[DFDL-WG] clarification on when escape characters are needed
Mike Beckerle
mbeckerle.dfdl at gmail.com
Wed Jun 19 09:28:44 EDT 2013
The only for-sure fix to this issue I see is that you have to change the
model. You can't model the = as a separator, because it is legal to appear
unescaped in the content of the second child element.
So, you have to model this as a sequence with no separator, of two children
elements. The first of which has "=" as its terminator. Then there is no
interpretation of = as framing/syntax in the second element.
There is some discussion currently of whether the last child element should
require escaping of an infix separator, but regardless of the outcome of
that, the above technique will work, and is preferred in the sense that
there's no question about it.
...mike
On Wed, Jun 19, 2013 at 9:01 AM, Garriss Jr., James P.
<jgarriss at mitre.org>wrote:
> This origin of this issue is the Content-Type header in email, where the
> parameters can be quoted, but sometimes are not:****
>
> ** **
>
> Content-Type: text/html; charset=”UTF-8”****
>
> Content-Type: text/html; charset=UTF-8****
>
> ** **
>
> This was not a big deal until I ran into a parameter that included an = in
> the value:****
>
> ** **
>
> Content-Type: multipart/alternative;
> boundary="----=_Part_150709_149622714.1370937621731"****
>
> ** **
>
> When confronted with this issue, I was told:****
>
> ** **
>
> >> there's a pretty simple****
>
> >> fix: specify an escape scheme that says that anything inside quotes is*
> ***
>
> >> not a delimiter. And fortunately your DefaultProperties.xsd file****
>
> >> actually comes an escape scheme that does exactly that.****
>
> >>** **
>
> >> So all you have to do is add this:****
>
> >>** **
>
> >> dfdl:escapeSchemeRef="DefaultPropertiesEscapeScheme"****
>
> >>** **
>
> >> to this:****
>
> >>** **
>
> >> <xsd:element name="value" type="xsd:string" />****
>
> >>** **
>
> ** **
>
> You may well recognize this scheme, as it’s yours:****
>
> ** **
>
> <dfdl:defineEscapeScheme name=
> "DefaultPropertiesEscapeScheme">
> <dfdl:escapeSchemeescapeBlockEnd
> =""" escapeBlockStart="""
> escapeCharacter
> =""" escapeEscapeCharacter=""" escapeKind="escapeBlock"
>
> extraEscapedCharacters=", %#x0D; %#x0A;" generateEscapeBlock="whenNeeded"
> > </dfdl:escapeScheme>
> </dfdl:defineEscapeScheme>****
>
> ** **
>
> I used this solution for the parameters of the Content-Type header, which
> are key/value pairs.****
>
> ** **
>
> <xsd:sequence dfdl:separator="=">
> <!-- this init is a workaround for Daffodil 0.10 bug (see
> ContentType element above) -->
> <xsd:element name="key" dfdl:initiator="%WSP*;">
> <xsd:annotation>
> <xsd:appinfo source="http://www.ogf.org/dfdl/dfdl-1.0/
> ">
> <dfdl:assert test="{ dfdl:checkConstraints(.) }"message
> ="The parameter key must match one of the values on the enumerated list."
> />
> </xsd:appinfo>
> </xsd:annotation>
> <xsd:simpleType>
> <xsd:restriction base="xsd:string">
> <xsd:enumeration value="charset"/>
> <xsd:enumeration value="name"/>
> <xsd:enumeration value="boundary"/>
> </xsd:restriction>
> </xsd:simpleType>
> </xsd:element>
> <!-- Daffodil 0.10.1 fails here if there's an = in the value.
> -->
> <xsd:element name="value" type="xsd:string"dfdl:escapeSchemeRef
> ="DefaultPropertiesEscapeScheme"/>
> </xsd:sequence>****
>
> ** **
>
> Without the scheme, I get an error. With it, it works great.****
>
> ** **
>
> So is this an inappropriate use of an escape scheme? ****
>
> ** **
>
> *From:* Steve Hanson [mailto:smh at uk.ibm.com]
> *Sent:* Wednesday, June 19, 2013 8:47 AM
> *To:* Garriss Jr., James P.
> *Cc:* dfdl-wg at ogf.org; Mike Beckerle
> *Subject:* RE: [DFDL-WG] clarification on when escape characters are
> needed****
>
> ** **
>
> James
>
> I don't see how an escape scheme helps here. The "f82+=7&%q" is all
> data, there's no escape character.
>
> Regards
>
> Steve Hanson
> Architect, IBM Data Format Description Language (DFDL)
> Co-Chair, OGF DFDL Working Group <http://www.ogf.org/dfdl/>
> IBM SWG, Hursley, UK*
> *smh at uk.ibm.com
> tel:+44-1962-815848 <+44-1962-815848>
>
>
>
> From: "Garriss Jr., James P." <jgarriss at mitre.org>
> To: Steve Hanson/UK/IBM at IBMGB, Mike Beckerle <
> mbeckerle.dfdl at gmail.com>,
> Cc: "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>
> Date: 19/06/2013 12:33
> Subject: RE: [DFDL-WG] clarification on when escape characters are
> needed ****
> ------------------------------
>
>
>
>
> > The DFDL 1.0 spec implies the behaviour where you get…
>
> If this is the direction the WG goes, can you please make this explicit
> rather than implicit? Using Mike’s excellent example below would go a long
> way to making the issue clear.
>
> As for a solution, would it not be better to use an escape scheme, like
> this?
>
> <sequence dfdl:separator="=" dfdl:separatorPosition="infix">
> <element name="a" type="xs:string"/>
> <element name="b" type="xs:string"
> dfdl:escapeSchemeRef="DefaultPropertiesEscapeScheme"/>
> </sequence>
>
> (Cred to Taylor)
>
> If so, it would be helpful to include that in the example.
>
> *From:* dfdl-wg-bounces at ogf.org [mailto:dfdl-wg-bounces at ogf.org<dfdl-wg-bounces at ogf.org>]
> *On Behalf Of *Steve Hanson*
> Sent:* Wednesday, June 19, 2013 5:29 AM*
> To:* Mike Beckerle*
> Cc:* dfdl-wg at ogf.org*
> Subject:* Re: [DFDL-WG] clarification on when escape characters are needed
>
> The DFDL 1.0 spec implies the behaviour where you get:
>
> <a>password</a>
> <b>f82+</b>
>
> followed by a processing error. There is no special casing of the last
> element in the group.
>
> Changing the model to the following achieves the desired infoset:
>
> <sequence dfdl:separator="=" dfdl:separatorPosition="infix">
> <element name="a" type="xs:string"/>
> <sequence dfdl:separator="">
> <element name="b" type="xs:string"/>
> </sequence>
> </sequence>
>
>
> Regards
>
> Steve Hanson
> Architect, IBM Data Format Description Language (DFDL)
> Co-Chair, OGF DFDL Working Group <http://www.ogf.org/dfdl/>
> IBM SWG, Hursley, UK*
> *smh at uk.ibm.com*
> *tel:+44-1962-815848 <+44-1962-815848>
>
>
>
> From: Tim Kimber/UK/IBM at IBMGB
> To: dfdl-wg at ogf.org,
> Date: 19/06/2013 09:37
> Subject: Re: [DFDL-WG] clarification on when escape characters are
> needed
> Sent by: dfdl-wg-bounces at ogf.org ****
> ------------------------------
>
>
>
>
>
> In the IBM implementation we have taken the view that the separator
> defines the format for all of the group's content. That means that all
> separators are counted as being significant, even if they occur within the
> content region of the final group member.
> I agree that other interpretations are possible - the MRM parser in
> earlier versions of WebSphere Message Broker takes an infix separator out
> of scope when it encounters the final declared child of a group.
>
> I intend to address this point when I write up the rules for matching
> string literals and delimiters.
>
> regards,
>
> Tim Kimber, DFDL Team,
> Hursley, UK
> Internet: kimbert at uk.ibm.com
> Tel. 01962-816742
> Internal tel. 37246742
>
>
>
>
> From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
> To: dfdl-wg at ogf.org,
> Date: 19/06/2013 03:52
> Subject: [DFDL-WG] clarification on when escape characters are
> needed
> Sent by: dfdl-wg-bounces at ogf.org ****
> ------------------------------
>
>
>
>
>
>
> Suppose I have a sequence. It has an infix separator which is "=".
>
> <sequence dfdl:separator="=" dfdl:separatorPosition="infix">
> <element name="a" type="xs:string"/>
> <element name="b" type="xs:string"/>
> </sequence>
>
> Now, consider this data:
>
> password=f82+=7&%q
>
> I want
>
> <a>password</a>
> <b>f82+=7&%q</b>
>
> Notice how the b element contains an '=' which was not escaped in any way
> in the sequence. Element b is statically known to be last, the separator is
> infix; hence, things are unambiguous even if there is no escaping.
>
> However, there is an alternative interpretation, which is that the above
> data should fail, because it produces <a>password</a><b>f82+</b> but then
> does not find the expected stuff next. Rather it finds the '=7&%q' data. In
> other words, the sequence separator divides the sequence content into 3
> content regions, but there aren't 3 things to consume those, so it is a
> processing error.
>
> Which is correct?
>
> --
> Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
> www.tresys.com
> --
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> *https://www.ogf.org/mailman/listinfo/dfdl-wg
>
> Unless stated otherwise above:
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> 741598.
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> Unless stated otherwise above:
> IBM United Kingdom Limited - Registered in England and Wales with number
> 741598.
> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
>
> Unless stated otherwise above:
> IBM United Kingdom Limited - Registered in England and Wales with number
> 741598.
> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
> ****
>
> --
> dfdl-wg mailing list
> dfdl-wg at ogf.org
> https://www.ogf.org/mailman/listinfo/dfdl-wg
>
--
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
www.tresys.com
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