MQTT publishing and subscribing on Arduino

/*
 Basic MQTT example
*/

#include <SPI.h>
#include <Ethernet.h>
#include <PubSubClient.h>

// Built-in LED on your Arduino is pin 13, or LED_BUILTIN (which also returns 13)
const int ledPin = 13;
unsigned long readTime;

// Update these with values suitable for your network.
byte mac[] = {  0x5C, 0xCF, 0x7F, 0x33, 0x7C, 0x7A };      // Arduino MAC address
IPAddress ip(10, 0, 0, 64);                                // Arduino IP address
IPAddress server(10, 0, 0, 101);                           // OpenHab Raspberry Pi IP address
char message_buff[100]; // this buffers our incoming messages so we can do something on certain commands

// Connect the PubSub client to the network
EthernetClient ethClient;
PubSubClient client(ethClient);


// When connected to OpenHab Pi MQTT broker, do this with the message:
void callback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] ");
  
  int i=0;
  for (i=0;i<length;i++) {
    Serial.print((char)payload[i]);
    message_buff[i] = payload[i];
  }
  message_buff[i] = '\0';
  String msgString = String(message_buff);
  
  if (msgString.equals("OFF")) {
    client.publish("openhab/arduino/command","acknowedging OFF");
    sensorWrite(msgString);
  }
  else if(msgString.equals("ON")){
    client.publish("openhab/arduino/command","acknowedging ON");
    sensorWrite(msgString);
  }
  Serial.println();
}


void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
    if (client.connect("arduinoClient")) {
      Serial.println("connected");
      // Once connected, publish an announcement...
      client.publish("openhab/arduino/status","Arduino client connected");
      // ... and resubscribe
      client.subscribe("openhab/arduino/command");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

void setup()
{
  Serial.begin(57600);
  
  // Set IP of your OpenHab install (Raspberry Pi)
  client.setServer("10.0.0.101", 1883);
  client.setCallback(callback);

  Ethernet.begin(mac);
  
  // Allow the hardware to sort itself out
  delay(1500);
  Serial.println(Ethernet.localIP());
  readTime = 0;
}

void loop()
{
  
  if (!client.connected()) {
    reconnect();
  }
  
  client.loop();
  
  //check if 5 seconds has elapsed since the last time we read the sensors. 
  if(millis() > readTime+60000){
    sensorRead();
  }
  
}

void sensorRead(){
  readTime = millis();
  
  // Get the position of the led, HIGH or LOW (true or false)
  char led_status;
  if(digitalRead(ledPin)){
     led_status = "ON";
  } else {
     led_status = "OFF";
  }
  
  // Publish the position to the broker, with this topic
  client.publish("openhab/arduino/led",led_status);
  
  Serial.print("Sensor Read: ");
  Serial.println(led_status);
 
}

void sensorWrite(String cmd){
  
  // Set the position of the led, HIGH or LOW (true or false)
  if(cmd == "ON"){
     digitalWrite(ledPin, HIGH);
     client.publish("openhab/arduino/command","executed command ON");
  }
  if(cmd == "OFF") {
     digitalWrite(ledPin, LOW);
     client.publish("openhab/arduino/command","executed command OFF");
  }
  
  Serial.print("Sensor Write: ");
  Serial.println(cmd);
 
}