Thanks, Steve. Once you told me where to look, I was able to search the xml
and find the fixed attribute's value directly in
BinaryIntegerKnownLengthCodeGenerator using two lines of code:
val fixed = e.xml.attribute("fixed")
val fixedValue = if (fixed.isDefined) fixed.get.text else ""
Since this code runs only once for each integer element while generating C code
in runtime2, I don't expect performance to be affected significantly. If
people want runtime1 to perform limited validation on the fixed attribute, then
we'd have to add new members to the DSOM as you suggested below. How often do
people run Daffodil in limited validation mode and would they want Daffodil
runtime1 to check the fixed attribute in limited validation mode too?
We can make runtime2 pay attention to the validation mode later - for now I
plan to always generate the validation check in runtime2 since we want the C
code to enforce message field restrictions as best as it can. Is that OK with
people?
John
-----Original Message-----
From: Steve Lawrence <[email protected]>
Sent: Monday, February 15, 2021 4:59 PM
To: [email protected]
Subject: EXT: Re: runtime2: how to find "fixed" attribute in compiled schema
objects?
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
>
