Re: [rest-discuss] Re: the meaning of stateless
- Bob Haugen wrote:
>I'd say that how RESTful it is, depends entirely on the ubiquity of the
> 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?
media type used (text/html good, application/vnd.order+xml bad), and
depends on at least item#, quantity, and price being present in the
IOW, the hypertext of the order confirmation shouldn't amount to an
agreement to buy x number of item y "at the agreed price" but should
contain either the price agreed to before the transaction, or an
updated price needing confirmation from the user before proceeding.
Which means the hypertext MUST NOT contain only a link to the current
price, or a link to the item# for a description -- such representation-
by-reference is a bad thing. Sometimes, item #'s are re-used.
I don't get this concept of substituting a link to shave bytes, because
I use compression and it doesn't amount to much even on Amazon's scale,
especially when considering those lost properties Roy mentions -- the
cost of doing business in the modern world is bandwidth, cutting corners
to shave bytes is sloppy business practice.
- 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.
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/purchaseContent-Length: 0would be stateful and undesirable for conformance with REST whereas:POST /purchaseContent-Length: 1234items=...&in_quantities=...&with_payment_method=...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 /purchaseContent-Length: 0Cookie: client=12345seems 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--