[rfc-i] Re: ABNF (RFC2234) vs HTTP's augmented BNF syntax (RFC822 + RFC2616)

Bruce Lilly blilly at erols.com
Mon Feb 14 08:31:03 PST 2005


>  Date: 2005-02-12 16:06
>  From: Julian Reschke <julian.reschke at gmx.de>

> So the summary would be that it's ok to invoke the "implied LWS" rule 

Note that that is a rich source of potential interoperability
problems.  For example, RFC 822 has such a rule, and an RFC 822
Date field might look like:
  Date: 1 Jan 2004 12 : 34 : 56 -0700
or like
  Date:1Jan2004 12:34:56-0700
etc.
Parser implementations from incautious developers might fail to
correctly parse field instances where the optional LWS is absent,
as in the second example above, or in cases where optional LWS is
present, such as around the colons in the first example above.
Note that RFC 2822 explicitly specifies where FWS and CFWS are
permitted, required, and (by omission) prohibited -- the rules
are explicit rather than implicit.


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