Re: the meaning of stateless

On Tue, Apr 23, 2013 at 12:14 PM, Brian Craft <[email protected]> wrote:
>> > Fielding's definition didn't do much for me, because the terms aren't
>> > adequately defined,
>>
>> They are, and the definition is most definitely adequate, trust me on
>> that.
>
>
> I don't agree. Take this statement, for example:
>
> "Each request from client to server must contain all of the information
> necessary to understand the request, and cannot take advantage of any stored
> context on the server. "
>
> What does "understand" mean in this sentence? I'm not aware of a technical
> definition of "understand" as it applies to computer systems, and it's not
> defined in the paper.

This is what I'm talking about when I suggest focusing on the
interface, aka the message.

HTTP messages are generally sent between parties that know nothing of
each other, so "understand" here means exactly that; that the meaning
of the message can be understood by the recipient so its clear what
the sender is asking be done when it sends the message.

> Again, take the "query by POST" pattern. The eventual
> GET depends on a previous POST. Does the server "understand" a request that
> depends on a previous request? What about "stored context"? One would
> reasonably believe that POSTing a query creates stored context on the server
> which later requests may take advantage of. But this sentence says that it
> must not "take advantage of any stored context on the server." I assume this
> apparent contradiction is due to some different use of terms, that "stored
> context" doesn't mean what one would reasonably assume it means, or
> something. If this is a different usage of the terms, they should be defined
> somewhere.
>
> My current guess is that "understand" means that the communications layer
> can read the request and generate a valid response, including the case where
> the POST goes missing and it must return a 404: that it still "understands"
> the request even though the app can't process it since the depends on a
> previous request.
>
> But then it gets really odd with claims like "the server doesn’t have to
> manage resource usage across requests." How is a POSTed query not a resource
> on the server that must be managed across requests?

It is, but the *meaning* of future messages doesn't change if the
state of that resource changes.

Mark.


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