Fix handling of storage that has multiple shared mounts

[christoph-bessei]

Fixes #254

Description

As described in #254 there are some edge cases where $mounts[0]->getUser()->getUID() returns a user ID that has no access to a given file. This PR fixes this by iterating through the mounts until it finds a user with access to the given file.

There might be cleaner solutions, but I wanted to reduce the changes as much as possible for an easier review. Assuming $mounts[0] is working in most cases, the performance impact should be minimal.

Notes

• This is my first PR related to Nextcloud. Please let me know if I missed something that's required before merge.

🤖 AI (if applicable)

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

[bakiburakogun]

Confirming this on a large instance, in case another data point helps it along.

We hit exactly the symptom from #254 on Nextcloud 34.0.3 with context_chat 5.4.0 and context_chat_backend 5.4.1: roughly 1.5 M eligible files, heavy use of shares and group folders, and a steady stream of

Exception: File not found or not a file
  at apps/context_chat/lib/Controller/QueueController.php:301
  in getFileSource()

on GET /ocs/v2.php/apps/context_chat/queues/documents.

What made it costly for us is what happens next to those entries. getDocumentsQueueItems() deletes the queue row when getFileSource() throws:

if ($queueMapper->lock($document->getId())) {
    try {
        $files[$document->getId()] = $this->getFileSource(...);
    } catch (\Exception $e) {
        $this->logger->warning($e->getMessage(), ['exception' => $e]);
        $queueMapper->delete($document);
    }
}

so the queue drained quickly while almost nothing reached the vector database — from the outside it looked like indexing had stopped, when in fact files were being consumed and discarded. Because the warning goes to the Nextcloud log rather than the backend container, it is easy to spend a long time looking in the wrong place.

With this patch applied, indexing ran to 32,879 documents and 490,387 chunks before we paused it for unrelated reasons, and the remaining per-file failures are the ordinary ones — Decoded content is empty for files with no text layer, and the occasional decode error on a malformed PDF.

One note on getFileSource() as it stands after this change: if none of the mounts can resolve the file, the exception is still thrown and the entry still deleted, which is right for a file that genuinely no longer exists but also silently drops anything that fails for a transient reason. That is outside the scope here, just worth being aware of.

Thanks for writing it — happy to test further revisions on an instance of this size if that is useful.

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