Re: Empty lists in Structured Headers (#781)

[Mark Nottingham <[e-mail]>]

On 2 May 2019, at 4:24 pm, Julian Reschke <[e-mail]> wrote:
> 
> In
> <https://greenbytes.de/tech/webdav/draft-ietf-httpbis-header-structure-10.html#specify>,
> we currently say:
> 
> "Specify the header field’s allowed syntax for values, in terms of the
> types described in Section 3, along with their associated semantics.
> Syntax definitions are encouraged to use the ABNF rules beginning with
> “sh-“ defined in this specification."
> 
> Does this mean, that a definition like
> 
>  MyField = [ sh-list ]
> 
> is an acceptable use of the syntax? (see
> <https://github.com/httpwg/http-extensions/issues/781#issue-426418064>).

I think it's a *possible* use of the syntax; however, you'd need to accompany it with some prose that directed the parser what to do when SH parsing fails on an empty value. SH pretty strongly steers people away form doing that, so if by "acceptable" you mean "recommended", I think no.

Happy to clarify the text you quote above to make that more clear (we probably need to take another pass at the author recommendations anyway).

Cheers,



--
Mark Nottingham   https://www.mnot.net/