Folders not shown - Error 500 - unavailable federated share

Expected behaviour

Application shows all my folders

Actual behaviour

Application only shows my favorites and, an error is shown "500: Internal server error".

I believe this issue is also the cause of various slowdowns in my application

Steps to reproduce

1- create a share on serverA and share it with serverB
2- once confirmed the share is accessible on serverB and synchronised on your iOS client, shutdown serverA

Additional information

The following log line appears on the server's log when I open my iOS app:

{
  "reqId": "CAQq2Zh6BXg4h7K4M4uy",
  "level": 0,
  "time": "2020-07-14T12:15:17+00:00",
  "remoteAddr": "94.104.124.217",
  "user": "cyrille",
  "app": "webdav",
  "method": "PROPFIND",
  "url": "/remote.php/webdav/",
  "message": "{\"Exception\":\"OCP\\\\Files\\\\StorageNotAvailableException\",\"Message\":\"\",\"Code\":1,\"Trace\":[{\"file\":\"/var/www/nextcloud/lib/private/Files/Storage/Wrapper/Availability.php\",\"line\":243,\"function\":\"checkAvailability\",\"class\":\"OC\\\\Files\\\\Storage\\\\Wrapper\\\\Availability\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/lib/private/Files/Storage/Wrapper/Wrapper.php\",\"line\":226,\"function\":\"file_exists\",\"class\":\"OC\\\\Files\\\\Storage\\\\Wrapper\\\\Availability\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/lib/private/Files/View.php\",\"line\":1334,\"function\":\"file_exists\",\"class\":\"OC\\\\Files\\\\Storage\\\\Wrapper\\\\Wrapper\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/lib/private/Files/View.php\",\"line\":1383,\"function\":\"getCacheEntry\",\"class\":\"OC\\\\Files\\\\View\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/lib/private/Files/Node/Root.php\",\"line\":201,\"function\":\"getFileInfo\",\"class\":\"OC\\\\Files\\\\View\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/lib/private/Files/Node/Folder.php\",\"line\":138,\"function\":\"get\",\"class\":\"OC\\\\Files\\\\Node\\\\Root\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/lib/private/Files/Node/Folder.php\",\"line\":147,\"function\":\"get\",\"class\":\"OC\\\\Files\\\\Node\\\\Folder\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/apps/text/lib/Service/WorkspaceService.php\",\"line\":28,\"function\":\"nodeExists\",\"class\":\"OC\\\\Files\\\\Node\\\\Folder\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/apps/text/lib/DAV/WorkspacePlugin.php\",\"line\":101,\"function\":\"getFile\",\"class\":\"OCA\\\\Text\\\\Service\\\\WorkspaceService\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/PropFind.php\",\"line\":96,\"function\":\"OCA\\\\Text\\\\DAV\\\\{closure}\",\"class\":\"OCA\\\\Text\\\\DAV\\\\WorkspacePlugin\",\"type\":\"->\",\"args\":[\"*** sensitive parameters replaced ***\"]},{\"file\":\"/var/www/nextcloud/apps/text/lib/DAV/WorkspacePlugin.php\",\"line\":107,\"function\":\"handle\",\"class\":\"Sabre\\\\DAV\\\\PropFind\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/3rdparty/sabre/event/lib/WildcardEmitterTrait.php\",\"line\":89,\"function\":\"propFind\",\"class\":\"OCA\\\\Text\\\\DAV\\\\WorkspacePlugin\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php\",\"line\":1063,\"function\":\"emit\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php\",\"line\":989,\"function\":\"getPropertiesByNode\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php\",\"line\":1678,\"function\":\"getPropertiesIteratorForPath\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php\",\"line\":1661,\"function\":\"writeMultiStatus\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/CorePlugin.php\",\"line\":363,\"function\":\"generateMultiStatus\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/3rdparty/sabre/event/lib/WildcardEmitterTrait.php\",\"line\":89,\"function\":\"httpPropFind\",\"class\":\"Sabre\\\\DAV\\\\CorePlugin\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php\",\"line\":474,\"function\":\"emit\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php\",\"line\":251,\"function\":\"invokeMethod\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php\",\"line\":319,\"function\":\"start\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/apps/dav/appinfo/v1/webdav.php\",\"line\":82,\"function\":\"exec\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\"},{\"file\":\"/var/www/nextcloud/remote.php\",\"line\":167,\"args\":[\"/var/www/nextcloud/apps/dav/appinfo/v1/webdav.php\"],\"function\":\"require_once\"}],\"File\":\"/var/www/nextcloud/lib/private/Files/Storage/Wrapper/Availability.php\",\"Line\":94,\"Hint\":\"Storage is temporarily not available\",\"CustomMessage\":\"--\"}",
  "userAgent": "Mozilla/5.0 (iOS) Nextcloud-iOS/3.0.0",
  "version": "19.0.0.12"
}

I suspect this issue is due to https://github.com/nextcloud/server/issues/14797

Eventualy, after deleting the external share's corresponding row in table oc_share_external, the issue goes away

MariaDB [nextcloud]> select * from oc_share_external;
+----+--------+------------+---------------------------+-----------+-----------------+----------+-----------+-------+---------+------------+----------------------------------+----------+
| id | parent | share_type | remote                    | remote_id | share_token     | password | name      | owner | user    | mountpoint | mountpoint_hash                  | accepted |
+----+--------+------------+---------------------------+-----------+-----------------+----------+-----------+-------+---------+------------+----------------------------------+----------+
|  3 |     -1 |          0 | https://private.bollu.be/ |         3 | GL8M76GbVHk0nkv |          | /external | admin | cyrille | /external  | 48d7eb60b23e97e7d76b33e669c372da |        1 |
+----+--------+------------+---------------------------+-----------+-----------------+----------+-----------+-------+---------+------------+----------------------------------+----------+
1 row in set (0.000 sec)

MariaDB [nextcloud]> delete from oc_share_external where id=3;
Query OK, 1 row affected (0.019 sec)

Reasoning or why should it be changed/implemented?

This is a bug

iOS version

13.5.1

App version

3.0.0.76

Server configuration

Operating system:
Debian bullseye
Web server:
apache
Database:
MariaDB
PHP version:
7.4
Nextcloud version: (see Nextcloud admin page)
19.0

Start by reproducing the iOS folder listing with serverA shut down, using the reported federated share and the WebDAV StorageNotAvailableException log. Inspect how the iOS app handles the failed WebDAV response and the external share state; done means folders remain usable without a 500 error or the reported slowdown. No test file is named in the issue.