How to communicate an ESP8266 or ESP32 via UDP protocol

First, the main loop of the program looks like this.

We will see that the only relevant points are that we have included the necessary files, and the functions ‘ConnectUDP()’ and ‘GetUDP_Packet()’ that we will see below.

We also have commented out the function ‘SendUDP_Packet(“abcde”)’ which would illustrate sending a String via UDP. We won’t use it in this example, but it’s there.

#include <ESP8266WiFi.h>
#include <WiFiUDP.h>

#include "config.h"  // Replace with your network data
#include "UDP.hpp"
#include "ESP8266_Utils.hpp"
#include "ESP8266_Utils_UDP.hpp"

void setup() 
{
  Serial.begin(115200);

  ConnectWiFi_STA();
  ConnectUDP();
}

void loop() 
{
  GetUDP_Packet();
  
  //SendUDP_Packet("abcde");
}

On the other hand, we have the file ‘UDP.hpp’, in which we have put all the functions related to the UDP of our program.

In this file, we have instantiated a ‘WiFiUDP’ object, the ports on which the connection will work, and defined the ‘ProcessPacket(String response)’ function that collects the response we want to give to a UDP request.

// UDP variables
WiFiUDP UDP;

unsigned int localPort = 8888;
unsigned int remotePort = 8889;
char packetBuffer[UDP_TX_PACKET_MAX_SIZE]; //buffer to hold incoming packet,

void ProcessPacket(String response)
{
   Serial.println(response);
}

Finally, we have the file ‘ESP8266_Utils_UDP.hpp’ in which, following the philosophy of this series of posts, we have defined a series of common functions that we can reuse between programs.

Here we have the ‘ConnectUDP()’ function that establishes the UDP connection, the ‘SendUDP_ACK()’ functions that sends an acknowledgment, ‘SendUDP_Packet(String content)’ that sends a String via UDP, and the ‘GetUDP_Packet(bool sendACK = true)’ function that receives a UDP packet and processes it with the function we have defined in the previous file.

boolean ConnectUDP() {
  Serial.println();
  Serial.println("Starting UDP");

  // in UDP error, block execution
  if (UDP.begin(localPort) != 1) 
  {
    Serial.println("Connection failed");
    while (true) { delay(1000); } 
  }

  Serial.println("UDP successful");
}

void SendUDP_ACK()
{
  UDP.beginPacket(UDP.remoteIP(), remotePort);
  UDP.write("ACK");
  UDP.endPacket();
}

void SendUDP_Packet(String content)
{
  UDP.beginPacket(UDP.remoteIP(), remotePort);
  UDP.write(content.c_str());
  UDP.endPacket();
}

void GetUDP_Packet(bool sendACK = true)
{
  int packetSize = UDP.parsePacket();
  if (packetSize)
  {
    // read the packet into packetBufffer
    UDP.read(packetBuffer, UDP_TX_PACKET_MAX_SIZE);

    Serial.println();
    Serial.print("Received packet of size ");
    Serial.print(packetSize);
    Serial.print(" from ");
    Serial.print(UDP.remoteIP());
    Serial.print(":");
    Serial.println(UDP.remotePort());
    Serial.print("Payload: ");
    Serial.write((uint8_t*)packetBuffer, (size_t)packetSize);
    Serial.println();
    ProcessPacket(String(packetBuffer));

    //// send a reply, to the IP address and port that sent us the packet we received
    if(sendACK) SendUDP_ACK();
  }
  delay(10);
}

The ‘recieveUDP.py’ script that receives a UDP packet and displays it on the screen.

import socket

UDP_PORT = 8889

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.bind(('', UDP_PORT))

while True:
  data, addr = sock.recvfrom(1024)
  print("received message:")
  print(data.decode('utf-8'))  

The ‘sendUDP.py’ file that sends an example packet via UDP.

import socket

UDP_IP = '192.168.43.237'
UDP_PORT = 8888
UDP_PAYLOAD = 'abcdef'

def yes_or_no(question):
    reply = str(input(question)).lower().strip()
    if reply[0] == 'y':
        return 0
    elif reply[0] == 'n':
        return 1
    else:
        return yes_or_no("Please Enter (y/n) ")
    
while True:
  try:
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    sock.sendto(bytes(UDP_PAYLOAD, "utf-8"), (UDP_IP, UDP_PORT))    
    sock.close()
    print("UDP target IP:", UDP_IP)
    print("UDP target port:", UDP_PORT)
    print("message:", UDP_PAYLOAD)
    if(yes_or_no('Send again (y/n): ')):
      break
  except:
    pass