Adapter for modbus/more complex protocols

[mStirner]

Its possible to create stream in objectMode=true, which accept a object as write input.
With this its possible to implement more complex/user input based protocols like modbus.

Example:

const { Transform } = require("stream");

class Encode extends Transform {

    constructor(opts) {
        super({
            ...opts,
            objectMode: true
        });
    }

    _transform({
        id = 255,
        addr = 0,
        data = null,
        fnc = Encode.FNC_CODE_4,
        size = 2
    }, enc, cb) {

        addr = Buffer.from(`${addr}`);
        //fnc = Buffer.from(`${fnc}`);
        let crc = Buffer.from([
            0xAB,
            0xCD,
            0xEF
        ]);

        let msg = Buffer.concat([
            Buffer.from([id]),
            fnc,
            Buffer.from([addr]),
            crc
        ]);

        cb(null, msg);

    }

    static FNC_CODE_1 = Buffer.from([0x01]);
    static FNC_CODE_2 = Buffer.from([0x02]);
    static FNC_CODE_3 = Buffer.from([0x03]);
    static FNC_CODE_4 = Buffer.from([0x04]);

}


const encode = new Encode();

encode.on("data", (data) => {
    console.log("Message", data);
});


encode.write({
    addr: 1234,
    size: 2,
    //fnc: Encode.FNC_CODE_1,
    data: Buffer.from("foo bar")
});

See https://github.com/OpenHausIO/playground/tree/main/object-mode-streams