fix(sharing): do not notify remote if owner and sharee are local users

If both the owner and the sharee are local users, no remote notification is required.
If either the owner or the sharee is not a local user, the change must be propagated.

Based on owncloud/core#37534

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>
Co-authored-by: Victor Dubiniuk <victor.dubiniuk@gmail.com>

Author: kesselb

apps/federatedfilesharing/lib/FederatedShareProvider.php

@@ -339,14 +339,29 @@ public function update(IShare $share) {
 			->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() !== $share->getSharedBy()) {
+		/*
+		 * If the share owner and share initiator are on the same instance,
+		 * then we're done here as the share was just updated above.
+		 *
+		 * However, if the share owner/sharee is on a remote instance (and thus we're dealing with a federated share),
+		 * then we are supposed to let the share owner/ sharee on the remote instance know.
+		 */
+		if ($this->shouldNotifyRemote($share)) {
 			$this->sendPermissionUpdate($share);
 		}
 
 		return $share;
 	}
 
+	/**
+	 * Notify owner/sharee if they are not the same and ANY of them is a remote user.
+	 */
+	protected function shouldNotifyRemote(IShare $share): bool {
+		$ownerOrSharerIsRemoteUser = !$this->userManager->userExists($share->getShareOwner())
+			|| !$this->userManager->userExists($share->getSharedBy());
+		return $ownerOrSharerIsRemoteUser && $share->getShareOwner() !== $share->getSharedBy();
+	}
+
 	/**
 	 * send the updated permission to the owner/initiator, if they are not the same
 	 *
@@ -485,13 +500,8 @@ public function delete(IShare $share) {
 	 * @throws HintException
 	 */
 	protected function revokeShare($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() !== $share->getSharedBy()) {
+		if ($this->shouldNotifyRemote($share)) {
 			if ($isOwner) {
 				[, $remote] = $this->addressHandler->splitUserRemote($share->getSharedBy());
 			} else {