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3837Re: [rest-discuss] 403 vs. 409

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  • Walden Mathews
    Aug 3, 2003
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      Mark,

      > > What would you be telling intermediaries if you used 200 to reply
      > > to a POST of some malformed content:
      > >
      > > a. that something was successfully appended or annotated?
      > > b. that some data processing was successfully performed?
      >
      > b, I'd say, keeping in mind that "successful data processing" can
      > include the determination of some "invalid" information within that
      > data, such as non-well-formed XML, or an invalid credit card number.
      > Where you draw this line is up to the needs of your application,
      > which is why I say "sometimes 400, sometimes 200" (but mostly 200,
      > in my experience).

      Well, in my *inexperience* that looks like a loss of visibility. I
      understand
      syntax error to be a condition that aborts meaningful processing, and this
      is application level protocol, so the status code should tell us about how
      effectively state was transferred, not how effectively bits were
      transported.

      >
      > > Why wouldn't 400 in this case be the ideal way to drive the
      > > application in asking for the data again after correcting syntax?
      > >
      > > How does 400 prevent the application from making progress?
      >
      > Because it's an error. An error response describes the specifics of the
      > error, leaving the client no way to proceed through the application,
      > except to do a logical "Back"; as far as the state of the application is
      > concerned (which the client maintains), that interaction never happened.

      "Back" seems more like a browser idiom. I would say that the absence
      of a 2xx is the absence of a forward transition, which leaves application
      state
      right where it was. In this case, the "way to proceed" is to correct syntax
      and try again. What am I missing?

      Another thought: the details of a malformed request and an aborted
      state transition are analogous to (or perhaps just examples of)
      conversational state. Not part of the "application state" model.

      >
      > > Also, in general, where did I get the impression that an application
      > > unsure about specific status codes can/should punt and use the x00
      > > in the appropriate category? Doesn't seem to say that in 2616 for
      > > the 400 family.
      >
      > Sec 6.1.1;
      >
      > "HTTP status codes are extensible. HTTP applications are not required
      > to understand the meaning of all registered status codes, though such
      > understanding is obviously desirable. However, applications MUST
      > understand the class of any status code, as indicated by the first
      > digit, and treat any unrecognized response as being equivalent to the
      > x00 status code of that class, with the exception that an
      > unrecognized response MUST NOT be cached."

      Ah, thanks. So it would seem the part of 2616 that says 400 is about
      syntax error specifically kind of violates that class/subclass thing, since
      other 4xx responses are not about syntax. Season to taste?

      -Walden
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