Hi Marcos Your email is in our DFDL WG call calendar invite, which also has all the links; are you not receiving them? Next call is Thurs 15/4 @ 4pm UK. OGF DFDL WG call dial-in details. https://ibm.webex.com/meet/smh GitHub DFDL: https://github.com/OpenGridForum/DFDL Regards Steve Hanson IBM Hybrid Integration, Hursley, UK Architect, IBM DFDL Co-Chair, OGF DFDL Working Group smh@uk.ibm.com tel:+44-1962-815848 mob:+44-7717-378890 Note: I work Tuesday to Friday From: "Marcos Bento (external)" <Marcos.Bento@esa.int> To: DFDL-WG <dfdl-wg@ogf.org> Date: 13/04/2021 08:54 Subject: [EXTERNAL] Re: [DFDL-WG] newVariableInstance direction property discussion - PCAP example Sent by: "dfdl-wg" <dfdl-wg-bounces@ogf.org> Hi, We are currently working on supporting newVariableInstance in DFDL4S, so I'd like attend the next conference call and tune in on this discussion. Can anyone help me, and pointing me to the next call(s) schedule/coordinates? I've noticed that there was a move to Github, and I couldn't locate this information. --Marcos On Mon, Apr 12, 2021 at 7:26 PM Mike Beckerle <mbeckerle.dfdl@gmail.com> wrote:
For our next conference call, I said I would walk through the Apache
Daffodil newVariableInstance feature, and how for unparsing we had to add a direction property to variables so they can be evaluated with forward referencing for unparsing.
The code I'd like to discuss is here:
https://github.com/DFDLSchemas/PCAP/blob/cb9ee66aa565d982f01130918bcd785def5...
The defineVariable that is the best motivating example is defined at
line 104, and is used at line 213. This is a simple common-subexpression elimination, but it is used to avoid redundant calls to dfdl:valueLength in the dfdl:outputValueCalc of the stored length field named InclLen.
There is a second example of using newVariableInstance at unparse time
in this schema also, with the variable definitions starting at line 115, and usage in the group defined starting at line 320. This usage is far more complex, and in hindsight I think a DFDL parse of PCAP data should not be creating IP addresses in the Infoset that look like "1.2.3.4", because it requires all this complexity to unparse from that back to the binary representation. However, it is a good exercise in how the newVariableInstance feature works.
-mikeb
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Owl Cyber Defense |
www.owlcyberdefense.com
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