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Subject: RE: [Openxri-users] [xri] iquery, ifragment and xref
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Wil and Harry, Sorry for my delay on responding; lots
going on as we work up to getting the XRI GRS launched next week. Harry’s right – I didn’t
understand the full extent of what Wil was originally asking. Wil, I think the
disconnect is that there is an inherent assumption in XRI syntax that XRI parsers
understand cross-references. To take your example: xri://@example*(xri://=foo/bar#baz) An XRI parser should not have any problem
understanding the embedded cross-reference “(xri://=foo/bar#baz)”,
even though it contains a pound sign, because as soon as it sees the opening
paren “(“, it should know this is the start of a cross-reference and
it should ignore any other character between it and the closing paren “)”.
In other words, to an XRI parser, the XRI should effectively be as transparent
as: xri://@example*(xxxxxxxxxxxxxxxxxx) I am pretty sure that Epok said that the
XRI parser they originally contributed did not “do” cross-references
completely, and maybe that’s what you are now discovering. So for an XRI in XRI-normal form, “xri://@example*(xri://=foo/bar#baz)”
does not require any escaping. The embedded cross-reference only requires
escaping in conversion to IRI-normal form. However the following XRI *does* require escaping even in XRI-normal
form in order for the full cross-reference (which is meant to include “)foo”)
to not be ambiguous: xri://@example*(xri://=foo/bar#baz)foo) must
be escaped to… xri://@example*(xri://=foo/bar#baz%29foo) Hope this helps, =Drummond From: Dirty Harry
[mailto:dirty-harry@users.sourceforge.net] Hello everybody I agree with Wil, that it's not section
2.3.2 we can apply to the given problem. But section 2.2.2 says “It is important that the value of a
cross-reference be syntactically unambiguous, whether it is an absolute IRI or
one of the various forms of an XRI reference”.
Maybe this sentence implies the escaping requirement mentionned by Drummond. Regards Harry From:
openxri-users-bounces@lists.sourceforge.net [mailto:openxri-users-bounces@lists.sourceforge.net]
On Behalf Of Tan, William I’m confused now. Section 2.3.2 says
“To avoid this type of misinterpretation, certain characters in a
cross-reference must be percent-encoded when transforming an XRI reference into
IRI-normal form.” This seems to be about the rules for an XRI reference
in IRI-normal form. I’m talking about an XRI reference
in XRI normal form. If I would like to embed an XRI
“xri://=foo/bar#baz” in a cross reference to become: xri://@example*(xri://=foo/bar#baz) That is legal according to the XRI syntax,
but the parser (or rather the lexer component of) has a hard time recognizing
the final “)” as belonging to the enclosing cross reference because
when it encounters the “#”, it is consuming “ifragment”
characters, which expands out to *(ipchar / “/” / “?”)
in the syntax. Since “)” is part of “ipchar”, it could
belong to the fragment. The workaround I’m doing right now
is to use xri-pchar instead of pchar in in iquery and ifragment, essentially
creating two new productions: xri-query and xri-fragment, which is at odds with
2.2.4 and 2.2.5. From: Wil, This problem is described in detail in
section 2.3.2 of the XRI Syntax 2.0 spec. IRIs (or other XRIs) that are
embedded as cross-references in an XRI will always need to be escaped so that
the cross-reference itself is not ambiguous. For example, if the actual query string in
the XRI below…
xri://=foo*(xri://bar?baz=bar)) …is supposed to be
“baz=bar)” (not the closing paren is part of the query), then this
MUST be escaped to…
xri://=foo*(xri://bar?baz=bar%29) Again, see the rules at the end of section
2.3.2. (I imagine these were the ones not implemented in the OpenXRI parser yet
because they are, frankly, the tough ones!) =Drummond From: Hi folks, Sorry for the cross posting. This is an issue that I
encountered in the OpenXRI parser and triggered by Harry’s test case that
the parser currently is not able to process: xri://@example/(http://www.openxri.org/) Looking at the above example, because the identifier within
the parenthesis above is an IRI, and the closing parenthesis “)” is
a legal character in an IRI, the parser doesn’t know when the IRI
terminates and consumes everything resulting in an IRI
“http://www.openxri.org/)” and leaves the cross reference open. Ok,
this is not the reason that the parser choked – it choked because IRI
cross references are simply not implemented but I’ve encountered another
two anomalies with the XRI syntax: The ABNF for XRI uses IRI’s “iquery” and
“ifragment” which also boils down to “sub-delims”,
unlike XRI path-* productions which boil down to a much smaller
“xri-sub-delims”. This means that the parser would not be able to
disambiguate: xri://=foo*(xri://bar?baz=bar)) when the query in the embedded XRI reference is
“baz=bar)”. I’m not sure if this has been discussed on the list
before.. =wil (http://xri.net/=wil) |
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