HTTP status code for async tasks

Question

I am implementing a REST API which involves creating a object on the server. The object creation involves multiple steps and may take a while. I do not want the user to wait on it. I simply return a 202 response with a unique request id for the client request and start some threads on the server to create the object. The client is supposed to check back to see whether the request is completed or not, in the future. The flow goes like this:

1. The client POSTs the object.
2. The server responds with a 202 Accepted code with a Location header /my-app/<reqId>
3. The client does a GET on /my-app/<reqId>

Now at the third step, these things might happen:

1. Object creation is still in progress(client should check again after sometime).
2. Some Error occured.
3. Object is successfully created.

Now what http code should my API /my-app/<reqId> respond for the above three scenarios?

Answer 1

I might do it a bit differently from the start. The Location header has a specific meaning, pointing to the actual resource connected to the request, basically the "result" of whatever was requested, not the resource indicating the state of the request itself. This might be a small difference, might nonetheless be confusing later.

Also the specification says the 202 should return content indicating or linking to the "state" resource that describes the progress of the request itself.

So the flow might be:

1. Client does POST
2. Server sends 202 Accepted. Location header points to the URI where the requested resource will be (this is not the state), this will be 404 until the processing is done. Also, the content of the 202 might include the "state" representation. The Content-Location header has the link to this "state" resource.
3. Client GETs the state resource to check on the progress. This resource always exists, so it always returns 200.
4. If the state indicates success, the resource indicated in the Location now exists, otherwise it will never exist. State resource continues to exists indefinitely.