Re: [EAI] UTF-8 in Message-IDs

Frank Ellermann <hmdmhdfmhdjmzdtjmzdtzktdkztdjz@gmail.com> Wed, 05 October 2011 23:18 UTC

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From: Frank Ellermann <hmdmhdfmhdjmzdtjmzdtzktdkztdjz@gmail.com>
Date: Thu, 6 Oct 2011 01:20:39 +0200
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To: John C Klensin <klensin@jck.com>
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Subject: Re: [EAI] UTF-8 in Message-IDs
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On 5 October 2011 23:13, John C Klensin wrote:

 [Naive or broken]
> I would not presume to try to categorize all of the
> transformations I've seen, but some of them probably don't
> fall under your description above.

> This isn't trivial.

ACK, but thinking that it's trivial would be covered by naive.

I never had anything to do with MIXER.  All I vaguely recall
is related to "dupes" (= the same message arriving more than
once where it is expected at most once) and "nopes" (= if an
expected message arrives less than once, i.e., never, null,
nada, nope).  For Netnews "same message" means by definition
"same Message-ID", it is a fundmental concept.

Because I had a hard time to grok this years ago (in FTN the
Message-ID is only optional, the real thing in FTN echos are
the "Seen-By" thingies) I'm now reluctant to touch this "holy
cow" of what used to be the "RFC822" side from my FTN (Fido
technology network) POV.

> Remember that simple transcoding of header fields from
> net-ASCII into, e.g., EBCDIC or what we call ISO-2022-JP
> means that dumb octet-string comparisons of Message-IDs
> (and other things) will fail.

Actually I don't remember this issue, the "gatebau" problems
with Message-IDs were limited to ASCII-compatible networks.

But I can imagine how "ASCII-incompatible" offers wild and
wonderful ways to get it wrong.  If "they" can't do UTF-8 or
at least UTF-EBCDIC they have only one EAI-option:  Reject.

The corner cases where only the EAI-ID causes this "reject",
because everything else happens to work for say EBCDIC, are
too odd to consider.

> If someone asked my opinion about whether a gateway should mess
> with Message-IDs, I'd say "no, unless it is absolutely required
> by the systems on the other end".  But lots of people don't ask
> and even fewer listen.   Neither RFC 5321/5322 nor RFC 5536
> offer any reciprocal guarantees.

RFC 1849 has a very good advice:  "Avove all, prevent loops."

The Usefor folks, or rather Russ, considered to write a gateway
memo after 5537 (not the same as 5536).  Some of the topics you
didn't find in 5322 & 5536 are covered in 5321 & 5537.  Sadly you
can't put more about this in 5321bis, and actually it should get
its own memo -- 5321 & 5537 aren't the place for gateway details.

>> EAI won't make that worse.

> If there are fragile systems out there -- and there almost
> certainly still are-- how can you possibly know that?

It is a guess:  Gateway operators who manage to get it right for
message/rfc822 <-> something based on EBCDIC could also manage
to get it right for message/global <-> something UTF-EBCDIC, or
simply reject message/global.  In other words, when I'm opposed
to UTF-8 in message-IDs I'm not worried about breaking gateways.

> In spite of being co-author of CRAM-MD5, I don't understand this
> comment at all.  Certainly the CRAM-MD5 spec, regardless of its
> other strengths and weaknesses, doesn't even mention Message-IDs

Quoth 2195:  "The syntax of the unencoded form must correspond to
that of an RFC 822 'msg-id' [RFC822] as described in [POP3]."

APOP and CRAM-MD5 use the syntactical form of a Message-ID for
their challenges.  You didn't write "globally unique forever", but
the Message-ID challenges are still supposed to be "unique".

-Frank