-	 * Normalizes a result grom getAttributes(), i.e. handles DNs and binary
-	 * data if present.
-	 *
-	 * @param array $result from ILDAPWrapper::getAttributes()
-	 * @param string $attribute the attribute name that was read
-	 * @return string[]
-	 */
-	public function extractAttributeValuesFromResult($result, $attribute) {
-		$values = [];
-		if(isset($result[$attribute]) && $result[$attribute]['count'] > 0) {
-			$lowercaseAttribute = strtolower($attribute);
-			for($i=0;$i<$result[$attribute]['count'];$i++) {
-				if($this->resemblesDN($attribute)) {
-					$values[] = $this->helper->sanitizeDN($result[$attribute][$i]);
-				} elseif($lowercaseAttribute === 'objectguid' || $lowercaseAttribute === 'guid') {
-					$values[] = $this->convertObjectGUID2Str($result[$attribute][$i]);
-				} else {
-					$values[] = $result[$attribute][$i];
-				}
-			}
-		}
-		return $values;
-	}
-
-	/**
-	 * Attempts to find ranged data in a getAttribute results and extracts the
-	 * returned values as well as information on the range and full attribute
-	 * name for further processing.
-	 *
-	 * @param array $result from ILDAPWrapper::getAttributes()
-	 * @param string $attribute the attribute name that was read. Without ";range=…"
-	 * @return array If a range was detected with keys 'values', 'attributeName',
-	 *               'attributeFull' and 'rangeHigh', otherwise empty.
-	 */
-	public function extractRangeData($result, $attribute) {
-		$keys = array_keys($result);
-		foreach($keys as $key) {
-			if($key !== $attribute && strpos($key, $attribute) === 0) {
-				$queryData = explode(';', $key);
-				if(strpos($queryData[1], 'range=') === 0) {
-					$high = substr($queryData[1], 1 + strpos($queryData[1], '-'));
-					$data = [
-						'values' => $result[$key],
-						'attributeName' => $queryData[0],
-						'attributeFull' => $key,
-						'rangeHigh' => $high,
-					];
-					return $data;
-				}
-			}
-		}
-		return [];
-	}
-
-	/**
-	 * Set password for an LDAP user identified by a DN
-	 *
-	 * @param string $userDN the user in question
-	 * @param string $password the new password
-	 * @return bool
-	 * @throws HintException
-	 * @throws \Exception
-	 */
-	public function setPassword($userDN, $password) {
-		if((int)$this->connection->turnOnPasswordChange !== 1) {
-			throw new \Exception('LDAP password changes are disabled.');
-		}
-		$cr = $this->connection->getConnectionResource();
-		if(!$this->ldap->isResource($cr)) {
-			//LDAP not available
-			\OCP\Util::writeLog('user_ldap', 'LDAP resource not available.', ILogger::DEBUG);
-			return false;
-		}
-		try {
-			// try PASSWD extended operation first
-			return @$this->invokeLDAPMethod('exopPasswd', $cr, $userDN, '', $password) ||
-						@$this->invokeLDAPMethod('modReplace', $cr, $userDN, $password);
-		} catch(ConstraintViolationException $e) {
-			throw new HintException('Password change rejected.', \OC::$server->getL10N('user_ldap')->t('Password change rejected. Hint: ').$e->getMessage(), $e->getCode());
-		}
-	}
-
-	/**
-	 * checks whether the given attributes value is probably a DN
-	 * @param string $attr the attribute in question
-	 * @return boolean if so true, otherwise false
-	 */
-	private function resemblesDN($attr) {
-		$resemblingAttributes = array(
-			'dn',
-			'uniquemember',
-			'member',
-			// memberOf is an "operational" attribute, without a definition in any RFC
-			'memberof'
-		);
-		return in_array($attr, $resemblingAttributes);
-	}
-
-	/**
-	 * checks whether the given string is probably a DN
-	 * @param string $string
-	 * @return boolean
-	 */
-	public function stringResemblesDN($string) {
-		$r = $this->ldap->explodeDN($string, 0);
-		// if exploding a DN succeeds and does not end up in
-		// an empty array except for $r[count] being 0.
-		return (is_array($r) && count($r) > 1);
-	}
-
-	/**
-	 * returns a DN-string that is cleaned from not domain parts, e.g.
-	 * cn=foo,cn=bar,dc=foobar,dc=server,dc=org
-	 * becomes dc=foobar,dc=server,dc=org
-	 * @param string $dn
-	 * @return string
-	 */
-	public function getDomainDNFromDN($dn) {
-		$allParts = $this->ldap->explodeDN($dn, 0);
-		if($allParts === false) {
-			//not a valid DN
-			return '';
-		}
-		$domainParts = array();
-		$dcFound = false;
-		foreach($allParts as $part) {
-			if(!$dcFound && strpos($part, 'dc=') === 0) {
-				$dcFound = true;
-			}
-			if($dcFound) {
-				$domainParts[] = $part;
-			}
-		}
-		return implode(',', $domainParts);
-	}
-
-	/**
-	 * returns the LDAP DN for the given internal Nextcloud name of the group
-	 * @param string $name the Nextcloud name in question
-	 * @return string|false LDAP DN on success, otherwise false
-	 */
-	public function groupname2dn($name) {
-		return $this->groupMapper->getDNByName($name);
-	}
-
-	/**
-	 * returns the LDAP DN for the given internal Nextcloud name of the user
-	 * @param string $name the Nextcloud name in question
-	 * @return string|false with the LDAP DN on success, otherwise false
-	 */
-	public function username2dn($name) {
-		$fdn = $this->userMapper->getDNByName($name);
-
-		//Check whether the DN belongs to the Base, to avoid issues on multi-
-		//server setups
-		if(is_string($fdn) && $this->isDNPartOfBase($fdn, $this->connection->ldapBaseUsers)) {
-			return $fdn;
-		}
-
-		return false;
-	}
-
-	/**
-	 * returns the internal Nextcloud name for the given LDAP DN of the group, false on DN outside of search DN or failure
-	 *
-	 * @param string $fdn the dn of the group object
-	 * @param string $ldapName optional, the display name of the object
-	 * @return string|false with the name to use in Nextcloud, false on DN outside of search DN
-	 * @throws \Exception
-	 */
-	public function dn2groupname($fdn, $ldapName = null) {
-		//To avoid bypassing the base DN settings under certain circumstances
-		//with the group support, check whether the provided DN matches one of
-		//the given Bases
-		if(!$this->isDNPartOfBase($fdn, $this->connection->ldapBaseGroups)) {
-			return false;
-		}
-
-		return $this->dn2ocname($fdn, $ldapName, false);
-	}
-
-	/**
-	 * accepts an array of group DNs and tests whether they match the user
-	 * filter by doing read operations against the group entries. Returns an
-	 * array of DNs that match the filter.
-	 *
-	 * @param string[] $groupDNs
-	 * @return string[]
-	 * @throws ServerNotAvailableException
-	 */
-	public function groupsMatchFilter($groupDNs) {
-		$validGroupDNs = [];
-		foreach($groupDNs as $dn) {
-			$cacheKey = 'groupsMatchFilter-'.$dn;
-			$groupMatchFilter = $this->connection->getFromCache($cacheKey);
-			if(!is_null($groupMatchFilter)) {
-				if($groupMatchFilter) {
-					$validGroupDNs[] = $dn;
-				}
-				continue;
-			}
-
-			// Check the base DN first. If this is not met already, we don't
-			// need to ask the server at all.
-			if(!$this->isDNPartOfBase($dn, $this->connection->ldapBaseGroups)) {
-				$this->connection->writeToCache($cacheKey, false);
-				continue;
-			}
-
-			$result = $this->readAttribute($dn, '', $this->connection->ldapGroupFilter);
-			if(is_array($result)) {
-				$this->connection->writeToCache($cacheKey, true);
-				$validGroupDNs[] = $dn;
-			} else {
-				$this->connection->writeToCache($cacheKey, false);
-			}
-
-		}
-		return $validGroupDNs;
-	}
-
-	/**
-	 * returns the internal Nextcloud name for the given LDAP DN of the user, false on DN outside of search DN or failure
-	 *
-	 * @param string $dn the dn of the user object
-	 * @param string $ldapName optional, the display name of the object
-	 * @return string|false with with the name to use in Nextcloud
-	 * @throws \Exception
-	 */
-	public function dn2username($fdn, $ldapName = null) {
-		//To avoid bypassing the base DN settings under certain circumstances
-		//with the group support, check whether the provided DN matches one of
-		//the given Bases
-		if(!$this->isDNPartOfBase($fdn, $this->connection->ldapBaseUsers)) {
-			return false;
-		}
-
-		return $this->dn2ocname($fdn, $ldapName, true);
-	}
-
-	/**
-	 * returns an internal Nextcloud name for the given LDAP DN, false on DN outside of search DN
-	 *
-	 * @param string $fdn the dn of the user object
-	 * @param string|null $ldapName optional, the display name of the object
-	 * @param bool $isUser optional, whether it is a user object (otherwise group assumed)
-	 * @param bool|null $newlyMapped
-	 * @param array|null $record
-	 * @return false|string with with the name to use in Nextcloud
-	 * @throws \Exception
-	 */
-	public function dn2ocname($fdn, $ldapName = null, $isUser = true, &$newlyMapped = null, array $record = null) {
-		$newlyMapped = false;
-		if($isUser) {
-			$mapper = $this->getUserMapper();
-			$nameAttribute = $this->connection->ldapUserDisplayName;
-			$filter = $this->connection->ldapUserFilter;
-		} else {
-			$mapper = $this->getGroupMapper();
-			$nameAttribute = $this->connection->ldapGroupDisplayName;
-			$filter = $this->connection->ldapGroupFilter;
-		}
-
-		//let's try to retrieve the Nextcloud name from the mappings table
-		$ncName = $mapper->getNameByDN($fdn);
-		if(is_string($ncName)) {
-			return $ncName;
-		}
-
-		//second try: get the UUID and check if it is known. Then, update the DN and return the name.
-		$uuid = $this->getUUID($fdn, $isUser, $record);
-		if(is_string($uuid)) {
-			$ncName = $mapper->getNameByUUID($uuid);
-			if(is_string($ncName)) {
-				$mapper->setDNbyUUID($fdn, $uuid);
-				return $ncName;
-			}
-		} else {
-			//If the UUID can't be detected something is foul.
-			\OCP\Util::writeLog('user_ldap', 'Cannot determine UUID for '.$fdn.'. Skipping.', ILogger::INFO);
-			return false;
-		}
-
-		if(is_null($ldapName)) {
-			$ldapName = $this->readAttribute($fdn, $nameAttribute, $filter);
-			if(!isset($ldapName[0]) && empty($ldapName[0])) {
-				\OCP\Util::writeLog('user_ldap', 'No or empty name for '.$fdn.' with filter '.$filter.'.', ILogger::INFO);
-				return false;
-			}
-			$ldapName = $ldapName[0];
-		}
-
-		if($isUser) {
-			$usernameAttribute = (string)$this->connection->ldapExpertUsernameAttr;
-			if ($usernameAttribute !== '') {
-				$username = $this->readAttribute($fdn, $usernameAttribute);
-				$username = $username[0];
-			} else {
-				$username = $uuid;
-			}
-			try {
-				$intName = $this->sanitizeUsername($username);
-			} catch (\InvalidArgumentException $e) {
-				\OC::$server->getLogger()->logException($e, [
-					'app' => 'user_ldap',
-					'level' => ILogger::WARN,
-				]);
-				// we don't attempt to set a username here. We can go for
-				// for an alternative 4 digit random number as we would append
-				// otherwise, however it's likely not enough space in bigger
-				// setups, and most importantly: this is not intended.
-				return false;
-			}
-		} else {
-			$intName = $ldapName;
-		}
-
-		//a new user/group! Add it only if it doesn't conflict with other backend's users or existing groups
-		//disabling Cache is required to avoid that the new user is cached as not-existing in fooExists check
-		//NOTE: mind, disabling cache affects only this instance! Using it
-		// outside of core user management will still cache the user as non-existing.
-		$originalTTL = $this->connection->ldapCacheTTL;
-		$this->connection->setConfiguration(['ldapCacheTTL' => 0]);
-		if( $intName !== ''
-			&& (($isUser && !$this->ncUserManager->userExists($intName))
-				|| (!$isUser && !\OC::$server->getGroupManager()->groupExists($intName))
-			)
-		) {
-			$this->connection->setConfiguration(['ldapCacheTTL' => $originalTTL]);
-			$newlyMapped = $this->mapAndAnnounceIfApplicable($mapper, $fdn, $intName, $uuid, $isUser);
-			if($newlyMapped) {
-				return $intName;
-			}
-		}
-
-		$this->connection->setConfiguration(['ldapCacheTTL' => $originalTTL]);
-		$altName = $this->createAltInternalOwnCloudName($intName, $isUser);
-		if (is_string($altName)) {
-			if($this->mapAndAnnounceIfApplicable($mapper, $fdn, $altName, $uuid, $isUser)) {
-				$newlyMapped = true;
-				return $altName;
-			}
-		}
-
-		//if everything else did not help..
-		\OCP\Util::writeLog('user_ldap', 'Could not create unique name for '.$fdn.'.', ILogger::INFO);
-		return false;
-	}
-
-	public function mapAndAnnounceIfApplicable(
-		AbstractMapping $mapper,
-		string $fdn,
-		string $name,
-		string $uuid,
-		bool $isUser
-	) :bool {
-		if($mapper->map($fdn, $name, $uuid)) {
-			if ($this->ncUserManager instanceof PublicEmitter && $isUser) {
-				$this->cacheUserExists($name);
-				$this->ncUserManager->emit('\OC\User', 'assignedUserId', [$name]);
-			} elseif (!$isUser) {
-				$this->cacheGroupExists($name);
-			}
-			return true;
-		}
-		return false;
-	}
-
-	/**
-	 * gives back the user names as they are used ownClod internally
-	 *
-	 * @param array $ldapUsers as returned by fetchList()
-	 * @return array an array with the user names to use in Nextcloud
-	 *
-	 * gives back the user names as they are used ownClod internally
-	 * @throws \Exception
-	 */
-	public function nextcloudUserNames($ldapUsers) {
-		return $this->ldap2NextcloudNames($ldapUsers, true);
-	}
-
-	/**
-	 * gives back the group names as they are used ownClod internally
-	 *
-	 * @param array $ldapGroups as returned by fetchList()
-	 * @return array an array with the group names to use in Nextcloud
-	 *
-	 * gives back the group names as they are used ownClod internally
-	 * @throws \Exception
-	 */
-	public function nextcloudGroupNames($ldapGroups) {
-		return $this->ldap2NextcloudNames($ldapGroups, false);
-	}
-
-	/**
-	 * @param array $ldapObjects as returned by fetchList()
-	 * @param bool $isUsers
-	 * @return array
-	 * @throws \Exception
-	 */
-	private function ldap2NextcloudNames($ldapObjects, $isUsers) {
-		if($isUsers) {
-			$nameAttribute = $this->connection->ldapUserDisplayName;
-			$sndAttribute  = $this->connection->ldapUserDisplayName2;
-		} else {
-			$nameAttribute = $this->connection->ldapGroupDisplayName;
-		}
-		$nextcloudNames = [];
-
-		foreach($ldapObjects as $ldapObject) {
-			$nameByLDAP = null;
-			if(    isset($ldapObject[$nameAttribute])
-				&& is_array($ldapObject[$nameAttribute])
-				&& isset($ldapObject[$nameAttribute][0])
-			) {
-				// might be set, but not necessarily. if so, we use it.
-				$nameByLDAP = $ldapObject[$nameAttribute][0];
-			}
-
-			$ncName = $this->dn2ocname($ldapObject['dn'][0], $nameByLDAP, $isUsers);
-			if($ncName) {
-				$nextcloudNames[] = $ncName;
-				if($isUsers) {
-					$this->updateUserState($ncName);
-					//cache the user names so it does not need to be retrieved
-					//again later (e.g. sharing dialogue).
-					if(is_null($nameByLDAP)) {
-						continue;
-					}
-					$sndName = isset($ldapObject[$sndAttribute][0])
-						? $ldapObject[$sndAttribute][0] : '';
-					$this->cacheUserDisplayName($ncName, $nameByLDAP, $sndName);
-				} else if($nameByLDAP !== null) {
-					$this->cacheGroupDisplayName($ncName, $nameByLDAP);
-				}
-			}
-		}
-		return $nextcloudNames;
-	}
-
-	/**
-	 * removes the deleted-flag of a user if it was set
-	 *
-	 * @param string $ncname
-	 * @throws \Exception
-	 */
-	public function updateUserState($ncname) {
-		$user = $this->userManager->get($ncname);
-		if($user instanceof OfflineUser) {
-			$user->unmark();
-		}
-	}
-
-	/**
-	 * caches the user display name
-	 * @param string $ocName the internal Nextcloud username
-	 * @param string|false $home the home directory path
-	 */
-	public function cacheUserHome($ocName, $home) {
-		$cacheKey = 'getHome'.$ocName;
-		$this->connection->writeToCache($cacheKey, $home);
-	}
-
-	/**
-	 * caches a user as existing
-	 * @param string $ocName the internal Nextcloud username
-	 */
-	public function cacheUserExists($ocName) {
-		$this->connection->writeToCache('userExists'.$ocName, true);
-	}
-
-	/**
-	 * caches a group as existing
-	 */
-	public function cacheGroupExists(string $gid): void {
-		$this->connection->writeToCache('groupExists'.$gid, true);
-	}
-
-	/**
-	 * caches the user display name
-	 *
-	 * @param string $ocName the internal Nextcloud username
-	 * @param string $displayName the display name
-	 * @param string $displayName2 the second display name
-	 * @throws \Exception
-	 */
-	public function cacheUserDisplayName($ocName, $displayName, $displayName2 = '') {
-		$user = $this->userManager->get($ocName);
-		if($user === null) {
-			return;
-		}
-		$displayName = $user->composeAndStoreDisplayName($displayName, $displayName2);
-		$cacheKeyTrunk = 'getDisplayName';
-		$this->connection->writeToCache($cacheKeyTrunk.$ocName, $displayName);
-	}
-
-	public function cacheGroupDisplayName(string $ncName, string $displayName): void {
-		$cacheKey = 'group_getDisplayName' . $ncName;
-		$this->connection->writeToCache($cacheKey, $displayName);
-	}
-
-	/**
-	 * creates a unique name for internal Nextcloud use for users. Don't call it directly.
-	 * @param string $name the display name of the object
-	 * @return string|false with with the name to use in Nextcloud or false if unsuccessful
-	 *
-	 * Instead of using this method directly, call
-	 * createAltInternalOwnCloudName($name, true)
-	 */
-	private function _createAltInternalOwnCloudNameForUsers($name) {
-		$attempts = 0;
-		//while loop is just a precaution. If a name is not generated within
-		//20 attempts, something else is very wrong. Avoids infinite loop.
-		while($attempts < 20){
-			$altName = $name . '_' . rand(1000,9999);
-			if(!$this->ncUserManager->userExists($altName)) {
-				return $altName;
-			}
-			$attempts++;
-		}
-		return false;
-	}
-
-	/**
-	 * creates a unique name for internal Nextcloud use for groups. Don't call it directly.
-	 * @param string $name the display name of the object
-	 * @return string|false with with the name to use in Nextcloud or false if unsuccessful.
-	 *
-	 * Instead of using this method directly, call
-	 * createAltInternalOwnCloudName($name, false)
-	 *
-	 * Group names are also used as display names, so we do a sequential
-	 * numbering, e.g. Developers_42 when there are 41 other groups called
-	 * "Developers"
-	 */
-	private function _createAltInternalOwnCloudNameForGroups($name) {
-		$usedNames = $this->groupMapper->getNamesBySearch($name, "", '_%');
-		if(!$usedNames || count($usedNames) === 0) {
-			$lastNo = 1; //will become name_2
-		} else {
-			natsort($usedNames);
-			$lastName = array_pop($usedNames);
-			$lastNo = (int)substr($lastName, strrpos($lastName, '_') + 1);
-		}
-		$altName = $name.'_'. (string)($lastNo+1);
-		unset($usedNames);
-
-		$attempts = 1;
-		while($attempts < 21){
-			// Check to be really sure it is unique
-			// while loop is just a precaution. If a name is not generated within
-			// 20 attempts, something else is very wrong. Avoids infinite loop.
-			if(!\OC::$server->getGroupManager()->groupExists($altName)) {
-				return $altName;
-			}
-			$altName = $name . '_' . ($lastNo + $attempts);
-			$attempts++;
-		}
-		return false;
-	}
-
-	/**
-	 * creates a unique name for internal Nextcloud use.
-	 * @param string $name the display name of the object
-	 * @param boolean $isUser whether name should be created for a user (true) or a group (false)
-	 * @return string|false with with the name to use in Nextcloud or false if unsuccessful
-	 */
-	private function createAltInternalOwnCloudName($name, $isUser) {
-		$originalTTL = $this->connection->ldapCacheTTL;
-		$this->connection->setConfiguration(array('ldapCacheTTL' => 0));
-		if($isUser) {
-			$altName = $this->_createAltInternalOwnCloudNameForUsers($name);
-		} else {
-			$altName = $this->_createAltInternalOwnCloudNameForGroups($name);
-		}
-		$this->connection->setConfiguration(array('ldapCacheTTL' => $originalTTL));
-
-		return $altName;
-	}
-
-	/**
-	 * fetches a list of users according to a provided loginName and utilizing
-	 * the login filter.
-	 *
-	 * @param string $loginName
-	 * @param array $attributes optional, list of attributes to read
-	 * @return array
-	 */
-	public function fetchUsersByLoginName($loginName, $attributes = array('dn')) {
-		$loginName = $this->escapeFilterPart($loginName);
-		$filter = str_replace('%uid', $loginName, $this->connection->ldapLoginFilter);
-		return $this->fetchListOfUsers($filter, $attributes);
-	}
-
-	/**
-	 * counts the number of users according to a provided loginName and
-	 * utilizing the login filter.
-	 *
-	 * @param string $loginName
-	 * @return int
-	 */
-	public function countUsersByLoginName($loginName) {
-		$loginName = $this->escapeFilterPart($loginName);
-		$filter = str_replace('%uid', $loginName, $this->connection->ldapLoginFilter);
-		return $this->countUsers($filter);
-	}
-
-	/**
-	 * @param string $filter
-	 * @param string|string[] $attr
-	 * @param int $limit
-	 * @param int $offset
-	 * @param bool $forceApplyAttributes
-	 * @return array
-	 * @throws \Exception
-	 */
-	public function fetchListOfUsers($filter, $attr, $limit = null, $offset = null, $forceApplyAttributes = false) {
-		$ldapRecords = $this->searchUsers($filter, $attr, $limit, $offset);
-		$recordsToUpdate = $ldapRecords;
-		if(!$forceApplyAttributes) {
-			$isBackgroundJobModeAjax = $this->config
-					->getAppValue('core', 'backgroundjobs_mode', 'ajax') === 'ajax';
-			$recordsToUpdate = array_filter($ldapRecords, function($record) use ($isBackgroundJobModeAjax) {
-				$newlyMapped = false;
-				$uid = $this->dn2ocname($record['dn'][0], null, true, $newlyMapped, $record);
-				if(is_string($uid)) {
-					$this->cacheUserExists($uid);
-				}
-				return ($uid !== false) && ($newlyMapped || $isBackgroundJobModeAjax);
-			});
-		}
-		$this->batchApplyUserAttributes($recordsToUpdate);
-		return $this->fetchList($ldapRecords, $this->manyAttributes($attr));
-	}
-
-	/**
-	 * provided with an array of LDAP user records the method will fetch the
-	 * user object and requests it to process the freshly fetched attributes and
-	 * and their values
-	 *
-	 * @param array $ldapRecords
-	 * @throws \Exception
-	 */
-	public function batchApplyUserAttributes(array $ldapRecords){
-		$displayNameAttribute = strtolower($this->connection->ldapUserDisplayName);
-		foreach($ldapRecords as $userRecord) {
-			if(!isset($userRecord[$displayNameAttribute])) {
-				// displayName is obligatory
-				continue;
-			}
-			$ocName  = $this->dn2ocname($userRecord['dn'][0], null, true);
-			if($ocName === false) {
-				continue;
-			}
-			$this->updateUserState($ocName);
-			$user = $this->userManager->get($ocName);
-			if ($user !== null) {
-				$user->processAttributes($userRecord);
-			} else {
-				\OC::$server->getLogger()->debug(
-					"The ldap user manager returned null for $ocName",
-					['app'=>'user_ldap']
-				);
-			}
-		}
-	}
-
-	/**
-	 * @param string $filter
-	 * @param string|string[] $attr
-	 * @param int $limit
-	 * @param int $offset
-	 * @return array
-	 */
-	public function fetchListOfGroups($filter, $attr, $limit = null, $offset = null) {
-		$groupRecords = $this->searchGroups($filter, $attr, $limit, $offset);
-		array_walk($groupRecords, function($record) {
-			$newlyMapped = false;
-			$gid = $this->dn2ocname($record['dn'][0], null, false, $newlyMapped, $record);
-			if(!$newlyMapped && is_string($gid)) {
-				$this->cacheGroupExists($gid);
-			}
-		});
-		return $this->fetchList($groupRecords, $this->manyAttributes($attr));
-	}
-
-	/**
-	 * @param array $list
-	 * @param bool $manyAttributes
-	 * @return array
-	 */
-	private function fetchList($list, $manyAttributes) {
-		if(is_array($list)) {
-			if($manyAttributes) {
-				return $list;
-			} else {
-				$list = array_reduce($list, function($carry, $item) {
-					$attribute = array_keys($item)[0];
-					$carry[] = $item[$attribute][0];
-					return $carry;
-				}, array());
-				return array_unique($list, SORT_LOCALE_STRING);
-			}
-		}
-
-		//error cause actually, maybe throw an exception in future.
-		return array();
-	}
-
-	/**
-	 * executes an LDAP search, optimized for Users
-	 *
-	 * @param string $filter the LDAP filter for the search
-	 * @param string|string[] $attr optional, when a certain attribute shall be filtered out
-	 * @param integer $limit
-	 * @param integer $offset
-	 * @return array with the search result
-	 *
-	 * Executes an LDAP search
-	 * @throws ServerNotAvailableException
-	 */
-	public function searchUsers($filter, $attr = null, $limit = null, $offset = null) {
-		$result = [];
-		foreach($this->connection->ldapBaseUsers as $base) {
-			$result = array_merge($result, $this->search($filter, [$base], $attr, $limit, $offset));
-		}
-		return $result;
-	}
-
-	/**
-	 * @param string $filter
-	 * @param string|string[] $attr
-	 * @param int $limit
-	 * @param int $offset
-	 * @return false|int
-	 * @throws ServerNotAvailableException
-	 */
-	public function countUsers($filter, $attr = array('dn'), $limit = null, $offset = null) {
-		$result = false;
-		foreach($this->connection->ldapBaseUsers as $base) {
-			$count = $this->count($filter, [$base], $attr, $limit, $offset);
-			$result = is_int($count) ? (int)$result + $count : $result;
-		}
-		return $result;
-	}
-
-	/**
-	 * executes an LDAP search, optimized for Groups
-	 *
-	 * @param string $filter the LDAP filter for the search
-	 * @param string|string[] $attr optional, when a certain attribute shall be filtered out
-	 * @param integer $limit
-	 * @param integer $offset
-	 * @return array with the search result
-	 *
-	 * Executes an LDAP search
-	 * @throws ServerNotAvailableException
-	 */
-	public function searchGroups($filter, $attr = null, $limit = null, $offset = null) {
-		$result = [];
-		foreach($this->connection->ldapBaseGroups as $base) {
-			$result = array_merge($result, $this->search($filter, [$base], $attr, $limit, $offset));
-		}
-		return $result;
-	}
-
-	/**
-	 * returns the number of available groups
-	 *
-	 * @param string $filter the LDAP search filter
-	 * @param string[] $attr optional
-	 * @param int|null $limit
-	 * @param int|null $offset
-	 * @return int|bool
-	 * @throws ServerNotAvailableException
-	 */
-	public function countGroups($filter, $attr = array('dn'), $limit = null, $offset = null) {
-		$result = false;
-		foreach($this->connection->ldapBaseGroups as $base) {
-			$count = $this->count($filter, [$base], $attr, $limit, $offset);
-			$result = is_int($count) ? (int)$result + $count : $result;
-		}
-		return $result;
-	}
-
-	/**
-	 * returns the number of available objects on the base DN
-	 *
-	 * @param int|null $limit
-	 * @param int|null $offset
-	 * @return int|bool
-	 * @throws ServerNotAvailableException
-	 */
-	public function countObjects($limit = null, $offset = null) {
-		$result = false;
-		foreach($this->connection->ldapBase as $base) {
-			$count = $this->count('objectclass=*', [$base], ['dn'], $limit, $offset);
-			$result = is_int($count) ? (int)$result + $count : $result;
-		}
-		return $result;
-	}
-
-	/**
-	 * Returns the LDAP handler
-	 * @throws \OC\ServerNotAvailableException
-	 */
-
-	/**
-	 * @return mixed
-	 * @throws \OC\ServerNotAvailableException
-	 */
-	private function invokeLDAPMethod() {
-		$arguments = func_get_args();
-		$command = array_shift($arguments);
-		$cr = array_shift($arguments);
-		if (!method_exists($this->ldap, $command)) {
-			return null;
-		}
-		array_unshift($arguments, $cr);
-		// php no longer supports call-time pass-by-reference
-		// thus cannot support controlPagedResultResponse as the third argument
-		// is a reference
-		$doMethod = function () use ($command, &$arguments) {
-			if ($command == 'controlPagedResultResponse') {
-				throw new \InvalidArgumentException('Invoker does not support controlPagedResultResponse, call LDAP Wrapper directly instead.');
-			} else {
-				return call_user_func_array(array($this->ldap, $command), $arguments);
-			}
-		};
-		try {
-			$ret = $doMethod();
-		} catch (ServerNotAvailableException $e) {
-			/* Server connection lost, attempt to reestablish it
+    const UUID_ATTRIBUTES = ['entryuuid', 'nsuniqueid', 'objectguid', 'guid', 'ipauniqueid'];
+
+    /** @var \OCA\User_LDAP\Connection */
+    public $connection;
+    /** @var Manager */
+    public $userManager;
+    //never ever check this var directly, always use getPagedSearchResultState
+    protected $pagedSearchedSuccessful;
+
+    /**
+     * @var string[] $cookies an array of returned Paged Result cookies
+     */
+    protected $cookies = array();
+
+    /**
+     * @var string $lastCookie the last cookie returned from a Paged Results
+     * operation, defaults to an empty string
+     */
+    protected $lastCookie = '';
+
+    /**
+     * @var AbstractMapping $userMapper
+     */
+    protected $userMapper;
+
+    /**
+     * @var AbstractMapping $userMapper
+     */
+    protected $groupMapper;
+
+    /**
+     * @var \OCA\User_LDAP\Helper
+     */
+    private $helper;
+    /** @var IConfig */
+    private $config;
+    /** @var IUserManager */
+    private $ncUserManager;
+
+    public function __construct(
+        Connection $connection,
+        ILDAPWrapper $ldap,
+        Manager $userManager,
+        Helper $helper,
+        IConfig $config,
+        IUserManager $ncUserManager
+    ) {
+        parent::__construct($ldap);
+        $this->connection = $connection;
+        $this->userManager = $userManager;
+        $this->userManager->setLdapAccess($this);
+        $this->helper = $helper;
+        $this->config = $config;
+        $this->ncUserManager = $ncUserManager;
+    }
+
+    /**
+     * sets the User Mapper
+     * @param AbstractMapping $mapper
+     */
+    public function setUserMapper(AbstractMapping $mapper) {
+        $this->userMapper = $mapper;
+    }
+
+    /**
+     * returns the User Mapper
+     * @throws \Exception
+     * @return AbstractMapping
+     */
+    public function getUserMapper() {
+        if(is_null($this->userMapper)) {
+            throw new \Exception('UserMapper was not assigned to this Access instance.');
+        }
+        return $this->userMapper;
+    }
+
+    /**
+     * sets the Group Mapper
+     * @param AbstractMapping $mapper
+     */
+    public function setGroupMapper(AbstractMapping $mapper) {
+        $this->groupMapper = $mapper;
+    }
+
+    /**
+     * returns the Group Mapper
+     * @throws \Exception
+     * @return AbstractMapping
+     */
+    public function getGroupMapper() {
+        if(is_null($this->groupMapper)) {
+            throw new \Exception('GroupMapper was not assigned to this Access instance.');
+        }
+        return $this->groupMapper;
+    }
+
+    /**
+     * @return bool
+     */
+    private function checkConnection() {
+        return ($this->connection instanceof Connection);
+    }
+
+    /**
+     * returns the Connection instance
+     * @return \OCA\User_LDAP\Connection
+     */
+    public function getConnection() {
+        return $this->connection;
+    }
+
+    /**
+     * reads a given attribute for an LDAP record identified by a DN
+     *
+     * @param string $dn the record in question
+     * @param string $attr the attribute that shall be retrieved
+     *        if empty, just check the record's existence
+     * @param string $filter
+     * @return array|false an array of values on success or an empty
+     *          array if $attr is empty, false otherwise
+     * @throws ServerNotAvailableException
+     */
+    public function readAttribute($dn, $attr, $filter = 'objectClass=*') {
+        if(!$this->checkConnection()) {
+            \OCP\Util::writeLog('user_ldap',
+                'No LDAP Connector assigned, access impossible for readAttribute.',
+                ILogger::WARN);
+            return false;
+        }
+        $cr = $this->connection->getConnectionResource();
+        if(!$this->ldap->isResource($cr)) {
+            //LDAP not available
+            \OCP\Util::writeLog('user_ldap', 'LDAP resource not available.', ILogger::DEBUG);
+            return false;
+        }
+        //Cancel possibly running Paged Results operation, otherwise we run in
+        //LDAP protocol errors
+        $this->abandonPagedSearch();
+        // openLDAP requires that we init a new Paged Search. Not needed by AD,
+        // but does not hurt either.
+        $pagingSize = (int)$this->connection->ldapPagingSize;
+        // 0 won't result in replies, small numbers may leave out groups
+        // (cf. #12306), 500 is default for paging and should work everywhere.
+        $maxResults = $pagingSize > 20 ? $pagingSize : 500;
+        $attr = mb_strtolower($attr, 'UTF-8');
+        // the actual read attribute later may contain parameters on a ranged
+        // request, e.g. member;range=99-199. Depends on server reply.
+        $attrToRead = $attr;
+
+        $values = [];
+        $isRangeRequest = false;
+        do {
+            $result = $this->executeRead($cr, $dn, $attrToRead, $filter, $maxResults);
+            if(is_bool($result)) {
+                // when an exists request was run and it was successful, an empty
+                // array must be returned
+                return $result ? [] : false;
+            }
+
+            if (!$isRangeRequest) {
+                $values = $this->extractAttributeValuesFromResult($result, $attr);
+                if (!empty($values)) {
+                    return $values;
+                }
+            }
+
+            $isRangeRequest = false;
+            $result = $this->extractRangeData($result, $attr);
+            if (!empty($result)) {
+                $normalizedResult = $this->extractAttributeValuesFromResult(
+                    [ $attr => $result['values'] ],
+                    $attr
+                );
+                $values = array_merge($values, $normalizedResult);
+
+                if($result['rangeHigh'] === '*') {
+                    // when server replies with * as high range value, there are
+                    // no more results left
+                    return $values;
+                } else {
+                    $low  = $result['rangeHigh'] + 1;
+                    $attrToRead = $result['attributeName'] . ';range=' . $low . '-*';
+                    $isRangeRequest = true;
+                }
+            }
+        } while($isRangeRequest);
+
+        \OCP\Util::writeLog('user_ldap', 'Requested attribute '.$attr.' not found for '.$dn, ILogger::DEBUG);
+        return false;
+    }
+
+    /**
+     * Runs an read operation against LDAP
+     *
+     * @param resource $cr the LDAP connection
+     * @param string $dn
+     * @param string $attribute
+     * @param string $filter
+     * @param int $maxResults
+     * @return array|bool false if there was any error, true if an exists check
+     *                    was performed and the requested DN found, array with the
+     *                    returned data on a successful usual operation
+     * @throws ServerNotAvailableException
+     */
+    public function executeRead($cr, $dn, $attribute, $filter, $maxResults) {
+        $this->initPagedSearch($filter, array($dn), array($attribute), $maxResults, 0);
+        $dn = $this->helper->DNasBaseParameter($dn);
+        $rr = @$this->invokeLDAPMethod('read', $cr, $dn, $filter, array($attribute));
+        if (!$this->ldap->isResource($rr)) {
+            if ($attribute !== '') {
+                //do not throw this message on userExists check, irritates
+                \OCP\Util::writeLog('user_ldap', 'readAttribute failed for DN ' . $dn, ILogger::DEBUG);
+            }
+            //in case an error occurs , e.g. object does not exist
+            return false;
+        }
+        if ($attribute === '' && ($filter === 'objectclass=*' || $this->invokeLDAPMethod('countEntries', $cr, $rr) === 1)) {
+            \OCP\Util::writeLog('user_ldap', 'readAttribute: ' . $dn . ' found', ILogger::DEBUG);
+            return true;
+        }
+        $er = $this->invokeLDAPMethod('firstEntry', $cr, $rr);
+        if (!$this->ldap->isResource($er)) {
+            //did not match the filter, return false
+            return false;
+        }
+        //LDAP attributes are not case sensitive
+        $result = \OCP\Util::mb_array_change_key_case(
+            $this->invokeLDAPMethod('getAttributes', $cr, $er), MB_CASE_LOWER, 'UTF-8');
+
+        return $result;
+    }
+
+    /**
+     * Normalizes a result grom getAttributes(), i.e. handles DNs and binary
+     * data if present.
+     *
+     * @param array $result from ILDAPWrapper::getAttributes()
+     * @param string $attribute the attribute name that was read
+     * @return string[]
+     */
+    public function extractAttributeValuesFromResult($result, $attribute) {
+        $values = [];
+        if(isset($result[$attribute]) && $result[$attribute]['count'] > 0) {
+            $lowercaseAttribute = strtolower($attribute);
+            for($i=0;$i<$result[$attribute]['count'];$i++) {
+                if($this->resemblesDN($attribute)) {
+                    $values[] = $this->helper->sanitizeDN($result[$attribute][$i]);
+                } elseif($lowercaseAttribute === 'objectguid' || $lowercaseAttribute === 'guid') {
+                    $values[] = $this->convertObjectGUID2Str($result[$attribute][$i]);
+                } else {
+                    $values[] = $result[$attribute][$i];
+                }
+            }
+        }
+        return $values;
+    }
+
+    /**
+     * Attempts to find ranged data in a getAttribute results and extracts the
+     * returned values as well as information on the range and full attribute
+     * name for further processing.
+     *
+     * @param array $result from ILDAPWrapper::getAttributes()
+     * @param string $attribute the attribute name that was read. Without ";range=…"
+     * @return array If a range was detected with keys 'values', 'attributeName',
+     *               'attributeFull' and 'rangeHigh', otherwise empty.
+     */
+    public function extractRangeData($result, $attribute) {
+        $keys = array_keys($result);
+        foreach($keys as $key) {
+            if($key !== $attribute && strpos($key, $attribute) === 0) {
+                $queryData = explode(';', $key);
+                if(strpos($queryData[1], 'range=') === 0) {
+                    $high = substr($queryData[1], 1 + strpos($queryData[1], '-'));
+                    $data = [
+                        'values' => $result[$key],
+                        'attributeName' => $queryData[0],
+                        'attributeFull' => $key,
+                        'rangeHigh' => $high,
+                    ];
+                    return $data;
+                }
+            }
+        }
+        return [];
+    }
+
+    /**
+     * Set password for an LDAP user identified by a DN
+     *
+     * @param string $userDN the user in question
+     * @param string $password the new password
+     * @return bool
+     * @throws HintException
+     * @throws \Exception
+     */
+    public function setPassword($userDN, $password) {
+        if((int)$this->connection->turnOnPasswordChange !== 1) {
+            throw new \Exception('LDAP password changes are disabled.');
+        }
+        $cr = $this->connection->getConnectionResource();
+        if(!$this->ldap->isResource($cr)) {
+            //LDAP not available
+            \OCP\Util::writeLog('user_ldap', 'LDAP resource not available.', ILogger::DEBUG);
+            return false;
+        }
+        try {
+            // try PASSWD extended operation first
+            return @$this->invokeLDAPMethod('exopPasswd', $cr, $userDN, '', $password) ||
+                        @$this->invokeLDAPMethod('modReplace', $cr, $userDN, $password);
+        } catch(ConstraintViolationException $e) {
+            throw new HintException('Password change rejected.', \OC::$server->getL10N('user_ldap')->t('Password change rejected. Hint: ').$e->getMessage(), $e->getCode());
+        }
+    }
+
+    /**
+     * checks whether the given attributes value is probably a DN
+     * @param string $attr the attribute in question
+     * @return boolean if so true, otherwise false
+     */
+    private function resemblesDN($attr) {
+        $resemblingAttributes = array(
+            'dn',
+            'uniquemember',
+            'member',
+            // memberOf is an "operational" attribute, without a definition in any RFC
+            'memberof'
+        );
+        return in_array($attr, $resemblingAttributes);
+    }
+
+    /**
+     * checks whether the given string is probably a DN
+     * @param string $string
+     * @return boolean
+     */
+    public function stringResemblesDN($string) {
+        $r = $this->ldap->explodeDN($string, 0);
+        // if exploding a DN succeeds and does not end up in
+        // an empty array except for $r[count] being 0.
+        return (is_array($r) && count($r) > 1);
+    }
+
+    /**
+     * returns a DN-string that is cleaned from not domain parts, e.g.
+     * cn=foo,cn=bar,dc=foobar,dc=server,dc=org
+     * becomes dc=foobar,dc=server,dc=org
+     * @param string $dn
+     * @return string
+     */
+    public function getDomainDNFromDN($dn) {
+        $allParts = $this->ldap->explodeDN($dn, 0);
+        if($allParts === false) {
+            //not a valid DN
+            return '';
+        }
+        $domainParts = array();
+        $dcFound = false;
+        foreach($allParts as $part) {
+            if(!$dcFound && strpos($part, 'dc=') === 0) {
+                $dcFound = true;
+            }
+            if($dcFound) {
+                $domainParts[] = $part;
+            }
+        }
+        return implode(',', $domainParts);
+    }
+
+    /**
+     * returns the LDAP DN for the given internal Nextcloud name of the group
+     * @param string $name the Nextcloud name in question
+     * @return string|false LDAP DN on success, otherwise false
+     */
+    public function groupname2dn($name) {
+        return $this->groupMapper->getDNByName($name);
+    }
+
+    /**
+     * returns the LDAP DN for the given internal Nextcloud name of the user
+     * @param string $name the Nextcloud name in question
+     * @return string|false with the LDAP DN on success, otherwise false
+     */
+    public function username2dn($name) {
+        $fdn = $this->userMapper->getDNByName($name);
+
+        //Check whether the DN belongs to the Base, to avoid issues on multi-
+        //server setups
+        if(is_string($fdn) && $this->isDNPartOfBase($fdn, $this->connection->ldapBaseUsers)) {
+            return $fdn;
+        }
+
+        return false;
+    }
+
+    /**
+     * returns the internal Nextcloud name for the given LDAP DN of the group, false on DN outside of search DN or failure
+     *
+     * @param string $fdn the dn of the group object
+     * @param string $ldapName optional, the display name of the object
+     * @return string|false with the name to use in Nextcloud, false on DN outside of search DN
+     * @throws \Exception
+     */
+    public function dn2groupname($fdn, $ldapName = null) {
+        //To avoid bypassing the base DN settings under certain circumstances
+        //with the group support, check whether the provided DN matches one of
+        //the given Bases
+        if(!$this->isDNPartOfBase($fdn, $this->connection->ldapBaseGroups)) {
+            return false;
+        }
+
+        return $this->dn2ocname($fdn, $ldapName, false);
+    }
+
+    /**
+     * accepts an array of group DNs and tests whether they match the user
+     * filter by doing read operations against the group entries. Returns an
+     * array of DNs that match the filter.
+     *
+     * @param string[] $groupDNs
+     * @return string[]
+     * @throws ServerNotAvailableException
+     */
+    public function groupsMatchFilter($groupDNs) {
+        $validGroupDNs = [];
+        foreach($groupDNs as $dn) {
+            $cacheKey = 'groupsMatchFilter-'.$dn;
+            $groupMatchFilter = $this->connection->getFromCache($cacheKey);
+            if(!is_null($groupMatchFilter)) {
+                if($groupMatchFilter) {
+                    $validGroupDNs[] = $dn;
+                }
+                continue;
+            }
+
+            // Check the base DN first. If this is not met already, we don't
+            // need to ask the server at all.
+            if(!$this->isDNPartOfBase($dn, $this->connection->ldapBaseGroups)) {
+                $this->connection->writeToCache($cacheKey, false);
+                continue;
+            }
+
+            $result = $this->readAttribute($dn, '', $this->connection->ldapGroupFilter);
+            if(is_array($result)) {
+                $this->connection->writeToCache($cacheKey, true);
+                $validGroupDNs[] = $dn;
+            } else {
+                $this->connection->writeToCache($cacheKey, false);
+            }
+
+        }
+        return $validGroupDNs;
+    }
+
+    /**
+     * returns the internal Nextcloud name for the given LDAP DN of the user, false on DN outside of search DN or failure
+     *
+     * @param string $dn the dn of the user object
+     * @param string $ldapName optional, the display name of the object
+     * @return string|false with with the name to use in Nextcloud
+     * @throws \Exception
+     */
+    public function dn2username($fdn, $ldapName = null) {
+        //To avoid bypassing the base DN settings under certain circumstances
+        //with the group support, check whether the provided DN matches one of
+        //the given Bases
+        if(!$this->isDNPartOfBase($fdn, $this->connection->ldapBaseUsers)) {
+            return false;
+        }
+
+        return $this->dn2ocname($fdn, $ldapName, true);
+    }
+
+    /**
+     * returns an internal Nextcloud name for the given LDAP DN, false on DN outside of search DN
+     *
+     * @param string $fdn the dn of the user object
+     * @param string|null $ldapName optional, the display name of the object
+     * @param bool $isUser optional, whether it is a user object (otherwise group assumed)
+     * @param bool|null $newlyMapped
+     * @param array|null $record
+     * @return false|string with with the name to use in Nextcloud
+     * @throws \Exception
+     */
+    public function dn2ocname($fdn, $ldapName = null, $isUser = true, &$newlyMapped = null, array $record = null) {
+        $newlyMapped = false;
+        if($isUser) {
+            $mapper = $this->getUserMapper();
+            $nameAttribute = $this->connection->ldapUserDisplayName;
+            $filter = $this->connection->ldapUserFilter;
+        } else {
+            $mapper = $this->getGroupMapper();
+            $nameAttribute = $this->connection->ldapGroupDisplayName;
+            $filter = $this->connection->ldapGroupFilter;
+        }
+
+        //let's try to retrieve the Nextcloud name from the mappings table
+        $ncName = $mapper->getNameByDN($fdn);
+        if(is_string($ncName)) {
+            return $ncName;
+        }
+
+        //second try: get the UUID and check if it is known. Then, update the DN and return the name.
+        $uuid = $this->getUUID($fdn, $isUser, $record);
+        if(is_string($uuid)) {
+            $ncName = $mapper->getNameByUUID($uuid);
+            if(is_string($ncName)) {
+                $mapper->setDNbyUUID($fdn, $uuid);
+                return $ncName;
+            }
+        } else {
+            //If the UUID can't be detected something is foul.
+            \OCP\Util::writeLog('user_ldap', 'Cannot determine UUID for '.$fdn.'. Skipping.', ILogger::INFO);
+            return false;
+        }
+
+        if(is_null($ldapName)) {
+            $ldapName = $this->readAttribute($fdn, $nameAttribute, $filter);
+            if(!isset($ldapName[0]) && empty($ldapName[0])) {
+                \OCP\Util::writeLog('user_ldap', 'No or empty name for '.$fdn.' with filter '.$filter.'.', ILogger::INFO);
+                return false;
+            }
+            $ldapName = $ldapName[0];
+        }
+
+        if($isUser) {
+            $usernameAttribute = (string)$this->connection->ldapExpertUsernameAttr;
+            if ($usernameAttribute !== '') {
+                $username = $this->readAttribute($fdn, $usernameAttribute);
+                $username = $username[0];
+            } else {
+                $username = $uuid;
+            }
+            try {
+                $intName = $this->sanitizeUsername($username);
+            } catch (\InvalidArgumentException $e) {
+                \OC::$server->getLogger()->logException($e, [
+                    'app' => 'user_ldap',
+                    'level' => ILogger::WARN,
+                ]);
+                // we don't attempt to set a username here. We can go for
+                // for an alternative 4 digit random number as we would append
+                // otherwise, however it's likely not enough space in bigger
+                // setups, and most importantly: this is not intended.
+                return false;
+            }
+        } else {
+            $intName = $ldapName;
+        }
+
+        //a new user/group! Add it only if it doesn't conflict with other backend's users or existing groups
+        //disabling Cache is required to avoid that the new user is cached as not-existing in fooExists check
+        //NOTE: mind, disabling cache affects only this instance! Using it
+        // outside of core user management will still cache the user as non-existing.
+        $originalTTL = $this->connection->ldapCacheTTL;
+        $this->connection->setConfiguration(['ldapCacheTTL' => 0]);
+        if( $intName !== ''
+            && (($isUser && !$this->ncUserManager->userExists($intName))
+                || (!$isUser && !\OC::$server->getGroupManager()->groupExists($intName))
+            )
+        ) {
+            $this->connection->setConfiguration(['ldapCacheTTL' => $originalTTL]);
+            $newlyMapped = $this->mapAndAnnounceIfApplicable($mapper, $fdn, $intName, $uuid, $isUser);
+            if($newlyMapped) {
+                return $intName;
+            }
+        }
+
+        $this->connection->setConfiguration(['ldapCacheTTL' => $originalTTL]);
+        $altName = $this->createAltInternalOwnCloudName($intName, $isUser);
+        if (is_string($altName)) {
+            if($this->mapAndAnnounceIfApplicable($mapper, $fdn, $altName, $uuid, $isUser)) {
+                $newlyMapped = true;
+                return $altName;
+            }
+        }
+
+        //if everything else did not help..
+        \OCP\Util::writeLog('user_ldap', 'Could not create unique name for '.$fdn.'.', ILogger::INFO);
+        return false;
+    }
+
+    public function mapAndAnnounceIfApplicable(
+        AbstractMapping $mapper,
+        string $fdn,
+        string $name,
+        string $uuid,
+        bool $isUser
+    ) :bool {
+        if($mapper->map($fdn, $name, $uuid)) {
+            if ($this->ncUserManager instanceof PublicEmitter && $isUser) {
+                $this->cacheUserExists($name);
+                $this->ncUserManager->emit('\OC\User', 'assignedUserId', [$name]);
+            } elseif (!$isUser) {
+                $this->cacheGroupExists($name);
+            }
+            return true;
+        }
+        return false;
+    }
+
+    /**
+     * gives back the user names as they are used ownClod internally
+     *
+     * @param array $ldapUsers as returned by fetchList()
+     * @return array an array with the user names to use in Nextcloud
+     *
+     * gives back the user names as they are used ownClod internally
+     * @throws \Exception
+     */
+    public function nextcloudUserNames($ldapUsers) {
+        return $this->ldap2NextcloudNames($ldapUsers, true);
+    }
+
+    /**
+     * gives back the group names as they are used ownClod internally
+     *
+     * @param array $ldapGroups as returned by fetchList()
+     * @return array an array with the group names to use in Nextcloud
+     *
+     * gives back the group names as they are used ownClod internally
+     * @throws \Exception
+     */
+    public function nextcloudGroupNames($ldapGroups) {
+        return $this->ldap2NextcloudNames($ldapGroups, false);
+    }
+
+    /**
+     * @param array $ldapObjects as returned by fetchList()
+     * @param bool $isUsers
+     * @return array
+     * @throws \Exception
+     */
+    private function ldap2NextcloudNames($ldapObjects, $isUsers) {
+        if($isUsers) {
+            $nameAttribute = $this->connection->ldapUserDisplayName;
+            $sndAttribute  = $this->connection->ldapUserDisplayName2;
+        } else {
+            $nameAttribute = $this->connection->ldapGroupDisplayName;
+        }
+        $nextcloudNames = [];
+
+        foreach($ldapObjects as $ldapObject) {
+            $nameByLDAP = null;
+            if(    isset($ldapObject[$nameAttribute])
+                && is_array($ldapObject[$nameAttribute])
+                && isset($ldapObject[$nameAttribute][0])
+            ) {
+                // might be set, but not necessarily. if so, we use it.
+                $nameByLDAP = $ldapObject[$nameAttribute][0];
+            }
+
+            $ncName = $this->dn2ocname($ldapObject['dn'][0], $nameByLDAP, $isUsers);
+            if($ncName) {
+                $nextcloudNames[] = $ncName;
+                if($isUsers) {
+                    $this->updateUserState($ncName);
+                    //cache the user names so it does not need to be retrieved
+                    //again later (e.g. sharing dialogue).
+                    if(is_null($nameByLDAP)) {
+                        continue;
+                    }
+                    $sndName = isset($ldapObject[$sndAttribute][0])
+                        ? $ldapObject[$sndAttribute][0] : '';
+                    $this->cacheUserDisplayName($ncName, $nameByLDAP, $sndName);
+                } else if($nameByLDAP !== null) {
+                    $this->cacheGroupDisplayName($ncName, $nameByLDAP);
+                }
+            }
+        }
+        return $nextcloudNames;
+    }
+
+    /**
+     * removes the deleted-flag of a user if it was set
+     *
+     * @param string $ncname
+     * @throws \Exception
+     */
+    public function updateUserState($ncname) {
+        $user = $this->userManager->get($ncname);
+        if($user instanceof OfflineUser) {
+            $user->unmark();
+        }
+    }
+
+    /**
+     * caches the user display name
+     * @param string $ocName the internal Nextcloud username
+     * @param string|false $home the home directory path
+     */
+    public function cacheUserHome($ocName, $home) {
+        $cacheKey = 'getHome'.$ocName;
+        $this->connection->writeToCache($cacheKey, $home);
+    }
+
+    /**
+     * caches a user as existing
+     * @param string $ocName the internal Nextcloud username
+     */
+    public function cacheUserExists($ocName) {
+        $this->connection->writeToCache('userExists'.$ocName, true);
+    }
+
+    /**
+     * caches a group as existing
+     */
+    public function cacheGroupExists(string $gid): void {
+        $this->connection->writeToCache('groupExists'.$gid, true);
+    }
+
+    /**
+     * caches the user display name
+     *
+     * @param string $ocName the internal Nextcloud username
+     * @param string $displayName the display name
+     * @param string $displayName2 the second display name
+     * @throws \Exception
+     */
+    public function cacheUserDisplayName($ocName, $displayName, $displayName2 = '') {
+        $user = $this->userManager->get($ocName);
+        if($user === null) {
+            return;
+        }
+        $displayName = $user->composeAndStoreDisplayName($displayName, $displayName2);
+        $cacheKeyTrunk = 'getDisplayName';
+        $this->connection->writeToCache($cacheKeyTrunk.$ocName, $displayName);
+    }
+
+    public function cacheGroupDisplayName(string $ncName, string $displayName): void {
+        $cacheKey = 'group_getDisplayName' . $ncName;
+        $this->connection->writeToCache($cacheKey, $displayName);
+    }
+
+    /**
+     * creates a unique name for internal Nextcloud use for users. Don't call it directly.
+     * @param string $name the display name of the object
+     * @return string|false with with the name to use in Nextcloud or false if unsuccessful
+     *
+     * Instead of using this method directly, call
+     * createAltInternalOwnCloudName($name, true)
+     */
+    private function _createAltInternalOwnCloudNameForUsers($name) {
+        $attempts = 0;
+        //while loop is just a precaution. If a name is not generated within
+        //20 attempts, something else is very wrong. Avoids infinite loop.
+        while($attempts < 20){
+            $altName = $name . '_' . rand(1000,9999);
+            if(!$this->ncUserManager->userExists($altName)) {
+                return $altName;
+            }
+            $attempts++;
+        }
+        return false;
+    }
+
+    /**
+     * creates a unique name for internal Nextcloud use for groups. Don't call it directly.
+     * @param string $name the display name of the object
+     * @return string|false with with the name to use in Nextcloud or false if unsuccessful.
+     *
+     * Instead of using this method directly, call
+     * createAltInternalOwnCloudName($name, false)
+     *
+     * Group names are also used as display names, so we do a sequential
+     * numbering, e.g. Developers_42 when there are 41 other groups called
+     * "Developers"
+     */
+    private function _createAltInternalOwnCloudNameForGroups($name) {
+        $usedNames = $this->groupMapper->getNamesBySearch($name, "", '_%');
+        if(!$usedNames || count($usedNames) === 0) {
+            $lastNo = 1; //will become name_2
+        } else {
+            natsort($usedNames);
+            $lastName = array_pop($usedNames);
+            $lastNo = (int)substr($lastName, strrpos($lastName, '_') + 1);
+        }
+        $altName = $name.'_'. (string)($lastNo+1);
+        unset($usedNames);
+
+        $attempts = 1;
+        while($attempts < 21){
+            // Check to be really sure it is unique
+            // while loop is just a precaution. If a name is not generated within
+            // 20 attempts, something else is very wrong. Avoids infinite loop.
+            if(!\OC::$server->getGroupManager()->groupExists($altName)) {
+                return $altName;
+            }
+            $altName = $name . '_' . ($lastNo + $attempts);
+            $attempts++;
+        }
+        return false;
+    }
+
+    /**
+     * creates a unique name for internal Nextcloud use.
+     * @param string $name the display name of the object
+     * @param boolean $isUser whether name should be created for a user (true) or a group (false)
+     * @return string|false with with the name to use in Nextcloud or false if unsuccessful
+     */
+    private function createAltInternalOwnCloudName($name, $isUser) {
+        $originalTTL = $this->connection->ldapCacheTTL;
+        $this->connection->setConfiguration(array('ldapCacheTTL' => 0));
+        if($isUser) {
+            $altName = $this->_createAltInternalOwnCloudNameForUsers($name);
+        } else {
+            $altName = $this->_createAltInternalOwnCloudNameForGroups($name);
+        }
+        $this->connection->setConfiguration(array('ldapCacheTTL' => $originalTTL));
+
+        return $altName;
+    }
+
+    /**
+     * fetches a list of users according to a provided loginName and utilizing
+     * the login filter.
+     *
+     * @param string $loginName
+     * @param array $attributes optional, list of attributes to read
+     * @return array
+     */
+    public function fetchUsersByLoginName($loginName, $attributes = array('dn')) {
+        $loginName = $this->escapeFilterPart($loginName);
+        $filter = str_replace('%uid', $loginName, $this->connection->ldapLoginFilter);
+        return $this->fetchListOfUsers($filter, $attributes);
+    }
+
+    /**
+     * counts the number of users according to a provided loginName and
+     * utilizing the login filter.
+     *
+     * @param string $loginName
+     * @return int
+     */
+    public function countUsersByLoginName($loginName) {
+        $loginName = $this->escapeFilterPart($loginName);
+        $filter = str_replace('%uid', $loginName, $this->connection->ldapLoginFilter);
+        return $this->countUsers($filter);
+    }
+
+    /**
+     * @param string $filter
+     * @param string|string[] $attr
+     * @param int $limit
+     * @param int $offset
+     * @param bool $forceApplyAttributes
+     * @return array
+     * @throws \Exception
+     */
+    public function fetchListOfUsers($filter, $attr, $limit = null, $offset = null, $forceApplyAttributes = false) {
+        $ldapRecords = $this->searchUsers($filter, $attr, $limit, $offset);
+        $recordsToUpdate = $ldapRecords;
+        if(!$forceApplyAttributes) {
+            $isBackgroundJobModeAjax = $this->config
+                    ->getAppValue('core', 'backgroundjobs_mode', 'ajax') === 'ajax';
+            $recordsToUpdate = array_filter($ldapRecords, function($record) use ($isBackgroundJobModeAjax) {
+                $newlyMapped = false;
+                $uid = $this->dn2ocname($record['dn'][0], null, true, $newlyMapped, $record);
+                if(is_string($uid)) {
+                    $this->cacheUserExists($uid);
+                }
+                return ($uid !== false) && ($newlyMapped || $isBackgroundJobModeAjax);
+            });
+        }
+        $this->batchApplyUserAttributes($recordsToUpdate);
+        return $this->fetchList($ldapRecords, $this->manyAttributes($attr));
+    }
+
+    /**
+     * provided with an array of LDAP user records the method will fetch the
+     * user object and requests it to process the freshly fetched attributes and
+     * and their values
+     *
+     * @param array $ldapRecords
+     * @throws \Exception
+     */
+    public function batchApplyUserAttributes(array $ldapRecords){
+        $displayNameAttribute = strtolower($this->connection->ldapUserDisplayName);
+        foreach($ldapRecords as $userRecord) {
+            if(!isset($userRecord[$displayNameAttribute])) {
+                // displayName is obligatory
+                continue;
+            }
+            $ocName  = $this->dn2ocname($userRecord['dn'][0], null, true);
+            if($ocName === false) {
+                continue;
+            }
+            $this->updateUserState($ocName);
+            $user = $this->userManager->get($ocName);
+            if ($user !== null) {
+                $user->processAttributes($userRecord);
+            } else {
+                \OC::$server->getLogger()->debug(
+                    "The ldap user manager returned null for $ocName",
+                    ['app'=>'user_ldap']
+                );
+            }
+        }
+    }
+
+    /**
+     * @param string $filter
+     * @param string|string[] $attr
+     * @param int $limit
+     * @param int $offset
+     * @return array
+     */
+    public function fetchListOfGroups($filter, $attr, $limit = null, $offset = null) {
+        $groupRecords = $this->searchGroups($filter, $attr, $limit, $offset);
+        array_walk($groupRecords, function($record) {
+            $newlyMapped = false;
+            $gid = $this->dn2ocname($record['dn'][0], null, false, $newlyMapped, $record);
+            if(!$newlyMapped && is_string($gid)) {
+                $this->cacheGroupExists($gid);
+            }
+        });
+        return $this->fetchList($groupRecords, $this->manyAttributes($attr));
+    }
+
+    /**
+     * @param array $list
+     * @param bool $manyAttributes
+     * @return array
+     */
+    private function fetchList($list, $manyAttributes) {
+        if(is_array($list)) {
+            if($manyAttributes) {
+                return $list;
+            } else {
+                $list = array_reduce($list, function($carry, $item) {
+                    $attribute = array_keys($item)[0];
+                    $carry[] = $item[$attribute][0];
+                    return $carry;
+                }, array());
+                return array_unique($list, SORT_LOCALE_STRING);
+            }
+        }
+
+        //error cause actually, maybe throw an exception in future.
+        return array();
+    }
+
+    /**
+     * executes an LDAP search, optimized for Users
+     *
+     * @param string $filter the LDAP filter for the search
+     * @param string|string[] $attr optional, when a certain attribute shall be filtered out
+     * @param integer $limit
+     * @param integer $offset
+     * @return array with the search result
+     *
+     * Executes an LDAP search
+     * @throws ServerNotAvailableException
+     */
+    public function searchUsers($filter, $attr = null, $limit = null, $offset = null) {
+        $result = [];
+        foreach($this->connection->ldapBaseUsers as $base) {
+            $result = array_merge($result, $this->search($filter, [$base], $attr, $limit, $offset));
+        }
+        return $result;
+    }
+
+    /**
+     * @param string $filter
+     * @param string|string[] $attr
+     * @param int $limit
+     * @param int $offset
+     * @return false|int
+     * @throws ServerNotAvailableException
+     */
+    public function countUsers($filter, $attr = array('dn'), $limit = null, $offset = null) {
+        $result = false;
+        foreach($this->connection->ldapBaseUsers as $base) {
+            $count = $this->count($filter, [$base], $attr, $limit, $offset);
+            $result = is_int($count) ? (int)$result + $count : $result;
+        }
+        return $result;
+    }
+
+    /**
+     * executes an LDAP search, optimized for Groups
+     *
+     * @param string $filter the LDAP filter for the search
+     * @param string|string[] $attr optional, when a certain attribute shall be filtered out
+     * @param integer $limit
+     * @param integer $offset
+     * @return array with the search result
+     *
+     * Executes an LDAP search
+     * @throws ServerNotAvailableException
+     */
+    public function searchGroups($filter, $attr = null, $limit = null, $offset = null) {
+        $result = [];
+        foreach($this->connection->ldapBaseGroups as $base) {
+            $result = array_merge($result, $this->search($filter, [$base], $attr, $limit, $offset));
+        }
+        return $result;
+    }
+
+    /**
+     * returns the number of available groups
+     *
+     * @param string $filter the LDAP search filter
+     * @param string[] $attr optional
+     * @param int|null $limit
+     * @param int|null $offset
+     * @return int|bool
+     * @throws ServerNotAvailableException
+     */
+    public function countGroups($filter, $attr = array('dn'), $limit = null, $offset = null) {
+        $result = false;
+        foreach($this->connection->ldapBaseGroups as $base) {
+            $count = $this->count($filter, [$base], $attr, $limit, $offset);
+            $result = is_int($count) ? (int)$result + $count : $result;
+        }
+        return $result;
+    }
+
+    /**
+     * returns the number of available objects on the base DN
+     *
+     * @param int|null $limit
+     * @param int|null $offset
+     * @return int|bool
+     * @throws ServerNotAvailableException
+     */
+    public function countObjects($limit = null, $offset = null) {
+        $result = false;
+        foreach($this->connection->ldapBase as $base) {
+            $count = $this->count('objectclass=*', [$base], ['dn'], $limit, $offset);
+            $result = is_int($count) ? (int)$result + $count : $result;
+        }
+        return $result;
+    }
+
+    /**
+     * Returns the LDAP handler
+     * @throws \OC\ServerNotAvailableException
+     */
+
+    /**
+     * @return mixed
+     * @throws \OC\ServerNotAvailableException
+     */
+    private function invokeLDAPMethod() {
+        $arguments = func_get_args();
+        $command = array_shift($arguments);
+        $cr = array_shift($arguments);
+        if (!method_exists($this->ldap, $command)) {
+            return null;
+        }
+        array_unshift($arguments, $cr);
+        // php no longer supports call-time pass-by-reference
+        // thus cannot support controlPagedResultResponse as the third argument
+        // is a reference
+        $doMethod = function () use ($command, &$arguments) {
+            if ($command == 'controlPagedResultResponse') {
+                throw new \InvalidArgumentException('Invoker does not support controlPagedResultResponse, call LDAP Wrapper directly instead.');
+            } else {
+                return call_user_func_array(array($this->ldap, $command), $arguments);
+            }
+        };
+        try {
+            $ret = $doMethod();
+        } catch (ServerNotAvailableException $e) {
+            /* Server connection lost, attempt to reestablish it
 			 * Maybe implement exponential backoff?
 			 * This was enough to get solr indexer working which has large delays between LDAP fetches.
 			 */
-			\OCP\Util::writeLog('user_ldap', "Connection lost on $command, attempting to reestablish.", ILogger::DEBUG);
-			$this->connection->resetConnectionResource();
-			$cr = $this->connection->getConnectionResource();
-
-			if(!$this->ldap->isResource($cr)) {
-				// Seems like we didn't find any resource.
-				\OCP\Util::writeLog('user_ldap', "Could not $command, because resource is missing.", ILogger::DEBUG);
-				throw $e;
-			}
-
-			$arguments[0] = array_pad([], count($arguments[0]), $cr);
-			$ret = $doMethod();
-		}
-		return $ret;
-	}
-
-	/**
-	 * retrieved. Results will according to the order in the array.
-	 *
-	 * @param $filter
-	 * @param $base
-	 * @param string[]|string|null $attr
-	 * @param int $limit optional, maximum results to be counted
-	 * @param int $offset optional, a starting point
-	 * @return array|false array with the search result as first value and pagedSearchOK as
-	 * second | false if not successful
-	 * @throws ServerNotAvailableException
-	 */
-	private function executeSearch($filter, $base, &$attr = null, $limit = null, $offset = null) {
-		if(!is_null($attr) && !is_array($attr)) {
-			$attr = array(mb_strtolower($attr, 'UTF-8'));
-		}
-
-		// See if we have a resource, in case not cancel with message
-		$cr = $this->connection->getConnectionResource();
-		if(!$this->ldap->isResource($cr)) {
-			// Seems like we didn't find any resource.
-			// Return an empty array just like before.
-			\OCP\Util::writeLog('user_ldap', 'Could not search, because resource is missing.', ILogger::DEBUG);
-			return false;
-		}
-
-		//check whether paged search should be attempted
-		$pagedSearchOK = $this->initPagedSearch($filter, $base, $attr, (int)$limit, $offset);
-
-		$linkResources = array_pad(array(), count($base), $cr);
-		$sr = $this->invokeLDAPMethod('search', $linkResources, $base, $filter, $attr);
-		// cannot use $cr anymore, might have changed in the previous call!
-		$error = $this->ldap->errno($this->connection->getConnectionResource());
-		if(!is_array($sr) || $error !== 0) {
-			\OCP\Util::writeLog('user_ldap', 'Attempt for Paging?  '.print_r($pagedSearchOK, true), ILogger::ERROR);
-			return false;
-		}
-
-		return array($sr, $pagedSearchOK);
-	}
-
-	/**
-	 * processes an LDAP paged search operation
-	 *
-	 * @param array $sr the array containing the LDAP search resources
-	 * @param string $filter the LDAP filter for the search
-	 * @param array $base an array containing the LDAP subtree(s) that shall be searched
-	 * @param int $iFoundItems number of results in the single search operation
-	 * @param int $limit maximum results to be counted
-	 * @param int $offset a starting point
-	 * @param bool $pagedSearchOK whether a paged search has been executed
-	 * @param bool $skipHandling required for paged search when cookies to
-	 * prior results need to be gained
-	 * @return bool cookie validity, true if we have more pages, false otherwise.
-	 * @throws ServerNotAvailableException
-	 */
-	private function processPagedSearchStatus($sr, $filter, $base, $iFoundItems, $limit, $offset, $pagedSearchOK, $skipHandling) {
-		$cookie = null;
-		if($pagedSearchOK) {
-			$cr = $this->connection->getConnectionResource();
-			foreach($sr as $key => $res) {
-				if($this->ldap->controlPagedResultResponse($cr, $res, $cookie)) {
-					$this->setPagedResultCookie($base[$key], $filter, $limit, $offset, $cookie);
-				}
-			}
-
-			//browsing through prior pages to get the cookie for the new one
-			if($skipHandling) {
-				return false;
-			}
-			// if count is bigger, then the server does not support
-			// paged search. Instead, he did a normal search. We set a
-			// flag here, so the callee knows how to deal with it.
-			if($iFoundItems <= $limit) {
-				$this->pagedSearchedSuccessful = true;
-			}
-		} else {
-			if(!is_null($limit) && (int)$this->connection->ldapPagingSize !== 0) {
-				\OC::$server->getLogger()->debug(
-					'Paged search was not available',
-					[ 'app' => 'user_ldap' ]
-				);
-			}
-		}
-		/* ++ Fixing RHDS searches with pages with zero results ++
+            \OCP\Util::writeLog('user_ldap', "Connection lost on $command, attempting to reestablish.", ILogger::DEBUG);
+            $this->connection->resetConnectionResource();
+            $cr = $this->connection->getConnectionResource();
+
+            if(!$this->ldap->isResource($cr)) {
+                // Seems like we didn't find any resource.
+                \OCP\Util::writeLog('user_ldap', "Could not $command, because resource is missing.", ILogger::DEBUG);
+                throw $e;
+            }
+
+            $arguments[0] = array_pad([], count($arguments[0]), $cr);
+            $ret = $doMethod();
+        }
+        return $ret;
+    }
+
+    /**
+     * retrieved. Results will according to the order in the array.
+     *
+     * @param $filter
+     * @param $base
+     * @param string[]|string|null $attr
+     * @param int $limit optional, maximum results to be counted
+     * @param int $offset optional, a starting point
+     * @return array|false array with the search result as first value and pagedSearchOK as
+     * second | false if not successful
+     * @throws ServerNotAvailableException
+     */
+    private function executeSearch($filter, $base, &$attr = null, $limit = null, $offset = null) {
+        if(!is_null($attr) && !is_array($attr)) {
+            $attr = array(mb_strtolower($attr, 'UTF-8'));
+        }
+
+        // See if we have a resource, in case not cancel with message
+        $cr = $this->connection->getConnectionResource();
+        if(!$this->ldap->isResource($cr)) {
+            // Seems like we didn't find any resource.
+            // Return an empty array just like before.
+            \OCP\Util::writeLog('user_ldap', 'Could not search, because resource is missing.', ILogger::DEBUG);
+            return false;
+        }
+
+        //check whether paged search should be attempted
+        $pagedSearchOK = $this->initPagedSearch($filter, $base, $attr, (int)$limit, $offset);
+
+        $linkResources = array_pad(array(), count($base), $cr);
+        $sr = $this->invokeLDAPMethod('search', $linkResources, $base, $filter, $attr);
+        // cannot use $cr anymore, might have changed in the previous call!
+        $error = $this->ldap->errno($this->connection->getConnectionResource());
+        if(!is_array($sr) || $error !== 0) {
+            \OCP\Util::writeLog('user_ldap', 'Attempt for Paging?  '.print_r($pagedSearchOK, true), ILogger::ERROR);
+            return false;
+        }
+
+        return array($sr, $pagedSearchOK);
+    }
+
+    /**
+     * processes an LDAP paged search operation
+     *
+     * @param array $sr the array containing the LDAP search resources
+     * @param string $filter the LDAP filter for the search
+     * @param array $base an array containing the LDAP subtree(s) that shall be searched
+     * @param int $iFoundItems number of results in the single search operation
+     * @param int $limit maximum results to be counted
+     * @param int $offset a starting point
+     * @param bool $pagedSearchOK whether a paged search has been executed
+     * @param bool $skipHandling required for paged search when cookies to
+     * prior results need to be gained
+     * @return bool cookie validity, true if we have more pages, false otherwise.
+     * @throws ServerNotAvailableException
+     */
+    private function processPagedSearchStatus($sr, $filter, $base, $iFoundItems, $limit, $offset, $pagedSearchOK, $skipHandling) {
+        $cookie = null;
+        if($pagedSearchOK) {
+            $cr = $this->connection->getConnectionResource();
+            foreach($sr as $key => $res) {
+                if($this->ldap->controlPagedResultResponse($cr, $res, $cookie)) {
+                    $this->setPagedResultCookie($base[$key], $filter, $limit, $offset, $cookie);
+                }
+            }
+
+            //browsing through prior pages to get the cookie for the new one
+            if($skipHandling) {
+                return false;
+            }
+            // if count is bigger, then the server does not support
+            // paged search. Instead, he did a normal search. We set a
+            // flag here, so the callee knows how to deal with it.
+            if($iFoundItems <= $limit) {
+                $this->pagedSearchedSuccessful = true;
+            }
+        } else {
+            if(!is_null($limit) && (int)$this->connection->ldapPagingSize !== 0) {
+                \OC::$server->getLogger()->debug(
+                    'Paged search was not available',
+                    [ 'app' => 'user_ldap' ]
+                );
+            }
+        }
+        /* ++ Fixing RHDS searches with pages with zero results ++
 		 * Return cookie status. If we don't have more pages, with RHDS
 		 * cookie is null, with openldap cookie is an empty string and
 		 * to 386ds '0' is a valid cookie. Even if $iFoundItems == 0
 		 */
-		return !empty($cookie) || $cookie === '0';
-	}
-
-	/**
-	 * executes an LDAP search, but counts the results only
-	 *
-	 * @param string $filter the LDAP filter for the search
-	 * @param array $base an array containing the LDAP subtree(s) that shall be searched
-	 * @param string|string[] $attr optional, array, one or more attributes that shall be
-	 * retrieved. Results will according to the order in the array.
-	 * @param int $limit optional, maximum results to be counted
-	 * @param int $offset optional, a starting point
-	 * @param bool $skipHandling indicates whether the pages search operation is
-	 * completed
-	 * @return int|false Integer or false if the search could not be initialized
-	 * @throws ServerNotAvailableException
-	 */
-	private function count($filter, $base, $attr = null, $limit = null, $offset = null, $skipHandling = false) {
-		\OCP\Util::writeLog('user_ldap', 'Count filter:  '.print_r($filter, true), ILogger::DEBUG);
-
-		$limitPerPage = (int)$this->connection->ldapPagingSize;
-		if(!is_null($limit) && $limit < $limitPerPage && $limit > 0) {
-			$limitPerPage = $limit;
-		}
-
-		$counter = 0;
-		$count = null;
-		$this->connection->getConnectionResource();
-
-		do {
-			$search = $this->executeSearch($filter, $base, $attr, $limitPerPage, $offset);
-			if($search === false) {
-				return $counter > 0 ? $counter : false;
-			}
-			list($sr, $pagedSearchOK) = $search;
-
-			/* ++ Fixing RHDS searches with pages with zero results ++
+        return !empty($cookie) || $cookie === '0';
+    }
+
+    /**
+     * executes an LDAP search, but counts the results only
+     *
+     * @param string $filter the LDAP filter for the search
+     * @param array $base an array containing the LDAP subtree(s) that shall be searched
+     * @param string|string[] $attr optional, array, one or more attributes that shall be
+     * retrieved. Results will according to the order in the array.
+     * @param int $limit optional, maximum results to be counted
+     * @param int $offset optional, a starting point
+     * @param bool $skipHandling indicates whether the pages search operation is
+     * completed
+     * @return int|false Integer or false if the search could not be initialized
+     * @throws ServerNotAvailableException
+     */
+    private function count($filter, $base, $attr = null, $limit = null, $offset = null, $skipHandling = false) {
+        \OCP\Util::writeLog('user_ldap', 'Count filter:  '.print_r($filter, true), ILogger::DEBUG);
+
+        $limitPerPage = (int)$this->connection->ldapPagingSize;
+        if(!is_null($limit) && $limit < $limitPerPage && $limit > 0) {
+            $limitPerPage = $limit;
+        }
+
+        $counter = 0;
+        $count = null;
+        $this->connection->getConnectionResource();
+
+        do {
+            $search = $this->executeSearch($filter, $base, $attr, $limitPerPage, $offset);
+            if($search === false) {
+                return $counter > 0 ? $counter : false;
+            }
+            list($sr, $pagedSearchOK) = $search;
+
+            /* ++ Fixing RHDS searches with pages with zero results ++
 			 * countEntriesInSearchResults() method signature changed
 			 * by removing $limit and &$hasHitLimit parameters
 			 */
-			$count = $this->countEntriesInSearchResults($sr);
-			$counter += $count;
+            $count = $this->countEntriesInSearchResults($sr);
+            $counter += $count;
 
-			$hasMorePages = $this->processPagedSearchStatus($sr, $filter, $base, $count, $limitPerPage,
-										$offset, $pagedSearchOK, $skipHandling);
-			$offset += $limitPerPage;
-			/* ++ Fixing RHDS searches with pages with zero results ++
+            $hasMorePages = $this->processPagedSearchStatus($sr, $filter, $base, $count, $limitPerPage,
+                                        $offset, $pagedSearchOK, $skipHandling);
+            $offset += $limitPerPage;
+            /* ++ Fixing RHDS searches with pages with zero results ++
 			 * Continue now depends on $hasMorePages value
 			 */
-			$continue = $pagedSearchOK && $hasMorePages;
-		} while($continue && (is_null($limit) || $limit <= 0 || $limit > $counter));
-
-		return $counter;
-	}
-
-	/**
-	 * @param array $searchResults
-	 * @return int
-	 * @throws ServerNotAvailableException
-	 */
-	private function countEntriesInSearchResults($searchResults) {
-		$counter = 0;
-
-		foreach($searchResults as $res) {
-			$count = (int)$this->invokeLDAPMethod('countEntries', $this->connection->getConnectionResource(), $res);
-			$counter += $count;
-		}
-
-		return $counter;
-	}
-
-	/**
-	 * Executes an LDAP search
-	 *
-	 * @param string $filter the LDAP filter for the search
-	 * @param array $base an array containing the LDAP subtree(s) that shall be searched
-	 * @param string|string[] $attr optional, array, one or more attributes that shall be
-	 * @param int $limit
-	 * @param int $offset
-	 * @param bool $skipHandling
-	 * @return array with the search result
-	 * @throws ServerNotAvailableException
-	 */
-	public function search($filter, $base, $attr = null, $limit = null, $offset = null, $skipHandling = false) {
-		$limitPerPage = (int)$this->connection->ldapPagingSize;
-		if(!is_null($limit) && $limit < $limitPerPage && $limit > 0) {
-			$limitPerPage = $limit;
-		}
-
-		/* ++ Fixing RHDS searches with pages with zero results ++
+            $continue = $pagedSearchOK && $hasMorePages;
+        } while($continue && (is_null($limit) || $limit <= 0 || $limit > $counter));
+
+        return $counter;
+    }
+
+    /**
+     * @param array $searchResults
+     * @return int
+     * @throws ServerNotAvailableException
+     */
+    private function countEntriesInSearchResults($searchResults) {
+        $counter = 0;
+
+        foreach($searchResults as $res) {
+            $count = (int)$this->invokeLDAPMethod('countEntries', $this->connection->getConnectionResource(), $res);
+            $counter += $count;
+        }
+
+        return $counter;
+    }
+
+    /**
+     * Executes an LDAP search
+     *
+     * @param string $filter the LDAP filter for the search
+     * @param array $base an array containing the LDAP subtree(s) that shall be searched
+     * @param string|string[] $attr optional, array, one or more attributes that shall be
+     * @param int $limit
+     * @param int $offset
+     * @param bool $skipHandling
+     * @return array with the search result
+     * @throws ServerNotAvailableException
+     */
+    public function search($filter, $base, $attr = null, $limit = null, $offset = null, $skipHandling = false) {
+        $limitPerPage = (int)$this->connection->ldapPagingSize;
+        if(!is_null($limit) && $limit < $limitPerPage && $limit > 0) {
+            $limitPerPage = $limit;
+        }
+
+        /* ++ Fixing RHDS searches with pages with zero results ++
 		 * As we can have pages with zero results and/or pages with less
 		 * than $limit results but with a still valid server 'cookie',
 		 * loops through until we get $continue equals true and
 		 * $findings['count'] < $limit
 		 */
-		$findings = [];
-		$savedoffset = $offset;
-		do {
-			$search = $this->executeSearch($filter, $base, $attr, $limitPerPage, $offset);
-			if($search === false) {
-				return [];
-			}
-			list($sr, $pagedSearchOK) = $search;
-			$cr = $this->connection->getConnectionResource();
-
-			if($skipHandling) {
-				//i.e. result do not need to be fetched, we just need the cookie
-				//thus pass 1 or any other value as $iFoundItems because it is not
-				//used
-				$this->processPagedSearchStatus($sr, $filter, $base, 1, $limitPerPage,
-								$offset, $pagedSearchOK,
-								$skipHandling);
-				return array();
-			}
-
-			$iFoundItems = 0;
-			foreach($sr as $res) {
-				$findings = array_merge($findings, $this->invokeLDAPMethod('getEntries', $cr, $res));
-				$iFoundItems = max($iFoundItems, $findings['count']);
-				unset($findings['count']);
-			}
-
-			$continue = $this->processPagedSearchStatus($sr, $filter, $base, $iFoundItems,
-				$limitPerPage, $offset, $pagedSearchOK,
-										$skipHandling);
-			$offset += $limitPerPage;
-		} while ($continue && $pagedSearchOK && ($limit === null || count($findings) < $limit));
-		// reseting offset
-		$offset = $savedoffset;
-
-		// if we're here, probably no connection resource is returned.
-		// to make Nextcloud behave nicely, we simply give back an empty array.
-		if(is_null($findings)) {
-			return array();
-		}
-
-		if(!is_null($attr)) {
-			$selection = [];
-			$i = 0;
-			foreach($findings as $item) {
-				if(!is_array($item)) {
-					continue;
-				}
-				$item = \OCP\Util::mb_array_change_key_case($item, MB_CASE_LOWER, 'UTF-8');
-				foreach($attr as $key) {
-					if(isset($item[$key])) {
-						if(is_array($item[$key]) && isset($item[$key]['count'])) {
-							unset($item[$key]['count']);
-						}
-						if($key !== 'dn') {
-							if($this->resemblesDN($key)) {
-								$selection[$i][$key] = $this->helper->sanitizeDN($item[$key]);
-							} else if($key === 'objectguid' || $key === 'guid') {
-								$selection[$i][$key] = [$this->convertObjectGUID2Str($item[$key][0])];
-							} else {
-								$selection[$i][$key] = $item[$key];
-							}
-						} else {
-							$selection[$i][$key] = [$this->helper->sanitizeDN($item[$key])];
-						}
-					}
-
-				}
-				$i++;
-			}
-			$findings = $selection;
-		}
-		//we slice the findings, when
-		//a) paged search unsuccessful, though attempted
-		//b) no paged search, but limit set
-		if((!$this->getPagedSearchResultState()
-			&& $pagedSearchOK)
-			|| (
-				!$pagedSearchOK
-				&& !is_null($limit)
-			)
-		) {
-			$findings = array_slice($findings, (int)$offset, $limit);
-		}
-		return $findings;
-	}
-
-	/**
-	 * @param string $name
-	 * @return string
-	 * @throws \InvalidArgumentException
-	 */
-	public function sanitizeUsername($name) {
-		$name = trim($name);
-
-		if($this->connection->ldapIgnoreNamingRules) {
-			return $name;
-		}
-
-		// Transliteration to ASCII
-		$transliterated = @iconv('UTF-8', 'ASCII//TRANSLIT', $name);
-		if($transliterated !== false) {
-			// depending on system config iconv can work or not
-			$name = $transliterated;
-		}
-
-		// Replacements
-		$name = str_replace(' ', '_', $name);
-
-		// Every remaining disallowed characters will be removed
-		$name = preg_replace('/[^a-zA-Z0-9_.@-]/u', '', $name);
-
-		if($name === '') {
-			throw new \InvalidArgumentException('provided name template for username does not contain any allowed characters');
-		}
-
-		return $name;
-	}
-
-	/**
-	* escapes (user provided) parts for LDAP filter
-	* @param string $input, the provided value
-	* @param bool $allowAsterisk whether in * at the beginning should be preserved
-	* @return string the escaped string
-	*/
-	public function escapeFilterPart($input, $allowAsterisk = false) {
-		$asterisk = '';
-		if($allowAsterisk && strlen($input) > 0 && $input[0] === '*') {
-			$asterisk = '*';
-			$input = mb_substr($input, 1, null, 'UTF-8');
-		}
-		$search  = array('*', '\\', '(', ')');
-		$replace = array('\\*', '\\\\', '\\(', '\\)');
-		return $asterisk . str_replace($search, $replace, $input);
-	}
-
-	/**
-	 * combines the input filters with AND
-	 * @param string[] $filters the filters to connect
-	 * @return string the combined filter
-	 */
-	public function combineFilterWithAnd($filters) {
-		return $this->combineFilter($filters, '&');
-	}
-
-	/**
-	 * combines the input filters with OR
-	 * @param string[] $filters the filters to connect
-	 * @return string the combined filter
-	 * Combines Filter arguments with OR
-	 */
-	public function combineFilterWithOr($filters) {
-		return $this->combineFilter($filters, '|');
-	}
-
-	/**
-	 * combines the input filters with given operator
-	 * @param string[] $filters the filters to connect
-	 * @param string $operator either & or |
-	 * @return string the combined filter
-	 */
-	private function combineFilter($filters, $operator) {
-		$combinedFilter = '('.$operator;
-		foreach($filters as $filter) {
-			if ($filter !== '' && $filter[0] !== '(') {
-				$filter = '('.$filter.')';
-			}
-			$combinedFilter.=$filter;
-		}
-		$combinedFilter.=')';
-		return $combinedFilter;
-	}
-
-	/**
-	 * creates a filter part for to perform search for users
-	 * @param string $search the search term
-	 * @return string the final filter part to use in LDAP searches
-	 */
-	public function getFilterPartForUserSearch($search) {
-		return $this->getFilterPartForSearch($search,
-			$this->connection->ldapAttributesForUserSearch,
-			$this->connection->ldapUserDisplayName);
-	}
-
-	/**
-	 * creates a filter part for to perform search for groups
-	 * @param string $search the search term
-	 * @return string the final filter part to use in LDAP searches
-	 */
-	public function getFilterPartForGroupSearch($search) {
-		return $this->getFilterPartForSearch($search,
-			$this->connection->ldapAttributesForGroupSearch,
-			$this->connection->ldapGroupDisplayName);
-	}
-
-	/**
-	 * creates a filter part for searches by splitting up the given search
-	 * string into single words
-	 * @param string $search the search term
-	 * @param string[] $searchAttributes needs to have at least two attributes,
-	 * otherwise it does not make sense :)
-	 * @return string the final filter part to use in LDAP searches
-	 * @throws \Exception
-	 */
-	private function getAdvancedFilterPartForSearch($search, $searchAttributes) {
-		if(!is_array($searchAttributes) || count($searchAttributes) < 2) {
-			throw new \Exception('searchAttributes must be an array with at least two string');
-		}
-		$searchWords = explode(' ', trim($search));
-		$wordFilters = array();
-		foreach($searchWords as $word) {
-			$word = $this->prepareSearchTerm($word);
-			//every word needs to appear at least once
-			$wordMatchOneAttrFilters = array();
-			foreach($searchAttributes as $attr) {
-				$wordMatchOneAttrFilters[] = $attr . '=' . $word;
-			}
-			$wordFilters[] = $this->combineFilterWithOr($wordMatchOneAttrFilters);
-		}
-		return $this->combineFilterWithAnd($wordFilters);
-	}
-
-	/**
-	 * creates a filter part for searches
-	 * @param string $search the search term
-	 * @param string[]|null $searchAttributes
-	 * @param string $fallbackAttribute a fallback attribute in case the user
-	 * did not define search attributes. Typically the display name attribute.
-	 * @return string the final filter part to use in LDAP searches
-	 */
-	private function getFilterPartForSearch($search, $searchAttributes, $fallbackAttribute) {
-		$filter = array();
-		$haveMultiSearchAttributes = (is_array($searchAttributes) && count($searchAttributes) > 0);
-		if($haveMultiSearchAttributes && strpos(trim($search), ' ') !== false) {
-			try {
-				return $this->getAdvancedFilterPartForSearch($search, $searchAttributes);
-			} catch(\Exception $e) {
-				\OCP\Util::writeLog(
-					'user_ldap',
-					'Creating advanced filter for search failed, falling back to simple method.',
-					ILogger::INFO
-				);
-			}
-		}
-
-		$search = $this->prepareSearchTerm($search);
-		if(!is_array($searchAttributes) || count($searchAttributes) === 0) {
-			if ($fallbackAttribute === '') {
-				return '';
-			}
-			$filter[] = $fallbackAttribute . '=' . $search;
-		} else {
-			foreach($searchAttributes as $attribute) {
-				$filter[] = $attribute . '=' . $search;
-			}
-		}
-		if(count($filter) === 1) {
-			return '('.$filter[0].')';
-		}
-		return $this->combineFilterWithOr($filter);
-	}
-
-	/**
-	 * returns the search term depending on whether we are allowed
-	 * list users found by ldap with the current input appended by
-	 * a *
-	 * @return string
-	 */
-	private function prepareSearchTerm($term) {
-		$config = \OC::$server->getConfig();
-
-		$allowEnum = $config->getAppValue('core', 'shareapi_allow_share_dialog_user_enumeration', 'yes');
-
-		$result = $term;
-		if ($term === '') {
-			$result = '*';
-		} else if ($allowEnum !== 'no') {
-			$result = $term . '*';
-		}
-		return $result;
-	}
-
-	/**
-	 * returns the filter used for counting users
-	 * @return string
-	 */
-	public function getFilterForUserCount() {
-		$filter = $this->combineFilterWithAnd(array(
-			$this->connection->ldapUserFilter,
-			$this->connection->ldapUserDisplayName . '=*'
-		));
-
-		return $filter;
-	}
-
-	/**
-	 * @param string $name
-	 * @param string $password
-	 * @return bool
-	 */
-	public function areCredentialsValid($name, $password) {
-		$name = $this->helper->DNasBaseParameter($name);
-		$testConnection = clone $this->connection;
-		$credentials = array(
-			'ldapAgentName' => $name,
-			'ldapAgentPassword' => $password
-		);
-		if(!$testConnection->setConfiguration($credentials)) {
-			return false;
-		}
-		return $testConnection->bind();
-	}
-
-	/**
-	 * reverse lookup of a DN given a known UUID
-	 *
-	 * @param string $uuid
-	 * @return string
-	 * @throws \Exception
-	 */
-	public function getUserDnByUuid($uuid) {
-		$uuidOverride = $this->connection->ldapExpertUUIDUserAttr;
-		$filter       = $this->connection->ldapUserFilter;
-		$base         = $this->connection->ldapBaseUsers;
-
-		if ($this->connection->ldapUuidUserAttribute === 'auto' && $uuidOverride === '') {
-			// Sacrebleu! The UUID attribute is unknown :( We need first an
-			// existing DN to be able to reliably detect it.
-			$result = $this->search($filter, $base, ['dn'], 1);
-			if(!isset($result[0]) || !isset($result[0]['dn'])) {
-				throw new \Exception('Cannot determine UUID attribute');
-			}
-			$dn = $result[0]['dn'][0];
-			if(!$this->detectUuidAttribute($dn, true)) {
-				throw new \Exception('Cannot determine UUID attribute');
-			}
-		} else {
-			// The UUID attribute is either known or an override is given.
-			// By calling this method we ensure that $this->connection->$uuidAttr
-			// is definitely set
-			if(!$this->detectUuidAttribute('', true)) {
-				throw new \Exception('Cannot determine UUID attribute');
-			}
-		}
-
-		$uuidAttr = $this->connection->ldapUuidUserAttribute;
-		if($uuidAttr === 'guid' || $uuidAttr === 'objectguid') {
-			$uuid = $this->formatGuid2ForFilterUser($uuid);
-		}
-
-		$filter = $uuidAttr . '=' . $uuid;
-		$result = $this->searchUsers($filter, ['dn'], 2);
-		if(is_array($result) && isset($result[0]) && isset($result[0]['dn']) && count($result) === 1) {
-			// we put the count into account to make sure that this is
-			// really unique
-			return $result[0]['dn'][0];
-		}
-
-		throw new \Exception('Cannot determine UUID attribute');
-	}
-
-	/**
-	 * auto-detects the directory's UUID attribute
-	 *
-	 * @param string $dn a known DN used to check against
-	 * @param bool $isUser
-	 * @param bool $force the detection should be run, even if it is not set to auto
-	 * @param array|null $ldapRecord
-	 * @return bool true on success, false otherwise
-	 * @throws ServerNotAvailableException
-	 */
-	private function detectUuidAttribute($dn, $isUser = true, $force = false, array $ldapRecord = null) {
-		if($isUser) {
-			$uuidAttr     = 'ldapUuidUserAttribute';
-			$uuidOverride = $this->connection->ldapExpertUUIDUserAttr;
-		} else {
-			$uuidAttr     = 'ldapUuidGroupAttribute';
-			$uuidOverride = $this->connection->ldapExpertUUIDGroupAttr;
-		}
-
-		if(!$force) {
-			if($this->connection->$uuidAttr !== 'auto') {
-				return true;
-			} else if (is_string($uuidOverride) && trim($uuidOverride) !== '') {
-				$this->connection->$uuidAttr = $uuidOverride;
-				return true;
-			}
-
-			$attribute = $this->connection->getFromCache($uuidAttr);
-			if(!$attribute === null) {
-				$this->connection->$uuidAttr = $attribute;
-				return true;
-			}
-		}
-
-		foreach(self::UUID_ATTRIBUTES as $attribute) {
-			if($ldapRecord !== null) {
-				// we have the info from LDAP already, we don't need to talk to the server again
-				if(isset($ldapRecord[$attribute])) {
-					$this->connection->$uuidAttr = $attribute;
-					return true;
-				}
-			}
-
-			$value = $this->readAttribute($dn, $attribute);
-			if(is_array($value) && isset($value[0]) && !empty($value[0])) {
-				\OC::$server->getLogger()->debug(
-					'Setting {attribute} as {subject}',
-					[
-						'app' => 'user_ldap',
-						'attribute' => $attribute,
-						'subject' => $uuidAttr
-					]
-				);
-				$this->connection->$uuidAttr = $attribute;
-				$this->connection->writeToCache($uuidAttr, $attribute);
-				return true;
-			}
-		}
-		\OC::$server->getLogger()->debug('Could not autodetect the UUID attribute', ['app' => 'user_ldap']);
-
-		return false;
-	}
-
-	/**
-	 * @param string $dn
-	 * @param bool $isUser
-	 * @param null $ldapRecord
-	 * @return bool|string
-	 * @throws ServerNotAvailableException
-	 */
-	public function getUUID($dn, $isUser = true, $ldapRecord = null) {
-		if($isUser) {
-			$uuidAttr     = 'ldapUuidUserAttribute';
-			$uuidOverride = $this->connection->ldapExpertUUIDUserAttr;
-		} else {
-			$uuidAttr     = 'ldapUuidGroupAttribute';
-			$uuidOverride = $this->connection->ldapExpertUUIDGroupAttr;
-		}
-
-		$uuid = false;
-		if($this->detectUuidAttribute($dn, $isUser, false, $ldapRecord)) {
-			$attr = $this->connection->$uuidAttr;
-			$uuid = isset($ldapRecord[$attr]) ? $ldapRecord[$attr] : $this->readAttribute($dn, $attr);
-			if( !is_array($uuid)
-				&& $uuidOverride !== ''
-				&& $this->detectUuidAttribute($dn, $isUser, true, $ldapRecord))
-			{
-				$uuid = isset($ldapRecord[$this->connection->$uuidAttr])
-					? $ldapRecord[$this->connection->$uuidAttr]
-					: $this->readAttribute($dn, $this->connection->$uuidAttr);
-			}
-			if(is_array($uuid) && isset($uuid[0]) && !empty($uuid[0])) {
-				$uuid = $uuid[0];
-			}
-		}
-
-		return $uuid;
-	}
-
-	/**
-	 * converts a binary ObjectGUID into a string representation
-	 * @param string $oguid the ObjectGUID in it's binary form as retrieved from AD
-	 * @return string
-	 * @link http://www.php.net/manual/en/function.ldap-get-values-len.php#73198
-	 */
-	private function convertObjectGUID2Str($oguid) {
-		$hex_guid = bin2hex($oguid);
-		$hex_guid_to_guid_str = '';
-		for($k = 1; $k <= 4; ++$k) {
-			$hex_guid_to_guid_str .= substr($hex_guid, 8 - 2 * $k, 2);
-		}
-		$hex_guid_to_guid_str .= '-';
-		for($k = 1; $k <= 2; ++$k) {
-			$hex_guid_to_guid_str .= substr($hex_guid, 12 - 2 * $k, 2);
-		}
-		$hex_guid_to_guid_str .= '-';
-		for($k = 1; $k <= 2; ++$k) {
-			$hex_guid_to_guid_str .= substr($hex_guid, 16 - 2 * $k, 2);
-		}
-		$hex_guid_to_guid_str .= '-' . substr($hex_guid, 16, 4);
-		$hex_guid_to_guid_str .= '-' . substr($hex_guid, 20);
-
-		return strtoupper($hex_guid_to_guid_str);
-	}
-
-	/**
-	 * the first three blocks of the string-converted GUID happen to be in
-	 * reverse order. In order to use it in a filter, this needs to be
-	 * corrected. Furthermore the dashes need to be replaced and \\ preprended
-	 * to every two hax figures.
-	 *
-	 * If an invalid string is passed, it will be returned without change.
-	 *
-	 * @param string $guid
-	 * @return string
-	 */
-	public function formatGuid2ForFilterUser($guid) {
-		if(!is_string($guid)) {
-			throw new \InvalidArgumentException('String expected');
-		}
-		$blocks = explode('-', $guid);
-		if(count($blocks) !== 5) {
-			/*
+        $findings = [];
+        $savedoffset = $offset;
+        do {
+            $search = $this->executeSearch($filter, $base, $attr, $limitPerPage, $offset);
+            if($search === false) {
+                return [];
+            }
+            list($sr, $pagedSearchOK) = $search;
+            $cr = $this->connection->getConnectionResource();
+
+            if($skipHandling) {
+                //i.e. result do not need to be fetched, we just need the cookie
+                //thus pass 1 or any other value as $iFoundItems because it is not
+                //used
+                $this->processPagedSearchStatus($sr, $filter, $base, 1, $limitPerPage,
+                                $offset, $pagedSearchOK,
+                                $skipHandling);
+                return array();
+            }
+
+            $iFoundItems = 0;
+            foreach($sr as $res) {
+                $findings = array_merge($findings, $this->invokeLDAPMethod('getEntries', $cr, $res));
+                $iFoundItems = max($iFoundItems, $findings['count']);
+                unset($findings['count']);
+            }
+
+            $continue = $this->processPagedSearchStatus($sr, $filter, $base, $iFoundItems,
+                $limitPerPage, $offset, $pagedSearchOK,
+                                        $skipHandling);
+            $offset += $limitPerPage;
+        } while ($continue && $pagedSearchOK && ($limit === null || count($findings) < $limit));
+        // reseting offset
+        $offset = $savedoffset;
+
+        // if we're here, probably no connection resource is returned.
+        // to make Nextcloud behave nicely, we simply give back an empty array.
+        if(is_null($findings)) {
+            return array();
+        }
+
+        if(!is_null($attr)) {
+            $selection = [];
+            $i = 0;
+            foreach($findings as $item) {
+                if(!is_array($item)) {
+                    continue;
+                }
+                $item = \OCP\Util::mb_array_change_key_case($item, MB_CASE_LOWER, 'UTF-8');
+                foreach($attr as $key) {
+                    if(isset($item[$key])) {
+                        if(is_array($item[$key]) && isset($item[$key]['count'])) {
+                            unset($item[$key]['count']);
+                        }
+                        if($key !== 'dn') {
+                            if($this->resemblesDN($key)) {
+                                $selection[$i][$key] = $this->helper->sanitizeDN($item[$key]);
+                            } else if($key === 'objectguid' || $key === 'guid') {
+                                $selection[$i][$key] = [$this->convertObjectGUID2Str($item[$key][0])];
+                            } else {
+                                $selection[$i][$key] = $item[$key];
+                            }
+                        } else {
+                            $selection[$i][$key] = [$this->helper->sanitizeDN($item[$key])];
+                        }
+                    }
+
+                }
+                $i++;
+            }
+            $findings = $selection;
+        }
+        //we slice the findings, when
+        //a) paged search unsuccessful, though attempted
+        //b) no paged search, but limit set
+        if((!$this->getPagedSearchResultState()
+            && $pagedSearchOK)
+            || (
+                !$pagedSearchOK
+                && !is_null($limit)
+            )
+        ) {
+            $findings = array_slice($findings, (int)$offset, $limit);
+        }
+        return $findings;
+    }
+
+    /**
+     * @param string $name
+     * @return string
+     * @throws \InvalidArgumentException
+     */
+    public function sanitizeUsername($name) {
+        $name = trim($name);
+
+        if($this->connection->ldapIgnoreNamingRules) {
+            return $name;
+        }
+
+        // Transliteration to ASCII
+        $transliterated = @iconv('UTF-8', 'ASCII//TRANSLIT', $name);
+        if($transliterated !== false) {
+            // depending on system config iconv can work or not
+            $name = $transliterated;
+        }
+
+        // Replacements
+        $name = str_replace(' ', '_', $name);
+
+        // Every remaining disallowed characters will be removed
+        $name = preg_replace('/[^a-zA-Z0-9_.@-]/u', '', $name);
+
+        if($name === '') {
+            throw new \InvalidArgumentException('provided name template for username does not contain any allowed characters');
+        }
+
+        return $name;
+    }
+
+    /**
+     * escapes (user provided) parts for LDAP filter
+     * @param string $input, the provided value
+     * @param bool $allowAsterisk whether in * at the beginning should be preserved
+     * @return string the escaped string
+     */
+    public function escapeFilterPart($input, $allowAsterisk = false) {
+        $asterisk = '';
+        if($allowAsterisk && strlen($input) > 0 && $input[0] === '*') {
+            $asterisk = '*';
+            $input = mb_substr($input, 1, null, 'UTF-8');
+        }
+        $search  = array('*', '\\', '(', ')');
+        $replace = array('\\*', '\\\\', '\\(', '\\)');
+        return $asterisk . str_replace($search, $replace, $input);
+    }
+
+    /**
+     * combines the input filters with AND
+     * @param string[] $filters the filters to connect
+     * @return string the combined filter
+     */
+    public function combineFilterWithAnd($filters) {
+        return $this->combineFilter($filters, '&');
+    }
+
+    /**
+     * combines the input filters with OR
+     * @param string[] $filters the filters to connect
+     * @return string the combined filter
+     * Combines Filter arguments with OR
+     */
+    public function combineFilterWithOr($filters) {
+        return $this->combineFilter($filters, '|');
+    }
+
+    /**
+     * combines the input filters with given operator
+     * @param string[] $filters the filters to connect
+     * @param string $operator either & or |
+     * @return string the combined filter
+     */
+    private function combineFilter($filters, $operator) {
+        $combinedFilter = '('.$operator;
+        foreach($filters as $filter) {
+            if ($filter !== '' && $filter[0] !== '(') {
+                $filter = '('.$filter.')';
+            }
+            $combinedFilter.=$filter;
+        }
+        $combinedFilter.=')';
+        return $combinedFilter;
+    }
+
+    /**
+     * creates a filter part for to perform search for users
+     * @param string $search the search term
+     * @return string the final filter part to use in LDAP searches
+     */
+    public function getFilterPartForUserSearch($search) {
+        return $this->getFilterPartForSearch($search,
+            $this->connection->ldapAttributesForUserSearch,
+            $this->connection->ldapUserDisplayName);
+    }
+
+    /**
+     * creates a filter part for to perform search for groups
+     * @param string $search the search term
+     * @return string the final filter part to use in LDAP searches
+     */
+    public function getFilterPartForGroupSearch($search) {
+        return $this->getFilterPartForSearch($search,
+            $this->connection->ldapAttributesForGroupSearch,
+            $this->connection->ldapGroupDisplayName);
+    }
+
+    /**
+     * creates a filter part for searches by splitting up the given search
+     * string into single words
+     * @param string $search the search term
+     * @param string[] $searchAttributes needs to have at least two attributes,
+     * otherwise it does not make sense :)
+     * @return string the final filter part to use in LDAP searches
+     * @throws \Exception
+     */
+    private function getAdvancedFilterPartForSearch($search, $searchAttributes) {
+        if(!is_array($searchAttributes) || count($searchAttributes) < 2) {
+            throw new \Exception('searchAttributes must be an array with at least two string');
+        }
+        $searchWords = explode(' ', trim($search));
+        $wordFilters = array();
+        foreach($searchWords as $word) {
+            $word = $this->prepareSearchTerm($word);
+            //every word needs to appear at least once
+            $wordMatchOneAttrFilters = array();
+            foreach($searchAttributes as $attr) {
+                $wordMatchOneAttrFilters[] = $attr . '=' . $word;
+            }
+            $wordFilters[] = $this->combineFilterWithOr($wordMatchOneAttrFilters);
+        }
+        return $this->combineFilterWithAnd($wordFilters);
+    }
+
+    /**
+     * creates a filter part for searches
+     * @param string $search the search term
+     * @param string[]|null $searchAttributes
+     * @param string $fallbackAttribute a fallback attribute in case the user
+     * did not define search attributes. Typically the display name attribute.
+     * @return string the final filter part to use in LDAP searches
+     */
+    private function getFilterPartForSearch($search, $searchAttributes, $fallbackAttribute) {
+        $filter = array();
+        $haveMultiSearchAttributes = (is_array($searchAttributes) && count($searchAttributes) > 0);
+        if($haveMultiSearchAttributes && strpos(trim($search), ' ') !== false) {
+            try {
+                return $this->getAdvancedFilterPartForSearch($search, $searchAttributes);
+            } catch(\Exception $e) {
+                \OCP\Util::writeLog(
+                    'user_ldap',
+                    'Creating advanced filter for search failed, falling back to simple method.',
+                    ILogger::INFO
+                );
+            }
+        }
+
+        $search = $this->prepareSearchTerm($search);
+        if(!is_array($searchAttributes) || count($searchAttributes) === 0) {
+            if ($fallbackAttribute === '') {
+                return '';
+            }
+            $filter[] = $fallbackAttribute . '=' . $search;
+        } else {
+            foreach($searchAttributes as $attribute) {
+                $filter[] = $attribute . '=' . $search;
+            }
+        }
+        if(count($filter) === 1) {
+            return '('.$filter[0].')';
+        }
+        return $this->combineFilterWithOr($filter);
+    }
+
+    /**
+     * returns the search term depending on whether we are allowed
+     * list users found by ldap with the current input appended by
+     * a *
+     * @return string
+     */
+    private function prepareSearchTerm($term) {
+        $config = \OC::$server->getConfig();
+
+        $allowEnum = $config->getAppValue('core', 'shareapi_allow_share_dialog_user_enumeration', 'yes');
+
+        $result = $term;
+        if ($term === '') {
+            $result = '*';
+        } else if ($allowEnum !== 'no') {
+            $result = $term . '*';
+        }
+        return $result;
+    }
+
+    /**
+     * returns the filter used for counting users
+     * @return string
+     */
+    public function getFilterForUserCount() {
+        $filter = $this->combineFilterWithAnd(array(
+            $this->connection->ldapUserFilter,
+            $this->connection->ldapUserDisplayName . '=*'
+        ));
+
+        return $filter;
+    }
+
+    /**
+     * @param string $name
+     * @param string $password
+     * @return bool
+     */
+    public function areCredentialsValid($name, $password) {
+        $name = $this->helper->DNasBaseParameter($name);
+        $testConnection = clone $this->connection;
+        $credentials = array(
+            'ldapAgentName' => $name,
+            'ldapAgentPassword' => $password
+        );
+        if(!$testConnection->setConfiguration($credentials)) {
+            return false;
+        }
+        return $testConnection->bind();
+    }
+
+    /**
+     * reverse lookup of a DN given a known UUID
+     *
+     * @param string $uuid
+     * @return string
+     * @throws \Exception
+     */
+    public function getUserDnByUuid($uuid) {
+        $uuidOverride = $this->connection->ldapExpertUUIDUserAttr;
+        $filter       = $this->connection->ldapUserFilter;
+        $base         = $this->connection->ldapBaseUsers;
+
+        if ($this->connection->ldapUuidUserAttribute === 'auto' && $uuidOverride === '') {
+            // Sacrebleu! The UUID attribute is unknown :( We need first an
+            // existing DN to be able to reliably detect it.
+            $result = $this->search($filter, $base, ['dn'], 1);
+            if(!isset($result[0]) || !isset($result[0]['dn'])) {
+                throw new \Exception('Cannot determine UUID attribute');
+            }
+            $dn = $result[0]['dn'][0];
+            if(!$this->detectUuidAttribute($dn, true)) {
+                throw new \Exception('Cannot determine UUID attribute');
+            }
+        } else {
+            // The UUID attribute is either known or an override is given.
+            // By calling this method we ensure that $this->connection->$uuidAttr
+            // is definitely set
+            if(!$this->detectUuidAttribute('', true)) {
+                throw new \Exception('Cannot determine UUID attribute');
+            }
+        }
+
+        $uuidAttr = $this->connection->ldapUuidUserAttribute;
+        if($uuidAttr === 'guid' || $uuidAttr === 'objectguid') {
+            $uuid = $this->formatGuid2ForFilterUser($uuid);
+        }
+
+        $filter = $uuidAttr . '=' . $uuid;
+        $result = $this->searchUsers($filter, ['dn'], 2);
+        if(is_array($result) && isset($result[0]) && isset($result[0]['dn']) && count($result) === 1) {
+            // we put the count into account to make sure that this is
+            // really unique
+            return $result[0]['dn'][0];
+        }
+
+        throw new \Exception('Cannot determine UUID attribute');
+    }
+
+    /**
+     * auto-detects the directory's UUID attribute
+     *
+     * @param string $dn a known DN used to check against
+     * @param bool $isUser
+     * @param bool $force the detection should be run, even if it is not set to auto
+     * @param array|null $ldapRecord
+     * @return bool true on success, false otherwise
+     * @throws ServerNotAvailableException
+     */
+    private function detectUuidAttribute($dn, $isUser = true, $force = false, array $ldapRecord = null) {
+        if($isUser) {
+            $uuidAttr     = 'ldapUuidUserAttribute';
+            $uuidOverride = $this->connection->ldapExpertUUIDUserAttr;
+        } else {
+            $uuidAttr     = 'ldapUuidGroupAttribute';
+            $uuidOverride = $this->connection->ldapExpertUUIDGroupAttr;
+        }
+
+        if(!$force) {
+            if($this->connection->$uuidAttr !== 'auto') {
+                return true;
+            } else if (is_string($uuidOverride) && trim($uuidOverride) !== '') {
+                $this->connection->$uuidAttr = $uuidOverride;
+                return true;
+            }
+
+            $attribute = $this->connection->getFromCache($uuidAttr);
+            if(!$attribute === null) {
+                $this->connection->$uuidAttr = $attribute;
+                return true;
+            }
+        }
+
+        foreach(self::UUID_ATTRIBUTES as $attribute) {
+            if($ldapRecord !== null) {
+                // we have the info from LDAP already, we don't need to talk to the server again
+                if(isset($ldapRecord[$attribute])) {
+                    $this->connection->$uuidAttr = $attribute;
+                    return true;
+                }
+            }
+
+            $value = $this->readAttribute($dn, $attribute);
+            if(is_array($value) && isset($value[0]) && !empty($value[0])) {
+                \OC::$server->getLogger()->debug(
+                    'Setting {attribute} as {subject}',
+                    [
+                        'app' => 'user_ldap',
+                        'attribute' => $attribute,
+                        'subject' => $uuidAttr
+                    ]
+                );
+                $this->connection->$uuidAttr = $attribute;
+                $this->connection->writeToCache($uuidAttr, $attribute);
+                return true;
+            }
+        }
+        \OC::$server->getLogger()->debug('Could not autodetect the UUID attribute', ['app' => 'user_ldap']);
+
+        return false;
+    }
+
+    /**
+     * @param string $dn
+     * @param bool $isUser
+     * @param null $ldapRecord
+     * @return bool|string
+     * @throws ServerNotAvailableException
+     */
+    public function getUUID($dn, $isUser = true, $ldapRecord = null) {
+        if($isUser) {
+            $uuidAttr     = 'ldapUuidUserAttribute';
+            $uuidOverride = $this->connection->ldapExpertUUIDUserAttr;
+        } else {
+            $uuidAttr     = 'ldapUuidGroupAttribute';
+            $uuidOverride = $this->connection->ldapExpertUUIDGroupAttr;
+        }
+
+        $uuid = false;
+        if($this->detectUuidAttribute($dn, $isUser, false, $ldapRecord)) {
+            $attr = $this->connection->$uuidAttr;
+            $uuid = isset($ldapRecord[$attr]) ? $ldapRecord[$attr] : $this->readAttribute($dn, $attr);
+            if( !is_array($uuid)
+                && $uuidOverride !== ''
+                && $this->detectUuidAttribute($dn, $isUser, true, $ldapRecord))
+            {
+                $uuid = isset($ldapRecord[$this->connection->$uuidAttr])
+                    ? $ldapRecord[$this->connection->$uuidAttr]
+                    : $this->readAttribute($dn, $this->connection->$uuidAttr);
+            }
+            if(is_array($uuid) && isset($uuid[0]) && !empty($uuid[0])) {
+                $uuid = $uuid[0];
+            }
+        }
+
+        return $uuid;
+    }
+
+    /**
+     * converts a binary ObjectGUID into a string representation
+     * @param string $oguid the ObjectGUID in it's binary form as retrieved from AD
+     * @return string
+     * @link http://www.php.net/manual/en/function.ldap-get-values-len.php#73198
+     */
+    private function convertObjectGUID2Str($oguid) {
+        $hex_guid = bin2hex($oguid);
+        $hex_guid_to_guid_str = '';
+        for($k = 1; $k <= 4; ++$k) {
+            $hex_guid_to_guid_str .= substr($hex_guid, 8 - 2 * $k, 2);
+        }
+        $hex_guid_to_guid_str .= '-';
+        for($k = 1; $k <= 2; ++$k) {
+            $hex_guid_to_guid_str .= substr($hex_guid, 12 - 2 * $k, 2);
+        }
+        $hex_guid_to_guid_str .= '-';
+        for($k = 1; $k <= 2; ++$k) {
+            $hex_guid_to_guid_str .= substr($hex_guid, 16 - 2 * $k, 2);
+        }
+        $hex_guid_to_guid_str .= '-' . substr($hex_guid, 16, 4);
+        $hex_guid_to_guid_str .= '-' . substr($hex_guid, 20);
+
+        return strtoupper($hex_guid_to_guid_str);
+    }
+
+    /**
+     * the first three blocks of the string-converted GUID happen to be in
+     * reverse order. In order to use it in a filter, this needs to be
+     * corrected. Furthermore the dashes need to be replaced and \\ preprended
+     * to every two hax figures.
+     *
+     * If an invalid string is passed, it will be returned without change.
+     *
+     * @param string $guid
+     * @return string
+     */
+    public function formatGuid2ForFilterUser($guid) {
+        if(!is_string($guid)) {
+            throw new \InvalidArgumentException('String expected');
+        }
+        $blocks = explode('-', $guid);
+        if(count($blocks) !== 5) {
+            /*
 			 * Why not throw an Exception instead? This method is a utility
 			 * called only when trying to figure out whether a "missing" known
 			 * LDAP user was or was not renamed on the LDAP server. And this
@@ -1846,283 +1846,283 @@ 
 			 * an exception here would kill the experience for a valid, acting
 			 * user. Instead we write a log message.
 			 */
-			\OC::$server->getLogger()->info(
-				'Passed string does not resemble a valid GUID. Known UUID ' .
-				'({uuid}) probably does not match UUID configuration.',
-				[ 'app' => 'user_ldap', 'uuid' => $guid ]
-			);
-			return $guid;
-		}
-		for($i=0; $i < 3; $i++) {
-			$pairs = str_split($blocks[$i], 2);
-			$pairs = array_reverse($pairs);
-			$blocks[$i] = implode('', $pairs);
-		}
-		for($i=0; $i < 5; $i++) {
-			$pairs = str_split($blocks[$i], 2);
-			$blocks[$i] = '\\' . implode('\\', $pairs);
-		}
-		return implode('', $blocks);
-	}
-
-	/**
-	 * gets a SID of the domain of the given dn
-	 *
-	 * @param string $dn
-	 * @return string|bool
-	 * @throws ServerNotAvailableException
-	 */
-	public function getSID($dn) {
-		$domainDN = $this->getDomainDNFromDN($dn);
-		$cacheKey = 'getSID-'.$domainDN;
-		$sid = $this->connection->getFromCache($cacheKey);
-		if(!is_null($sid)) {
-			return $sid;
-		}
-
-		$objectSid = $this->readAttribute($domainDN, 'objectsid');
-		if(!is_array($objectSid) || empty($objectSid)) {
-			$this->connection->writeToCache($cacheKey, false);
-			return false;
-		}
-		$domainObjectSid = $this->convertSID2Str($objectSid[0]);
-		$this->connection->writeToCache($cacheKey, $domainObjectSid);
-
-		return $domainObjectSid;
-	}
-
-	/**
-	 * converts a binary SID into a string representation
-	 * @param string $sid
-	 * @return string
-	 */
-	public function convertSID2Str($sid) {
-		// The format of a SID binary string is as follows:
-		// 1 byte for the revision level
-		// 1 byte for the number n of variable sub-ids
-		// 6 bytes for identifier authority value
-		// n*4 bytes for n sub-ids
-		//
-		// Example: 010400000000000515000000a681e50e4d6c6c2bca32055f
-		//  Legend: RRNNAAAAAAAAAAAA11111111222222223333333344444444
-		$revision = ord($sid[0]);
-		$numberSubID = ord($sid[1]);
-
-		$subIdStart = 8; // 1 + 1 + 6
-		$subIdLength = 4;
-		if (strlen($sid) !== $subIdStart + $subIdLength * $numberSubID) {
-			// Incorrect number of bytes present.
-			return '';
-		}
-
-		// 6 bytes = 48 bits can be represented using floats without loss of
-		// precision (see https://gist.github.com/bantu/886ac680b0aef5812f71)
-		$iav = number_format(hexdec(bin2hex(substr($sid, 2, 6))), 0, '', '');
-
-		$subIDs = array();
-		for ($i = 0; $i < $numberSubID; $i++) {
-			$subID = unpack('V', substr($sid, $subIdStart + $subIdLength * $i, $subIdLength));
-			$subIDs[] = sprintf('%u', $subID[1]);
-		}
-
-		// Result for example above: S-1-5-21-249921958-728525901-1594176202
-		return sprintf('S-%d-%s-%s', $revision, $iav, implode('-', $subIDs));
-	}
-
-	/**
-	 * checks if the given DN is part of the given base DN(s)
-	 * @param string $dn the DN
-	 * @param string[] $bases array containing the allowed base DN or DNs
-	 * @return bool
-	 */
-	public function isDNPartOfBase($dn, $bases) {
-		$belongsToBase = false;
-		$bases = $this->helper->sanitizeDN($bases);
-
-		foreach($bases as $base) {
-			$belongsToBase = true;
-			if(mb_strripos($dn, $base, 0, 'UTF-8') !== (mb_strlen($dn, 'UTF-8')-mb_strlen($base, 'UTF-8'))) {
-				$belongsToBase = false;
-			}
-			if($belongsToBase) {
-				break;
-			}
-		}
-		return $belongsToBase;
-	}
-
-	/**
-	 * resets a running Paged Search operation
-	 *
-	 * @throws ServerNotAvailableException
-	 */
-	private function abandonPagedSearch() {
-		$cr = $this->connection->getConnectionResource();
-		$this->invokeLDAPMethod('controlPagedResult', $cr, 0, false, $this->lastCookie);
-		$this->getPagedSearchResultState();
-		$this->lastCookie = '';
-		$this->cookies = [];
-	}
-
-	/**
-	 * get a cookie for the next LDAP paged search
-	 * @param string $base a string with the base DN for the search
-	 * @param string $filter the search filter to identify the correct search
-	 * @param int $limit the limit (or 'pageSize'), to identify the correct search well
-	 * @param int $offset the offset for the new search to identify the correct search really good
-	 * @return string containing the key or empty if none is cached
-	 */
-	private function getPagedResultCookie($base, $filter, $limit, $offset) {
-		if($offset === 0) {
-			return '';
-		}
-		$offset -= $limit;
-		//we work with cache here
-		$cacheKey = 'lc' . crc32($base) . '-' . crc32($filter) . '-' . (int)$limit . '-' . (int)$offset;
-		$cookie = '';
-		if(isset($this->cookies[$cacheKey])) {
-			$cookie = $this->cookies[$cacheKey];
-			if(is_null($cookie)) {
-				$cookie = '';
-			}
-		}
-		return $cookie;
-	}
-
-	/**
-	 * checks whether an LDAP paged search operation has more pages that can be
-	 * retrieved, typically when offset and limit are provided.
-	 *
-	 * Be very careful to use it: the last cookie value, which is inspected, can
-	 * be reset by other operations. Best, call it immediately after a search(),
-	 * searchUsers() or searchGroups() call. count-methods are probably safe as
-	 * well. Don't rely on it with any fetchList-method.
-	 * @return bool
-	 */
-	public function hasMoreResults() {
-		if(empty($this->lastCookie) && $this->lastCookie !== '0') {
-			// as in RFC 2696, when all results are returned, the cookie will
-			// be empty.
-			return false;
-		}
-
-		return true;
-	}
-
-	/**
-	 * set a cookie for LDAP paged search run
-	 * @param string $base a string with the base DN for the search
-	 * @param string $filter the search filter to identify the correct search
-	 * @param int $limit the limit (or 'pageSize'), to identify the correct search well
-	 * @param int $offset the offset for the run search to identify the correct search really good
-	 * @param string $cookie string containing the cookie returned by ldap_control_paged_result_response
-	 * @return void
-	 */
-	private function setPagedResultCookie($base, $filter, $limit, $offset, $cookie) {
-		// allow '0' for 389ds
-		if(!empty($cookie) || $cookie === '0') {
-			$cacheKey = 'lc' . crc32($base) . '-' . crc32($filter) . '-' . (int)$limit . '-' . (int)$offset;
-			$this->cookies[$cacheKey] = $cookie;
-			$this->lastCookie = $cookie;
-		}
-	}
-
-	/**
-	 * Check whether the most recent paged search was successful. It flushed the state var. Use it always after a possible paged search.
-	 * @return boolean|null true on success, null or false otherwise
-	 */
-	public function getPagedSearchResultState() {
-		$result = $this->pagedSearchedSuccessful;
-		$this->pagedSearchedSuccessful = null;
-		return $result;
-	}
-
-	/**
-	 * Prepares a paged search, if possible
-	 *
-	 * @param string $filter the LDAP filter for the search
-	 * @param string[] $bases an array containing the LDAP subtree(s) that shall be searched
-	 * @param string[] $attr optional, when a certain attribute shall be filtered outside
-	 * @param int $limit
-	 * @param int $offset
-	 * @return bool|true
-	 * @throws ServerNotAvailableException
-	 */
-	private function initPagedSearch($filter, $bases, $attr, $limit, $offset) {
-		$pagedSearchOK = false;
-		if ($limit !== 0) {
-			$offset = (int)$offset; //can be null
-			\OCP\Util::writeLog('user_ldap',
-				'initializing paged search for  Filter '.$filter.' base '.print_r($bases, true)
-				.' attr '.print_r($attr, true). ' limit ' .$limit.' offset '.$offset,
-				ILogger::DEBUG);
-			//get the cookie from the search for the previous search, required by LDAP
-			foreach($bases as $base) {
-
-				$cookie = $this->getPagedResultCookie($base, $filter, $limit, $offset);
-				if(empty($cookie) && $cookie !== "0" && ($offset > 0)) {
-					// no cookie known from a potential previous search. We need
-					// to start from 0 to come to the desired page. cookie value
-					// of '0' is valid, because 389ds
-					$reOffset = ($offset - $limit) < 0 ? 0 : $offset - $limit;
-					$this->search($filter, array($base), $attr, $limit, $reOffset, true);
-					$cookie = $this->getPagedResultCookie($base, $filter, $limit, $offset);
-					//still no cookie? obviously, the server does not like us. Let's skip paging efforts.
-					// '0' is valid, because 389ds
-					//TODO: remember this, probably does not change in the next request...
-					if(empty($cookie) && $cookie !== '0') {
-						$cookie = null;
-					}
-				}
-				if(!is_null($cookie)) {
-					//since offset = 0, this is a new search. We abandon other searches that might be ongoing.
-					$this->abandonPagedSearch();
-					$pagedSearchOK = $this->invokeLDAPMethod('controlPagedResult',
-						$this->connection->getConnectionResource(), $limit,
-						false, $cookie);
-					if(!$pagedSearchOK) {
-						return false;
-					}
-					\OCP\Util::writeLog('user_ldap', 'Ready for a paged search', ILogger::DEBUG);
-				} else {
-					$e = new \Exception('No paged search possible, Limit '.$limit.' Offset '.$offset);
-					\OC::$server->getLogger()->logException($e, ['level' => ILogger::DEBUG]);
-				}
-
-			}
-		/* ++ Fixing RHDS searches with pages with zero results ++
+            \OC::$server->getLogger()->info(
+                'Passed string does not resemble a valid GUID. Known UUID ' .
+                '({uuid}) probably does not match UUID configuration.',
+                [ 'app' => 'user_ldap', 'uuid' => $guid ]
+            );
+            return $guid;
+        }
+        for($i=0; $i < 3; $i++) {
+            $pairs = str_split($blocks[$i], 2);
+            $pairs = array_reverse($pairs);
+            $blocks[$i] = implode('', $pairs);
+        }
+        for($i=0; $i < 5; $i++) {
+            $pairs = str_split($blocks[$i], 2);
+            $blocks[$i] = '\\' . implode('\\', $pairs);
+        }
+        return implode('', $blocks);
+    }
+
+    /**
+     * gets a SID of the domain of the given dn
+     *
+     * @param string $dn
+     * @return string|bool
+     * @throws ServerNotAvailableException
+     */
+    public function getSID($dn) {
+        $domainDN = $this->getDomainDNFromDN($dn);
+        $cacheKey = 'getSID-'.$domainDN;
+        $sid = $this->connection->getFromCache($cacheKey);
+        if(!is_null($sid)) {
+            return $sid;
+        }
+
+        $objectSid = $this->readAttribute($domainDN, 'objectsid');
+        if(!is_array($objectSid) || empty($objectSid)) {
+            $this->connection->writeToCache($cacheKey, false);
+            return false;
+        }
+        $domainObjectSid = $this->convertSID2Str($objectSid[0]);
+        $this->connection->writeToCache($cacheKey, $domainObjectSid);
+
+        return $domainObjectSid;
+    }
+
+    /**
+     * converts a binary SID into a string representation
+     * @param string $sid
+     * @return string
+     */
+    public function convertSID2Str($sid) {
+        // The format of a SID binary string is as follows:
+        // 1 byte for the revision level
+        // 1 byte for the number n of variable sub-ids
+        // 6 bytes for identifier authority value
+        // n*4 bytes for n sub-ids
+        //
+        // Example: 010400000000000515000000a681e50e4d6c6c2bca32055f
+        //  Legend: RRNNAAAAAAAAAAAA11111111222222223333333344444444
+        $revision = ord($sid[0]);
+        $numberSubID = ord($sid[1]);
+
+        $subIdStart = 8; // 1 + 1 + 6
+        $subIdLength = 4;
+        if (strlen($sid) !== $subIdStart + $subIdLength * $numberSubID) {
+            // Incorrect number of bytes present.
+            return '';
+        }
+
+        // 6 bytes = 48 bits can be represented using floats without loss of
+        // precision (see https://gist.github.com/bantu/886ac680b0aef5812f71)
+        $iav = number_format(hexdec(bin2hex(substr($sid, 2, 6))), 0, '', '');
+
+        $subIDs = array();
+        for ($i = 0; $i < $numberSubID; $i++) {
+            $subID = unpack('V', substr($sid, $subIdStart + $subIdLength * $i, $subIdLength));
+            $subIDs[] = sprintf('%u', $subID[1]);
+        }
+
+        // Result for example above: S-1-5-21-249921958-728525901-1594176202
+        return sprintf('S-%d-%s-%s', $revision, $iav, implode('-', $subIDs));
+    }
+
+    /**
+     * checks if the given DN is part of the given base DN(s)
+     * @param string $dn the DN
+     * @param string[] $bases array containing the allowed base DN or DNs
+     * @return bool
+     */
+    public function isDNPartOfBase($dn, $bases) {
+        $belongsToBase = false;
+        $bases = $this->helper->sanitizeDN($bases);
+
+        foreach($bases as $base) {
+            $belongsToBase = true;
+            if(mb_strripos($dn, $base, 0, 'UTF-8') !== (mb_strlen($dn, 'UTF-8')-mb_strlen($base, 'UTF-8'))) {
+                $belongsToBase = false;
+            }
+            if($belongsToBase) {
+                break;
+            }
+        }
+        return $belongsToBase;
+    }
+
+    /**
+     * resets a running Paged Search operation
+     *
+     * @throws ServerNotAvailableException
+     */
+    private function abandonPagedSearch() {
+        $cr = $this->connection->getConnectionResource();
+        $this->invokeLDAPMethod('controlPagedResult', $cr, 0, false, $this->lastCookie);
+        $this->getPagedSearchResultState();
+        $this->lastCookie = '';
+        $this->cookies = [];
+    }
+
+    /**
+     * get a cookie for the next LDAP paged search
+     * @param string $base a string with the base DN for the search
+     * @param string $filter the search filter to identify the correct search
+     * @param int $limit the limit (or 'pageSize'), to identify the correct search well
+     * @param int $offset the offset for the new search to identify the correct search really good
+     * @return string containing the key or empty if none is cached
+     */
+    private function getPagedResultCookie($base, $filter, $limit, $offset) {
+        if($offset === 0) {
+            return '';
+        }
+        $offset -= $limit;
+        //we work with cache here
+        $cacheKey = 'lc' . crc32($base) . '-' . crc32($filter) . '-' . (int)$limit . '-' . (int)$offset;
+        $cookie = '';
+        if(isset($this->cookies[$cacheKey])) {
+            $cookie = $this->cookies[$cacheKey];
+            if(is_null($cookie)) {
+                $cookie = '';
+            }
+        }
+        return $cookie;
+    }
+
+    /**
+     * checks whether an LDAP paged search operation has more pages that can be
+     * retrieved, typically when offset and limit are provided.
+     *
+     * Be very careful to use it: the last cookie value, which is inspected, can
+     * be reset by other operations. Best, call it immediately after a search(),
+     * searchUsers() or searchGroups() call. count-methods are probably safe as
+     * well. Don't rely on it with any fetchList-method.
+     * @return bool
+     */
+    public function hasMoreResults() {
+        if(empty($this->lastCookie) && $this->lastCookie !== '0') {
+            // as in RFC 2696, when all results are returned, the cookie will
+            // be empty.
+            return false;
+        }
+
+        return true;
+    }
+
+    /**
+     * set a cookie for LDAP paged search run
+     * @param string $base a string with the base DN for the search
+     * @param string $filter the search filter to identify the correct search
+     * @param int $limit the limit (or 'pageSize'), to identify the correct search well
+     * @param int $offset the offset for the run search to identify the correct search really good
+     * @param string $cookie string containing the cookie returned by ldap_control_paged_result_response
+     * @return void
+     */
+    private function setPagedResultCookie($base, $filter, $limit, $offset, $cookie) {
+        // allow '0' for 389ds
+        if(!empty($cookie) || $cookie === '0') {
+            $cacheKey = 'lc' . crc32($base) . '-' . crc32($filter) . '-' . (int)$limit . '-' . (int)$offset;
+            $this->cookies[$cacheKey] = $cookie;
+            $this->lastCookie = $cookie;
+        }
+    }
+
+    /**
+     * Check whether the most recent paged search was successful. It flushed the state var. Use it always after a possible paged search.
+     * @return boolean|null true on success, null or false otherwise
+     */
+    public function getPagedSearchResultState() {
+        $result = $this->pagedSearchedSuccessful;
+        $this->pagedSearchedSuccessful = null;
+        return $result;
+    }
+
+    /**
+     * Prepares a paged search, if possible
+     *
+     * @param string $filter the LDAP filter for the search
+     * @param string[] $bases an array containing the LDAP subtree(s) that shall be searched
+     * @param string[] $attr optional, when a certain attribute shall be filtered outside
+     * @param int $limit
+     * @param int $offset
+     * @return bool|true
+     * @throws ServerNotAvailableException
+     */
+    private function initPagedSearch($filter, $bases, $attr, $limit, $offset) {
+        $pagedSearchOK = false;
+        if ($limit !== 0) {
+            $offset = (int)$offset; //can be null
+            \OCP\Util::writeLog('user_ldap',
+                'initializing paged search for  Filter '.$filter.' base '.print_r($bases, true)
+                .' attr '.print_r($attr, true). ' limit ' .$limit.' offset '.$offset,
+                ILogger::DEBUG);
+            //get the cookie from the search for the previous search, required by LDAP
+            foreach($bases as $base) {
+
+                $cookie = $this->getPagedResultCookie($base, $filter, $limit, $offset);
+                if(empty($cookie) && $cookie !== "0" && ($offset > 0)) {
+                    // no cookie known from a potential previous search. We need
+                    // to start from 0 to come to the desired page. cookie value
+                    // of '0' is valid, because 389ds
+                    $reOffset = ($offset - $limit) < 0 ? 0 : $offset - $limit;
+                    $this->search($filter, array($base), $attr, $limit, $reOffset, true);
+                    $cookie = $this->getPagedResultCookie($base, $filter, $limit, $offset);
+                    //still no cookie? obviously, the server does not like us. Let's skip paging efforts.
+                    // '0' is valid, because 389ds
+                    //TODO: remember this, probably does not change in the next request...
+                    if(empty($cookie) && $cookie !== '0') {
+                        $cookie = null;
+                    }
+                }
+                if(!is_null($cookie)) {
+                    //since offset = 0, this is a new search. We abandon other searches that might be ongoing.
+                    $this->abandonPagedSearch();
+                    $pagedSearchOK = $this->invokeLDAPMethod('controlPagedResult',
+                        $this->connection->getConnectionResource(), $limit,
+                        false, $cookie);
+                    if(!$pagedSearchOK) {
+                        return false;
+                    }
+                    \OCP\Util::writeLog('user_ldap', 'Ready for a paged search', ILogger::DEBUG);
+                } else {
+                    $e = new \Exception('No paged search possible, Limit '.$limit.' Offset '.$offset);
+                    \OC::$server->getLogger()->logException($e, ['level' => ILogger::DEBUG]);
+                }
+
+            }
+        /* ++ Fixing RHDS searches with pages with zero results ++
 		 * We coudn't get paged searches working with our RHDS for login ($limit = 0),
 		 * due to pages with zero results.
 		 * So we added "&& !empty($this->lastCookie)" to this test to ignore pagination
 		 * if we don't have a previous paged search.
 		 */
-		} else if ($limit === 0 && !empty($this->lastCookie)) {
-			// a search without limit was requested. However, if we do use
-			// Paged Search once, we always must do it. This requires us to
-			// initialize it with the configured page size.
-			$this->abandonPagedSearch();
-			// in case someone set it to 0 … use 500, otherwise no results will
-			// be returned.
-			$pageSize = (int)$this->connection->ldapPagingSize > 0 ? (int)$this->connection->ldapPagingSize : 500;
-			$pagedSearchOK = $this->invokeLDAPMethod('controlPagedResult',
-				$this->connection->getConnectionResource(),
-				$pageSize, false, '');
-		}
-
-		return $pagedSearchOK;
-	}
-
-	/**
-	 * Is more than one $attr used for search?
-	 *
-	 * @param string|string[]|null $attr
-	 * @return bool
-	 */
-	private function manyAttributes($attr): bool {
-		if (\is_array($attr)) {
-			return \count($attr) > 1;
-		}
-		return false;
-	}
+        } else if ($limit === 0 && !empty($this->lastCookie)) {
+            // a search without limit was requested. However, if we do use
+            // Paged Search once, we always must do it. This requires us to
+            // initialize it with the configured page size.
+            $this->abandonPagedSearch();
+            // in case someone set it to 0 … use 500, otherwise no results will
+            // be returned.
+            $pageSize = (int)$this->connection->ldapPagingSize > 0 ? (int)$this->connection->ldapPagingSize : 500;
+            $pagedSearchOK = $this->invokeLDAPMethod('controlPagedResult',
+                $this->connection->getConnectionResource(),
+                $pageSize, false, '');
+        }
+
+        return $pagedSearchOK;
+    }
+
+    /**
+     * Is more than one $attr used for search?
+     *
+     * @param string|string[]|null $attr
+     * @return bool
+     */
+    private function manyAttributes($attr): bool {
+        if (\is_array($attr)) {
+            return \count($attr) > 1;
+        }
+        return false;
+    }
 
 }