Hex to Base64 function

[vangalvin]

The project I am working on requires me to set the ID and channel data of a device.
Both are in HEX, I managed to get the ID data working fine but the channel data is an issue
becaue its a 16bit hex value

0x00FF,0x0000,0x0000,0x0000,0x0000,0x0000
Node Red is viving me "/wAAAAAA"
And it should be "AP8AAAAAAAAAAAAA"

This is how im doing it in the function

let buff = new Buffer([0x00FF,0x0000,0x0000,0x0000,0x0000,0x0000]);
let base64data = buff.toString('base64');
msg.payload.data = base64data;

Im assuming the reason for this is that the buffer is only 8bit and it needs to be 16bit?

[Steve-Mcl]

Hi @vangalvin

Couple of points...

• You cannot initialise a Buffer with 16 bit data.
  • as you suspected, it is truncating your integers to bytes
• Also, new Buffer is depreciated (so wont work in the future anyhow)
  • use Buffer.from(...) instead.

So two ways:

1: You can iterate the 16 bit data and write it to a buffer using the buffer functions e.g. buf.writeUInt16LE() then call toString("base64").

2: Alternatively, you could use a Uint16Array as an intermediate variable for conversion ...

var data = [0x00FF,0x0000,0x0000,0x0000,0x0000,0x0000];
var arr = new Uint16Array(data);
var buf = Buffer.from(arr.buffer);
buf.swap16();
msg.payload = {
    srcData: data,
    asBuffer: buf,
    asBase64: buf.toString("base64")
}
return msg;

[vangalvin]

That works a treat thanks!
Is there a way to concatinate the buffer as well?

Initially I was going to allow each part to be set indavidually, Like the devEui and appEui but thinking about it this would end up being a pain.

var devEui = [0x32, 0x42, 0x33, 0x00, 0x00, 0x88, 0x88, 0x06];
var appEui = [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00];
var appKey = [0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x66, 0x01];
var data = [0x00FF,0x0000,0x0000,0x0000,0x0000,0x0000];

var arr = new Uint16Array(data);
var buf = Buffer.from(arr.buffer);

buf.swap16();
msg.payload = {
    srcData: data,
    asBuffer: buf,
    asBase64: buf.toString("base64")
}
return msg;

The output should end up something like
MkIzAACIiAYAAAAAAAAAAIiIiIiIiIiIiIiIiIiIZgEA/wAAAAAAAAAAAAA=

Or would I be better off sending them in seperate packets?

[Steve-Mcl]

@vangalvin

Is there a way to concatinate the buffer as well?

Sure see the buffer documentation

var devEui = Buffer.from( [0x32, 0x42, 0x33, 0x00, 0x00, 0x88, 0x88, 0x06] );
var appEui = Buffer.from( [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00] );
var appKey = Buffer.from( [0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x66, 0x01] );

var data = [0x00FF,0x0000,0x0000,0x0000,0x0000,0x0000];
var arr = new Uint16Array(data);
var buf = Buffer.from(arr.buffer);
buf.swap16();

const totalLength = buf.length + devEui.length + appEui.length + appKey.length;

var finalBuffer = Buffer.concat([devEui, appEui, appKey, buf], totalLength);

msg.payload = {
    srcData: data,
    asBuffer: buf,
    asBase64: buf.toString("base64"),
    finalBuffer: finalBuffer,
    finalBufferB64: finalBuffer.toString("base64")
}
return msg;

[vangalvin]

Awesome, thanks for that and I see what i was doing wrong when i tried to do it..
var finalBuffer = Buffer.concat([devEui, appEui, appKey, buf], totalLength);

not the way I was trying to do it.
var finalBuffer = Buffer.concat(devEui, appEui, appKey, buf);

Now I just have to hope the data rates are up to the task. If the radio drops below DR3 they its limited to 51 bytes

Thanks you so much for you help with this
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