So this is the first analysis of your issues...
So here is an example flow demonstrating how you access bytes of a buffer, check values & reply as required - note in the demo GIF i get different responses in the debug window and the terminal depending on what I write.
In the terminal I enter ok followed by a new line (CTRL+J) - i get the response from node-red "I got OK!"
Try entering hi followed by a newline (CTRL+J)
...
the function code "check and reply"
//some really simple buffer access, validation & reply
//first lets see what we are playing with - send some info to the debug window...
try {
node.warn(["msg.payload.constructor.name", msg.payload.constructor.name]);
} catch(e){}
var data = msg.payload; //create an easy to access var named 'data'
//check to see if it is > than 1 in length
if(data && data.length > 1){
//get individual bytes
msg.byte0 = data[0]; //get byte 0
msg.byte1 = data[1]; //get byte 1
//read first 2 bytes as an UINT16
msg.uint16 = data.readUInt16BE(0); //refer to "nodejs buffer" documentation for more functions
//show the data in debug window
node.warn(["byte0=",msg.byte0,"byte1=",msg.byte1]);
//now some simple processing of data so we can reply appropriately
if((msg.byte0 == 79 && msg.byte1 == 75) || (msg.byte0 == 111 && msg.byte1 == 107)) {
msg.info = "Excellent - I got 'OK' in the first 2 bytes of " + msg.payload.length
msg.payload = "I got OK!\r\n";//send a string response
} else if(msg.uint16 == 26729) {
msg.info = "Good stuff - I got UINT 26729 in the first 2 bytes of " + msg.payload.length
msg.payload = "You entered 26729 (or 'hi' which is 26729 as a UINT!)\r\n";//send a string response
} else {
msg.info = "Sending a NAK - You did not sent OK or 26729 in the first 2 bytes of " + msg.payload.length
msg.payload = new Buffer([2,16,3]);//create an NAK (as a buffer response) reply
}
} else {
msg.info = "The buffer is too short - try sending more characters next time!"
msg.payload = new Buffer([2,0xff,3]);//create an ERR (as a buffer response) reply
}
return msg;
demo flow...
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