這是筆者關於此主題所整理出來的程式碼，關於 AP mode，STA mode，HTTP Web Server，HTTP Client，透過本地端的網頁更新本地端，本地端自動連上遠端網址以作更新。功能上都已測過可用。因此基礎的應用應都可從此攫取來用應已足夠了吧我想。另外關於將檔案存放到 flash 上面以 SPIFFS 檔案系統形式作存取的相關用法請谷歌。並且還有 HTTPS 相關主題或許當前筆者還用不上，使用者可自行研究。
對了，ap 只能接上最多 4 個 stations。第 5 個 station 或以上，雖然能找到並連接該 ap，但無法完成連線，即會一直等待連線成功。

/*
 *  This sketch demonstrates how to set up a simple HTTP-like server.
 *  The server will set a GPIO pin depending on the request
 *    http://server_ip/gpio/0 will set the GPIO2 low,
 *    http://server_ip/gpio/1 will set the GPIO2 high
 *  server_ip is the IP address of the ESP8266 module, will be 
 *  printed to Serial when the module is connected.
 */

#include <ESP8266WiFi.h>
#include <ESP8266WebServer.h>
#include <ESP8266mDNS.h>
#include <ESP8266HTTPUpdateServer.h>
#include <ESP8266WiFiMulti.h>
#include <ESP8266HTTPClient.h>
#include <ESP8266httpUpdate.h>

#ifdef ESP8266
extern "C" {
    #include "user_interface.h"
}
#endif


// Set up output serial port (could be a SoftwareSerial
// if really wanted).
// Wired to the blue LED on an ESP-01 board, active LOW.
//
// Cannot be used simultaneously with Serial.print/println()
// calls, as TX is wired to the same pin. 
//
// UNLESS: You swap the TX pin using the alternate pinout.


#define AP_MODE_MYSSID      "ESP_TESTAP"
#define AP_MODE_MYPW        "87654321"


#if 0
    #define STA_MODE_SSID    "--------"
    #define STA_MODE_PW      "--------"
#else
    #define STA_MODE_SSID    AP_MODE_MYSSID
    #define STA_MODE_PW      AP_MODE_MYPW
#endif


const char *const WIFI_CRED[][2]={
    {"ESP_TESTAP", "87654321"},
    {"Office", "123456"},
    {"Xperia X Performance_bc10", "e848acbcfd98"},
};


// use either of one
#define HTTP_SERVER 1
#define HTTP_CLIENT (!HTTP_SERVER)


// use either of one
#define AP_MODE 1
#define STA_MODE (!AP_MODE)


// use either of one
//#define USE_STA_NATIVE
#define USE_STA_WIFI_MULTI


// use either of one
//#define USE_HTTP_HTTP_CLIENT
//#define USE_HTTP_WIFI_CLIENT
#define USE_HTTP_WIFIHTTP_HYBRID


#define HOSTNAME "esp8266-iot" // i.e., http://esp8266-iot.local/
#define UPDFILE "a.bin" // the facility has no version check, so should do it by user.
// the webpage for updating to local is http://HOSTNAME.local/update
// local updated from remote is http://HOSTNAME.local/upd




#if defined(USE_STA_WIFI_MULTI)
ESP8266WiFiMulti *WiFiMulti=0;
#endif

Stream &ehConsolePort(Serial);

// for http server
ESP8266WebServer *server_p;

// for remote ip
char remote_ip[16] = {0};

// for url
String web_link;

// for station mode is entered
bool is_station_entered=false;

// webupdater
ESP8266HTTPUpdateServer httpUpdater;




// ==================================================================
const char * const RST_REASONS[] =
{
    "REASON_DEFAULT_RST",
    "REASON_WDT_RST",
    "REASON_EXCEPTION_RST",
    "REASON_SOFT_WDT_RST",
    "REASON_SOFT_RESTART",
    "REASON_DEEP_SLEEP_AWAKE",
    "REASON_EXT_SYS_RST"
};

const char * const FLASH_SIZE_MAP_NAMES[] =
{
    "FLASH_SIZE_4M_MAP_256_256",
    "FLASH_SIZE_2M",
    "FLASH_SIZE_8M_MAP_512_512",
    "FLASH_SIZE_16M_MAP_512_512",
    "FLASH_SIZE_32M_MAP_512_512",
    "FLASH_SIZE_16M_MAP_1024_1024",
    "FLASH_SIZE_32M_MAP_1024_1024"
};

const char * const OP_MODE_NAMES[] 
{
    "NULL_MODE",
    "STATION_MODE",
    "SOFTAP_MODE",
    "STATIONAP_MODE"
};

const char * const AUTH_MODE_NAMES[] 
{
    "AUTH_OPEN",
    "AUTH_WEP",
    "AUTH_WPA_PSK",
    "AUTH_WPA2_PSK",
    "AUTH_WPA_WPA2_PSK",
    "AUTH_MAX"
};

const char * const PHY_MODE_NAMES[]
{
    "",
    "PHY_MODE_11B",
    "PHY_MODE_11G",
    "PHY_MODE_11N"
};

const char * const EVENT_NAMES[]
{
    "EVENT_STAMODE_CONNECTED",
    "EVENT_STAMODE_DISCONNECTED",
    "EVENT_STAMODE_AUTHMODE_CHANGE",
    "EVENT_STAMODE_GOT_IP",
    "EVENT_SOFTAPMODE_STACONNECTED",
    "EVENT_SOFTAPMODE_STADISCONNECTED",
    "EVENT_MAX"
};

const char * const EVENT_REASONS[]
{
    "",
    "REASON_UNSPECIFIED",
    "REASON_AUTH_EXPIRE",
    "REASON_AUTH_LEAVE",
    "REASON_ASSOC_EXPIRE",
    "REASON_ASSOC_TOOMANY",
    "REASON_NOT_AUTHED",
    "REASON_NOT_ASSOCED",
    "REASON_ASSOC_LEAVE",
    "REASON_ASSOC_NOT_AUTHED",
    "REASON_DISASSOC_PWRCAP_BAD",
    "REASON_DISASSOC_SUPCHAN_BAD",
    "REASON_IE_INVALID",
    "REASON_MIC_FAILURE",
    "REASON_4WAY_HANDSHAKE_TIMEOUT",
    "REASON_GROUP_KEY_UPDATE_TIMEOUT",
    "REASON_IE_IN_4WAY_DIFFERS",
    "REASON_GROUP_CIPHER_INVALID",
    "REASON_PAIRWISE_CIPHER_INVALID",
    "REASON_AKMP_INVALID",
    "REASON_UNSUPP_RSN_IE_VERSION",
    "REASON_INVALID_RSN_IE_CAP",
    "REASON_802_1X_AUTH_FAILED",
    "REASON_CIPHER_SUITE_REJECTED",
};


void print_system_info(Stream & consolePort)
{
    const rst_info * resetInfo = system_get_rst_info();
    consolePort.print(F("system_get_rst_info() reset reason: "));
    consolePort.println(RST_REASONS[resetInfo->reason]);

    consolePort.print(F("system_get_free_heap_size(): "));
    consolePort.println(system_get_free_heap_size());

    consolePort.print(F("system_get_os_print(): "));
    consolePort.println(system_get_os_print());
    system_set_os_print(1);
    consolePort.print(F("system_get_os_print(): "));
    consolePort.println(system_get_os_print());

    consolePort.print(F("system_print_meminfo(): "));
    consolePort.println(system_get_os_print());
    system_print_meminfo();

    consolePort.print(F("system_get_chip_id(): 0x"));
    consolePort.println(system_get_chip_id(), HEX);

    consolePort.print(F("system_get_sdk_version(): "));
    consolePort.println(system_get_sdk_version());

    consolePort.print(F("system_get_boot_version(): "));
    consolePort.println(system_get_boot_version());

    consolePort.print(F("system_get_userbin_addr(): 0x"));
    consolePort.println(system_get_userbin_addr(), HEX);

    consolePort.print(F("system_get_boot_mode(): "));
    consolePort.println(system_get_boot_mode() == 0 ? F("SYS_BOOT_ENHANCE_MODE") : F("SYS_BOOT_NORMAL_MODE"));

    consolePort.print(F("system_get_cpu_freq(): "));
    consolePort.println(system_get_cpu_freq());

    consolePort.print(F("spi_flash_get_id(): 0x"));
    consolePort.println(spi_flash_get_id(), HEX);

    consolePort.print(F("system_get_flash_size_map(): "));
    consolePort.println(FLASH_SIZE_MAP_NAMES[system_get_flash_size_map()]);
}


void pre_setup(){

    print_system_info(Serial);

    // Try pushing frequency to 160MHz.
    system_update_cpu_freq(SYS_CPU_160MHZ);

    // System usually boots up in about 200ms.
    Serial.print(F("system_get_time(): "));
    Serial.println(system_get_time());

    Serial.print(F("system_get_cpu_freq(): "));
    Serial.println(system_get_cpu_freq());

    Serial.print(F("wifi_get_opmode(): "));
    Serial.print(wifi_get_opmode());
    Serial.print(F(" - "));
    Serial.println(OP_MODE_NAMES[wifi_get_opmode()]);

    Serial.print(F("wifi_get_opmode_default(): "));
    Serial.print(wifi_get_opmode_default());
    Serial.print(F(" - "));
    Serial.println(OP_MODE_NAMES[wifi_get_opmode_default()]);

    Serial.print(F("wifi_get_broadcast_if(): "));
    Serial.println(wifi_get_broadcast_if());
}


void post_setup(){
    Serial.printf("getResetReason: %s\r\n",         ESP.getResetReason().c_str());
    Serial.printf("getFreeHeap: %d\r\n",            ESP.getFreeHeap());
    Serial.printf("getChipId: %d\r\n",              ESP.getChipId());
    Serial.printf("getCoreVersion: %s\r\n",         ESP.getCoreVersion().c_str());
    Serial.printf("getSdkVersion: %s\r\n",          ESP.getSdkVersion());
    Serial.printf("getCpuFreqMHz: %u\r\n",          ESP.getCpuFreqMHz());
    Serial.printf("getSketchSize: %u\r\n",          ESP.getSketchSize());
    Serial.printf("getFreeSketchSpace: %u\r\n",     ESP.getFreeSketchSpace());
    Serial.printf("getSketchMD5: %s\r\n",           ESP.getSketchMD5().c_str());
    Serial.printf("getFlashChipId: %d\r\n",         ESP.getFlashChipId());
    Serial.printf("getFlashChipSize: %u\r\n",       ESP.getFlashChipSize());
    Serial.printf("getFlashChipRealSize: %u\r\n",   ESP.getFlashChipRealSize());
    Serial.printf("getFlashChipSpeed: %u\r\n",      ESP.getFlashChipSpeed());
    Serial.printf("getCycleCount: %u\r\n",          ESP.getCycleCount());
    Serial.printf("getVcc: %d\r\n",                 ESP.getVcc());
}


// callback function for wifi auto-messages
void wifi_event_handler_cb(System_Event_t * event)
{
    if (int(event->event)>=7) return;

    if (event->event<sizeof(EVENT_NAMES)/sizeof(EVENT_NAMES[0]))
        Serial.print(EVENT_NAMES[event->event]);
    Serial.print(" [wifi_auto_info] (");
    
    switch (event->event)
    {
        case EVENT_STAMODE_CONNECTED:
            break;
        case EVENT_STAMODE_DISCONNECTED:
            break;
        case EVENT_STAMODE_AUTHMODE_CHANGE:
            break;
        case EVENT_STAMODE_GOT_IP:
            break;
        case EVENT_SOFTAPMODE_STACONNECTED:
        case EVENT_SOFTAPMODE_STADISCONNECTED:
            {
                char mac[32] = {0};
                snprintf(mac, 32, MACSTR ", aid: %d" , MAC2STR(event->event_info.sta_connected.mac), event->event_info.sta_connected.aid);
                
                Serial.print(mac);
            }
            break;
        default:
            Serial.print(int(event->event));
    }

    Serial.println(")");
}


void print_softap_config(Stream &consolePort, softap_config const &config)
{
    consolePort.println();
    consolePort.println(F("SoftAP Configuration"));
    consolePort.println(F("--------------------"));

    consolePort.print(F("ssid:            "));
    consolePort.println((char *) config.ssid);

    consolePort.print(F("password:        "));
    consolePort.println((char *) config.password);

    consolePort.print(F("ssid_len:        "));
    consolePort.println(config.ssid_len);

    consolePort.print(F("channel:         "));
    consolePort.println(config.channel);

    consolePort.print(F("authmode:        "));
    consolePort.println(AUTH_MODE_NAMES[config.authmode]);

    consolePort.print(F("ssid_hidden:     "));
    consolePort.println(config.ssid_hidden);

    consolePort.print(F("max_connection:  "));
    consolePort.println(config.max_connection);

    consolePort.print(F("beacon_interval: "));
    consolePort.print(config.beacon_interval);
    consolePort.println("ms");

    consolePort.println(F("--------------------"));
    consolePort.println();
}


void print_wifi_general(Stream &consolePort)
{
    consolePort.print(F("wifi_get_channel(): "));
    consolePort.println(wifi_get_channel());
    
    consolePort.print(F("wifi_get_phy_mode(): "));
    consolePort.println(PHY_MODE_NAMES[wifi_get_phy_mode()]);
}


void secure_softap_config(softap_config *config, const char *ssid, const char *password)
{ // hidden mode
    // it tests if new data size over the storage and truncates.
    size_t ssidLen     = strlen(ssid)     < sizeof(config->ssid)     ? strlen(ssid)     : sizeof(config->ssid);
    size_t passwordLen = strlen(password) < sizeof(config->password) ? strlen(password) : sizeof(config->password);

    memset(config->ssid, 0, sizeof(config->ssid));
    memcpy(config->ssid, ssid, ssidLen);

    memset(config->password, 0, sizeof(config->password));
    memcpy(config->password, password, passwordLen);

    config->ssid_len = ssidLen;
    config->channel  = 1;
    config->authmode = AUTH_WPA2_PSK;
    config->ssid_hidden = 1;
    config->max_connection = 4;
    config->beacon_interval = 1000;
}


void enter_ap_mode(){
    WiFi.softAP(AP_MODE_MYSSID, AP_MODE_MYPW);
    IPAddress myIP = WiFi.softAPIP();

    Serial.println("");
    Serial.println("[-= Enter AP Mode =-]");
    Serial.print("AP IP ADDR: ");
    Serial.println(myIP);

    // get the default config and print it.
    softap_config config;
    wifi_softap_get_config(&config);
    /// if want to be more secure(hidden), modify the configurations.
    /// secure_softap_config(&config, AP_MODE_MYSSID, AP_MODE_MYPW);
    /// after config is arranged, set it in.
    /// wifi_softap_set_config(&config);
    print_softap_config(Serial, config);

    print_wifi_general(Serial);

    // start dhcps
    wifi_softap_dhcps_start();
    if (wifi_softap_dhcps_status()==DHCP_STARTED) Serial.println(F("DHCP started"));
    else Serial.println(F("DHCP stopped"));

    // get the AP basic info and print it.
    ip_info info;
    wifi_get_ip_info(SOFTAP_IF, &info);

    /// method 1
    /// Serial.printf("AP IP ADDR: %3d.%3d.%3d.%3d\r\n", ip4_addr1(&info.ip), ip4_addr2(&info.ip), ip4_addr3(&info.ip), ip4_addr4(&info.ip));
    /// Serial.printf("AP GATEWAY: %3d.%3d.%3d.%3d\r\n", ip4_addr1(&info.gw), ip4_addr2(&info.gw), ip4_addr3(&info.gw), ip4_addr4(&info.gw));
    /// Serial.printf("AP NETMASK: %3d.%3d.%3d.%3d\r\n", ip4_addr1(&info.netmask), ip4_addr2(&info.netmask), ip4_addr3(&info.netmask), ip4_addr4(&info.netmask));

    // method2
    Serial.printf("AP IP ADDR: " IPSTR "\r\n", IP2STR(&info.ip));
    Serial.printf("AP GATEWAY: " IPSTR "\r\n", IP2STR(&info.gw));
    Serial.printf("AP NETMASK: " IPSTR "\r\n", IP2STR(&info.netmask));

    // This doesn't work on an ESP-01.
    // wifi_set_sleep_type(LIGHT_SLEEP_T);
    // Try this dirty little thing.
    // Doesn't work because ESP-01 module doesn't link XPD_DCDC -> RST.
    // ESP.deepSleep(15000);
}


int connected_station_status(){

    ///// this function for count couldn't sync the number of stat_infos retrieved at realtime.
    unsigned char number_client=wifi_softap_get_station_num(); // Count of stations

    struct station_info *stat_info;
    IPAddress address;
    int i;

    Serial.print("Total connected clients: ");
    Serial.println(number_client);

    for (i=0, stat_info=wifi_softap_get_station_info(); stat_info!=NULL && i<number_client; i++){
        address=(stat_info->ip).addr;

        snprintf(remote_ip, 16, "" IPSTR, IP2STR(&(stat_info->ip)));

        Serial.printf("Station %d. ", i+1);
        Serial.print("IP= ");
        Serial.print(address);
        Serial.print(" with MAC= ");
        Serial.print(stat_info->bssid[0],HEX);
        Serial.print(stat_info->bssid[1],HEX);
        Serial.print(stat_info->bssid[2],HEX);
        Serial.print(stat_info->bssid[3],HEX);
        Serial.print(stat_info->bssid[4],HEX);
        Serial.print(stat_info->bssid[5],HEX);
        Serial.println();

        stat_info = STAILQ_NEXT(stat_info, next);
    }
    wifi_softap_free_station_info();
    delay(100);
    return i; // not the number_client
}


#if defined(USE_STA_NATIVE) // --------------------------
// 12 seconds waiting
bool enter_station_mode(){
    unsigned char u=0;
    
    // Connect to WiFi network
    Serial.println("");
    Serial.println("[-= Enter Station Mode =-]");
    Serial.print("Connecting to ");
    Serial.print(STA_MODE_SSID);

    WiFi.mode(WIFI_STA);
    WiFi.begin(STA_MODE_SSID, STA_MODE_PW);
    
    while (WiFi.status() != WL_CONNECTED) {
        delay(200);
        Serial.print(".");
        if (u++>60) break; // 12 seconds, might not enough
    }
    Serial.println("");
    if (WiFi.status() != WL_CONNECTED){
        Serial.println(" WiFi connection failed...");
        return false;
    }
    Serial.println("WiFi connected");

    // Print the remote MAC address
    uint8_t macAddr[6];
    WiFi.macAddress(macAddr);
    Serial.printf("Remote MAC adr: %02X:%02X:%02X:%02X:%02X:%02X\r\n", macAddr[0], macAddr[1], macAddr[2], macAddr[3], macAddr[4], macAddr[5]);
    
    ip_info info;
    wifi_get_ip_info(STATION_IF, &info);
    Serial.printf("IP ADDR: " IPSTR "\r\n", IP2STR(&info.ip));
    Serial.printf("GATEWAY: " IPSTR "\r\n", IP2STR(&info.gw));
    Serial.printf("NETMASK: " IPSTR "\r\n", IP2STR(&info.netmask));

    // resolve the remote ip
    uint32 x=*(uint32*)(&info.ip)&*(uint32*)(&info.netmask);
    ip_addr y=*(ip_addr*)(&x);
    snprintf(remote_ip, 16, "%d.%d.%d.%d",\
        ip4_addr1(&y)? ip4_addr1(&y): 1,\
        ip4_addr2(&y)? ip4_addr2(&y): 1,\
        ip4_addr3(&y)? ip4_addr3(&y): 1,\
        ip4_addr4(&y)? ip4_addr4(&y): 1
        );
    Serial.print(F("Remote AP IP: "));
    Serial.println(remote_ip);

    Serial.printf("Default local hostname: %s\r\n", WiFi.hostname().c_str());
    Serial.print("DNS #1, #2 IP: ");
    WiFi.dnsIP().printTo(Serial);
    Serial.print(", ");
    WiFi.dnsIP(1).printTo(Serial);
    Serial.println();
    Serial.printf("RSSI: %d dBm\r\n", WiFi.RSSI());
    WiFi.printDiag(Serial);
    
    // Print the local IP address
    Serial.println("");
    Serial.print("IP is assigned: ");
    Serial.println(WiFi.localIP());
    return true;
}
#elif defined(USE_STA_WIFI_MULTI) // --------------------------
// 12 seconds waiting
bool enter_station_mode(){
    unsigned char u=0;

    // Connect to WiFi network
    Serial.println("");
    Serial.println("[-= Enter Station Mode =-]");
    Serial.print("WiFi Connecting...");

    WiFi.mode(WIFI_STA);
    if (!WiFiMulti){
        WiFiMulti=new ESP8266WiFiMulti;
        if (!WiFiMulti) return false;
        for (int i=0; i<(sizeof(WIFI_CRED)/sizeof(WIFI_CRED[0])); i++)
            WiFiMulti->addAP(WIFI_CRED[i][0], WIFI_CRED[i][1]);
    }

    while (WiFiMulti->run() != WL_CONNECTED) {
        delay(200);
        Serial.print(".");
        if (u++>60){ // 12 seconds, might not enough
            Serial.println(" WiFi connection failed...");
            return false;
        }
    }
    Serial.println("WiFi connected");

    // Print the remote MAC address
    uint8_t macAddr[6];
    WiFi.macAddress(macAddr);
    Serial.printf("Remote MAC adr: %02X:%02X:%02X:%02X:%02X:%02X\r\n", macAddr[0], macAddr[1], macAddr[2], macAddr[3], macAddr[4], macAddr[5]);
    
    ip_info info;
    wifi_get_ip_info(STATION_IF, &info);
    Serial.printf("IP ADDR: " IPSTR "\r\n", IP2STR(&info.ip));
    Serial.printf("GATEWAY: " IPSTR "\r\n", IP2STR(&info.gw));
    Serial.printf("NETMASK: " IPSTR "\r\n", IP2STR(&info.netmask));

    // resolve the remote ip
    uint32 x=*(uint32*)(&info.ip)&*(uint32*)(&info.netmask);
    ip_addr y=*(ip_addr*)(&x);
    snprintf(remote_ip, 16, "%d.%d.%d.%d",\
        ip4_addr1(&y)? ip4_addr1(&y): 1,\
        ip4_addr2(&y)? ip4_addr2(&y): 1,\
        ip4_addr3(&y)? ip4_addr3(&y): 1,\
        ip4_addr4(&y)? ip4_addr4(&y): 1
        );
    Serial.print(F("Remote AP IP: "));
    Serial.println(remote_ip);

    Serial.printf("Default local hostname: %s\r\n", WiFi.hostname().c_str());
    Serial.print("DNS #1, #2 IP: ");
    WiFi.dnsIP().printTo(Serial);
    Serial.print(", ");
    WiFi.dnsIP(1).printTo(Serial);
    Serial.println();
    Serial.printf("RSSI: %d dBm\r\n", WiFi.RSSI());
    WiFi.printDiag(Serial);
    
    // Print the local IP address
    Serial.println("");
    Serial.print("IP is assigned: ");
    Serial.println(WiFi.localIP());
    return true;
}
#endif // USE_STA_x // --------------------------


// The certificate is stored in PMEM
static const uint8_t x509[] PROGMEM = {
  0x30, 0x82, 0x01, 0x3d, 0x30, 0x81, 0xe8, 0x02, 0x09, 0x00, 0xfe, 0x56,
  0x46, 0xf2, 0x78, 0xc6, 0x51, 0x17, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x86,
  0x48, 0x86, 0xf7, 0x0d, 0x01, 0x01, 0x0b, 0x05, 0x00, 0x30, 0x26, 0x31,
  0x10, 0x30, 0x0e, 0x06, 0x03, 0x55, 0x04, 0x0a, 0x0c, 0x07, 0x45, 0x53,
  0x50, 0x38, 0x32, 0x36, 0x36, 0x31, 0x12, 0x30, 0x10, 0x06, 0x03, 0x55,
  0x04, 0x03, 0x0c, 0x09, 0x31, 0x32, 0x37, 0x2e, 0x30, 0x2e, 0x30, 0x2e,
  0x31, 0x30, 0x1e, 0x17, 0x0d, 0x31, 0x37, 0x30, 0x33, 0x31, 0x38, 0x31,
  0x34, 0x34, 0x39, 0x31, 0x38, 0x5a, 0x17, 0x0d, 0x33, 0x30, 0x31, 0x31,
  0x32, 0x35, 0x31, 0x34, 0x34, 0x39, 0x31, 0x38, 0x5a, 0x30, 0x26, 0x31,
  0x10, 0x30, 0x0e, 0x06, 0x03, 0x55, 0x04, 0x0a, 0x0c, 0x07, 0x45, 0x53,
  0x50, 0x38, 0x32, 0x36, 0x36, 0x31, 0x12, 0x30, 0x10, 0x06, 0x03, 0x55,
  0x04, 0x03, 0x0c, 0x09, 0x31, 0x32, 0x37, 0x2e, 0x30, 0x2e, 0x30, 0x2e,
  0x31, 0x30, 0x5c, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7,
  0x0d, 0x01, 0x01, 0x01, 0x05, 0x00, 0x03, 0x4b, 0x00, 0x30, 0x48, 0x02,
  0x41, 0x00, 0xc6, 0x72, 0x6c, 0x12, 0xe1, 0x20, 0x4d, 0x10, 0x0c, 0xf7,
  0x3a, 0x2a, 0x5a, 0x49, 0xe2, 0x2d, 0xc9, 0x7a, 0x63, 0x1d, 0xef, 0xc6,
  0xbb, 0xa3, 0xd6, 0x6f, 0x59, 0xcb, 0xd5, 0xf6, 0xbe, 0x34, 0x83, 0x33,
  0x50, 0x80, 0xec, 0x49, 0x63, 0xbf, 0xee, 0x59, 0x94, 0x67, 0x8b, 0x8d,
  0x81, 0x85, 0x23, 0x24, 0x06, 0x52, 0x76, 0x55, 0x9d, 0x18, 0x09, 0xb3,
  0x3c, 0x10, 0x40, 0x05, 0x01, 0xf3, 0x02, 0x03, 0x01, 0x00, 0x01, 0x30,
  0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x01, 0x0b,
  0x05, 0x00, 0x03, 0x41, 0x00, 0x69, 0xdc, 0x6c, 0x9b, 0xa7, 0x62, 0x57,
  0x7e, 0x03, 0x01, 0x45, 0xad, 0x9a, 0x83, 0x90, 0x3a, 0xe7, 0xdf, 0xe8,
  0x8f, 0x46, 0x00, 0xd3, 0x5f, 0x2b, 0x0a, 0xde, 0x92, 0x1b, 0xc5, 0x04,
  0xc5, 0xc0, 0x76, 0xf4, 0xf6, 0x08, 0x36, 0x97, 0x27, 0x82, 0xf1, 0x60,
  0x76, 0xc2, 0xcd, 0x67, 0x6c, 0x4b, 0x6c, 0xca, 0xfd, 0x97, 0xfd, 0x33,
  0x9e, 0x12, 0x67, 0x6b, 0x98, 0x7e, 0xd5, 0x80, 0x8f
};

// And so is the key.  These could also be in DRAM
static const uint8_t rsakey[] PROGMEM = {
  0x30, 0x82, 0x01, 0x3a, 0x02, 0x01, 0x00, 0x02, 0x41, 0x00, 0xc6, 0x72,
  0x6c, 0x12, 0xe1, 0x20, 0x4d, 0x10, 0x0c, 0xf7, 0x3a, 0x2a, 0x5a, 0x49,
  0xe2, 0x2d, 0xc9, 0x7a, 0x63, 0x1d, 0xef, 0xc6, 0xbb, 0xa3, 0xd6, 0x6f,
  0x59, 0xcb, 0xd5, 0xf6, 0xbe, 0x34, 0x83, 0x33, 0x50, 0x80, 0xec, 0x49,
  0x63, 0xbf, 0xee, 0x59, 0x94, 0x67, 0x8b, 0x8d, 0x81, 0x85, 0x23, 0x24,
  0x06, 0x52, 0x76, 0x55, 0x9d, 0x18, 0x09, 0xb3, 0x3c, 0x10, 0x40, 0x05,
  0x01, 0xf3, 0x02, 0x03, 0x01, 0x00, 0x01, 0x02, 0x40, 0x35, 0x0b, 0x74,
  0xd3, 0xff, 0x15, 0x51, 0x44, 0x0f, 0x13, 0x2e, 0x9b, 0x0f, 0x93, 0x5c,
  0x3f, 0xfc, 0xf1, 0x17, 0xf9, 0x72, 0x94, 0x5e, 0xa7, 0xc6, 0xb3, 0xf0,
  0xfe, 0xc9, 0x6c, 0xb1, 0x1e, 0x83, 0xb3, 0xc6, 0x45, 0x3a, 0x25, 0x60,
  0x7c, 0x3d, 0x92, 0x7d, 0x53, 0xec, 0x49, 0x8d, 0xb5, 0x45, 0x10, 0x99,
  0x9b, 0xc6, 0x22, 0x3a, 0x68, 0xc7, 0x13, 0x4e, 0xb6, 0x04, 0x61, 0x21,
  0x01, 0x02, 0x21, 0x00, 0xea, 0x8c, 0x21, 0xd4, 0x7f, 0x3f, 0xb6, 0x91,
  0xfa, 0xf8, 0xb9, 0x2d, 0xcb, 0x36, 0x36, 0x02, 0x5f, 0xf0, 0x0c, 0x6e,
  0x87, 0xaa, 0x5c, 0x14, 0xf6, 0x56, 0x8e, 0x12, 0x92, 0x25, 0xde, 0xb3,
  0x02, 0x21, 0x00, 0xd8, 0x99, 0x01, 0xf1, 0x04, 0x0b, 0x98, 0xa3, 0x71,
  0x56, 0x1d, 0xea, 0x6f, 0x45, 0xd1, 0x36, 0x70, 0x76, 0x8b, 0xab, 0x69,
  0x30, 0x58, 0x9c, 0xe0, 0x45, 0x97, 0xe7, 0xb6, 0xb5, 0xef, 0xc1, 0x02,
  0x21, 0x00, 0xa2, 0x01, 0x06, 0xc0, 0xf2, 0xdf, 0xbc, 0x28, 0x1a, 0xb4,
  0xbf, 0x9b, 0x5c, 0xd8, 0x65, 0xf7, 0xbf, 0xf2, 0x5b, 0x73, 0xe0, 0xeb,
  0x0f, 0xcd, 0x3e, 0xd5, 0x4c, 0x2e, 0x91, 0x99, 0xec, 0xb7, 0x02, 0x20,
  0x4b, 0x9d, 0x46, 0xd7, 0x3c, 0x01, 0x4c, 0x5d, 0x2a, 0xb0, 0xd4, 0xaa,
  0xc6, 0x03, 0xca, 0xa0, 0xc5, 0xac, 0x2c, 0xe0, 0x3f, 0x4d, 0x98, 0x71,
  0xd3, 0xbd, 0x97, 0xe5, 0x55, 0x9c, 0xb8, 0x41, 0x02, 0x20, 0x02, 0x42,
  0x9f, 0xd1, 0x06, 0x35, 0x3b, 0x42, 0xf5, 0x64, 0xaf, 0x6d, 0xbf, 0xcd,
  0x2c, 0x3a, 0xcd, 0x0a, 0x9a, 0x4d, 0x7c, 0xad, 0x29, 0xd6, 0x36, 0x57,
  0xd5, 0xdf, 0x34, 0xeb, 0x26, 0x03
};


#if 0
WiFiServer* create_http_server(){
    // Create an instance of the server
    // specify the 80 port to listen on as an argument
    WiFiServer *a=new WiFiServer(80);

    /// WiFiServerSecure *a=new WiFiServerSecure(443);
    /// a->setServerKeyAndCert_P(rsakey, sizeof(rsakey), x509, sizeof(x509));
    /// a->begin();
    
    // Start the server
    a->begin();
    Serial.println("HTTP Server started");
    return a;
}
#endif


ESP8266WebServer* create_http_server(){ // ESP8266WebServer & MDNS & Updater facilities
    // Create an instance of the server
    // specify the 80 port to listen on as an argument
    ESP8266WebServer *a=new ESP8266WebServer(80);

    MDNS.begin(HOSTNAME);

    httpUpdater.setup(a); // will be http://HOSTNAME.local/update

    // Start the http server
    a->begin();

    MDNS.addService("http", "tcp", 80);

    Serial.println("HTTP Server started");
    return a;
}


#if defined(USE_HTTP_HTTP_CLIENT) // faster but always got nothing // --------------------------
void http_client_connect(const char *url){
    /// #include <ESP8266HTTPClient.h>
    HTTPClient http;
    
    Serial.print("\r\n[HTTP begin...]\r\n");
    
    // configure traged server and url
    /// http.begin("https://192.168.1.12/test.html", "7a 9c f4 db 40 d3 62 5a 6e 21 bc 5c cc 66 c8 3e a1 45 59 38"); // HTTPS
    http.begin(url); // HTTP
    Serial.print("[HTTP GET...]\r\n");
    // start connection and send HTTP header
    int httpCode = http.GET();

    // httpCode will be negative on error
    if (httpCode > 0){
        // HTTP header has been send and Server response header has been handled
        Serial.printf("[HTTP GET... code: %d]\r\n", httpCode);
        
        // file found at server
        if (httpCode == HTTP_CODE_OK){ // the connection may be broken and stuck here
            Serial.println(" -= data =- ---------");
            Serial.println(http.getString()); // usually has no data return, so failed.
            Serial.println(" ===================");
        }
        else Serial.printf("[HTTP GET... failed, error: %s]\r\n", http.errorToString(httpCode).c_str());
    }
    else Serial.printf("[HTTP Protocol failed, error: %s]\r\n", http.errorToString(httpCode).c_str());
    
    http.end();
    delay(150);
}
#elif defined(USE_HTTP_WIFI_CLIENT) // slower but usually failed connection // --------------------------
void http_client_connect(const char *url){
    // Use WiFiClient class to create TCP connections
    WiFiClient client;
    int httpPort = 80;
    if (!client.connect(remote_ip, httpPort)) {
        Serial.println("");
        Serial.println("[HTTP Protocol failed, error: 0]");
        Serial.println("");
        return;
    }

    Serial.print("[Requesting URL: [");
    Serial.print(url);
    Serial.println("]");

    // This will send the request to the server
    client.print(String("GET ") + url + " HTTP/1.1\r\n" +\
        "Host: " + remote_ip + "\r\n" +\
        "Connection: close\r\n");

    unsigned long timeout = millis();
    while (client.available() == 0) {
        if (millis() - timeout > 4000) {
            Serial.println("[Client Timeout !]");
            client.stop();
            return;
        }
        delay(50);
    }

    // Read all the lines of the reply from server and print them to Serial
    Serial.println(" -= data =- ---------");
    while(client.available()){
        String line = client.readStringUntil('\r');
        Serial.println(line);
    }
    Serial.println(" ===================");
    delay(50);
}
#elif defined(USE_HTTP_WIFIHTTP_HYBRID) // --------------------------
void http_client_connect(const char *url){
    WiFiClient client;
    HTTPClient http; //must be declared after WiFiClient for correct destruction order, because used by http.begin(client,...)

    Serial.print("[HTTP begin...]\r\n");

    // configure server and url
    http.begin(client, url);
    /// http.begin(client, remote_ip, 80, url);

    Serial.print("[HTTP GET...]\r\n");
    // start connection and send HTTP header
    int httpCode = http.GET();
    if (httpCode > 0) {
        // HTTP header has been send and Server response header has been handled
        Serial.printf("[HTTP GET... code: %d]\r\n", httpCode);

        // file found at server
        if (httpCode == HTTP_CODE_OK) {
    
            // get lenght of document (is -1 when Server sends no Content-Length header)
            int len = http.getSize();
            
            // create buffer for read
            uint8_t buff[128] = { 0 };

#if 0 // with API
            Serial.println(http.getString());
#else // or "by hand"

            // get tcp stream
            WiFiClient * stream = &client;
            
            Serial.println(" -= data =- ---------");
            // read all data from server
            while (http.connected() && (len > 0 || len == -1)) {
                // read up to 128 byte
                int c = stream->readBytes(buff, std::min((size_t)len, sizeof(buff)));
                Serial.printf("[readBytes: %d]\r\n", c);
                if (!c) {
                    Serial.println("[read timeout]");
                    break; // must have or it will stuck here! and then if stuck at GET(), set timeout
                }

                // write it to Serial
                Serial.write(buff, c);

                if (len > 0) len -= c;
            }
            Serial.println(" ===================");
        }
#endif

        Serial.println();
        Serial.print("[HTTP connection closed or file end.]\r\n");
    }
    else Serial.printf("[HTTP GET... failed, error: %s]\r\n", http.errorToString(httpCode).c_str());
    http.end();
}
#endif // USE_HTTP_x // --------------------------


void gbl_update_started() {
  Serial.println("CALLBACK:  HTTP update process started");
}


void gbl_update_finished() {
  Serial.println("CALLBACK:  HTTP update process finished");
}


void gbl_update_progress(int cur, int total) {
  Serial.printf("CALLBACK:  HTTP update process at %d of %d bytes...\n", cur, total);
}


void gbl_update_error(int err) {
  Serial.printf("CALLBACK:  HTTP update fatal error code %d\n", err);
}


void gbl_updater(const char *url) {
    // wait for WiFi connection

    WiFiClient client;

    // The line below is optional. It can be used to blink the LED on the board during flashing
    // The LED will be on during download of one buffer of data from the network. The LED will
    // be off during writing that buffer to flash
    // On a good connection the LED should flash regularly. On a bad connection the LED will be
    // on much longer than it will be off. Other pins than LED_BUILTIN may be used. The second
    // value is used to put the LED on. If the LED is on with HIGH, that value should be passed
    ESPhttpUpdate.setLedPin(LED_BUILTIN, LOW);

    // Add optional callback notifiers
    ESPhttpUpdate.onStart(gbl_update_started);
    ESPhttpUpdate.onEnd(gbl_update_finished);
    ESPhttpUpdate.onProgress(gbl_update_progress);
    ESPhttpUpdate.onError(gbl_update_error);

    t_httpUpdate_return ret = ESPhttpUpdate.update(client, url);
    // Or:
    // t_httpUpdate_return ret = ESPhttpUpdate.update(client, "server", 80, "file.bin");

    switch (ret) {
        case HTTP_UPDATE_FAILED:
            Serial.printf("HTTP_UPDATE_FAILD Error (%d): %s\r\n", ESPhttpUpdate.getLastError(), ESPhttpUpdate.getLastErrorString().c_str());
            break;

        case HTTP_UPDATE_NO_UPDATES:
            Serial.println("HTTP_UPDATE_NO_UPDATES");
            break;

        case HTTP_UPDATE_OK:
            Serial.println("HTTP_UPDATE_OK");
            break;
    }
}


bool Timeout_60s(){
    static int current_time = millis();
    int new_time = millis();
    if (new_time < (current_time + 60000)) return false;
    current_time = new_time;
    return true;
}


bool Timeout_10s(){
    static int current_time = millis();
    int new_time = millis();
    if (new_time < (current_time + 10000)) return false;
    current_time = new_time;
    return true;
}


bool Timeout_4s(){
    static int current_time = millis();
    int new_time = millis();
    if (new_time < (current_time + 4000)) return false;
    current_time = new_time;
    return true;
}


void page_gpio_low_cb(){
    // Prepare the response
    String s = "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n<!DOCTYPE HTML>\r\n<html>\r\nLED is now ";
    s += "ON";
    s += "</html>\r\n";
    // Send the response to the client
    server_p->send(200, "text/plain", s.c_str());

    digitalWrite(2, LOW);
}


void page_gpio_high_cb(){
    // Prepare the response
    String s = "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n<!DOCTYPE HTML>\r\n<html>\r\nLED is now ";
    s += "OFF";
    s += "</html>\r\n";
    // Send the response to the client
    server_p->send(200, "text/plain", s.c_str());

    digitalWrite(2, HIGH);
}


void page_led_onoff_inst(){
    /// http://<ip address>/led?state=on will turn the led ON
    /// http://<ip address>/led?state=off will turn the led OFF
    server_p->on("/led", []() {
        String state=server_p->arg("state");
        if (state == "on") digitalWrite(2, LOW);
        else if (state == "off") digitalWrite(2, HIGH);
        server_p->send(200, "text/plain", "Led is now " + state);
    });
}


void page_a_bin_cb(){
    SPIFFS.begin();
    File file = SPIFFS.open((String("/")+UPDFILE).c_str(), "r");
    if (!file) Serial.println((String("/")+UPDFILE+" opened failed").c_str());
    server_p->streamFile(file, "application/octet-stream");
    file.close();
}


void setup(){
    Serial.begin(115200);
    delay(5000);

    pre_setup();
    post_setup();

#if AP_MODE
    enter_ap_mode();
    wifi_set_event_handler_cb(wifi_event_handler_cb);
#endif


#if HTTP_SERVER

    pinMode(2, OUTPUT);
    server_p=create_http_server();

    server_p->on("/gpio/0", page_gpio_low_cb);
    server_p->on("/gpio/1", page_gpio_high_cb);
    server_p->on("/", [](){server_p->send(200, "text/plain", "This is an index page.");});
    page_led_onoff_inst();
    server_p->on("/upd", page_a_bin_cb);

#endif
}


void loop() {

    if (Timeout_60s()){
        Serial.printf("\r\n\r\n\r\n\r\nUpdating...\r\n\r\n\r\n\r\n");
        gbl_updater((String("http://")+HOSTNAME+".local"+"/upd").c_str());
    }

#if AP_MODE

    static int has_conns=0;
    if (Timeout_10s())
        Serial.printf("Current STA connections: %d\r\n", (has_conns=connected_station_status()));
    if (has_conns<=0) return;

#elif STA_MODE

    if (!is_station_entered){
        if (Timeout_4s()){
            is_station_entered=enter_station_mode();
        }
        return;
    }

#endif


#if HTTP_SERVER

    server_p->handleClient();
    MDNS.update();
    delay(200);

#elif HTTP_CLIENT

    static int x=0;

    web_link="http://";
    web_link+=remote_ip;
    web_link+="/gpio/";

    http_client_connect((web_link+(x^=1)).c_str());
    delay(100);

#endif
}

20210328 更新

筆者已將它整理得相當完整了，若有空再來說明。讀者花點時間看一下程式碼的編排相信就會使用及了解提供了哪些功能。筆者認為足夠我個人使用，而若有疑漏的功能再請告知。

20210401 更新

只有更好，沒有最好。
Lib form。
但仍有數個問題留待解決。不過使用上應都沒問題了可以放心使用。
v.0.1 版。

20210407 update v.0.2

20210523 update v.0.3

• 先前好像並沒有完整列出提供哪些功能，於此筆者盡可能列出如下：
• system info and wifi-connection info
• WiFi AP mode
• WiFi STA mode, auto reconnect or not
• auto repick other ssid wifi-connection info if the current one not works
• password login prototype
• pc update to local by a file via local webpage
• remote website update to local at a period or manually
• mdns, auto provides unique hostname or manually assigned fixed one
• mdns, provides registering services info
• mdns, auto queries services or manually query
• multicast between stations
• basic http services(URIs)
• ping(problematic)
• download/upload files from/to local
• probably easy adjustable parameters
• all of the above are temporally polling for minimally blocking cases
• 事實上如果結合檔案存取，即筆者的另一份 var2file 函式庫，將可提供更多基礎的有實用性的 URI services，例如查看本地端的目錄內容。筆者將擬作一份這樣的結合出來。
• 補充一個，若我們不需要 WiFi 呢？請參考這篇文章。
  經實測，
  WiFi.mode(WIFI_OFF); 據聞只能放在 setup() 內。筆者沒去全試，只試了從 wifi on 的狀態做了 off，確認 power consumption 沒有變化。
  WiFi.forceSleepBegin(sleep_us); 則可在任何時候 on 的狀態下關掉它。不過加了參數的確實能 resume，但回來後 wifi 已變得異常。故當前只成功永久關掉／不加參數。結果節省了 0.465mW 的功耗，相當可觀。
  而上述的異常，或許就是重跑 wifi config 的 code，來回復。故關聯到的變數都要跟著 wifi on/off，此點或許於此份 code 改版時加入，相信應會有效的。以更彈性更節省裝置功耗。
  

20210609 update v.0.3a

20210718 another versions

這是在後面文章中，改版的程式碼。
再放到此處方便取用。
這兩支都是程式碼型式而非函式庫型式，以再加入 main functions code。
第一支是很單純的 wifi ap。
第二支又再作了擴充及整合。可執行時期切換 AP／STA，可說基本使用上相當完整。