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Re: [rest-discuss] the meaning of stateless

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  • Mark Baker
    [reposting as I initially sent it from the wrong address] ... Thanks for asking that question, Mike. It s why I ve found that there s not as much enlightenment
    Message 1 of 86 , May 5, 2013
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      [reposting as I initially sent it from the wrong address]

      On 2013-05-04 3:08 AM, "Mike Schinkel" <mike@...> wrote:
      > On May 3, 2013, at 10:54 AM, Mark Baker <distobj@...> wrote:
      >> But using a server-side shopping cart typically *does* violate that
      >> constraint... not while you're shopping and adding/removing stuff
      >> to/from the cart, but when you checkout by sending a message which
      >> means "Purchase what's in that cart", when the intended meaning is
      >> "Purchase size 9 Nike Air Max for $199".
      >> Forgive me, still trying to improve my evolving understanding.
      >> From comments in [1] Roy says the following:
      >>> Don’t confuse application state (the state of the user’s application of computing to a given task) with resource state (the state of the world as exposed by a given service). They are not the same thing.
      >> Isn't the server-side shopping cart not then "resource state?"

      Thanks for asking that question, Mike. It's why I've found that
      there's not as much enlightenment as you'd think in looking at the
      problem that way.

      Yes, the shopping cart is resource state, but it's also
      session/application state in the context of that final purchase

      When you think about it, *any* state can be given a URI, but doing so
      doesn't un-make it session state if its being used that way.
    • Nicholas Shanks
      Like the SMS example, this is another case of trying to avoid server state (i.e. be RESTful) in cases where the server needs to keep a permanent record of the
      Message 86 of 86 , Jun 11, 2013
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        Like the SMS example, this is another case of trying to avoid server state (i.e. be RESTful) in cases where the server needs to keep a permanent record of the transaction anyway, one per client. Statelessness is about avoiding the word "my". Pay for the items in my basket, vs Pay for the items in basket #54203. Replicating session files between load-balanced servers may even be cheaper than replicating database-based resources.

        As the linked post says: "Most of the value cases for REST apply to repeatable responses, not an application that can't be reused, can't be transformed, and can't be shared."
        "I do not believe in trying to apply all of REST's constraints unless there is a reason for doing so."

        Just because an architecture is good for document retrieval, doesn't mean it should be mindlessly applied to everything else too.

        Perhaps the next Roy Fielding can come along and deduce the optimum architectural constraints for a private, non-repeatable, yet scalable application, and from these direct the evolution of HTTP just as HTTP 1.1 was informed.

        — Nicholas.

        On 9 May 2013, at 19:27, Matt McClure <matthewlmcclure@...> wrote:


        On Thu, May 9, 2013 at 9:43 AM, Bob Haugen <bob.haugen@...> wrote:


        Eric Bowman wrote:
        > My nutshell explanation of REST from 50,000ft is that a system
        > designed to manipulate shopping carts MUST be based on
        > transferring actual representations of shopping-cart contents.

        I hesitated to get back into this issue after having lost an argument
        with Mark Baker about it a couple of years ago, but: the typical
        behavior of a system that saves shopping cart contents on servers
        (e.g. Amazon) is to send a representation of the shopping cart
        contents back to the client to confirm the order, in which case, a
        representation of the shopping cart contents then gets sent back to
        the server from the client.

        Would e.g. Mark and Eric agree that this is RESTful?

        I've also been following this conversation as a lurker. If I understood some of the earlier comments, it sounded as though someone made a case that a request like:

            POST /cart/12345/purchase
            Content-Length: 0

        would be stateful and undesirable for conformance with REST whereas:

            POST /purchase
            Content-Length: 1234

        would be more RESTful and less stateful.

        I guess I'm unclear why the former would violate statelessness. The state in the former is resource state, identified by an implicit /cart/12345 resource (assume I got the /cart/12345/purchase link from the cart resource).

        To contrast:

            POST /purchase
            Content-Length: 0
            Cookie: client=12345

        seems decidedly stateful because it requires shared state identified by the ID in the Cookie header rather than the URI to disambiguate which thing the client wants to purchase.

        It seems to me that a client need not include all of the detail of the cart contents and payment method in the purchase request to conform with a statelessness constraint. I'd be happy to hear why I'm wrong if I am.


        Matt McClure

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