How do I choose a HTTP status code in REST API for "Not Ready Yet, Try Again Later"?
I'm developing a RESTful API in which http://server/thingyapi/thingyblob/1234 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?
Answer
I suggest 202 - Accepted. From the documentation:
The request has been accepted for processing, but the processing has not been completed. [...] Its purpose is to allow a server to accept a request for some other process (perhaps a batch-oriented process that is only run once per day)