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https://issues.apache.org/jira/browse/DAFFODIL-2132?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16844294#comment-16844294
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Michael Beckerle commented on DAFFODIL-2132:
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Ultimately, the hasFraming method of Terms is what is giving entirely the wrong
answer due to this.
> isKnownNotEmpty for delimiters is misused. Need isKnownNonZeroLength for
> delimiters
> -----------------------------------------------------------------------------------
>
> Key: DAFFODIL-2132
> URL: https://issues.apache.org/jira/browse/DAFFODIL-2132
> Project: Daffodil
> Issue Type: Bug
> Components: Clean Ups, Middle "End"
> Affects Versions: 2.3.0
> Reporter: Michael Beckerle
> Priority: Major
>
> There are many optimizations based on whether a term (element or model group)
> has framing, which is defined as meaning if it has initiator/terminator, for
> example, and the expressions for those satisfy "isKnownNonEmpty".
> This is a bad mixup. The property being "isKnownNotEmpty" means that the
> property in the schema doesn't have "" as its value.
> That's not at all what is being asked of the these delimiter expressions.
> What the optimizations want to know is if the delimiter is able to occupy
> zero bits in the data stream, or known to require some non-zero number of
> bits in the data stream.
> Currently this expression:
> dfdl:terminator='\{ if (...) then "%WSP*;" else "%#x7F;" }
> satisfies the isKnownNonEmpty test. But depending on the predictate test, if
> this returns "%WSP*;", which is allowed when dfdl:lengthKind is NOT
> delimited, then this could match zero bits.
> To fix this, scaladoc has been added to hasInitiator, hasTerminator, and
> hasSeparator to warn about this.
> But we really need to define isKnownNonZeroLength for delimiters so that
> calculations for terms like isKnownNonZeroLength can be correct.
> isKnownNonZeroLength can be false for delimiters that have expressions as
> their values, always for initiators, and false for terminators/separators
> when lengthKind is not 'delimited'. So that it does not have to involve
> analysis of the expression.
>
>
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