nextcloud-server/apps/federatedfilesharing/lib/FederatedShareProvider.php

<?php

/**
 * SPDX-FileCopyrightText: 2016-2024 Nextcloud GmbH and Nextcloud contributors
 * SPDX-FileCopyrightText: 2016 ownCloud, Inc.
 * SPDX-License-Identifier: AGPL-3.0-only
 */
namespace OCA\FederatedFileSharing;

use OC\Share20\Exception\InvalidShare;
use OC\Share20\Share;
use OCP\Constants;
use OCP\DB\QueryBuilder\IQueryBuilder;
use OCP\Federation\ICloudFederationProviderManager;
use OCP\Federation\ICloudIdManager;
use OCP\Files\Folder;
use OCP\Files\IRootFolder;
use OCP\Files\Node;
use OCP\Files\NotFoundException;
use OCP\HintException;
use OCP\IConfig;
use OCP\IDBConnection;
use OCP\IL10N;
use OCP\IUserManager;
use OCP\Share\Exceptions\GenericShareException;
use OCP\Share\Exceptions\ShareNotFound;
use OCP\Share\IShare;
use OCP\Share\IShareProvider;
use Psr\Log\LoggerInterface;

/**
 * Class FederatedShareProvider
 *
 * @package OCA\FederatedFileSharing
 */
class FederatedShareProvider implements IShareProvider {
	public const SHARE_TYPE_REMOTE = 6;

	/** @var string */
	private $externalShareTable = 'share_external';

	/** @var array list of supported share types */
	private $supportedShareType = [IShare::TYPE_REMOTE_GROUP, IShare::TYPE_REMOTE, IShare::TYPE_CIRCLE];

	/**
	 * DefaultShareProvider constructor.
	 */
	public function __construct(
		private IDBConnection $dbConnection,
		private AddressHandler $addressHandler,
		private Notifications $notifications,
		private TokenHandler $tokenHandler,
		private IL10N $l,
		private IRootFolder $rootFolder,
		private IConfig $config,
		private IUserManager $userManager,
		private ICloudIdManager $cloudIdManager,
		private \OCP\GlobalScale\IConfig $gsConfig,
		private ICloudFederationProviderManager $cloudFederationProviderManager,
		private LoggerInterface $logger,
	) {
	}

	/**
	 * Return the identifier of this provider.
	 *
	 * @return string Containing only [a-zA-Z0-9]
	 */
	public function identifier() {
		return 'ocFederatedSharing';
	}

	/**
	 * Share a path
	 *
	 * @param IShare $share
	 * @return IShare The share object
	 * @throws ShareNotFound
	 * @throws \Exception
	 */
	public function create(IShare $share) {
		$shareWith = $share->getSharedWith();
		$itemSource = $share->getNodeId();
		$itemType = $share->getNodeType();
		$permissions = $share->getPermissions();
		$sharedBy = $share->getSharedBy();
		$shareType = $share->getShareType();
		$expirationDate = $share->getExpirationDate();

		if ($shareType === IShare::TYPE_REMOTE_GROUP &&
			!$this->isOutgoingServer2serverGroupShareEnabled()
		) {
			$message = 'It is not allowed to send federated group shares from this server.';
			$message_t = $this->l->t('It is not allowed to send federated group shares from this server.');
			$this->logger->debug($message, ['app' => 'Federated File Sharing']);
			throw new \Exception($message_t);
		}

		/*
		 * Check if file is not already shared with the remote user
		 */
		$alreadyShared = $this->getSharedWith($shareWith, IShare::TYPE_REMOTE, $share->getNode(), 1, 0);
		$alreadySharedGroup = $this->getSharedWith($shareWith, IShare::TYPE_REMOTE_GROUP, $share->getNode(), 1, 0);
		if (!empty($alreadyShared) || !empty($alreadySharedGroup)) {
			$message = 'Sharing %1$s failed, because this item is already shared with %2$s';
			$message_t = $this->l->t('Sharing %1$s failed, because this item is already shared with the account %2$s', [$share->getNode()->getName(), $shareWith]);
			$this->logger->debug(sprintf($message, $share->getNode()->getName(), $shareWith), ['app' => 'Federated File Sharing']);
			throw new \Exception($message_t);
		}


		// don't allow federated shares if source and target server are the same
		$cloudId = $this->cloudIdManager->resolveCloudId($shareWith);
		$currentServer = $this->addressHandler->generateRemoteURL();
		$currentUser = $sharedBy;
		if ($this->addressHandler->compareAddresses($cloudId->getUser(), $cloudId->getRemote(), $currentUser, $currentServer)) {
			$message = 'Not allowed to create a federated share to the same account.';
			$message_t = $this->l->t('Not allowed to create a federated share to the same account');
			$this->logger->debug($message, ['app' => 'Federated File Sharing']);
			throw new \Exception($message_t);
		}

		// Federated shares always have read permissions
		if (($share->getPermissions() & Constants::PERMISSION_READ) === 0) {
			$message = 'Federated shares require read permissions';
			$message_t = $this->l->t('Federated shares require read permissions');
			$this->logger->debug($message, ['app' => 'Federated File Sharing']);
			throw new \Exception($message_t);
		}

		$share->setSharedWith($cloudId->getId());

		try {
			$remoteShare = $this->getShareFromExternalShareTable($share);
		} catch (ShareNotFound $e) {
			$remoteShare = null;
		}

		if ($remoteShare) {
			try {
				$ownerCloudId = $this->cloudIdManager->getCloudId($remoteShare['owner'], $remoteShare['remote']);
				$shareId = $this->addShareToDB($itemSource, $itemType, $shareWith, $sharedBy, $ownerCloudId->getId(), $permissions, 'tmp_token_' . time(), $shareType, $expirationDate);
				$share->setId($shareId);
				[$token, $remoteId] = $this->askOwnerToReShare($shareWith, $share, $shareId);
				// remote share was create successfully if we get a valid token as return
				$send = is_string($token) && $token !== '';
			} catch (\Exception $e) {
				// fall back to old re-share behavior if the remote server
				// doesn't support flat re-shares (was introduced with Nextcloud 9.1)
				$this->removeShareFromTable($share);
				$shareId = $this->createFederatedShare($share);
			}
			if ($send) {
				$this->updateSuccessfulReshare($shareId, $token);
				$this->storeRemoteId($shareId, $remoteId);
			} else {
				$this->removeShareFromTable($share);
				$message_t = $this->l->t('File is already shared with %s', [$shareWith]);
				throw new \Exception($message_t);
			}
		} else {
			$shareId = $this->createFederatedShare($share);
		}

		$data = $this->getRawShare($shareId);
		return $this->createShareObject($data);
	}

	/**
	 * create federated share and inform the recipient
	 *
	 * @param IShare $share
	 * @return int
	 * @throws ShareNotFound
	 * @throws \Exception
	 */
	protected function createFederatedShare(IShare $share) {
		$token = $this->tokenHandler->generateToken();
		$shareId = $this->addShareToDB(
			$share->getNodeId(),
			$share->getNodeType(),
			$share->getSharedWith(),
			$share->getSharedBy(),
			$share->getShareOwner(),
			$share->getPermissions(),
			$token,
			$share->getShareType(),
			$share->getExpirationDate()
		);

		$failure = false;

		try {
			$sharedByFederatedId = $share->getSharedBy();
			if ($this->userManager->userExists($sharedByFederatedId)) {
				$cloudId = $this->cloudIdManager->getCloudId($sharedByFederatedId, $this->addressHandler->generateRemoteURL());
				$sharedByFederatedId = $cloudId->getId();
			}
			$ownerCloudId = $this->cloudIdManager->getCloudId($share->getShareOwner(), $this->addressHandler->generateRemoteURL());
			$send = $this->notifications->sendRemoteShare(
				$token,
				$share->getSharedWith(),
				$share->getNode()->getName(),
				$shareId,
				$share->getShareOwner(),
				$ownerCloudId->getId(),
				$share->getSharedBy(),
				$sharedByFederatedId,
				$share->getShareType()
			);

			if ($send === false) {
				$failure = true;
			}
		} catch (\Exception $e) {
			$this->logger->error('Failed to notify remote server of federated share, removing share.', [
				'app' => 'federatedfilesharing',
				'exception' => $e,
			]);
			$failure = true;
		}

		if ($failure) {
			$this->removeShareFromTableById($shareId);
			$message_t = $this->l->t('Sharing %1$s failed, could not find %2$s, maybe the server is currently unreachable or uses a self-signed certificate.',
				[$share->getNode()->getName(), $share->getSharedWith()]);
			throw new \Exception($message_t);
		}

		return $shareId;
	}

	/**
	 * @param string $shareWith
	 * @param IShare $share
	 * @param string $shareId internal share Id
	 * @return array
	 * @throws \Exception
	 */
	protected function askOwnerToReShare($shareWith, IShare $share, $shareId) {
		$remoteShare = $this->getShareFromExternalShareTable($share);
		$token = $remoteShare['share_token'];
		$remoteId = $remoteShare['remote_id'];
		$remote = $remoteShare['remote'];

		[$token, $remoteId] = $this->notifications->requestReShare(
			$token,
			$remoteId,
			$shareId,
			$remote,
			$shareWith,
			$share->getPermissions(),
			$share->getNode()->getName()
		);

		return [$token, $remoteId];
	}

	/**
	 * get federated share from the share_external table but exclude mounted link shares
	 *
	 * @param IShare $share
	 * @return array
	 * @throws ShareNotFound
	 */
	protected function getShareFromExternalShareTable(IShare $share) {
		$query = $this->dbConnection->getQueryBuilder();
		$query->select('*')->from($this->externalShareTable)
			->where($query->expr()->eq('user', $query->createNamedParameter($share->getShareOwner())))
			->andWhere($query->expr()->eq('mountpoint', $query->createNamedParameter($share->getTarget())));
		$qResult = $query->executeQuery();
		$result = $qResult->fetchAll();
		$qResult->closeCursor();

		if (isset($result[0]) && (int)$result[0]['remote_id'] > 0) {
			return $result[0];
		}

		throw new ShareNotFound('share not found in share_external table');
	}

	/**
	 * add share to the database and return the ID
	 *
	 * @param int $itemSource
	 * @param string $itemType
	 * @param string $shareWith
	 * @param string $sharedBy
	 * @param string $uidOwner
	 * @param int $permissions
	 * @param string $token
	 * @param int $shareType
	 * @param \DateTime $expirationDate
	 * @return int
	 */
	private function addShareToDB($itemSource, $itemType, $shareWith, $sharedBy, $uidOwner, $permissions, $token, $shareType, $expirationDate) {
		$qb = $this->dbConnection->getQueryBuilder();
		$qb->insert('share')
			->setValue('share_type', $qb->createNamedParameter($shareType))
			->setValue('item_type', $qb->createNamedParameter($itemType))
			->setValue('item_source', $qb->createNamedParameter($itemSource))
			->setValue('file_source', $qb->createNamedParameter($itemSource))
			->setValue('share_with', $qb->createNamedParameter($shareWith))
			->setValue('uid_owner', $qb->createNamedParameter($uidOwner))
			->setValue('uid_initiator', $qb->createNamedParameter($sharedBy))
			->setValue('permissions', $qb->createNamedParameter($permissions))
			->setValue('expiration', $qb->createNamedParameter($expirationDate, IQueryBuilder::PARAM_DATETIME_MUTABLE))
			->setValue('token', $qb->createNamedParameter($token))
			->setValue('stime', $qb->createNamedParameter(time()));

		/*
		 * Added to fix https://github.com/owncloud/core/issues/22215
		 * Can be removed once we get rid of ajax/share.php
		 */
		$qb->setValue('file_target', $qb->createNamedParameter(''));

		$qb->executeStatement();
		return $qb->getLastInsertId();
	}

	/**
	 * Update a share
	 *
	 * @param IShare $share
	 * @return IShare The share object
	 */
	public function update(IShare $share) {
		/*
		 * We allow updating the permissions of federated shares
		 */
		$qb = $this->dbConnection->getQueryBuilder();
		$qb->update('share')
			->where($qb->expr()->eq('id', $qb->createNamedParameter($share->getId())))
			->set('permissions', $qb->createNamedParameter($share->getPermissions()))
			->set('uid_owner', $qb->createNamedParameter($share->getShareOwner()))
			->set('uid_initiator', $qb->createNamedParameter($share->getSharedBy()))
			->set('expiration', $qb->createNamedParameter($share->getExpirationDate(), IQueryBuilder::PARAM_DATETIME_MUTABLE))
			->executeStatement();

		// send the updated permission to the owner/initiator, if they are not the same
		if ($share->getShareOwner() !== $share->getSharedBy()) {
			$this->sendPermissionUpdate($share);
		}

		return $share;
	}

	/**
	 * send the updated permission to the owner/initiator, if they are not the same
	 *
	 * @param IShare $share
	 * @throws ShareNotFound
	 * @throws HintException
	 */
	protected function sendPermissionUpdate(IShare $share) {
		$remoteId = $this->getRemoteId($share);
		// if the local user is the owner we send the permission change to the initiator
		if ($this->userManager->userExists($share->getShareOwner())) {
			[, $remote] = $this->addressHandler->splitUserRemote($share->getSharedBy());
		} else { // ... if not we send the permission change to the owner
			[, $remote] = $this->addressHandler->splitUserRemote($share->getShareOwner());
		}
		$this->notifications->sendPermissionChange($remote, $remoteId, $share->getToken(), $share->getPermissions());
	}


	/**
	 * update successful reShare with the correct token
	 *
	 * @param int $shareId
	 * @param string $token
	 */
	protected function updateSuccessfulReShare($shareId, $token) {
		$query = $this->dbConnection->getQueryBuilder();
		$query->update('share')
			->where($query->expr()->eq('id', $query->createNamedParameter($shareId)))
			->set('token', $query->createNamedParameter($token))
			->executeStatement();
	}

	/**
	 * store remote ID in federated reShare table
	 *
	 * @param $shareId
	 * @param $remoteId
	 */
	public function storeRemoteId(int $shareId, string $remoteId): void {
		$query = $this->dbConnection->getQueryBuilder();
		$query->insert('federated_reshares')
			->values(
				[
					'share_id' => $query->createNamedParameter($shareId),
					'remote_id' => $query->createNamedParameter($remoteId),
				]
			);
		$query->executeStatement();
	}

	/**
	 * get share ID on remote server for federated re-shares
	 *
	 * @param IShare $share
	 * @return string
	 * @throws ShareNotFound
	 */
	public function getRemoteId(IShare $share): string {
		$query = $this->dbConnection->getQueryBuilder();
		$query->select('remote_id')->from('federated_reshares')
			->where($query->expr()->eq('share_id', $query->createNamedParameter((int)$share->getId())));
		$result = $query->executeQuery();
		$data = $result->fetch();
		$result->closeCursor();

		if (!is_array($data) || !isset($data['remote_id'])) {
			throw new ShareNotFound();
		}

		return (string)$data['remote_id'];
	}

	/**
	 * @inheritdoc
	 */
	public function move(IShare $share, $recipient) {
		/*
		 * This function does nothing yet as it is just for outgoing
		 * federated shares.
		 */
		return $share;
	}

	/**
	 * Get all children of this share
	 *
	 * @param IShare $parent
	 * @return IShare[]
	 */
	public function getChildren(IShare $parent) {
		$children = [];

		$qb = $this->dbConnection->getQueryBuilder();
		$qb->select('*')
			->from('share')
			->where($qb->expr()->eq('parent', $qb->createNamedParameter($parent->getId())))
			->andWhere($qb->expr()->in('share_type', $qb->createNamedParameter($this->supportedShareType, IQueryBuilder::PARAM_INT_ARRAY)))
			->orderBy('id');

		$cursor = $qb->executeQuery();
		while ($data = $cursor->fetch()) {
			$children[] = $this->createShareObject($data);
		}
		$cursor->closeCursor();

		return $children;
	}

	/**
	 * Delete a share (owner unShares the file)
	 *
	 * @param IShare $share
	 * @throws ShareNotFound
	 * @throws HintException
	 */
	public function delete(IShare $share) {
		[, $remote] = $this->addressHandler->splitUserRemote($share->getSharedWith());

		// if the local user is the owner we can send the unShare request directly...
		if ($this->userManager->userExists($share->getShareOwner())) {
			$this->notifications->sendRemoteUnShare($remote, $share->getId(), $share->getToken());
			$this->revokeShare($share, true);
		} else { // ... if not we need to correct ID for the unShare request
			$remoteId = $this->getRemoteId($share);
			$this->notifications->sendRemoteUnShare($remote, $remoteId, $share->getToken());
			$this->revokeShare($share, false);
		}

		// only remove the share when all messages are send to not lose information
		// about the share to early
		$this->removeShareFromTable($share);
	}

	/**
	 * in case of a re-share we need to send the other use (initiator or owner)
	 * a message that the file was unshared
	 *
	 * @param IShare $share
	 * @param bool $isOwner the user can either be the owner or the user who re-sahred it
	 * @throws ShareNotFound
	 * @throws HintException
	 */
	protected function revokeShare($share, $isOwner) {
		if ($this->userManager->userExists($share->getShareOwner()) && $this->userManager->userExists($share->getSharedBy())) {
			// If both the owner and the initiator of the share are local users we don't have to notify anybody else
			return;
		}

		// also send a unShare request to the initiator, if this is a different user than the owner
		if ($share->getShareOwner() !== $share->getSharedBy()) {
			if ($isOwner) {
				[, $remote] = $this->addressHandler->splitUserRemote($share->getSharedBy());
			} else {
				[, $remote] = $this->addressHandler->splitUserRemote($share->getShareOwner());
			}
			$remoteId = $this->getRemoteId($share);
			$this->notifications->sendRevokeShare($remote, $remoteId, $share->getToken());
		}
	}

	/**
	 * remove share from table
	 *
	 * @param IShare $share
	 */
	public function removeShareFromTable(IShare $share) {
		$this->removeShareFromTableById($share->getId());
	}

	/**
	 * remove share from table
	 *
	 * @param string $shareId
	 */
	private function removeShareFromTableById($shareId) {
		$qb = $this->dbConnection->getQueryBuilder();
		$qb->delete('share')
			->where($qb->expr()->eq('id', $qb->createNamedParameter($shareId)))
			->andWhere($qb->expr()->neq('share_type', $qb->createNamedParameter(IShare::TYPE_CIRCLE)));
		$qb->executeStatement();

		$qb = $this->dbConnection->getQueryBuilder();
		$qb->delete('federated_reshares')
			->where($qb->expr()->eq('share_id', $qb->createNamedParameter($shareId)));
		$qb->executeStatement();
	}

	/**
	 * @inheritdoc
	 */
	public function deleteFromSelf(IShare $share, $recipient) {
		// nothing to do here. Technically deleteFromSelf in the context of federated
		// shares is a umount of an external storage. This is handled here
		// apps/files_sharing/lib/external/manager.php
		// TODO move this code over to this app
	}

	public function restore(IShare $share, string $recipient): IShare {
		throw new GenericShareException('not implemented');
	}


	public function getSharesInFolder($userId, Folder $node, $reshares, $shallow = true) {
		if (!$shallow) {
			throw new \Exception('non-shallow getSharesInFolder is no longer supported');
		}

		$qb = $this->dbConnection->getQueryBuilder();
		$qb->select('*')
			->from('share', 's')
			->andWhere($qb->expr()->orX(
				$qb->expr()->eq('item_type', $qb->createNamedParameter('file')),
				$qb->expr()->eq('item_type', $qb->createNamedParameter('folder'))
			))
			->andWhere(
				$qb->expr()->eq('share_type', $qb->createNamedParameter(IShare::TYPE_REMOTE))
			);

		/**
		 * Reshares for this user are shares where they are the owner.
		 */
		if ($reshares === false) {
			$qb->andWhere($qb->expr()->eq('uid_initiator', $qb->createNamedParameter($userId)));
		} else {
			$qb->andWhere(
				$qb->expr()->orX(
					$qb->expr()->eq('uid_owner', $qb->createNamedParameter($userId)),
					$qb->expr()->eq('uid_initiator', $qb->createNamedParameter($userId))
				)
			);
		}

		$qb->innerJoin('s', 'filecache', 'f', $qb->expr()->eq('s.file_source', 'f.fileid'));

		$qb->andWhere($qb->expr()->eq('f.parent', $qb->createNamedParameter($node->getId())));

		$qb->orderBy('id');

		$cursor = $qb->executeQuery();
		$shares = [];
		while ($data = $cursor->fetch()) {
			$shares[$data['fileid']][] = $this->createShareObject($data);
		}
		$cursor->closeCursor();

		return $shares;
	}

	/**
	 * @inheritdoc
	 */
	public function getSharesBy($userId, $shareType, $node, $reshares, $limit, $offset) {
		$qb = $this->dbConnection->getQueryBuilder();
		$qb->select('*')
			->from('share');

		$qb->andWhere($qb->expr()->eq('share_type', $qb->createNamedParameter($shareType)));

		/**
		 * Reshares for this user are shares where they are the owner.
		 */
		if ($reshares === false) {
			//Special case for old shares created via the web UI
			$or1 = $qb->expr()->andX(
				$qb->expr()->eq('uid_owner', $qb->createNamedParameter($userId)),
				$qb->expr()->isNull('uid_initiator')
			);

			$qb->andWhere(
				$qb->expr()->orX(
					$qb->expr()->eq('uid_initiator', $qb->createNamedParameter($userId)),
					$or1
				)
			);
		} else {
			$qb->andWhere(
				$qb->expr()->orX(
					$qb->expr()->eq('uid_owner', $qb->createNamedParameter($userId)),
					$qb->expr()->eq('uid_initiator', $qb->createNamedParameter($userId))
				)
			);
		}

		if ($node !== null) {
			$qb->andWhere($qb->expr()->eq('file_source', $qb->createNamedParameter($node->getId())));
		}

		if ($limit !== -1) {
			$qb->setMaxResults($limit);
		}

		$qb->setFirstResult($offset);
		$qb->orderBy('id');

		$cursor = $qb->executeQuery();
		$shares = [];
		while ($data = $cursor->fetch()) {
			$shares[] = $this->createShareObject($data);
		}
		$cursor->closeCursor();

		return $shares;
	}

	/**
	 * @inheritdoc
	 */
	public function getShareById($id, $recipientId = null) {
		$qb = $this->dbConnection->getQueryBuilder();

		$qb->select('*')
			->from('share')
			->where($qb->expr()->eq('id', $qb->createNamedParameter($id)))
			->andWhere($qb->expr()->in('share_type', $qb->createNamedParameter($this->supportedShareType, IQueryBuilder::PARAM_INT_ARRAY)));

		$cursor = $qb->executeQuery();
		$data = $cursor->fetch();
		$cursor->closeCursor();

		if ($data === false) {
			throw new ShareNotFound('Can not find share with ID: ' . $id);
		}

		try {
			$share = $this->createShareObject($data);
		} catch (InvalidShare $e) {
			throw new ShareNotFound();
		}

		return $share;
	}

	/**
	 * Get shares for a given path
	 *
	 * @param Node $path
	 * @return IShare[]
	 */
	public function getSharesByPath(Node $path) {
		$qb = $this->dbConnection->getQueryBuilder();

		// get federated user shares
		$cursor = $qb->select('*')
			->from('share')
			->andWhere($qb->expr()->eq('file_source', $qb->createNamedParameter($path->getId())))
			->andWhere($qb->expr()->in('share_type', $qb->createNamedParameter($this->supportedShareType, IQueryBuilder::PARAM_INT_ARRAY)))
			->executeQuery();

		$shares = [];
		while ($data = $cursor->fetch()) {
			$shares[] = $this->createShareObject($data);
		}
		$cursor->closeCursor();

		return $shares;
	}

	/**
	 * @inheritdoc
	 */
	public function getSharedWith($userId, $shareType, $node, $limit, $offset) {
		/** @var IShare[] $shares */
		$shares = [];

		//Get shares directly with this user
		$qb = $this->dbConnection->getQueryBuilder();
		$qb->select('*')
			->from('share');

		// Order by id
		$qb->orderBy('id');

		// Set limit and offset
		if ($limit !== -1) {
			$qb->setMaxResults($limit);
		}
		$qb->setFirstResult($offset);

		$qb->where($qb->expr()->in('share_type', $qb->createNamedParameter($this->supportedShareType, IQueryBuilder::PARAM_INT_ARRAY)));
		$qb->andWhere($qb->expr()->eq('share_with', $qb->createNamedParameter($userId)));

		// Filter by node if provided
		if ($node !== null) {
			$qb->andWhere($qb->expr()->eq('file_source', $qb->createNamedParameter($node->getId())));
		}

		$cursor = $qb->executeQuery();

		while ($data = $cursor->fetch()) {
			$shares[] = $this->createShareObject($data);
		}
		$cursor->closeCursor();


		return $shares;
	}

	/**
	 * Get a share by token
	 *
	 * @param string $token
	 * @return IShare
	 * @throws ShareNotFound
	 */
	public function getShareByToken($token) {
		$qb = $this->dbConnection->getQueryBuilder();

		$cursor = $qb->select('*')
			->from('share')
			->where($qb->expr()->in('share_type', $qb->createNamedParameter($this->supportedShareType, IQueryBuilder::PARAM_INT_ARRAY)))
			->andWhere($qb->expr()->eq('token', $qb->createNamedParameter($token)))
			->executeQuery();

		$data = $cursor->fetch();

		if ($data === false) {
			throw new ShareNotFound('Share not found', $this->l->t('Could not find share'));
		}

		try {
			$share = $this->createShareObject($data);
		} catch (InvalidShare $e) {
			throw new ShareNotFound('Share not found', $this->l->t('Could not find share'));
		}

		return $share;
	}

	/**
	 * get database row of a give share
	 *
	 * @param $id
	 * @return array
	 * @throws ShareNotFound
	 */
	private function getRawShare($id) {
		// Now fetch the inserted share and create a complete share object
		$qb = $this->dbConnection->getQueryBuilder();
		$qb->select('*')
			->from('share')
			->where($qb->expr()->eq('id', $qb->createNamedParameter($id)));

		$cursor = $qb->executeQuery();
		$data = $cursor->fetch();
		$cursor->closeCursor();

		if ($data === false) {
			throw new ShareNotFound;
		}

		return $data;
	}

	/**
	 * Create a share object from an database row
	 *
	 * @param array $data
	 * @return IShare
	 * @throws InvalidShare
	 * @throws ShareNotFound
	 */
	private function createShareObject($data) {
		$share = new Share($this->rootFolder, $this->userManager);
		$share->setId((int)$data['id'])
			->setShareType((int)$data['share_type'])
			->setPermissions((int)$data['permissions'])
			->setTarget($data['file_target'])
			->setMailSend((bool)$data['mail_send'])
			->setToken($data['token']);

		$shareTime = new \DateTime();
		$shareTime->setTimestamp((int)$data['stime']);
		$share->setShareTime($shareTime);
		$share->setSharedWith($data['share_with']);

		if ($data['uid_initiator'] !== null) {
			$share->setShareOwner($data['uid_owner']);
			$share->setSharedBy($data['uid_initiator']);
		} else {
			//OLD SHARE
			$share->setSharedBy($data['uid_owner']);
			$path = $this->getNode($share->getSharedBy(), (int)$data['file_source']);

			$owner = $path->getOwner();
			$share->setShareOwner($owner->getUID());
		}

		$share->setNodeId((int)$data['file_source']);
		$share->setNodeType($data['item_type']);

		$share->setProviderId($this->identifier());

		if ($data['expiration'] !== null) {
			$expiration = \DateTime::createFromFormat('Y-m-d H:i:s', $data['expiration']);
			$share->setExpirationDate($expiration);
		}

		return $share;
	}

	/**
	 * Get the node with file $id for $user
	 *
	 * @param string $userId
	 * @param int $id
	 * @return Node
	 * @throws InvalidShare
	 */
	private function getNode($userId, $id) {
		try {
			$userFolder = $this->rootFolder->getUserFolder($userId);
		} catch (NotFoundException $e) {
			throw new InvalidShare();
		}

		$node = $userFolder->getFirstNodeById($id);

		if (!$node) {
			throw new InvalidShare();
		}

		return $node;
	}

	/**
	 * A user is deleted from the system
	 * So clean up the relevant shares.
	 *
	 * @param string $uid
	 * @param int $shareType
	 */
	public function userDeleted($uid, $shareType) {
		//TODO: probably a good idea to send unshare info to remote servers

		$qb = $this->dbConnection->getQueryBuilder();

		$qb->delete('share')
			->where($qb->expr()->eq('share_type', $qb->createNamedParameter(IShare::TYPE_REMOTE)))
			->andWhere($qb->expr()->eq('uid_owner', $qb->createNamedParameter($uid)))
			->executeStatement();
	}

	/**
	 * This provider does not handle groups
	 *
	 * @param string $gid
	 */
	public function groupDeleted($gid) {
		// We don't handle groups here
	}

	/**
	 * This provider does not handle groups
	 *
	 * @param string $uid
	 * @param string $gid
	 */
	public function userDeletedFromGroup($uid, $gid) {
		// We don't handle groups here
	}

	/**
	 * check if users from other Nextcloud instances are allowed to mount public links share by this instance
	 *
	 * @return bool
	 */
	public function isOutgoingServer2serverShareEnabled() {
		if ($this->gsConfig->onlyInternalFederation()) {
			return false;
		}
		$result = $this->config->getAppValue('files_sharing', 'outgoing_server2server_share_enabled', 'yes');
		return ($result === 'yes');
	}

	/**
	 * check if users are allowed to mount public links from other Nextclouds
	 *
	 * @return bool
	 */
	public function isIncomingServer2serverShareEnabled() {
		if ($this->gsConfig->onlyInternalFederation()) {
			return false;
		}
		$result = $this->config->getAppValue('files_sharing', 'incoming_server2server_share_enabled', 'yes');
		return ($result === 'yes');
	}


	/**
	 * check if users from other Nextcloud instances are allowed to send federated group shares
	 *
	 * @return bool
	 */
	public function isOutgoingServer2serverGroupShareEnabled() {
		if ($this->gsConfig->onlyInternalFederation()) {
			return false;
		}
		$result = $this->config->getAppValue('files_sharing', 'outgoing_server2server_group_share_enabled', 'no');
		return ($result === 'yes');
	}

	/**
	 * check if users are allowed to receive federated group shares
	 *
	 * @return bool
	 */
	public function isIncomingServer2serverGroupShareEnabled() {
		if ($this->gsConfig->onlyInternalFederation()) {
			return false;
		}
		$result = $this->config->getAppValue('files_sharing', 'incoming_server2server_group_share_enabled', 'no');
		return ($result === 'yes');
	}

	/**
	 * check if federated group sharing is supported, therefore the OCM API need to be enabled
	 *
	 * @return bool
	 */
	public function isFederatedGroupSharingSupported() {
		return $this->cloudFederationProviderManager->isReady();
	}

	/**
	 * Check if querying sharees on the lookup server is enabled
	 *
	 * @return bool
	 */
	public function isLookupServerQueriesEnabled() {
		// in a global scale setup we should always query the lookup server
		if ($this->gsConfig->isGlobalScaleEnabled()) {
			return true;
		}
		$result = $this->config->getAppValue('files_sharing', 'lookupServerEnabled', 'yes');
		return ($result === 'yes');
	}


	/**
	 * Check if it is allowed to publish user specific data to the lookup server
	 *
	 * @return bool
	 */
	public function isLookupServerUploadEnabled() {
		// in a global scale setup the admin is responsible to keep the lookup server up-to-date
		if ($this->gsConfig->isGlobalScaleEnabled()) {
			return false;
		}
		$result = $this->config->getAppValue('files_sharing', 'lookupServerUploadEnabled', 'yes');
		return ($result === 'yes');
	}

	/**
	 * @inheritdoc
	 */
	public function getAccessList($nodes, $currentAccess) {
		$ids = [];
		foreach ($nodes as $node) {
			$ids[] = $node->getId();
		}

		$qb = $this->dbConnection->getQueryBuilder();
		$qb->select('share_with', 'token', 'file_source')
			->from('share')
			->where($qb->expr()->eq('share_type', $qb->createNamedParameter(IShare::TYPE_REMOTE)))
			->andWhere($qb->expr()->in('file_source', $qb->createNamedParameter($ids, IQueryBuilder::PARAM_INT_ARRAY)))
			->andWhere($qb->expr()->orX(
				$qb->expr()->eq('item_type', $qb->createNamedParameter('file')),
				$qb->expr()->eq('item_type', $qb->createNamedParameter('folder'))
			));
		$cursor = $qb->executeQuery();

		if ($currentAccess === false) {
			$remote = $cursor->fetch() !== false;
			$cursor->closeCursor();

			return ['remote' => $remote];
		}

		$remote = [];
		while ($row = $cursor->fetch()) {
			$remote[$row['share_with']] = [
				'node_id' => $row['file_source'],
				'token' => $row['token'],
			];
		}
		$cursor->closeCursor();

		return ['remote' => $remote];
	}

	public function getAllShares(): iterable {
		$qb = $this->dbConnection->getQueryBuilder();

		$qb->select('*')
			->from('share')
			->where(
				$qb->expr()->orX(
					$qb->expr()->eq('share_type', $qb->createNamedParameter(IShare::TYPE_REMOTE)),
					$qb->expr()->eq('share_type', $qb->createNamedParameter(IShare::TYPE_REMOTE_GROUP))
				)
			);

		$cursor = $qb->executeQuery();
		while ($data = $cursor->fetch()) {
			try {
				$share = $this->createShareObject($data);
			} catch (InvalidShare $e) {
				continue;
			} catch (ShareNotFound $e) {
				continue;
			}

			yield $share;
		}
		$cursor->closeCursor();
	}
}