Chunked upload ignores server's files.chunked_upload.max_size; uploads from slow networks fail #17469

⚠️ Before posting ⚠️

• This is a bug, not a question or an enhancement.
• I've searched for similar issues and didn't find a duplicate.
• I've written a clear and descriptive title for this issue, not just "Bug" or "Crash".
• I agree to follow Nextcloud's Code of Conduct.

Steps to reproduce

1. Connect to a Wi-Fi network with limited/fluctuating upload bandwidth (in our case the link delivered 0.1-1.5 MB/s).
2. Upload any file larger than ~10 MB from the Android app to a Nextcloud 34 server.
3. The chunked upload fails; the app retries and keeps failing.

Expected behaviour

The upload should complete on slow links. The server already advertises files.chunked_upload.max_size via capabilities — the client could use it and pick a chunk size that fits the current throughput and the transfer timeout, so chunks finish well before the deadline.

Actual behaviour

ChunkedFileUploadRemoteOperation uses hardcoded chunk sizes - 40 MB on Wi-Fi (CHUNK_SIZE_WIFI), 10 MB on mobile (CHUNK_SIZE_MOBILE) - and never reads the server's files.chunked_upload.max_size. The client's read timeout is fixed at 60 s (DEFAULT_DATA_TIMEOUT in OwnCloudClientFactory). The server answers a chunk PUT only after the whole body arrives, so on a slow link the 60 s read timeout fires mid-transfer:

• client aborts the connection (proxy logs 499),
• server gets a truncated chunk and answers 400 BadRequest "chunk smaller than expected",
• upload fails and retries forever.

Android version

14

Device brand and model

Samsung Galaxy S24

Stock or custom OS?

Stock

Nextcloud android app version

34.1.0

Nextcloud server version

34.0.2

Using a reverse proxy?

Yes

Android logs

No response

Server error logs

{"reqId":"JR0L5n4PhFC9tmyDp5in","level":3,"time":"2026-08-12T19:14:47+03:00","user":"sonya","method":"PUT","url":"/remote.php/dav/uploads/sonya/<id>/000001","message":"Expected filesize of 40960000 but read (from Nextcloud client) and wrote (to Nextcloud storage) 13336576. Could either be a network problem on the sending side or a problem writing to the storage on the server side.","exception":"Sabre\DAV\Exception\BadRequest"}

Additional information

Proposal for developers: size chunks dynamically instead of per connection type:

• respect files.chunked_upload.max_size from capabilities (min(serverMax, ...)),
• target a chunk size that fits the measured throughput, e.g. chunk = throughput * factor, keeping a sane floor,
• either scale the read timeout with the body size or skip the read deadline while the request body is still being written (writeTimeout already covers sending; the read timeout is what kills the request here).

That way a slow link degrades to smaller resumable chunks instead of a guaranteed failure.