A buffer as payload from function node

General
1

Hello,

I have a flow in Node-red in which a function will have to send a binary message to the serial port node.
I set up the function node with code similar to this

blReply =[217,181,0,75];
    for (i=0; i< blReply.length; i++){
        msg.payload = blReply[i];
        node.send(msg);
    }

When I receive the data on the serial port , the data received is actually a string (ASCII encoded)
the string received on the other end of the serial port is actually [217,181,0, 75].
I was expecting to receive the binary equivalent of the integers 217 181 0 and 75.
When I inject using the inject node the buffer [217,181,0, 75] the data recieved on the other end of the serial port is as expected the integers 217, 181, 0 and 75.
I Can't see what is wrong in the function node code, can you please help me out with this ?

Regards
lbh00

2

do you need to send one character at a time ? Why not just send the array as-is ? ie

msg.payload = [217,181,0,75];
node.send msg;

The serial port should send that as a binary payload.

3

Hello Dceejay,

Thanks for your reply.
Well sending 1 byte after the other was one way of debugging to understand what is going on.
I retried your proposal and I still get the data as an ASCII encoded message.
I connected a debug node to snoop on the data transiting from the function node to the serialport node I notice some differences:
the data sent from the function node the msg.payload is typed as array, while the msg.payload injected by the inject node is typed as buffer. What is the difference ?

Regards
lbh00

4

Hello,

I looked at the code of serialport node, and apparently if the typeof msg.payload is not a buffer, serial port will convert it to a string. a snip from the serialport node code:
encodePayload:

function (payload) {
                            if (!Buffer.isBuffer(payload)) {
                                if (typeof payload === "object") {
                                    payload = JSON.stringify(payload);
                                }
                                else {
                                    payload = payload.toString();
                                }
                                if (addchar !== "") { payload += addchar; }
                            }
                            else if (addchar !== "") {
                                payload = Buffer.concat([payload,Buffer.from(addchar)]);
                            }
                            return payload;
                        },

so what I did, is convert the array to a buffer inside my function as follows:

var payload = Buffer.from([217,181,0,75])

then send it to serialport node.

I hope this helps someone who is having this issue too.

Regards
lbh00

1 Like
5

Aha - of course... yes - do exactly that.

1 Like