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 "Fri, 02 Jun 1995 10:02:19 -0400."
             <sjnlbfm00WBwE9xsIM@andrew.cmu.edu> 
Date: Sun, 04 Jun 1995 09:35:17 +1000
Message-Id: <1786.802222517@munnari.OZ.AU>
From: Robert Elz <kre@munnari.oz.au>

    Date:        Fri,  2 Jun 1995 10:02:19 -0400 (EDT)
    From:        John Gardiner Myers <jgm+@CMU.EDU>
    Message-ID:  <sjnlbfm00WBwE9xsIM@andrew.cmu.edu>

    > @[ip:v:6]:user@[ip:v:6]

    It breaks existing correctly written deterministic parsers.

The example you gave is what was intended by "heuristic" I
suspect, that is, shortcut parsing, not looking at the syntax
in detail - if you were, then in stripping the leading parts
of the route addr you'd come across the '[' first, and know
that a matching ']' was required, and that stripping between
those, wherever found, would always be incorrect.

In any case, any stripping code that doesn't ensure that the final
'@' remains in the address, which seems to be what might go wrong
in the example you gave seems terribly fragile to me, similarly
any stripping without determining that the address is syntactically
correct first.   If you're doing the latter now, then the stray ":"
chars that might appear would cause your parser to say "fail",
and nothing would be stripped.

I see three solutions to this problem

1) convince IPng to use some character other than ':'.  That
has been tried before, however if you wish to try again, the
address is ipng@sunroof.eng.sun.com (subscribe by sending
"subscribe ipng" in the body of a message to majordomo@sunroof.eng.csun.com)

Its not easy as there aren't a lot of available characters, '.'
is not available (it is already used in IPv6 addresses), about
the only plausible alternative seems to be '-' which turns out to
look really ugly when written.

2) Note that this change is likely to happen, and re-write your
parsers to accept basically anything (but ']') inside '[' ']'
pairs.   You have years to get this deployed, you're not seriously
likely to see any IPv6 literal addresses inside any joe average
mailer anytime in the near future in normal business (someone
will stick one in a message to this list just to prove me wrong,
but that doesn't count as normal...)

3) Abolish literal addresses altogether.   This doesn't seem
practical to me, they're too useful when the DNS is broken, or
in the case I see a lot, hasn't been set up yet (people send me
mail asking for DNS delegations, if their setup is broken, I
can't reply without the [] address syntax to get to their mailer).

kre