...

As part of the work for

You can see this in PR: https://github.com/apache/daffodil/pull/643

These include an IPv4 checksum layer example/test,  a checkDigits example/test, and AIS Payload Armoring example/test. 

These illustrate This illustrates a way of doing "field extensibility" of layer transforms now, without any particular dynamic layer loading feature.

You pass the name of your layer transform using property

dfdlx:layerTransform=

...

"

...

someLayer"

That name must be the name associated with a class derived from LayerCompiler.

LayerCompilers are dynamically loaded service providers. See the META-INF/services/org.apache.daffodil.layers.LayerCompiler files in daffodil-runtime1-layers/src/main/resources, and daffodil-test/src/test/resources

The 'daffodil-runtime1-layers' Module

The following existing built-in layering transforms are found in the daffodil-runtime1-layers module.

• fourByteSwap
• base64_MIME
• gzip
• lineFolded_IMF
• lineFolded_iCalendar

In daffodil-test there are tests for the above built-ins, but also examples of separately defined layer transforms.

• aisPayloadArmoring 
• IPv4Checksum - stripped down version of IPv4 checksums
• CheckDigits - check digit calculation in the style of the "OTH-Gold" data format. 

Documentation

There are two kinds:

• user documentation for a DFDL schema author on how to use one of the built-in layers.
• developer documentation for how to define a new layer transform for use in a data format DFDL schema. 

User documentation should be via a web page on the Daffodil user site. 

Developer documentation should be within the scaladoc of the Layering API classes. 

• TBD: How to capture and exhibit this scaladoc for user-developers. 

Test Automation Plan

Testing of User-like Situations - Outside the Daffodil Repository Tree

DFDL Schemas Regression Testing Rig 

There is a general schema regression testing rig that enables developers to easily maintain a large tree of DFDL schemas for regression testing against daffodil. 

This tool/repo should be published. 

TODO: Create Apache Daffodil project repository for this.

This uses git submodules so that it does not copy schemas.

This should then test the "real" schemas mentioned below.

Updating "Real" DFDL Schema Examples that use Layers

Then somewhere in Scala/Java code before compiling the schema one must call LayerTransformFactory.register(MyLayerTransformFactory), and the MyLayerTransformFactory object has to be defined on the classpath.

In the case of my tests in daffodil-test, the scala test driver code does this call.

This is likely sufficient for application developers using Daffodil via API from software.

However: It won't let you run a new layer transform from the Daffodil CLI tool.

Enabling CLI Loading of Layers

To make the CLI work:

• The enum check in dfdlx.xsd should just be removed entirely, and the diagnostic message if the layer transform is not found should list all the currently registered layer transform names.
• Provide a way that the evaluation of dfdlx:layerTransform property, if the name does not correspond to a registered LayerTransformFactory, it could guess the name of the corresponding LayerTransformFactory object, (e.g, by uppercase first letter, and append "LayerTransformFactory" to the string value of the property) and try to dynamically load it.

Test Plan

Tests in daffodil-test will illustrate how dynamic loading of a layer from a jar works, but the jar in that case isn't a published jar.

The ethernet-ip DFDL schema (on github) can be made into a full exercise of dynamically loading an implementation of IPv4 checksumsof  IPv4 checksums.

• It could further be extended to do ICMP, TCP, UDP checksums also. 
• The PCAP schema which uses this ethernet-ip schema would inherit this also. 

The OpenDFDL (on github - note: should move to DFDLSchemas) example checkDigits schema can be made into a complete example.

The DFDLSchemas (on github) GPS-SPS example computes parity bits. This could also be made into a complete test example - though this is quite large.