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Re: [ietf-smtp] [dispatch] BCP proposal: regular expressions for Internet Mail identifiers

2016-03-29 11:34:51

--On Tuesday, March 29, 2016 11:45 -0400 "Dale R. Worley"
<worley(_at_)ariadne(_dot_)com> wrote:

Here's another ugly little bit of processing:  On some
systems, library routines that convert dotted-number IP
address strings into four-octet format treat a component that
starts with "0" as being written in octal. E.g.,
"" is equivalent to "".  (Try executing
"dig @" on a Linux system.)  As far as
I know, this isn't *specified* anywhere in the RFCs, and some
RFCs (e.g., RFC 997) have leading zeros on numbers that
contain "9".  So it's worth warning people not to use leading
zeros in IPv4 addresses.

And that comment identifies another ugly little issue.  An email
address of example-user@ implies that
"" is a domain name and "010" (the rightmost
label) is a TLD.   Because there is no such TLD (nor is there
one for "8."), such an address is an error, so, if a
mail-related regular expression document pursues that question
at all, it would allow something that violated 5321 no matter
whether 010 is interpreted as "2", "8", "10", "16", STX,
Backspace, DLE, or something else.

I'm not suggesting Sean would do that, only emphasizing (again)
the dangers of developing a second spec (or two specs more
generally) that is inadvertently not quite consistent with the
other one.


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