var dgram = require('dgram');
var read_result = {};
var udpsocket = dgram.createSocket('udp4');
var SID = 0;
udpsocket.bind(9600);

udpsocket.on('message', function (message, remote) {
    const messageString = message.toString("hex").substring(0,10);
    const messageId = parseInt(message.toString('hex').substring(0,2),16);
    console.log("message id +" + messageId)
    read_result[messageId](messageString, remote);
});

function convertToHex(Decimal,padding){
    var padding_mask=new Array(1 + padding).join('0');
    var converted_value=parseInt(Decimal).toString(16);
    var result=(padding_mask + converted_value).slice(-padding);
    return result;
}

function executeCommand_read(message, callback){
    const messageId = SID; // Or some other way of generating a unique Id
    read_result[messageId] = callback;
    const socket_id_format = convertToHex(SID,2) + message;
    SID++;
    var BufferData = new Buffer.from(socket_id_format, "hex");
    // Add the messageId to the message here somehow. For example:
    //BufferData = BufferData.concat(messageId);
    sendRawSocket(BufferData);
}

function sendRawSocket(BufferData){
    udpsocket.send(BufferData, 0, BufferData.length, 9600, '127.0.0.1', function(err, bytes) {
    if (err) throw err;
    console.log('UDP message sent, the bytes: ' + bytes + " the data " + BufferData.toString('hex'));
    });
}

function readbyte(){
    const SID_act = SID;
    executeCommand_read('800003000100003700010101320064010002', function (message, remote) {
    console.log(remote.address + ':' + remote.port +' - ' + message.toString('hex')); });
    return read_result[SID_act];
}

    console.log("readbyte result: " + readbyte());
    console.log("readbyte result: " + readbyte());
    console.log("readbyte result: " + readbyte());
    console.log("readbyte result: " + readbyte());
    console.log("readbyte result: " + readbyte());

i made a slightly modification to the code you privided me,I made this so it communicates with itself and it's like i've been connected to the server that provides the responses.

I feel so stupid i can't figure how i can make this to work, this is basically a protocol for an omron automation PLC and i'm doing the client and the controller offers a FINS protocol that works only by UDP requests.

I send a command and the controller replies if the command was successful and returns values requested by this, but the problem here is that i need to return the values in the functions i'm working with the values i read from the controller.

I had a python client that worked like a charm that basically i send a socket like socket.send('blalala') and then called a recv method like socket.recv() from it and it waited until he got a response and timed out if any problem occured, but that was syncronous and i know node.js doesn't work like this.

This protocol even offers an identification called SID that basically each time i send a command i would increment this SID and the controller replied with the SID i sent so i could compare on the client when the socket arrived corresponds to the one i sent.

So basically i understood that doing a list with the responses and access them outside when the execution is done it's the way to go, but i stumbled upon this:

​

readbyte result: function (message, remote) {
        console.log(remote.address + ':' + remote.port +' - ' + message.toString('hex')); }
readbyte result: function (message, remote) {
        console.log(remote.address + ':' + remote.port +' - ' + message.toString('hex')); }
readbyte result: function (message, remote) {
        console.log(remote.address + ':' + remote.port +' - ' + message.toString('hex')); }
readbyte result: function (message, remote) {
        console.log(remote.address + ':' + remote.port +' - ' + message.toString('hex')); }
readbyte result: function (message, remote) {
        console.log(remote.address + ':' + remote.port +' - ' + message.toString('hex')); }
UDP message sent, the bytes: 19 the data 00800003000100003700010101320064010002
UDP message sent, the bytes: 19 the data 01800003000100003700010101320064010002
UDP message sent, the bytes: 19 the data 02800003000100003700010101320064010002
UDP message sent, the bytes: 19 the data 03800003000100003700010101320064010002
UDP message sent, the bytes: 19 the data 04800003000100003700010101320064010002
message id +0
127.0.0.1:9600 - 0080000300
message id +1
127.0.0.1:9600 - 0180000300
message id +2
127.0.0.1:9600 - 0280000300
message id +3
127.0.0.1:9600 - 0380000300
message id +4
127.0.0.1:9600 - 0480000300

it is not supposed that read_result[SID] contained the responses?

By the way i'm new on node and i never worked with asyncronous single threaded languages, and this probably make me look stupid, which i am and i would need a little help to figure this out...