ESP8266 AccessPoint always fails after exactly 5 times of correct communications

Question

i'm practicing with ESP8266 since few months,in Arduino IDE. I tried to understand fundamentals reading Neil Kolban Book,but still i can't master the callback mechanism,and lot of other stuff,because my lack of experience in networks . Now communication is between my PC and NodeMCU,using TCP/IP,and i'm trying to detect data reception by a led blink(or a print on terminal)without any wifi related function called inside the loop. I am referring to this example https://internetofhomethings.com/homethings/?tag=using-sdk-functions-with-arduino-ide,using only a basic part of the code,

but for some reason,if i try to connect by a PC or a cellphone or a ESP12 StationPoint, it works only 5 times from reset.

Using a PC or cellphone, if i type in the address bar of a browser 192.168.4.15 i have the blink after pressing Enter key,but only for 5 times. If i print received data:

** GET / HTTP/1.1 Host: 192.168.4.15 Connection: keep-alive Cache-Control: max-age=0 DNT: 1 Upgrade-Insecure-Requests: 1 User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.83 Safari/537.36 Accept: text/html,application/xhtml +xml,application/xml;q=0.9,image/avif,image/webp,image/apng,/;q=0.8,application/signed- exchange;v=b3;q=0.9 Accept-Encoding: gzip, deflate Accept-Language: it-IT,it;q=0.9,en-US;q=0.8,en;q=0.7**

Please can you check the code?I'm spending hours every day trying to understand something . Many thanks, Diego

#include <ESP8266WiFi.h>

#define SVRPORT 80

unsigned char blink_flag;

// Include API-Headers
extern "C" {
#include "ets_sys.h"
#include "os_type.h"
#include "osapi.h"
//#include "mem_manager.h"
//#include "mem.h"
//#include "string.h"
#include "user_interface.h"
#include "cont.h"
#include "espconn.h"
#include "eagle_soc.h"
#include <pgmspace.h>
void * pvPortZalloc(int size,char *, int);
}

/*                                            _       _   
     /\                                      (_)     | |  
    /  \   ___ ___ ___  ___ ___   _ __   ___  _ _ __ | |_ 
   / /\ \ / __/ __/ _ \/ __/ __| | '_ \ / _ \| | '_ \| __|
  / ____ \ (_| (_|  __/\__ \__ \ | |_) | (_) | | | | | |_ 
 /_/    \_\___\___\___||___/___/ | .__/ \___/|_|_| |_|\__|
                                 | |                      
                                 |_|                      */  
byte ledPin = 2;


const IPAddress ipadd(192,168,4,15);      
const IPAddress ipgat(192,168,4,1);       
const IPAddress ipsub(255,255,255,0);    

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

 pinMode(ledPin, OUTPUT);

 WiFi.mode(WIFI_AP);
 WiFi.softAP("MyTest_AP_Id", "MyTest_AP_pw");
 WiFi.softAPConfig(ipadd, ipgat, ipsub);
 SdkWebServer_Init(SVRPORT); 


 Serial.println();
 Serial.println("accesspoint_bare_01.ino");
 Serial.println("Server started.");
 Serial.print("IP: "); Serial.println(WiFi.softAPIP());
 Serial.print("MAC:"); Serial.println(WiFi.softAPmacAddress());

 blink_led(4,400);

}
//************************************************************************************
void loop() {
  if(blink_flag)//if SdkWebServer_recv is triggered do a recognizable blink
  {
    blink_flag=0;//to stop blinking until new data is received
    blink_led(8,100);
  }
}
/********************************************************
 * SDK API Web Server Initialization
 * Function: SdkWebServer_Init(int port)
 ********************************************************/
void SdkWebServer_Init(int port) {
    LOCAL struct espconn esp_conn;
    LOCAL esp_tcp esptcp;

    //Fill the connection structure, including "listen" port
    esp_conn.type =  ESPCONN_TCP; //This is the type of connection we are going to use
    esp_conn.state = ESPCONN_NONE;//The state of the connection will change over time but we initialize it to have an initial empty state by supplying ESPCONN_NONE.
    esp_conn.proto.tcp = &esptcp;//structure called "esp_tcp". This structure contains TCP specific 
                                 //settings. For our story, this is where we supply the port number which our TCP connection will 
                                 //listen upon for client connections. This is supplied in the property called "local_port".
    esp_conn.proto.tcp->local_port = port;//80 for TCP/IP
    esp_conn.recv_callback = NULL;
    esp_conn.sent_callback = NULL;
    esp_conn.reverse = NULL;
    //Register the connection timeout(0=no timeout)
    espconn_regist_time(&esp_conn,0,0);
    //Register connection callback
    espconn_regist_connectcb(&esp_conn,    SdkWebServer_listen);//funzioni di libreria
    //espconn_regist_disconcb (&esp_conn,    MiaDiscCallback);
    
    //Start Listening for connections
    espconn_accept(&esp_conn); 
    Serial.print("Web Server initialized: Type = SDK API\n");
}

/********************************************************
 * SDK API Web Server TCP Client Connection Callback
 * Function: SdkWebServer_listen(void *arg)
 ********************************************************/
void SdkWebServer_listen(void *arg)
{
    struct espconn *pesp_conn = ( espconn *)arg;

    espconn_regist_recvcb(pesp_conn, SdkWebServer_recv);
    espconn_regist_reconcb(pesp_conn, SdkWebServer_recon);
    espconn_regist_disconcb(pesp_conn, SdkWebServer_discon);
 }
//************************************************************************************
void  SdkWebServer_recv(void *arg,  char *pData, unsigned short len)
{
  struct espconn *ptrespconn = ( espconn *)arg;
  espconn_set_opt(ptrespconn, ESPCONN_REUSEADDR);
  blink_flag=1;
}
/********************************************************
 * SDK API Web Server TCP Connection Closed Callback
 * Function: SdkWebServer_discon(void *arg)
 ********************************************************/
void SdkWebServer_discon(void *arg)
{
    struct espconn *pesp_conn = ( espconn *)arg;
}
/********************************************************
 * SDK API Web Server TCP Disconnect on error Callback
 * Function: SdkWebServer_recon(void *arg, sint8 err)
 ********************************************************/
void SdkWebServer_recon(void *arg, sint8 err)
{
    struct espconn *pesp_conn = ( espconn *)arg;
}
//************************************************************************************
void blink_led(unsigned char reps,unsigned int del)
{
  while(reps--)
  {
    digitalWrite(ledPin,HIGH); 
    delay(del);
    digitalWrite(ledPin,LOW); 
    delay(del);
  }
}
//************************************************************************************

Answer 1

Why are you using the SDK functions with Arduino code? There are good Arduino Core web >servers that are much easier to use

Why are you using the SDK functions with Arduino code? There are good Arduino Core web >servers that are much easier to use

Hello .I dont know what is better to use,i'm not an expert ESP8266 user.. I need that for an application that would need another post to be explained and i tried to put the question simple. That application failed wifi after few minutes,reading on web I've found that it was probably because i managed wrongly WiFi inside the loop. The example I've started from seemed inviting because all about wifi looks managed by callbacks. Is there any illegal use of SDK functions in Arduino code? I was not able to configure any other environment as Eclipse,it was a nightmare of many days of environment variables,paths and forbidden folder names with spaces. Probably i will try other Arduino examples that i recently was told about,the ones using inside the loop

void loop() {
  server.handleClient(); //Handling of incoming client requests
}

Anyway i'm still looking for an explanation about the reason why my code fails exactly after 5 times,regardless of receiving 20 bytes or 400 bytes(and this makes me think that is not because the 1460 bytes of TCP blocks,but i dont want to do any assumption).

Thanks.