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	Tue, 31 Mar 2020 08:32:50 +0000 (UTC)
Date: Tue, 31 Mar 2020 08:32:50 +0000
From: Eric Wong <e@yhbt.net>
To: meta@public-inbox.org
Subject: how to gracefully handle spaces in Message-IDs?
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There exist Message-IDs with spaces in them, at least (and
maybe other strangeness)

Take this example:

https://lore.kernel.org/lkml/200203040330.g243URr05337@3%20(NXDOMAIN)%20/

That is:

	Message-ID: <200203040330.g243URr05337@3 (NXDOMAIN) >

RFC 3977 (NNTP) struggles with that with HDR/XHDR commands,
since it's split-on-spaces-or-tabs behavior.

Not only that, even with a successful attempt to handle
parsing of spaces in the Message-ID for -nntpd requests,
Net::NNTP has trouble parsing responses with spaces in the
Message-ID.  I haven't tried other NNTP clients, but I don't
expect clients to know what to do with invalid Message-IDs
in responses, either...

RFC 5322, Appendix A.6.3. Obsolete White Space and Comments
<https://tools.ietf.org/html/rfc5322#appendix-A.6.3> has
a particularly nasty example:

	Message-ID  : <1234   @   local(blah)  .machine .example>

And RFC 733 is full of examples with spaces in Message-IDs for
the historically-inclined: <https://tools.ietf.org/html/rfc733>

But I haven't found relevant docs on how to handle that case
for NNTP in RFC 977 or 3977...

In innd(*), the nnrpd/article.c::CMDpat function for HDR/XHDR
commands calls lib/messageid.c::IsValidMessageID with the
`stripspaces' parameter as `true', but `stripspaces' only strips
leading and trailing whitespace.

So I'm thinking at least stripping leading+trailing spaces
is something we should be doing, and spaces in the middle
of the Message-ID need to be preserved.

But, maybe non-printable control characters can also be filtered
out entirely, since I've definitely seen those in headers when
they don't belong.  I suspect those were introduced by hardware
errors or software bugs.

Anyways, my head hurts :<

(*) svn co https://inn.eyrie.org/svn/trunk innd,