- From: Mark Nottingham <mnot@mnot.net>
- Date: Mon, 29 Jan 2018 12:00:06 +1100
- To: Chris Pacejo <chris@pacejo.net>
- Cc: Roy Fielding <fielding@gbiv.com>, RFC Errata System <rfc-editor@rfc-editor.org>, "Julian F. Reschke" <julian.reschke@greenbytes.de>, Ben Campbell <ben@nostrum.com>, Alexey Melnikov <aamelnikov@fastmail.fm>, adam@nostrum.com, pmcmanus@mozilla.com, ietf-http-wg@w3.org
FWIW, I think the source of confusion here is taking this statement out of context: """However, if a resource has distinct representations that differ only in their metadata, such as might occur with content negotiation over media types that happen to share the same data format, then the origin server needs to incorporate additional information in the validator to distinguish those representations.""" The complete paragraph is: """There are a variety of strong validators used in practice. The best are based on strict revision control, wherein each change to a representation always results in a unique node name and revision identifier being assigned before the representation is made accessible to GET. A collision-resistant hash function applied to the representation data is also sufficient if the data is available prior to the response header fields being sent and the digest does not need to be recalculated every time a validation request is received. However, if a resource has distinct representations that differ only in their metadata, such as might occur with content negotiation over media types that happen to share the same data format, then the origin server needs to incorporate additional information in the validator to distinguish those representations.""" I.e., the statement is being made in the context of generating strong validators based only upon the message body, when the headers might also change. Cheers, > On 17 Jan 2018, at 7:34 am, Chris Pacejo <chris@pacejo.net> wrote: > > Hi Roy and Julian, thanks for the replies. > > On Tue, Jan 16, 2018, at 2:33 PM, Roy T. Fielding wrote: >> The Original Text is about weak validators, which don't even require that >> the content be the same. The two do not conflict. The suggested change >> would be incorrect. > > The specific text which confuses me, from the section on weak validators, is (emphasis mine): > > "However, two simultaneous representations might share the same *strong* validator if they differ only in the representation metadata, such as when two different media types are available for the same representation data." > > Am I misunderstanding that this is in conflict with the example you gave? (text/plain and application/json representations with same octets must have different strong validators.) > > Similarly: > > "Likewise, a validator is weak if it is shared by two or more representations of a given resource at the same time, unless those representations have identical representation data." > > The "unless" clause would appear to apply to the example you gave, implying that both representations can have the same validator but need not be weak. > > Thanks, Chris -- Mark Nottingham https://www.mnot.net/
Received on Monday, 29 January 2018 01:00:39 UTC