feat(dav): Add occ dav:show-listeners to allow better insights into DAV stack

[DerDreschner]

Summary

Right now, there is no way to see which listeners are registered for events being fired in Sabre. This makes debugging and analyzing the situation pretty hard (see #61680 for example). I would even say that we're not being able to really master the whole event system right now, based on some input I've gathered.

To change the situation I've used Claude to generate me an occ command to see all listeners for a command, their priority and give some information about the execution order and how it behaves on exceptions and errors.

Example output

root@7a6bd926eee5:/var/www/html# sudo -u www-data php occ dav:show-listeners --help                   
Description:
  Show all Sabre event listeners with their event and priority

Usage:
  dav:show-listeners [options]

Options:
      --uri=URI         DAV request path the server is built for; controls which subtree plugins are loaded (e.g. "calendars/admin", "addressbooks/admin", "files/admin") [default: ""]
      --user=USER       Set up the given user's session and filesystem so that plugins registered lazily during an authenticated request are listed too
      --event=EVENT     Only show listeners whose event name contains this string (case-insensitive)
      --method=METHOD   Show the resolved firing order for the given HTTP method (e.g. "GET"), merging wildcard and method-specific listeners the way Sabre does at emit time

[...]

root@7a6bd926eee5:/var/www/html# sudo -u www-data php occ dav:show-listeners --user=admin --method=GET

beforeMethod:GET — 9 listener(s), executed top to bottom (lowest priority first):
  Always runs first. A listener returning false or throwing stops the request here (see skip rules below).
+---+----------+------------------+-------------------------------------------------------------------------------------+
| # | Priority | Registered on    | Listener                                                                            |
+---+----------+------------------+-------------------------------------------------------------------------------------+
| 1 | 1        | beforeMethod:*   | OCA\DAV\Connector\Sabre\MaintenancePlugin::checkMaintenanceMode                     |
| 2 | 9        | beforeMethod:*   | OCA\DAV\Connector\Sabre\AnonymousOptionsPlugin::handleAnonymousOptions              |
| 3 | 10       | beforeMethod:*   | Sabre\DAV\Auth\Plugin::beforeMethod                                                 |
| 4 | 20       | beforeMethod:*   | OCA\DAV\Connector\Sabre\DavAclPlugin::beforeMethod                                  |
| 5 | 50       | beforeMethod:*   | OCA\DAV\Connector\Sabre\LockPlugin::getLock                                         |
| 6 | 100      | beforeMethod:*   | OCA\DAV\Connector\Sabre\UserIdHeaderPlugin::beforeMethod                            |
| 7 | 100      | beforeMethod:*   | {closure:OCA\DAV\Server::__construct()} (/var/www/html/apps/dav/lib/Server.php:289) |
| 8 | 100      | beforeMethod:GET | {closure:OCA\DAV\Upload\ChunkingV2Plugin::beforeGet}                                |
| 9 | 200      | beforeMethod:*   | OCA\DAV\Connector\Sabre\BlockLegacyClientPlugin::beforeHandler                      |
+---+----------+------------------+-------------------------------------------------------------------------------------+

method:GET — 6 listener(s), executed top to bottom (lowest priority first):
  Runs only if beforeMethod completed and preconditions held; a handler here serves the request.
+---+----------+---------------+-------------------------------------------------------------------+
| # | Priority | Registered on | Listener                                                          |
+---+----------+---------------+-------------------------------------------------------------------+
| 1 | 90       | method:GET    | OCA\DAV\Provisioning\Apple\AppleProvisioningPlugin::httpGet       |
| 2 | 90       | method:GET    | OCA\DAV\DAV\ViewOnlyPlugin::checkViewOnly                         |
| 3 | 90       | method:GET    | Sabre\DAV\Browser\Plugin::httpGetEarly                            |
| 4 | 100      | method:GET    | Sabre\DAV\CorePlugin::httpGet                                     |
| 5 | 100      | method:GET    | {closure:OCA\DAV\Connector\Sabre\ZipFolderPlugin::handleDownload} |
| 6 | 200      | method:GET    | Sabre\DAV\Browser\Plugin::httpGet                                 |
+---+----------+---------------+-------------------------------------------------------------------+

afterMethod:GET — 7 listener(s), executed top to bottom (lowest priority first):
  Runs only after the method was served successfully (skipped on the early-exit paths listed below).
+---+----------+-----------------+------------------------------------------------------------------+
| # | Priority | Registered on   | Listener                                                         |
+---+----------+-----------------+------------------------------------------------------------------+
| 1 | 50       | afterMethod:*   | OCA\DAV\Connector\Sabre\LockPlugin::releaseLock                  |
| 2 | 100      | afterMethod:*   | OCA\DAV\Connector\Sabre\RequestIdHeaderPlugin::afterMethod       |
| 3 | 100      | afterMethod:*   | OCA\DAV\Connector\Sabre\CopyEtagHeaderPlugin::afterMethod        |
| 4 | 100      | afterMethod:*   | OCA\DAV\Profiler\ProfilerPlugin::afterMethod                     |
| 5 | 100      | afterMethod:GET | OCA\DAV\Connector\Sabre\FilesPlugin::handleDownloadToken         |
| 6 | 100      | afterMethod:GET | OCA\DAV\Connector\Sabre\FilesPlugin::httpGet                     |
| 7 | 999      | afterMethod:GET | {closure:OCA\DAV\Connector\Sabre\ZipFolderPlugin::afterDownload} |
+---+----------+-----------------+------------------------------------------------------------------+

At most one of the two chains below normally runs per request — several early-exit paths run neither:

afterResponse — 2 listener(s), executed top to bottom (lowest priority first):
  Runs on the success path, after the response has been sent.
+---+----------+---------------+------------------------------------------------------------------------------------------------------------------------------+
| # | Priority | Registered on | Listener                                                                                                                     |
+---+----------+---------------+------------------------------------------------------------------------------------------------------------------------------+
| 1 | 100      | afterResponse | OCA\DAV\Connector\Sabre\PropFindMonitorPlugin::afterResponse                                                                 |
| 2 | 100      | afterResponse | {closure:OCA\DAV\Connector\Sabre\FilesPlugin::initialize()} (/var/www/html/apps/dav/lib/Connector/Sabre/FilesPlugin.php:149) |
+---+----------+---------------+------------------------------------------------------------------------------------------------------------------------------+

exception — 2 listener(s), executed top to bottom (lowest priority first):
  Runs on the failure path, when a listener or handler throws. If an afterResponse listener throws, both chains run.
+---+----------+---------------+-------------------------------------------------------------+
| # | Priority | Registered on | Listener                                                    |
+---+----------+---------------+-------------------------------------------------------------+
| 1 | 10       | exception     | OCA\DAV\Connector\Sabre\ExceptionLoggerPlugin::logException |
| 2 | 100      | exception     | Sabre\DAV\CorePlugin::exception                             |
+---+----------+---------------+-------------------------------------------------------------+

When chains are skipped for this request:
  * a beforeMethod listener returns false -> method / afterMethod / afterResponse are skipped; that listener owns the response, and the exception chain does NOT run.
  * a beforeMethod listener throws        -> method / afterMethod / afterResponse are skipped; the exception chain runs and Sabre sends an error response.
  * conditional GET matches (304)         -> the 304 response is sent directly; method / afterMethod / afterResponse AND the exception chain are all skipped.
  * any other precondition fails          -> PreconditionFailed is thrown, so the exception chain runs and Sabre sends a 412 response.
  * no handler serves the method          -> NotImplemented is thrown, so the exception chain runs.
  * an afterMethod listener returns false -> the response is never sent and afterResponse is skipped; the exception chain does NOT run.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI

[provokateurin]

Nice stuff! I skimmed over it a bit.

[provokateurin]

Not sure if this comment should be kept, since it was fixed upstream.

[provokateurin]

This sounds really strange. Can you please check in the sabre code, that this is actually true? I kind of doubt it, because it would not really work well in reality.

[provokateurin]

This command should be registered at runtime and only when the debug mode is enabled. It is not intended to be used by admins.

[provokateurin]

Unfortunately we have like 2 or 3 ways to create this server object. The entry points in apps/dav/appinfo also add some more stuff on top of that.
Besides fixing the root cause of the entry point mess, I don't know how to workaround this situation.