We don't currently support the fixed attribute:
https://issues.apache.org/jira/browse/DAFFODIL-117
Validation="on" gives errors but that's because for that validation mode
we just feed Xerces the schema and the XML infoset and it performs
schema validation itself. We don't implement any of that validation code.
We do implement some custom validation code for "limited" validation,
but we currently only validate things like restrictions.
To support this, we would likely want to add new members to the DSOM to
extract this value from the schema so that grammars/runtimes could have
access to it. I imagine it would be very similar to how we handle the
default attribute. Which does something like this in ElementDeclMixin.scala:
final lazy val defaultAttr = xml.attribute("default")
final def hasDefaultValue: Boolean = defaultAttr.isDefined
final lazy val defaultValueAsString = {
...
}
There's also the following in ElementBase.scala which converts that
string value to value with the correct primitive type:
final lazy val defaultValue = {
...
}
Doing something similar for the fixed attribute would add new properties
to the DSOM, which would then make it available in the Grammar and runtimes.
On 2/15/21 4:23 PM, Interrante, John A (GE Research, US) wrote:
> I have a question for more experienced Daffodil maintainers. Suppose a
> schema contains some fixed="constant" attributes:
>
> <xs:complexType name="Limits">
> <xs:sequence>
> <xs:element name="sync0" fixed="210" type="idl:uint8"/>
> <xs:element name="sync1" fixed="13" type="idl:uint8"/>
> <xs:element name="id" fixed="34" type="idl:uint8"/>
> <xs:element name="length" fixed="0" type="idl:uint8"/>
> <xs:element name="checksum" type="idl:uint16"/>
> </xs:sequence>
> </xs:complexType>
> <xs:element name="LimitsDecl" type="idl:Limits"/>
> </xs:schema>
>
> If a TDML test suite turns on validation="on", Daffodil runtime1 will call
> Xerces to perform validation on an XML infoset and Xerces will report a
> validation error if, say, element sync0 does not contain the right value:
>
> [Fail] limits_parse
> Failure Information:
> (Implementation: daffodil) Validation errors found where none were
> expected by the test case.
> Validation Error: cvc-elt.5.2.2.2.2: The value '208' of element 'sync0'
> does not match the {value constraint} value '210'.
>
> I want Daffodil runtime2 to detect the presence of a fixed="constant"
> attribute on a schema grammar object and generate C code to check that the
> corresponding C struct member contains the right value. However, I don't
> know how to write code to find the "fixed" attribute on a schema grammar
> object when runtime2 calls a class like
> BinaryIntegerKnownLengthCodeGenerator. I set a breakpoint in the debugger
> but a quick search found the fixed attribute only in a shareKey value.
>
> How can I detect the presence of the fixed attribute and get its value in
> BinaryIntegerKnownLengthCodeGenerator?
>
> John
>
