Quicktype to generate W3C Thing Description Models for your Language

References

• W3C WoT Thing Description
• W3C WoT Modbus Binding

Prerequisits

• NodeJS: v18.16.0
• npm: 9.5.1
• ~/.npm-packages/bin should be in your PATH
• Toolchain for your language of choice

Installation

git clone [email protected]:hadjian/quicktype-td.git
npm install -g quicktype
chmod 755 ~/.npm-packages/bin/quicktype
cd quicktype-td
mkdir <name-of-programming-language>

In the last command, you should use the name of the programming language you want to use, e.g. "go", "C++", "JavaScript" etc. See the official quicktype project for a list of supported languages.

In the quicktype-td project you will already find three subdirectories:

- go      // Example project for the go programming language
- schemas // offical schemas for TD and Modbus binding
- things  // Example things

Now we can use quicktype to generate model files for a range of supported languages as follows:

quicktype --src-lang schema --lang go --out go/td-parser.go schemas/td-schema.json

The above command will generate model files for the go programming language. To generate models for a different language, provide a matching keyword to the --lang argument and change the name of the output directory/file extension.

quicktype --src-lang schema --lang go --out go/modbus-parser.go schemas/modbus.schema.json

Now you can add these model files to your project and make use of them to parse a TD with Modbus bindings. The example go directory contains a few lines of code to demonstrate this. But before you can compile your project, we need to employ a small manual hack, which we will try to automate in the future. Read on.

Manual Fix

Now you have your model files in your language sub-dicrectory, but the Modbus form class and the TD form class are separate. Use your programming language abstraction to inherit the TD form class from the Modbus Form class. In go for example we can use struct embeddings like so:

type FormElementProperty struct {
	ModbusForm          // manually inserted this line to make available the Modbus form fields
	Op                  *FormElementPropertyOp          `json:"op"`
	AdditionalResponses []AdditionalResponsesDefinition `json:"additionalResponses,omitempty"`
	ContentCoding       *string                         `json:"contentCoding,omitempty"`
	ContentType         *string                         `json:"contentType,omitempty"`
	Href                string                          `json:"href"`
	Response            *ExpectedResponse               `json:"response,omitempty"`
	Scopes              *TypeDeclaration                `json:"scopes"`
	Security            *TypeDeclaration                `json:"security"`
	Subprotocol         *string                         `json:"subprotocol,omitempty"`
}

Now you can use the the generated UnmarshalTdParser function to parse raw bytes read from the things/pac4200.json file into an instance of the TdParser class/struct. See go/main.go for reference.