[DFDL-WG] Clarification: zero-bit-long integer parses to value 0, or parse-error or?

[Steve Hanson]

This is covered by section 9.3.2 (establishing representation) and section 
9.5 (evaluation order). 

Your integer is not nillable, so can't have nil rep. Assuming compliance 
with dfdl:emptyValueDelimiterPolicy it therefore has empty representation. 
Assuming this is a local element with minOccurs-=1 implicitly, and no 
default value, it is a parsing error. Section 9.5 says the assert will 
never be executed as it is lower down the evaluation order. 

Regards
 
Steve Hanson
IBM Hybrid Integration, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh at uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890
Note: I work Tuesday to Friday 



From:   Mike Beckerle <mbeckerle.dfdl at gmail.com>
To:     DFDL-WG <dfdl-wg at ogf.org>
Date:   19/03/2020 22:50
Subject:        [EXTERNAL] [DFDL-WG] Clarification: zero-bit-long integer 
parses to value 0, or parse-error or?
Sent by:        "dfdl-wg" <dfdl-wg-bounces at ogf.org>




Consider: 
<xs:element name="spare" dfdl:length="{ $tns:WordPaddingBits }">
  <xs:simpleType dfdl:lengthKind="explicit">
   <xs:annotation>
    <xs:appinfo source="http://www.ogf.org/dfdl/">
      <dfdl:assert test="{ . eq 0 }" />
    </xs:appinfo>
   </xs:annotation>
   <xs:restriction base="xs:unsignedInt">
    <xs:enumeration value="0" />
   </xs:restriction>
  </xs:simpleType>
</xs:element>

Now, suppose the variable tns:WordPaddingBits has value 0. 
So this padding integer will be length 0 (this binary data with 
lengthUnits bits). 
Currently, Daffodil gives a runtime SDE on this. The assert test 
expression complains that "." has no value.
I would claim this should either provide a value of 0 for this integer, or 
it should be a parse error because you must have at least 1 bit.

Thoughts?
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Owl Cyber Defense | 
www.owlcyberdefense.com (Tresys is now part of Owl)
Please note: Contributions to the DFDL Workgroup's email discussions are 
subject to the OGF Intellectual Property Policy

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