How to fix Python ValueError: unsupported format character ‘ ‘ (0x20) at index 3

Problem:

You are trying to use Python format strings like

"Hello %.3 world" % 1.234

but you see an error message like

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-4-7cbe94e4525d> in <module>
----> 1 "Hello %.3 world" % 1.234

ValueError: unsupported format character ' ' (0x20) at index 9

Solution:

Your format string %.3 is incomplete ! You need to specify the type of value to format, e.g. f for floating point, d for integers, s for strings etc. So instead of %.3, write %.3f, or instead of just % write e.g. %f, %d or %s depending on the data type of the variable you want to insert there.

Posted by Uli Köhler in Python

How to auto-fit Pandas pd.to_excel() XLSX column width

If you export XLSX data using df.to_excel(), the column widths in the spreadsheet are left as default and are not adjusted automatically:

# Load example dataset
df = pd.read_csv("https://datasets.techoverflow.net/timeseries-example.csv", parse_dates=["Timestamp"])
df.set_index("Timestamp", inplace=True)

# Export dataset to XLSX
df.to_excel("example.xlsx")

Solution

You can use UliPlot‘s auto_adjust_xlsx_column_width in order to automatically adjust the column width.

pip install UliPlot

Then use it like this in order to  export the XLSX:

from UliPlot.XLSX import auto_adjust_xlsx_column_width

# Load example dataset
df = pd.read_csv("https://datasets.techoverflow.net/timeseries-example.csv", parse_dates=["Timestamp"])
df.set_index("Timestamp", inplace=True)

# Export dataset to XLSX
with pd.ExcelWriter("example.xlsx") as writer:
    df.to_excel(writer, sheet_name="MySheet")
    auto_adjust_xlsx_column_width(df, writer, sheet_name="MySheet", margin=0)

Note that the algorithm currently tends to oversize the columns a bit, but in most cases, every type of column will fit.

Posted by Uli Köhler in pandas, Python

How to fix Windows “echo $PATH” empty result

When you try to run

echo $PATH

you will always get an empty result.

Instead, if you are in cmd, use

echo %PATH%

but if you are using PowerShell, you need to use

$env:PATH

 

Posted by Uli Köhler in PowerShell, Windows

AWS / Wasabi S3 policy to allow a single user complete access to a single bucket

Use this S3 policy in your bucket configuration to allow a single user (identified by its ARN) complete access to a single bucket:

{
  "Id": "MyBucketPolicy",
  "Statement": [
    {
      "Sid": "AllAccess",
      "Action": "s3:*",
      "Effect": "Allow",
      "Resource": [
         "arn:aws:s3:::my-bucket-name",
         "arn:aws:s3:::my-bucket-name/*"
      ],
      "Principal": {"AWS":["arn:aws:iam::100000012345:user/MyUser"]}
    }
  ]
}

Replace both instances of arn:aws:s3:::my-bucket-name by your bucket ARN and replace arn:aws:iam::100000012345:user/MyUser by your user’s ARN. You can also add multiple user ARNs to "Principal": {"AWS": ... }.

Posted by Uli Köhler in Data science

How to allow your EtherPad to be included in IFrames using nginx

In our previous post A modern Docker-Compose config for Etherpad using nginx as reverse proxy we showed how to create a simple, reliable Etherpad installation.

However, if you want to include Etherpads on external websites, you’ll see connection refused errors like

Refused to display 'https://etherpad.nemeon.eu/p/Test123' in a frame because it set 'X-Frame-Options' to 'sameorigin'.

and the Etherpad iframe won’t load.

In order to fix this, we’ll add a line to the nginx config in . Using this approach, you’ll need to list all the domains that are allowed to include the Etherpad (https://gather.town in this example).

The line to add is

add_header "X-Frame-Options" "Allow-From https://gather.town";

which needs to be added inside the location / { ... } block. Full example for the location / block:

location / {
    proxy_pass http://localhost:17201/;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "Upgrade";
    proxy_redirect default;
    add_header "X-Frame-Options" "Allow-From https://gather.town";
}

Full nginx config example:

server {
    server_name  etherpad.mydomain.de;
    access_log off;
    error_log /var/log/nginx/etherpad.mydomain.de-error.log;

    location / {
        proxy_pass http://localhost:17201/;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";
        proxy_redirect default;
        add_header "X-Frame-Options" "Allow-From https://gather.town";
    }

    listen [::]:443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/etherpad.mydomain.de/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/etherpad.mydomain.de/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot

}

server {
    if ($host = etherpad.mydomain.de) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


    listen [::]:80; # managed by Certbot
    server_name  etherpad.mydomain.de;
    return 404; # managed by Certbot
}

How it works

The etherpad backend, which is reverse-proxied inside nginx, will add a X-Frame-Options: sameorigin header, effectively disallowing iframes from other domains. Using the add_header clause, nginx will overwrite this value with Allow-From https://gather.town. The browser will only see Allow-From https://gather.town, allowing iframe inclusion from the listed domains.

Posted by Uli Köhler in Networking, nginx

A modern Docker-Compose config for Etherpad using nginx as reverse proxy

This is the configuration I use to run my etherpad installations behind nginx:

docker-compose.yml

version: "3.5"
services:
  etherpad:
    image: etherpad/etherpad:latest
    environment:
      - TITLE=My Etherpad
      - DEFAULT_PAD_TEXT=My Etherpad
      - ADMIN_PASSWORD=${ETHERPAD_ADMIN_PASSWORD}
      - ADMIN_USER=admin
      - DB_TYPE=mysql
      - DB_HOST=mariadb
      - DB_PORT=3306
      - DB_USER=etherpad
      - DB_PASS=${MARIADB_PASSWORD}
      - DB_NAME=etherpad
      - DB_CHARSET=utf8mb4
      - API_KEY=${ETHERPAD_API_KEY}
      - SESSION_REQUIRED=false
    ports:
      - "17201:9001"
    depends_on:
      - mariadb

  mariadb:
    image: mariadb:latest
    environment:
      - MYSQL_ROOT_PASSWORD=${MARIADB_ROOT_PASSWORD}
      - MYSQL_DATABASE=etherpad
      - MYSQL_USER=etherpad
      - MYSQL_PASSWORD=${MARIADB_PASSWORD}
    volumes:
      - './mariadb_data:/var/lib/mysql'
    command: ['mysqld', '--character-set-server=utf8mb4', '--collation-server=utf8mb4_unicode_ci']
    healthcheck:
      test: mysqladmin -p${MARIADB_ROOT_PASSWORD} ping -h localhost
      interval: 20s
      start_period: 10s
      timeout: 10s
      retries: 3

.env

Remember to replace the passwords with your own random passwords !

MARIADB_ROOT_PASSWORD=ue9zahb8Poh1oeMieyaeFaicheecaz
MARIADB_PASSWORD=dieQuoghiu6sao9aiphei7eiquael5
ETHERPAD_API_KEY=een4Chohdiedohzaich0ega5thung6
ETHERPAD_ADMIN_PASSWORD=ahNee3OhR6aiCootaiy7uBui3rooco

nginx config

server {
    server_name  etherpad.mydomain.de;
    access_log off;
    error_log /var/log/nginx/etherpad.mydomain.de-error.log;

    location / {
        proxy_pass http://localhost:17201/;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";
        proxy_redirect default;
    }

    listen [::]:443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/etherpad.mydomain.de/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/etherpad.mydomain.de/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot

}

server {
    if ($host = etherpad.mydomain.de) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


    listen [::]:80; # managed by Certbot
    server_name  etherpad.mydomain.de;
    return 404; # managed by Certbot
}

How to autostart

Our post Create a systemd service for your docker-compose project in 10 seconds provides an extremely quick and easy-to-use one-liner to create and autostart a systemd service running docker-compose for your etherpad instance.

How to backup

This will be detailed in a future blogpost.

Posted by Uli Köhler in Container, Docker, nginx

Minimal ESP32 NTP client example using NTPClient_Generic and PlatformIO

Example of using NTPClient_Generic

main.cpp

#include <Arduino.h>
#include <WiFi.h>
#include <NTPClient_Generic.h>

#define TIME_ZONE_OFFSET_HRS 1 // UTC+1 for Germany, winter time
#define NTP_UPDATE_INTERVAL_MS 60000L // Update every 60s automatically
WiFiUDP ntpUDP;
NTPClient ntpClient(ntpUDP, "europe.pool.ntp.org", (3600 * TIME_ZONE_OFFSET_HRS), NTP_UPDATE_INTERVAL_MS);

void ntpUpdateTask(void* param) {
  while(true) {
    // Update NTP. This will only ACTUALLY update if
    // the NTP client has not updated for NTP_UPDATE_INTERVAL_MS
    ntpClient.update();
    vTaskDelay(1000 / portTICK_PERIOD_MS);
  }
}

void setup() {
  Serial.begin(115200);
  // Force reset Wifi to avoid failure to connect
  WiFi.disconnect(true);
  // Set hostname
  WiFi.config(INADDR_NONE, INADDR_NONE, INADDR_NONE);
  WiFi.setHostname("ESP-NTP");
  // Connect to Wifi
  WiFi.begin("MyWifiSSID", "MyWifiPassword");
  while (WiFi.status() != WL_CONNECTED) {
      delay(100);
      Serial.println("Wifi connecting...");
  }

  // Start NTP client (i.e. start listening for NTP packets)
  ntpClient.begin();
  // Create task to automatically update NTP in the background
  xTaskCreate(ntpUpdateTask, "NTP update", 2000, nullptr, 1, nullptr);
}

void loop() {
  delay(1000);
  if (ntpClient.updated()) {
    Serial.println("# Time in sync with NTP server");
  } else {
    Serial.println("# TIME NOT IN SYNC WITH NTP SERVER !");
    return; // Do not print time
  }

  Serial.println("UTC : " + ntpClient.getFormattedUTCTime());
  Serial.println("UTC : " + ntpClient.getFormattedUTCDateTime());
  Serial.println("LOC : " + ntpClient.getFormattedTime());
}

platformio.ini

[env:nodemcu-32s]
platform = espressif32
board = nodemcu-32s
framework = arduino
monitor_speed = 115200
lib_deps =
    khoih.prog/NTPClient_Generic @ ^3.2.2
    Time

Example output:

Wifi connecting...
Wifi connecting...
Wifi connecting...
# TIME NOT IN SYNC WITH NTP SERVER !
# Time in sync with NTP server
UTC : 01:22:07
UTC : 01:22:07 Sun 07 Feb 2021
LOC : 02:22:07
# Time in sync with NTP server
UTC : 01:22:08
UTC : 01:22:08 Sun 07 Feb 2021
LOC : 02:22:08
# Time in sync with NTP server
UTC : 01:22:09
UTC : 01:22:09 Sun 07 Feb 2021
LOC : 02:22:09

 

Posted by Uli Köhler in C/C++, ESP8266/ESP32, PlatformIO

How to get current gateway IP address on ESP8266/ESP32

In order to get the current gateway IP address on the ESP8266 or ESP32, use:

WiFi.gatewayIP();

In order to print the gateway IP address on the serial port, use

Serial.println("Gateway IP address: ");
Serial.println(WiFi.gatewayIP());

In order to get the gateway IP address as string, use

String gatewayIP = WiFi.gatewayIP().toString();

 

Posted by Uli Köhler in C/C++, Embedded, ESP8266/ESP32, PlatformIO

ESP32 Servo controllable via HTTP JSON API / web browser

This sketch for PlatformIO  allows you to use the ESP32 as a Servo controller (servo on pin D25) that connects to Wifi and can be controller using a simple HTTP API. The webserver is implemented using ESPAsyncWebserver. Also see ESP32 minimal JSON webserver example for PlatformIO (ESPAsyncWebserver) in case you are not familiar with that library. This example is not a finished application but a minimal starting point to build your own application.

main.cpp

#include <Arduino.h>
#include <Arduino.h>
#include <WiFi.h>
#include <ESP32Servo.h>

#include <ESPAsyncWebServer.h>
#include <ArduinoJson.h>

AsyncWebServer server(80);

/**
 * Wait for WiFi connection, and, if not connected, reboot
 */
void waitForWiFiConnectOrReboot(bool printOnSerial=true) {
  uint32_t notConnectedCounter = 0;
  while (WiFi.status() != WL_CONNECTED) {
      delay(100);
      if(printOnSerial) {
        Serial.println("Wifi connecting...");
      }
      notConnectedCounter++;
      if(notConnectedCounter > 50) { // Reset board if not connected after 5s
          if(printOnSerial) {
            Serial.println("Resetting due to Wifi not connecting...");
          }
          ESP.restart();
      }
  }
  if(printOnSerial) {
    // Print wifi IP addess
    Serial.println("IP address: ");
    Serial.println(WiFi.localIP());
  }
}

Servo servo;

void setup() {
  ESP32PWM::allocateTimer(0);
  ESP32PWM::allocateTimer(1);
  ESP32PWM::allocateTimer(2);
  ESP32PWM::allocateTimer(3);

  Serial.begin(115200);

  WiFi.config(INADDR_NONE, INADDR_NONE, INADDR_NONE);
  WiFi.setHostname("ESP-Servo");

  WiFi.begin("MyWifiSSID", "MyWifiPassword");
  waitForWiFiConnectOrReboot();

  // Attach servo to pin 25
  servo.attach(25, 1000, 2000);
  
  // Configure HTTP routes
  server.on("/api/set-servo", HTTP_GET, [](AsyncWebServerRequest *request) {
      float value = request->arg("value").toFloat();
      servo.write(value);
      // Send {status: "ok"}
      AsyncResponseStream *response = request->beginResponseStream("application/json");
      DynamicJsonDocument json(1024);
      json["status"] = "ok";
      serializeJson(json, *response);
      request->send(response);
  });
  
  // Start webserver
  server.begin();
}

void loop() {
}

platformio.ini

[env:nodemcu-32s]
platform = espressif32
board = nodemcu-32s
framework = arduino
monitor_speed = 115200
lib_deps =
    ESP Async [email protected]
    [email protected]
    ESP32Servo

How to use

Insert your Wifi credentials in the line

WiFi.begin("MyWifiSSID", "MyWifiPassword");

and upload the firmware. Now open http://[ip address of the ESP32]/api/set-servo?value=0.0. Note that in the current version of the firmware, you can not use value=10 but you must use value=10.0.

Posted by Uli Köhler in ESP8266/ESP32, PlatformIO

ESP32 minimal WebSocket example (ESPAsyncWebserver / PlatformIO)

Minimal firmware to use WebSockets on the ESP32 using ESPAsyncWebserver:

main.cpp

#include <Arduino.h>
#include <WiFi.h>
#include <ESPAsyncWebServer.h>
#include <ArduinoJson.h>

AsyncWebServer server(80);
AsyncWebSocket ws("/ws");

AsyncWebSocketClient* wsClient;
 
void onWsEvent(AsyncWebSocket * server, AsyncWebSocketClient * client, AwsEventType type, void * arg, uint8_t *data, size_t len){
  if(type == WS_EVT_CONNECT){
    wsClient = client;
  } else if(type == WS_EVT_DISCONNECT){
    wsClient = nullptr;
  }
}

/**
 * Wait for WiFi connection, and, if not connected, reboot
 */
void waitForWiFiConnectOrReboot(bool printOnSerial=true) {
  uint32_t notConnectedCounter = 0;
  while (WiFi.status() != WL_CONNECTED) {
      delay(100);
      if(printOnSerial) {
        Serial.println("Wifi connecting...");
      }
      notConnectedCounter++;
      if(notConnectedCounter > 50) { // Reset board if not connected after 5s
          if(printOnSerial) {
            Serial.println("Resetting due to Wifi not connecting...");
          }
          ESP.restart();
      }
  }
  if(printOnSerial) {
    // Print wifi IP addess
    Serial.println("IP address: ");
    Serial.println(WiFi.localIP());
  }
}


void setup() { 
  Serial.begin(115200);
  WiFi.config(INADDR_NONE, INADDR_NONE, INADDR_NONE);
  WiFi.setHostname("ESP-Websocket-Test");

  WiFi.begin("MyWifiSSID", "MyWifiPassword");
  waitForWiFiConnectOrReboot();

  // Start webserver
  ws.onEvent(onWsEvent);
  server.addHandler(&ws);
  server.begin();
}

uint64_t counter = 0;
void loop() {
  // If client is connected ...
  if(wsClient != nullptr && wsClient->canSend()) {
    // .. send hello message :-)
    wsClient->text("Hello client");
  }

  // Wait 10 ms
  delay(10);
}

platformio.ini:

[env:nodemcu-32s]
platform = espressif32
board = nodemcu-32s
framework = arduino
monitor_speed = 115200
lib_deps =
    ESP Async [email protected]
    [email protected]

Python code for testing:

import websocket
ws = websocket.WebSocket()
ws.connect("ws://192.168.1.211/ws")
while True:
    result = ws.recv()
    print(result)

This will print Hello Client many times a second.

Posted by Uli Köhler in C/C++, ESP8266/ESP32, PlatformIO

How to fix Python WebSocket ValueError: scheme http is invalid

Problem:

You want to use Python to connect to your WebSocket server:

import websocket
ws = websocket.WebSocket()
ws.connect("http://192.168.1.211/ws")

But you see an error message like

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-2-5108525d0b43> in <module>
      1 import websocket
      2 ws = websocket.WebSocket()
----> 3 ws.connect("http://10.228.152.103/ws")
      4 while True:
      5     result = ws.recv()

c:\python38\lib\site-packages\websocket\_core.py in connect(self, url, **options)
    220         # FIXME: "header", "cookie", "origin" and "host" too
    221         self.sock_opt.timeout = options.get('timeout', self.sock_opt.timeout)
--> 222         self.sock, addrs = connect(url, self.sock_opt, proxy_info(**options),
    223                                    options.pop('socket', None))
    224 

c:\python38\lib\site-packages\websocket\_http.py in connect(url, options, proxy, socket)
    106         return _open_proxied_socket(url, options, proxy)
    107 
--> 108     hostname, port, resource, is_secure = parse_url(url)
    109 
    110     if socket:

c:\python38\lib\site-packages\websocket\_url.py in parse_url(url)
     61             port = 443
     62     else:
---> 63         raise ValueError("scheme %s is invalid" % scheme)
     64 
     65     if parsed.path:

ValueError: scheme http is invalid

Solution:

The websocket-client library wants you to use ws://host/path instead of http://host/path. So instead of

ws.connect("http://10.228.152.103/ws")

use

ws.connect("http://10.228.152.103/ws")
Posted by Uli Köhler in Python

How to fix Python WebSocket TypeError: __init__() missing 3 required positional arguments: ‘environ’, ‘socket’, and ‘rfile’

Problem:

You are trying to connect a WebSocket in Python:

import websocket
ws = websocket.WebSocket()

but you see an error message like

TypeError                                 Traceback (most recent call last)
<ipython-input-3-5108525d0b43> in <module>
      1 import websocket
----> 2 ws = websocket.WebSocket()
      3 ws.connect("ws://192.168.1.211/ws")
      4 while True:
      5     result = ws.recv()

TypeError: __init__() missing 3 required positional arguments: 'environ', 'socket', and 'rfile'

Solution:

You have installed the wrong library ! You need to use websocket-client instead of websocket !

First, uninstall websocket:

pip uninstall websocket

Now install websocket-client:

pip install websocket-client

Now try again – your code should work now.

Posted by Uli Köhler in Python

How to fix ESP32 too few arguments to function ‘esp_err_t esp_wifi_sta_wpa2_ent_enable(const esp_wpa2_config_t*)’

Problem:

While trying to compile your ESP32 application, you see this compiler error:

src\main.cpp: In function 'void wifiConnectWPAEAP(const char*, const char*, const char*, const char*)':
src\main.cpp:23:32: error: too few arguments to function 'esp_err_t esp_wifi_sta_wpa2_ent_enable(const esp_wpa2_config_t*)'   esp_wifi_sta_wpa2_ent_enable();
                                ^

Solution:

Replace

esp_wifi_sta_wpa2_ent_enable();

by

esp_wpa2_config_t config = WPA2_CONFIG_INIT_DEFAULT();
esp_wifi_sta_wpa2_ent_enable(&config);
Posted by Uli Köhler in C/C++, Embedded, ESP8266/ESP32

How to fix ESP32 fatal error: ESP8266WiFi.h: No such file or directory

Problem:

While trying to compile your ESP32 application, you see this compiler error:

fatal error: ESP8266WiFi.h: No such file or directory

Solution:

ESP8266WiFi.h is the Wifi header for the ESP8266. For the ESP32, it’s named WiFi.h. In order to fix the issue, replae

#include <ESP8266WiFi.h>

by

#include <WiFi.h>
Posted by Uli Köhler in C/C++, Embedded, ESP8266/ESP32

How to fix Alpine Linux fatal error: stdio.h: No such file or directory

Problem:

When trying to compile a C/C++ program or library on Alpine Linux, you see an error message like

/home/user/test.cpp:5:10: fatal error: stdio.h: No such file or directory
  123 | #include <stdio.h>
      |          ^~~~~~~~~

Solution:

Install the libc headers using

apk add musl-dev

 

Posted by Uli Köhler in C/C++, GCC errors, Linux

ESP32 minimal JSON webserver example for PlatformIO (ESPAsyncWebserver)

This is my recommended starting point to get a webserver running on the ESP32 using PlatformIO:

#include <Arduino.h>
#include <WiFi.h>
#include <ESPAsyncWebServer.h>
#include <ArduinoJson.h>

AsyncWebServer server(80);

void setup() { 
  Serial.begin(115200);
  // Connect Wifi, restart if not connecting
  // https://techoverflow.net/2021/01/21/how-to-fix-esp32-not-connecting-to-the-wifi-network/
  WiFi.begin("MyWifiSSID", "MyWifiPassword");
  uint32_t notConnectedCounter = 0;
  while (WiFi.status() != WL_CONNECTED) {
      delay(100);
      Serial.println("Wifi connecting...");
      notConnectedCounter++;
      if(notConnectedCounter > 50) { // Reset board if not connected after 5s
          Serial.println("Resetting due to Wifi not connecting...");
          ESP.restart();
      }
  }
  Serial.print("Wifi connected, IP address: ");
  Serial.println(WiFi.localIP());

  // Initialize webserver URLs
  server.on("/api/wifi-info", HTTP_GET, [](AsyncWebServerRequest *request) {
      AsyncResponseStream *response = request->beginResponseStream("application/json");
      DynamicJsonDocument json(1024);
      json["status"] = "ok";
      json["ssid"] = WiFi.SSID();
      json["ip"] = WiFi.localIP().toString();
      serializeJson(json, *response);
      request->send(response);
  });

  // Start webserver
  server.begin();
}

void loop() {
  // put your main code here, to run repeatedly:
}

Remember to replace your Wifi credentials! WiFi.begin("MyWifiSSID", "MyWifiPassword");

To your platformio.ini add:

monitor_speed = 115200
lib_deps =
    ESP Async [email protected]
    [email protected]

My complete platformio.ini looks like this:

[env:nodemcu-32s]
platform = espressif32
board = nodemcu-32s
framework = arduino
monitor_speed = 115200
lib_deps =
    ESP Async [email protected]
    [email protected]

Use PlatformIO’s Upload and Monitor so you can see the IP address of the device in your Wifi network, for example:

Wifi connected, IP address: 192.168.178.90

then goto http://192.168.178.90/api/wifi-info (replace 192.168.178.90 by the IP address of the ESP32 that you can see on the command line!

You should now see JSON like:

{
     status: "ok",
     ssid: "MyWifiSSID",
     ip: "192.168.178.90"
}

Remember that you can use a browser plugin like JSON Viewer for Chrome in order to auto-format JSON documents!

Posted by Uli Köhler in ESP8266/ESP32