Errors-to: owner-drums@CS.UTK.EDU
To: John Gardiner Myers <jgm+@CMU.EDU>
Cc: drums@CS.UTK.EDU
Subject: Re: address syntax 
In-Reply-To: Your message of "Mon, 05 Jun 1995 10:34:07 -0400."
             <AjolLTy00WBw49xuhz@andrew.cmu.edu> 
Date: Tue, 06 Jun 1995 06:26:39 +1000
Message-Id: <2205.802383999@munnari.OZ.AU>
From: Robert Elz <kre@munnari.oz.au>

    Date:        Mon,  5 Jun 1995 10:34:07 -0400 (EDT)
    From:        John Gardiner Myers <jgm+@CMU.EDU>
    Message-ID:  <AjolLTy00WBw49xuhz@andrew.cmu.edu>

    Robert Elz <kre@munnari.oz.au> writes:
    > The example you gave is what was intended by "heuristic" I
    > suspect, that is, shortcut parsing, not looking at the syntax
    > in detail
    
    There is nothing heuristic about such parsers.

I think I'll need to find a dictionary, but I didn't think
heuristic meant non-deterministic.

    Take a modification of Harald's example:
    
    <@[ip:v:6]:user@final.host.com>
    
    This is syntactically illegal, so one can parse it
    as one wishes.

Ignoring the trivia that none of 'i', 'p', or 'v' are hex
digits, so that one in particuilar will probably never be
legal ...

You're right, it is syntactically illegal now, and you can
I suppose parse it however you like, but generating an "address
error" message would be much more intelligent.

However, the IPng group will write a new RFC (when they get
around to going through all of the RFCs - or at least all
of the standards RFCs, and making changes to anything that
refers to "IP address" or its syntax, anywhere).   When
that happens that address (modulo the bogus characters) will
be legal, and you'll have to parse it the way it is obviously
intended.

As I said last time, there are three things you could do
about this..

Alter your parser now (no correct addresses will be broken)
Convince the IPng group to adopt some character other than ':'
Eliminate address literals from 821 & 822 so the problem goes away

Perhaps there are more, but simply saying "it is illegal"
will get you nowhere.

kre