#include <SDRAM.h>#include <WiFi.h>#include <IPAddress.h>#include <WiFiUDP.h>// #define AP_TEST_ONLY                             // uncomment this line to avoid STA connection (thus only AP mode is acctivated)#define STA_CONNECT_TO_OPEN_NW        // comment this line to try to connect to protected nw instead of open#define AP_SSID     "ArduinoAP"#define AP_PWD      "ArduinoAP"#define AP_CHANNEL  5#define STA_SSID    "dummyNetwork"#define STA_PWD     "nopassword"uint8_t  _wifi_status = WL_IDLE_STATUS;WiFiUDP  _ap_udp;void _printWiFiStatus(){  Serial.println("-- WIFI INFO ----------------------------");  Serial.print("      SSID: ");   Serial.println(WiFi.SSID());  Serial.print("    status: ");   Serial.println(WiFi.status());  Serial.print("   IP addr: ");   Serial.println(WiFi.localIP());  Serial.print("  IP gatew: ");   Serial.println(WiFi.gatewayIP());  Serial.print("      RSSI: ");   Serial.print(WiFi.RSSI());  Serial.println("dBm\n-----------------------------------------");}/** Disconnect WiFi and reset default parameters. */void _wifiCleanup(){  Serial.println("\nWIFI CLEANUP:");  WiFi.disconnect();                              // close corrently opened connection  WiFi.end();  NetworkInterface* nif = WiFi.getNetwork();      // reset network paramenters  if (nif != nullptr)  { nif->set_default_parameters();  }  _wifi_status = WiFi.status();  _printWiFiStatus();                             // print WiFi status}/** Try to connect to an open WiFi network (which actually does not exist). */void _STADummyConnection(){  _wifiCleanup();                 // clean previous connection  WiFi.config(IPAddress());       // enable dhcp#ifdef STA_CONNECT_TO_OPEN_NW  WiFi.begin(STA_SSID);           // try to connect to inexistent open network#else  WiFi.begin(STA_SSID, STA_PWD);  // try to connect to inexistent private network#endif  _wifi_status = WiFi.status();   // update WiFi status variable  Serial.println("\nWIFI FAKE STA CONNECTION:");  _printWiFiStatus();             // print WiFi status}/** activate Arduino's Access Point (with pwd = ssid) */void _APOpening(){  _wifiCleanup();                                       // clean previous connection  IPAddress ip = IPAddress((char)random(11, 172), (char)random(0, 255), (char)random(0, 255), 0x01);  // Generate random IP adress in Private IP range  WiFi.config(ip, ip, ip, IPAddress(255,255,255,0));    // configure static IP  WiFi.beginAP(AP_SSID, AP_PWD, AP_CHANNEL);            // open access point with given ssid, password and channel  _wifi_status = WiFi.status();                         // update WiFi status variable  Serial.println("\nWIFI AP STATUS:");  _printWiFiStatus();                                   // print WiFi status}/** Send packet back to sender*/void UDPReply(int16_t packet_size){  Serial.println("UDP INFO: read and reply.");  int tmp_res;  IPAddress client_ip = _ap_udp.remoteIP();               // get client address  uint16_t client_port = _ap_udp.remotePort();  uint8_t *packet_buffer = (uint8_t*)SDRAM.malloc(sizeof(uint8_t) * (packet_size + 4));  // buffer to hold incoming and outgoing packets  int plen = _ap_udp.read(packet_buffer, packet_size);    // read packet from client  if (plen >= 0  &&  plen < (packet_size+4))              // safety null-terminated string  { packet_buffer[plen] = 0;  }  // skip own requests (ntp-pool time request from WiFi module)  if (client_ip != WiFi.localIP())  {    Serial.print("UDP INFO: received ");    Serial.print(packet_size);    Serial.print(" bytes from ");    Serial.print(client_ip);    Serial.write('-');    Serial.println(client_port);    tmp_res = _ap_udp.beginPacket(client_ip, client_port);    // get ready for UDP reply    Serial.print("UDP INFO: beginPacket() -> ");    Serial.println(tmp_res);    _ap_udp.write(packet_buffer, plen);                       // write answer for UDP reply    tmp_res = _ap_udp.endPacket();                            // send UDP reply    Serial.print("UDP INFO: endPacket() -> ");    Serial.println(tmp_res);  }  delay(40);  SDRAM.free(packet_buffer);}void setup() {    Serial.begin(115200);                                   // Init Serial for debugging messages  while (!Serial)  {};  Serial.println("Serial ready!");  SDRAM.begin();                                          // setup SDRAM  while (WiFi.status() == WL_NO_MODULE)                   // check WiFi module is working  {};#ifndef AP_TEST_ONLY  _STADummyConnection();                                  // try connecting to inexistent open network  delay(200);                                             // wait 0.2s#endif  _APOpening();                                           // open Access Point  if (_wifi_status != WL_AP_LISTENING)                    // check AP was successfully opened  { return;                                               // (otherwise stop and to nothing)  }  uint8_t tmp_res;  tmp_res = _ap_udp.begin(53);                            // start UDP manager  Serial.print("\n\nUDP INFO: begin(53) -> ");  Serial.println(tmp_res);  while (true)  {    if (WiFi.status() == WL_AP_LISTENING)                  // no client connected    {      if (_wifi_status != WL_AP_LISTENING)                      // Debug info      { Serial.println("WiFi status changed to WL_AP_LISTENING");        _wifi_status = WL_AP_LISTENING;      }    }        else if (WiFi.status() == WL_AP_CONNECTED)    {      if (_wifi_status != WL_AP_CONNECTED)                      // Debug info      { Serial.println("WiFi status changed to WL_AP_CONNECTED");        _wifi_status = WL_AP_CONNECTED;      }      int16_t packet_size = _ap_udp.parsePacket();              // get packet size, if available      if (packet_size > 0)                                      // packet available:      { UDPReply(packet_size);                                  // read it and send it back      }    }    else    {      Serial.print("ERROR: unexpected WiFi Status ");      Serial.println(WiFi.status());      delay(1000);    }  }}void loop() {}