To: Jacob Palme <jpalme@dsv.su.se>
Cc: ietf-drums <drums@cs.utk.edu>
Subject: Re: The conservative and liberal commandment 
In-Reply-To: Your message of "Fri, 05 Jan 1996 05:04:47 BST."
             <Pine.SUN.3.91.960105045713.28505A-100000@ester.dsv.su.se> 
Date: Fri, 05 Jan 1996 17:55:25 +1100
Message-Id: <1385.820824925@munnari.OZ.AU>
From: Robert Elz <kre@munnari.OZ.AU>

I mostly agree with Keith - however what must be remembered
(as well as gateway problems) is that the conservative/liberal
test is meant to handle all those things that we don't think
of specifying.

By all means where we know what we want, and agree upon it,
we can specify what should be generated and accepted, but there
will still be all those cases that we don't think of.

The principle can be restated as:

	Generate only what is expressly permitted, but
	don't be pedantic in checking that others are
	obeying the rules, if accepting what they send
	doesn't harm you.

This way there is less need to say things like ...

   Line length: Acccept 1000 character lines, but never send
   more than 80 character lines.

which will simply cause turf wars - if someone sends 200 byte
lines, and someone else refuses to accept them with that rule,
who is broken, each simply points the finger at the other,
where really both are wrong (by that spec).

But if the rule simply says "lines up to 128 bytes are legal"
then anyone sending 200 byte lines is clearly broken.  However
there's no need to check that - if your receiver code doesn't
need to enforce a line limit, at 128, 1000, or anywhere else,
then don't enforce one.

kre