However, it turns out to be convenient to have the blob hash and holder returned as well to avoid hacks (by passing them some other way) - it will be used in web client later (for blob deletion).

Isn't this data already available on the client? If the data comes from the client, then I'm a little confused why we're returning it from the endpoint

In D8257#243669, @ashoat wrote:

However, it turns out to be convenient to have the blob hash and holder returned as well to avoid hacks (by passing them some other way) - it will be used in web client later (for blob deletion).

Isn't this data already available on the client? If the data comes from the client, then I'm a little confused why we're returning it from the endpoint

Yes, it is. I don't know the beginnings of this convention, but we're doing the same with other values like loop, dimensions etc (probably the media could be processed on keyserver and these values could change).

Either way, I need to return UploadMediaMetadataResult from blobServiceUpload() in web/input-state-container. Alternatively, I can do it directly from there, just thought it would be cleaner to do it the same way other params are passed

Yes, it is. I don't know the beginnings of this convention, but we're doing the same with other values like loop, dimensions etc (probably the media could be processed on keyserver and these values could change).

I suspect that these other parameters either can be changed by the keyserver, or (perhaps more likely) at some point we thought we would want to be able to change them on the keyserver.

Either way, I need to return UploadMediaMetadataResult from blobServiceUpload() in web/input-state-container. Alternatively, I can do it directly from there, just thought it would be cleaner to do it the same way other params are passed

If we are confident that the keyserver will not change this parameter, then I think we should avoid wasting network traffic on it. My impression is that the keyserver won't be downloading the whole blob anyways, so there's no way to confirm the blob hash (or generate a new one).