Re: [IPv6] Case-sensitivity issue of zone identifiers in draft-ietf-6man-rfc6874bis-05

[Ted Hardie <[e-mail]>]

On Tue, Mar 14, 2023 at 8:42 PM Brian E Carpenter <
[e-mail]> wrote:

> Shang,
>
> You are correct, and I feel that the underlying issue here is that
> RFC 4007 under-specifies the Zone ID format, which is very hard to
> fix. But the URI syntax is very explicit that "the scheme and host
> are case-insensitive." I don't see that we can really override that
> with a SHOULD and expect the browsers to follow along.


I think that it is true, and that the guidance on this is pretty clear.
RFC 8820 has this text in Section 2.2:

Scheme definitions define the presence, format, and semantics of an
authority component in URIs; all other Specifications MUST NOT constrain or
define the structure or the semantics for URI authorities, unless they
update the scheme registration itself or the structures it relies upon
(e.g., DNS name syntax, as defined in Section 3.5
<https://www.rfc-editor.org/rfc/rfc1034#section-3.5> of [RFC1034
<https://www.rfc-editor.org/rfc/rfc8820#RFC1034>]).For example, an
Extension or Application cannot say that the "foo" prefix in "
https://foo_app.example.com" is meaningful or triggers special handling in
URIs, unless they update either the "http" URI scheme or the DNS hostname
syntax.Applications can nominate or constrain the port they use, when
applicable. For example, BarApp could run over port nnnn (provided that it
is properly registered).

regards,

Ted Hardie

> I understand
> that it's relatively easy for a stand-alone parser to do this, but
> the browser implementations are a different story.
>
>     Brian
>
> On 14-Mar-23 19:54, Shang Ye wrote:
> > Hi Brian,
> >
> > I notice that the current version of the draft mentions the
> case-sensitivity issue
> > of zone identifiers in this paragraph:
> >
> >> RFC 3986 also states that the host subcomponent of a URI is case-
> >> insensitive and is normalised to lower case.  The mechanism described
> >  > here will therefore fail for zone identifiers that contain upper case
> >  > letters, since RFC 4007 implies case-sensitivity.
> >
> > Indeed it has pointed out the issue, but it doesn't really tell people
> how a
> > zone identifier that contain upper case letters may be resolved. Should
> > they pass it directly to a mapping function, say `if_nametoindex`,
> normalize
> > it to lower case first, or, "fail" to resolve it as implied in the
> paragraph?
> >
> > When I modified my own URI parser to support rfc6874bis, I felt that the
> only
> > correct option is passing the zone identifier as it is, considering the
> fact that
> > interface names are case-sensitive on Linux. Personally I feel it quite
> wrong
> > to either reject an uppercase zone identifier or turn it into lower case
> first.
> >
> > Also, I notice that you doubted that making zone identifiers
> case-sensitive
> > would cause a major problem for the URI parsers in every browser,
> especially in Firefox.
> > I admit that some browsers may have their *URL* parsing code so
> convoluted that it can be very hard to make the change, but I believe that
> it isn't
> > the case with those relatively simple *URI* parsers that serve other use
> cases.
> >
> > Therefore, I'd suggest we instead say somewhere in Section 3 that "URI
> parsers SHOULD treat a
> > zone identifier as case-sensitive and preserve the letter case of a zone
> identifier when
> > it is normalized as part of a URI or mapped into a numeric zone index."
> > This way it'd be okay if browser people decide it's unreasonably hard to
> > follow this specific requirement, and it would benefit the users of
> other conforming
> > implementations by ensuring that everything goes just as expected.
> >
> > Regards,
> > Shang
> >
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