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Re: 505 response a MUST?

From: Roy T. Fielding <fielding@kiwi.ics.uci.edu>
Date: Sun, 01 Mar 1998 22:30:52 -0800
To: Scott Lawrence <lawrence@agranat.com>
Cc: Larry Masinter <masinter@parc.xerox.com>, HTTP Working Group <http-wg@cuckoo.hpl.hp.com>, jg@w3.org, http-wg@hplb.hpl.hp.com
Message-Id: <9803012231.aa19717@paris.ics.uci.edu>
>  That logic does not seem sound to me - if changing the major version
>number means that the protocol _may_ be not backward compatible, then a
>recipient that does not implement 2.0 cannot know whether or not it can
>_correctly_ interpret the message as a 1.1 message.  Your logic assumes
>that the authors of 2.0 will not make any semantic changes to existing
>protocol elements.

No, it assumes a client won't send a 2.0 message to a 1.x server unless
the 2.0 message is sufficiently semantically and syntactically compatible
such that there is some reasonable assurance that the 1.x server will
respond in an anticipated (and safe) manner, even if that means a 400
response.  Forcing a server to respond in error just for the sake of
an error only guarantees the worst-case behavior of an extra round-trip,
and offers no extra safety in any case because deployed HTTP/1.x servers
will never respond with 505.  That code is intended for future 2.x
servers to say "piss-off" to older clients in the format of an HTTP/1.1
message, since they will have to respond in the same major version as
the old client.

....Roy
Received on Sunday, 1 March 1998 22:34:47 EST

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