RE: [xri-editors] Xref escaping rules

["Dave McAlpin" <dave.mcalpin@epokinc.com>]

Here's the proposed text around this issue if you're interested.

XRIs MUST use escaped encoding as described in [RFC2396]. XRIs also have
additional escaping rules described below.

XRIs can contain nested URIs as cross-references (see section [TODO]). These
nested URIs can contain characters that, if unescaped, would cause
misinterpretation when parsing the enclosing XRI. Consider the following
XRI.

xri:@example/(http://www.example.com?id=1)

The generic parsing algorithm described in [RFC2396] would separate the
above XRI into the following components

scheme = xri
authority = <undefined>
path = @example/(http://www.example.com?
query = id=1)

The desired separation is

scheme = xri
authority = <undefined>
path = @example/(http://www.example.com?id=1)
query = <undefined>

To avoid this type of misinterpretation, a URI (including an XRI) must be
escaped before it can be used as a cross-reference. In particular, it  MUST
be converted such that the percent "%" character is escaped as "%25", the
question mark "?" character is escaped as "%3F" and the pound sign "#" is
escaped as "%28".

The example above, then, would be correctly expressed as

xri:@example/(http://www.example.com%3Fid=1)

Cross-references may be nested to any depth. The above rule is applied to
each nesting level. For example, if the above XRI was used as a
cross-reference, the percent sign "%" would be escaped to "%25".

xri:@example1/( xri:@example/(http://www.example.com%253Fid=1))

Furthermore, parentheses "(" and ")" MUST be escaped if they appear in a URI
but do not delimit an XRI cross-reference.  If an XRI cross-reference is
embedded within an enclosing cross-reference, the parentheses delimiting the
inner cross-reference MAY be escaped, but this is NOT RECOMMENDED because it
complicates comparison. For example

xri:@example1/( xri:@example/(http://www.example.com%253Fid=1))

is preferred to

xri:@example1/( xri:@example/%28http://www.example.com%253Fid=1%29)

although both are legal and equivalent.

Before a URI may be used as a cross-reference, then, the following steps
MUST be performed in order:

1.	Escape all percent "%" characters as "%25".
2.	Escape all parentheses "(" and ")" that do not delimit XRI
cross-references as "%28" and "%29", respectively.
3.	Escape all pound "#" characters as "%23".
4.	Escape all question mark "?" characters as "%3F".

Note that the URI is assumed to be in an "escaped" form appropriate to its
scheme before the above rules are applied.

Before a cross-reference is evaluated it MUST first be unescaped. If a
cross-reference is contained in an enclosing cross-reference, the enclosing
cross-reference MUST be unescaped before the inner cross-reference is
evaluated and unescaped.

-----Original Message-----
From: Drummond Reed [mailto:drummond.reed@onename.com] 
Sent: Monday, June 30, 2003 2:30 PM
To: Dave McAlpin; Wachob, Gabe; xri-editors@lists.oasis-open.org
Subject: RE: [xri-editors] Xref escaping rules

+2 (except that it's %28 not #28).

=Drummond 

-----Original Message-----
From: Dave McAlpin [mailto:dave.mcalpin@epokinc.com]
Sent: Monday, June 30, 2003 1:41 PM
To: 'Wachob, Gabe'; Drummond Reed; xri-editors@lists.oasis-open.org
Subject: RE: [xri-editors] Xref escaping rules

Sorry, I misunderstood the question. I'm allowing both in the normative
text
and saying the second is preferred.

-----Original Message-----
From: Wachob, Gabe [mailto:gwachob@visa.com]
Sent: Monday, June 30, 2003 1:35 PM
To: 'Dave McAlpin'; Wachob, Gabe; 'Drummond Reed';
xri-editors@lists.oasis-open.org
Subject: RE: [xri-editors] Xref escaping rules

Really?

So you'd prefer:

xri://foo.bar/(+Gabe/#28+stuff#29)

over

xri://foo.bar/(+Gabe/(+stuff))

I don't see a reason why we need to do escaping for the () on XRI values
as
cross references..

        -Gabe

> -----Original Message-----
> From: Dave McAlpin [mailto:dave.mcalpin@epokinc.com]
> Sent: Monday, June 30, 2003 12:48 PM
> To: 'Wachob, Gabe'; 'Drummond Reed'; xri-editors@lists.oasis-open.org
> Subject: RE: [xri-editors] Xref escaping rules
>
>
> I think these rules apply to cross-references in general,
> both general URIs
> and XRIs.
>
> -----Original Message-----
> From: Wachob, Gabe [mailto:gwachob@visa.com]
> Sent: Monday, June 30, 2003 12:05 PM
> To: 'Dave McAlpin'; Wachob, Gabe; 'Drummond Reed';
> xri-editors@lists.oasis-open.org
> Subject: RE: [xri-editors] Xref escaping rules
>
> Dave-
>       This seems straightforward and I don't know why it
> wasn't the first
> proposal on the table. I can't seem to figure out a problem
> with it, so +1
> unless someone can discover an issue with it.
>
>       BTW, the way I read it is that this escaping is only
> neccesary for
> URIs as xrefs, not XRI values as xrefs...
>
>       -Gabe
>
> > -----Original Message-----
> > From: Dave McAlpin [mailto:dave.mcalpin@epokinc.com]
> > Sent: Monday, June 30, 2003 10:08 AM
> > To: 'Wachob, Gabe'; 'Drummond Reed';
> xri-editors@lists.oasis-open.org
> > Subject: RE: [xri-editors] Xref escaping rules
> >
> >
> > I assumed we would escape iteratively, once for each level
> of nesting
> >
> > 1) Embed http://foo.com?id=21#bar in xri:@foo/baz as a
> cross-reference
> >
> > a) Escape cross-reference to get
> > http://foo.com%3Fid=21%23bar
> >
> > b) Add as cross-reference
> > xri:@foo/baz/(http://foo.com%3Fid=21%23bar)
> >
> > When the cross-reference is extracted, it's unescaped to
> >
> > http://foo.com?id=21#bar
> >
> > 2) Embed http://foo.com?id=21-%28widget#bar in xri:@foo/baz as a
> > cross-refrence
> >
> > a) Escape the cross-reference to get
> > http://foo.com%3Fid=21-%2528widget%23bar
> >
> > b) Append as cross-reference
> > xri:@foo/baz/(http://foo.com%3Fid=21-%2528widget%23bar)
> >
> > When the cross-reference is extracted, it's unescaped to
> >
> > http://foo.com?id=21-%28widget#bar
> >
> > 3) A complex nested example. Embed http://foo.com?id=21-%28widget in
> > xri:+foo.bar.<xref>, which is in turn embedded in
> > xri://foo.bar/<xref>/baz
> >
> > a) First escape the innermost cross-reference to get
> > http://foo.com%3Fid=21-%2528widget
> >
> > b) Add as cross-reference
> > xri:+foo.bar.(http://foo.com%3Fid=21-%2528widget)
> >
> > c) Escape the cross-reference to get
> > xri:+foo.bar.(http://foo.com%253Fid=21-%252528widget)
> >
> > d) Add as cross-reference
> > xri://foo.bar/(xri:+foo.bar.(http://foo.com%253Fid=21-%252528w
> > idget)))/baz
> >
> > When the XRI is evaluated, the outermost cross-reference is
> extracted
> >
> > xri:+foo.bar.(http://foo.com%253Fid=21-%252528widget))
> >
> > And unescaped to give
> >
> > xri:+foo.bar.(http://foo.com%3Fid=21-%2528widget))
> >
> > The next level cross-reference is extracted
> >
> > http://foo.com%3Fid=21-%2528widget
> >
> > and unescaped to give
> >
> > http://foo.com?id=21-%28widget
> >
> > Dave
> >
> > -----Original Message-----
> > From: Wachob, Gabe [mailto:gwachob@visa.com]
> > Sent: Monday, June 30, 2003 9:19 AM
> > To: 'Drummond Reed'; xri-editors@lists.oasis-open.org
> > Subject: RE: [xri-editors] Xref escaping rules
> >
> > Drummond-
> >     This seems pretty reasonable.
> >
> >     Have you considered the case where you have two levels of cross
> > referencing? That is, a cross reference which contains an XRI
> > value that
> > itself has a cross reference?
> >
> > xri://foo.bar/(+foo.bar.(http://www.foo.com#3ffoo))/baz
> >
> > vs
> >
> > xri://foo.bar/(+foo.bar.(http://www.foo.com(#3f)foo))/baz
> >
> > vs
> >
> > xri://foo.bar/(+foo.bar.(http://www.foo.com((#3f))foo))/baz
> >
> > I think you need to amend the rules about escaping/unescaping
> > to account for
> > nesting..
> >
> >     -Gabe
> >
> >
> > > -----Original Message-----
> > > From: Drummond Reed [mailto:drummond.reed@onename.com]
> > > Sent: Sunday, June 29, 2003 1:15 PM
> > > To: xri-editors@lists.oasis-open.org
> > > Subject: [xri-editors] Xref escaping rules
> > >
> > >
> > > Here's the escaping proposal that I brought up on the
> last TC call.
> > > 
> > > The issue is that an XRI or URI is used as a cross-reference
> > > may contain
> > > characters that must be escaped in order to conform with 2396.
> > > Specifically:
> > > 
> > > * "?" may not appear until the start of the one-and-only
> > query segment
> > > allowed by 2396.
> > > * The same is true with "#" for fragments
> > > * Lastly, an UNMATCHED opening or closing paren must be
> > > escaped or else
> > > the cross-reference will not parse correctly. (Note that
> > > MATCHED opening
> > > and closing parens inside do not need escaping because they
> > represent
> > > either a second-level nested cross-reference or a parenthetically
> > > enclosed string in a native URI but either way will not be
> > ambiguous.)
> > > 
> > > However we can't use just 2396 escaping rules (i.e., "%xx"
> > where xx is
> > > the hex value of the character) for these four characters
> > > because it if
> > > the embedded XRI or URI contained those same escape sequences
> > > natively,
> > > it would be ambiguous which to unescape and not to
> unescape when the
> > > cross-reference is extracted. For example, if a URI already
> > contained
> > > the escape sequence %3F (the "?" character) before it was
> > > turned into a
> > > cross-reference, how would the parser know NOT to unescape it when
> > > extracting the cross-reference?
> > > 
> > > The proposed solution is to apply two special escaping
> rules to any
> > > URI/XRI string being embedded as a cross-reference. They must
> > > be applied
> > > in the following order:
> > > 
> > > 1) Parse the string to find any instance of "%3F", "%23",
> "%28", or
> > > "%29" and enclose these in parens. Example: "(%3F)".
> > > 2) Escape any "?", "#", or UNMATCHED paren as per 2396 escaping.
> > > Example: a URI that contained a query would have the "?"
> turned into
> > > %3F.
> > > 
> > > To extract a cross-reference, apply the same two rules in
> > > reverse, i.e.:
> > > 
> > > 1) From the extracted cross-reference, escape any instance of
> > > %3F, %23,
> > > %28, or %29 EXCEPT those enclosed in parens.
> > > 2) For any instance of "%3F", "%23", "%28", or "%29" enclosed
> > > in parens,
> > > remove the parens.
> > > 
> > > Example:
> > > 
> > > Embed: URI "http://foo.com/?id=21#bar" in XRI "xri:@foo/baz/"
> > > Result: "xri:@foo/baz/(http://foo.com/%3Fid=21%23bar)"
> > > 
> > > 
> > > Embed: URI "http://foo.com/?id=21-%28widget#bar" in XRI
> > > "xri:@foo/baz/"
> > > Result: "xri:@foo/baz/(http://foo.com/%3Fid=21-(%28)widget%23bar)"
> > > 
> > > Does this work for everyone? Any other proposals?
> > > 
> > > =Drummond
> > > 
> > > 
> > > 
> > > 
> > >
> > >
> >
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