WifiClientEvent based library example; for logging to LittleFS, four WIFI events.

WIFI-Log--WifiClientEvent.ino

/*
 *  This sketch shows the WiFi event usage
 *  Based on ESP32 Core 2.0.4, WiFi library example for WiFiClientEvents.
 *  Logs five WIFI events  Watchdog events, Webserver starts, Brownout, WIFI Connect, and Disconnect.
 *  Modified by William Lucid 07/27/2022 @ 08:00 EDT
*/

/*
* WiFi Events

0  ARDUINO_EVENT_WIFI_READY                    < ESP32 WiFi ready
1  ARDUINO_EVENT_WIFI_SCAN_DONE                < ESP32 finish scanning AP
2  ARDUINO_EVENT_WIFI_STA_START                < ESP32 station start
3  ARDUINO_EVENT_WIFI_STA_STOP                 < ESP32 station stop
4  ARDUINO_EVENT_WIFI_STA_CONNECTED            < ESP32 station connected to AP
5  ARDUINO_EVENT_WIFI_STA_DISCONNECTED         < ESP32 station disconnected from AP
6  ARDUINO_EVENT_WIFI_STA_AUTHMODE_CHANGE      < the auth mode of AP connected by ESP32 station changed
7  ARDUINO_EVENT_WIFI_STA_GOT_IP               < ESP32 station got IP from connected AP
8  ARDUINO_EVENT_WIFI_STA_LOST_IP              < ESP32 station lost IP and the IP is reset to 0
9  ARDUINO_EVENT_WPS_ER_SUCCESS                < ESP32 station wps succeeds in enrollee mode
10 ARDUINO_EVENT_WPS_ER_FAILED                 < ESP32 station wps fails in enrollee mode
11 ARDUINO_EVENT_WPS_ER_TIMEOUT                < ESP32 station wps timeout in enrollee mode
12 ARDUINO_EVENT_WPS_ER_PIN                    < ESP32 station wps pin code in enrollee mode
13 ARDUINO_EVENT_WIFI_AP_START                 < ESP32 soft-AP start
14 ARDUINO_EVENT_WIFI_AP_STOP                  < ESP32 soft-AP stop
15 ARDUINO_EVENT_WIFI_AP_STACONNECTED          < a station connected to ESP32 soft-AP
16 ARDUINO_EVENT_WIFI_AP_STADISCONNECTED       < a station disconnected from ESP32 soft-AP
17 ARDUINO_EVENT_WIFI_AP_STAIPASSIGNED         < ESP32 soft-AP assign an IP to a connected station
18 ARDUINO_EVENT_WIFI_AP_PROBEREQRECVED        < Receive probe request packet in soft-AP interface
19 ARDUINO_EVENT_WIFI_AP_GOT_IP6               < ESP32 ap interface v6IP addr is preferred
19 ARDUINO_EVENT_WIFI_STA_GOT_IP6              < ESP32 station interface v6IP addr is preferred
20 ARDUINO_EVENT_ETH_START                     < ESP32 ethernet start
21 ARDUINO_EVENT_ETH_STOP                      < ESP32 ethernet stop
22 ARDUINO_EVENT_ETH_CONNECTED                 < ESP32 ethernet phy link up
23 ARDUINO_EVENT_ETH_DISCONNECTED              < ESP32 ethernet phy link down
24 ARDUINO_EVENT_ETH_GOT_IP                    < ESP32 ethernet got IP from connected AP
19 ARDUINO_EVENT_ETH_GOT_IP6                   < ESP32 ethernet interface v6IP addr is preferred
25 ARDUINO_EVENT_MAX
*/

#include <WiFi.h>
#include <WiFiUdp.h> 
#include <LittleFS.h>
#include <FTPServer.h>  //https://github.com/dplasa/FTPClientServer
#include <Ticker.h>
#include <rom/rtc.h

const char* ssid = "Your SSID";
const char* password = "Your WiFi PASSWORD";

//Server settings
#define ipaddress {10,0,0,110}
#define subnet {255,255,255,0}
#define gateway {10,0,0,1}
#define dns {10,0,0,1}

WiFiUDP udp;
// local port to listen for UDP packets
const int udpPort = 123;
char incomingPacket[255];
char replyPacket[] = "Hi there! Got the message :-)";
const char * udpAddress1 = "us.pool.ntp.org";
const char * udpAddress2 = "time.nist.gov";

#define TZ "EST+5EDT,M3.2.0/2,M11.1.0/2"

int DOW, MONTH, DATE, YEAR, HOUR, MINUTE, SECOND;

char daysOfTheWeek[7][12] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};

char strftime_buf[64];

String dtStamp(strftime_buf);

int lc = 0;
time_t tnow = 0;

FTPServer ftpSrv(LittleFS);

Ticker secondTick;

portMUX_TYPE mux = portMUX_INITIALIZER_UNLOCKED;

volatile int watchdogCounter;
volatile int watchDog = 0;

void IRAM_ATTR ISRwatchdog()
{

  portENTER_CRITICAL_ISR(&mux);
  
  watchdogCounter++;
  
  if (watchdogCounter >= 75) 
  {

    watchDog = 1;

  }

  portEXIT_CRITICAL_ISR(&mux);

}

int connect = 0;
int disconnect = 0;
int count = 1;
int brownout;
int softReset;
int powerOn;
int counter;

void WiFiEvent(WiFiEvent_t event) {
  //Serial.printf("[WiFi-event] event: %d\n", event);

  switch (event) {
    case ARDUINO_EVENT_WIFI_STA_CONNECTED:
      //Serial.println("Connected to access point");
      connect = 1;
      disconnect = 0;
      break;
    case ARDUINO_EVENT_WIFI_STA_DISCONNECTED:
      //Serial.println("Disconnected from WiFi access point");
      disconnect = 1;
      if(event == 7){  //ARDUINO_EVENT_WIFI_STA_GOT_IP
        disconnect = 0;
      }
      break;
    case ARDUINO_EVENT_WIFI_STA_GOT_IP:
      Serial.print("\nObtained IP address: ");
      Serial.println(WiFi.localIP());
      break;
    default: break;
  }
}

void WiFiGotIP(WiFiEvent_t event, WiFiEventInfo_t info) {
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(IPAddress(info.got_ip.ip_info.ip.addr));
}

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

  if (rtc_get_reset_reason(0) == 1)  //VBAT_RESET --brownout restart
  {
  
    brownout = 1;

    Serial.println("Brownout reset previous boot");
      
  }
  
  if (rtc_get_reset_reason(0) == 12)  //SOFTWARE_RESET --watchdog restart 
  {
  
    softReset = 1;

    Serial.println("Software reset previous boot");
      
  }

  // delete old config
  WiFi.disconnect(true);

  delay(1000);

   // Examples of different ways to register wifi events
  WiFi.onEvent(WiFiEvent);
  WiFi.onEvent(WiFiGotIP, WiFiEvent_t::ARDUINO_EVENT_WIFI_STA_GOT_IP);
  WiFiEventId_t eventID = WiFi.onEvent([](WiFiEvent_t event, WiFiEventInfo_t info){
      //Serial.print("WiFi lost connection. Reason: \n");
      //Serial.println(info.wifi_sta_disconnected.reason);
  }, WiFiEvent_t::ARDUINO_EVENT_WIFI_STA_DISCONNECTED);

  // Remove WiFi event
  //Serial.print("WiFi Event ID: ");
  ////Serial.println(eventID);
  //WiFi.removeEvent(eventID);

  WiFi.begin(ssid, password);

  //setting the addresses
  IPAddress ipaddress;
  IPAddress gateway;
  IPAddress subnet;
  IPAddress dns;

  WiFi.config(ipaddress, gateway, subnet, dns);

  Serial.println("Wait for WiFi Connection...");

  secondTick.attach(1, ISRwatchdog);  //watchdog ISR increase watchdogCounter by 1 every 1 second

  if(LittleFS.begin(true))
  {

    Serial.println("LittleFS opened!");
    Serial.println("");
    ftpSrv.begin("admin", "admin"); //username, password for ftp.  set ports in ESP8266FtpServer.h  (default 21, 50009 for PASV)

  }

  powerOn = 1;

}

void loop() {
 
  if ((brownout == 1) || (softReset == 1))  
  {
        
    watchdogCounter = 0;  //Resets the watchdogCounter
    
    getDateTime();
    
    //Open a "WIFI.TXT" for appended writing.   Client access ip address logged.
    File logFile =LittleFS.open("/WIFI.TXT", "a");

    if (!logFile)
    {
      Serial.println("File: '/WIFI.TXT' failed to open");
    }
    
    if((brownout == 1) && (powerOn != 1)) 
    {
      
      logFile.println("ESP32 Restart caused by Brownout Detection...");

      Serial.println("ESP32 Restart caused by Brownout Detection...");

      brownout = 0;

      connect = 1;

    }

    if((brownout == 1) && (powerOn == 1)) 
    {
      
      logFile.println("ESP32 Webserver Started...");

      Serial.println("ESP32 Webserver Started...");

      brownout = 0;

      powerOn = 0;

    }

    if (softReset == 1)
    {

      logFile.println("ESP32 Restart caused by Watchdog Event...");

      Serial.println("ESP32 Restart caused by Watchdog Event...");

      softReset = 0;

    }  

    logFile.close();
        
  }

  if(WiFi.status() == WL_NO_SSID_AVAIL )  //Prevent watchdog triggering if no wifi
  {

    watchdogCounter = 0;

  }

  if (connect == 1) 
  {

    configTime();

    //Open a "WIFI.TXT" for appended writing.   
    File logFile = LittleFS.open("/WIFI.TXT", "a");

    if (!logFile)
    {
      Serial.println("File: '/WIFI.TXT' failed to open");
    }

    logFile.print("WiFi Connected:      ");

    logFile.print(dtStamp);

    logFile.printf("   Connection result: %d\n", WiFi.waitForConnectResult());

    logFile.println("");
    
    logFile.close();

    Serial.println("Logged WiFi connection, timestamp\n");

    Serial.println("Ready...\n");

    watchdogCounter = 0;  //Resets the watchdogCounter

    connect = 0;
    counter = 1;      
    
  }
  
  if((disconnect == 1) && (counter == 1))
  {

    watchdogCounter = 0;  //Resets the watchdogCounter

    //Open "WIFI.TXT" for appended writing.   Client access ip address logged.
    File logFile = LittleFS.open("/WIFI.TXT", "a");

    if (!logFile)
    {
      Serial.println("File: '/WIFI.TXT' failed to open");
    }

    getDateTime(); 

    logFile.print("WiFi Disconnected:   ");  

    logFile.print(dtStamp);

    logFile.print("   Connection result: ");

    logFile.println(WiFi.waitForConnectResult());

    logFile.close();

    Serial.println("\nLogged WiFi disconnection, timestamp\n");
      
    watchdogCounter = 0;

    disconnect = 0;
    counter = 0;

  }

  for (int x = 1; x < 5000; x++)
  {
    ftpSrv.handleFTP();
  }

  if (watchDog == 1)
  {

     portENTER_CRITICAL(&mux);
     watchdogCounter--;
     portEXIT_CRITICAL(&mux);
     getDateTime();

     logWatchdog();
		
  }

  watchdogCounter = 0;
  
}

void configTime()
{

  configTime(0, 0, udpAddress1, udpAddress2);
  setenv("TZ", "EST+5EDT,M3.2.0/2,M11.1.0/2", 3);   // this sets TZ to Indianapolis, Indiana
  tzset();

  Serial.print("wait for first valid timestamp");

  while (time(nullptr) < 100000ul)
  {
    Serial.print(".");
    delay(5000);
  }

  Serial.println("\nSystem Time set\n");

  getDateTime();

  Serial.println(dtStamp);

}

String getDateTime()
{
  struct tm *ti;

  tnow = time(nullptr) + 1;
  //strftime(strftime_buf, sizeof(strftime_buf), "%c", localtime(&tnow));
  ti = localtime(&tnow);
  DOW = ti->tm_wday;
  YEAR = ti->tm_year + 1900;
  MONTH = ti->tm_mon + 1;
  DATE = ti->tm_mday;
  HOUR  = ti->tm_hour;
  MINUTE  = ti->tm_min;
  SECOND = ti->tm_sec;

  strftime(strftime_buf, sizeof(strftime_buf), "%a , %m/%d/%Y , %H:%M:%S %Z", localtime(&tnow));
  dtStamp = strftime_buf;
  return (dtStamp);

}

void logWatchdog()
{

  Serial.println("");
  Serial.println("Watchdog event triggered.");

  Serial.println("Watchdog Restart  " + dtStamp);

  ESP.restart();

}