Mike Beckerle created DAFFODIL-2429:
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Summary: newVariableInstance and setVariable require 'direction'
property
Key: DAFFODIL-2429
URL: https://issues.apache.org/jira/browse/DAFFODIL-2429
Project: Daffodil
Issue Type: Bug
Components: Back End, Front End
Affects Versions: 3.0.0
Reporter: Mike Beckerle
I have updated the PCAP schema on github to illustrate this issue.
This is a pull request (code review) of the changes
[https://github.com/DFDLSchemas/PCAP/pull/10]
In the PCAP schema the IPSrcGrp group ref appears immediately before the IPSrc
element. Similarly the IPDestGrp reference appears immediately before the
IPDest element.
These groups contain elements which are the individual binary bytes of the IP
Source and IP Dest addresses. They are 4 unsigned bytes.
When parsing these are parsed and then their values concatenated as strings
into a string like "1.2.3.4".
When unparsing, these groups use dfdl:outputValueCalc to take apart a string
like "1.2.3.4" (which appears in the infoset after parsing), back into its
individual digits 1, 2, 3, 4, and creates an unsignedByte value of each number.
The problem is, these groups are absolute nonsense if you view the
dfdl:newVariableInstance defaultValue expression as being evaluated at parse
time. The expression is for use *only* at unparse time and immediately does a
forward reference to the following IPSrc member containing the "1.2.3.4" type
string.
Without some sort of additional property on dfdl:newVariableInstance and
dfdl:setVariable to indicate that this only should be evaluated at unparse
time, there is no way to suppress evaluation and perform it only at unparse
time.
I suggest we need an additional property on newVariableInstance and setVariable
which I suggest is called 'direction', with values 'parse', 'unparse', 'both'.
This property defaults to 'both', but if set to 'unparse' only evaluates the
expression (and binds/sets variable) during that direction of processing.
...mikeb{color:#888888}
{color}
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