I had tried using BackBlaze 8 months ago as a much cheaper (especially with B2 and CF's Free Data Transfer partnership) replacement for Amazon S3 and was running into a limitation on B2.

I had a scenario where my users can upload images from the browser to BackBlaze. I wanted the ability to control the file name of the uploaded file. I don't want the user to be able to modify the network request to upload the file with a different file name. Nor do I want the users to be able to upload files with names which would overwrite existing files.

B2 didn't let me upload files with a specific filename in the pre-signed URL.

For example there's this API:

curl https://apiXXX.backblazeb2.com/b2api/v2/b2_get_upload_url -H 'Authorization: XXXXXXXXXXXXXXXXXXXXXXXXX=' -d '{"bucketId": "XXXXXXXXXXXXXXX"}'

which gave me an upload URL where I can upload the file to.

And then there's this:

https://www.backblaze.com/b2/docs/b2_upload_file.html

which lets users upload files to that URL.

But this allowed my users to upload file with any name they want. It would also allow them to overwrite existing files (from other users).

My question is more from a security point of view so preventing one user from overwriting another user's content is crucial. For example, lets say you right click on an image from someone else on facebook and get the actual image's file name. Now you try to upload an image on facebook and you edit the network request in the browser's inspector tool to the image file name which you got for another user. Facebook obviously prevents this in their own way using pre-signed urls which include the filename in the signature. However on BackBlaze if I try this, the "pod" url which is received doesn't include any file name signature. The pod URL is just where the image gets stored on your end. A user can easily edit the network request and modify the "X-Bz-File-Name" Header to another user's filename. This would be a major security vulnerability if I went with BackBlaze. As a workaround, right now it seems like users would first have to upload files to my own server, then my server would have to upload them to BackBlaze to avoid this issue. This sounded like hassle.

Amazon S3 solves this problem using createPresignedPost which includes a signature of the filename in the URL. I contacted BackBlaze's support and got a response their S3 api doesn't support createPresignedPost:

https://www.reddit.com/r/backblaze/comments/kzszym/is_backbl...

You can read B2's staff's response to my question:

https://www.reddit.com/r/backblaze/comments/l0c9s7/is_there_...

Is there a way to prevent this on R2? Something where the link provided by b2_get_upload_url (whatever R2's equivalent will be) only works for specific a file name?