Construct a packet with no payload

[larkolab]

Hello Anthony,

And first of all, things for this library, it's great! :)

I'm trying to use it with Node-Red do do a minimal LoRaWAN server, and I'm trying to send a downlink packet to respond to a "Confirmed Data Up". This kind of response does not require a FRMPayload, and so does not require a FPort.

But I can't find the way to specify such a packet to the fromFields() function. When I set the 'payload' field empty, I still get the FPort set. Can we avoid it?

My code is like:

var constructedPacket = lora_packet.fromFields(
    {
        payload:'',
        MType: 'Unconfirmed Data Down',
        DevAddr: new Buffer('11223344', 'hex'),
        FCtrl: {
            ADR: false,       // default = false
            ACK: true,        // default = false
            ADRACKReq: false, // default = false
            FPending: false   // default = false
        },
        FCnt: new Buffer('0000', 'hex'), // can supply a buffer or a number
    },
    null,
    new Buffer("2B7E151628AED2A6ABF7158809CF4F3C", 'hex') // NwkSKey
);

And I get the frame: YK8BzAAgAAABmjJuDQ==

( MACPayload = FHDR | FPort | FRMPayload ) FHDR = AF01CC00200000 FPort = 01 FRMPayload =

It's not really critical, but we could avoid this extra-byte for FPort. Is that possible?

Thanks a lot

[anthonykirby]

looking at the LoRa spec 4.3.2 Port field the port field is optional "If the frame payload field is not empty, the port field must be present" so that's a reasonable request!

[anthonykirby]

done - thank you for the suggestion! Ant

[larkolab]

great, thanks! :)