Chunked file upload

Introduction

Uploading large files is always a bit problematic as your connection can be interrupted which will fail your entire upload. Nextcloud has a chunking API where you can upload smaller chunks which will be assembled on the server once they are all uploaded.

There are two versions of the chunking API. Version 1 is the original version and version 2 was built as a backward compatible extension to support uploads directly to supporting target storages like S3. Version 2 is the recommended version to use.

Version 2 comes with a few additional requirements and limitations to consider (compared to version 1):

  • The MKCOL, chunk PUT, and final MOVE requests need to have a Destination header present which specifies the target path of the file

  • The naming of the individual chunks is limited to be a number between 1 and 10000

  • The chunks will be assembled in the order of their names

  • The size of chunks must be between 5MB and 5GB (except for the last chunk, which can be smaller)

  • Chunks cannot be downloaded from the upload directory

The Destination header is not required when aborting an upload with DELETE. The destination and backend upload token are stored when the upload is created.

Nextcloud will expire the upload directory after 24 hours of inactivity. This means that if you start an upload and do not finish it within 24 hours, the upload directory will be deleted and the upload will fail.

Chunked upload v2

The API is only available for registered users of your instance. And uses the path: <server>/remote.php/dav/uploads/<userid>. For this guide we will assume: https://server/remote.php/dav/uploads/roeland

Starting a chunked upload

A chunked upload is handled in 1 folder. This is the location all the chunks are uploaded to.

Start by creating a folder with a unique name. You can list the current available folder but if you take a random UUID chances of collision are tiny.

curl -X MKCOL -u roeland:pass \
    https://server/remote.php/dav/uploads/roeland/myapp-e1663913-4423-4efe-a9cd-26e7beeca3c0 \
    --header 'Destination: https://server/remote.php/dav/files/roeland/dest/file.zip'

Uploading chunks

Once a folder for the chunks has been created we can start uploading the chunks.

  • The naming of the individual chunks is limited to be a number between 1 and 10000

  • The chunks will be assembled in the order of their names

  • The size of chunks must be between 5MB and 5GB (except for the last chunk, which can be smaller)

  • To have the quota of the user checked, you need to provide the header OC-Total-Length with the total size of the file. It will reject the chunk with a 507 Insufficient Storage error. If you do not provide it, the upload will only fail on the MOVE assembling step.

curl -X PUT -u roeland:pass \
    https://server/remote.php/dav/uploads/roeland/myapp-e1663913-4423-4efe-a9cd-26e7beeca3c0/00001 \
    --data-binary @chunk1 \
    --header 'Destination: https://server/remote.php/dav/files/roeland/dest/file.zip' \
    --header 'OC-Total-Length: 15000000'

curl -X PUT -u roeland:pass \
    https://server/remote.php/dav/uploads/roeland/myapp-e1663913-4423-4efe-a9cd-26e7beeca3c0/00002 \
    --data-binary @chunk2 \
    --header 'Destination: https://server/remote.php/dav/files/roeland/dest/file.zip' \
    --header 'OC-Total-Length: 15000000'

This will upload 2 chunks of a file. The first chunk is 10MB in size and the second chunk is 5MB in size.

Assembling the chunks

Assembling the chunk on the server is a matter of initiating a move from the client.

curl -X MOVE -u roeland:pass \
    https://server/remote.php/dav/uploads/roeland/myapp-e1663913-4423-4efe-a9cd-26e7beeca3c0/.file \
    --header 'Destination: https://server/remote.php/dav/files/roeland/dest/file.zip' \
    --header 'OC-Total-Length: 15000000'

The server will now assemble the chunks and move the final file to the folder dest/file.zip.

Setting the modification time

If a modification time should be set, you can by adding it as header with date as unixtime:

curl -X MOVE -u roeland:pass
    --header 'Destination: https://server/remote.php/dav/files/roeland/dest/file.zip' \
    --header 'X-OC-Mtime: 1547545326' \
    --header 'OC-Total-Length: 15000000'

Otherwise the current upload date will be used as modification date.

The chunks and the temporary upload folder will be deleted afterwards.

Aborting the upload

If the upload has to be aborted, delete the upload folder:

curl -X DELETE -u roeland:pass \
    https://server/remote.php/dav/uploads/roeland/myapp-e1663913-4423-4efe-a9cd-26e7beeca3c0/

For a Chunking v2 upload, Nextcloud uses the stored upload metadata to cancel the backend chunked write before deleting the upload folder. This also aborts the underlying multipart upload when the target storage supports multipart uploads. No Destination header is needed for this request.

Uploads without Chunking v2 metadata are handled by normal DAV deletion.