Does a server have to carry out an operation before redirection?

Question

In Is HTTP 303 acceptable for other HTTP methods? we established that HTTP 303 can be used for other HTTP methods.

The Post/Redirect/Get pattern requires the server to carry out an operation before returning HTTP 303. Is the same true for HTTP PUT and DELETE for this and other types of redirects? Is the server required to carry out the operation before redirection? Or can it assume that the client will repeat the request on the canonical URL as necessary?

This becomes even more interesting when you consider the fact that redirection is often used for load-balancing.

Answer 1

Quoting RESTful Web Services page 378:

303 ("See Other")

The request has been processed, but instead of the server sending a response document, it’s sending the client the URI of a response document. This may be the URI to a static status message, or the URI to some more interesting resource.

A few pages later...

307 (“Temporary Redirect”)

The request has not been processed, because the requested resource is not home: it’s located at some other URI. The client should resubmit the request to another URI. For GET requests, where the only thing being requested is that the server send a representation, this status code is identical to 303 (“See Other”). A typical case where 307 is a good response to a GET is when the server wants to send a client to a mirror site. But for POST, PUT, and DELETE requests, where the server is expected to take some action in response to the request, this status code is significantly different from 303. A 303 in response to a POST, PUT, or DELETE means that the operation has succeeded but that the response entity-body is not being sent along with this request. If the client wants the response entity-body, it needs to make a GET request to another URI. A 307 in response to a POST, PUT, or DELETE means that the server has not even tried to perform the operation. The client needs to resubmit the entire request to the URI in the Location header.

An analogy may help. You go to a pharmacy with a prescription to be filled. A 303 is the pharmacist saying “We’ve filled your prescription. Go to the next window to pick up your medicine.” A 307 is the pharmacist saying “We can’t fill that prescription. Go to the pharmacy next door.”