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#186: Document HTTP's error-handling philosophy

From: Mark Nottingham <mnot@mnot.net>
Date: Mon, 2 May 2011 12:09:42 +1000
Message-Id: <086A82E0-400B-4A73-87D1-8652156BE855@mnot.net>
To: httpbis Group <ietf-http-wg@w3.org>
<http://trac.tools.ietf.org/wg/httpbis/trac/ticket/186>

Straw-man proposal: replace "Requirements" sections (in all parts) with the following.

> Conformance and Error Handling
> 
> The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
> 
> This document defines conformance criteria for several roles in HTTP communication, including Senders, Recipients, Clients, Servers, User-Agents, Origin Servers, Intermediaries, Proxies and Gateways. See [ref to Terminology] for a definitions of these terms.
> 
> An implementation is considered conformant if it complies with all of the requirements associated with its role(s). Note that SHOULD-level requirements are relevant here, unless one of the documented exceptions is applicable.
> 
> This document also uses ABNF to define valid protocol elements. In addition to the prose requirements placed upon them, Senders MUST NOT generate protocol elements that are invalid.
> 
> Unless noted otherwise, Recipients MAY take steps to recover a usable protocol element from an invalid construct, and SHOULD NOT reject the message outright. However, HTTP does not define specific error handling mechanisms, except in cases where it has direct impact on security. This is because different uses of the protocol require different error handling strategies; for example, a Web browser may wish to transparently recover from a response where the Content-Type header doesn't match the body, whereby in a systems control protocol using HTTP, this type of error recovery could lead to dangerous consequences.

Note that this removes the "conditionally compliant" level of conformance; i.e., SHOULD is no longer overloaded, and returns to is original RFC2119 semantic of identifying requirements that can be violated for reasonable reasons (see also <http://trac.tools.ietf.org/wg/httpbis/trac/ticket/271>, which proposes that we try to enumerate those reasons wherever possible).

That's a fairly big change. I'd argue that "conditional compliance" doesn't promote interop and should be dropped. Thoughts?

--
Mark Nottingham   http://www.mnot.net/
Received on Monday, 2 May 2011 02:10:08 GMT

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