I'm developing a RESTful API in which
returns the file (aka "blob") associated with thingy #1234 to download. But it may be that the request is made at a time the file does not exist in the server but most definitely will
be available at a later time. There's a batch process in the server that generates all the blobs for all the thingies. Thingy 1234 already exists and its data, other than the blob, is already available. The server hasn't got to generating thingy 1234's blob yet.
I don't want to return 404; that's for thingies that do not exist. This is a thingy that exists, but its blob hasn't been generated yet. Kinda like a YouTube video that's "processing." I don't think redirection codes would be proper either; there's no "other" URL to try.
What's the correct HTTP status code to return in such a case?