Use Husarnet on ESP32 (beta) - Arduino IDE


Husarnet VPN Client can run not only on servers, laptops and mobile phones (soon), but also on microcontrollers with very limited computing power and memory. Thanks to that you can run a single VPN network containing not only computers, but also cheap and low-power Wi-Fi sensors/actuators without any additional server or bridge in between. In other words you can build an IoT network connected to your computer without any kind of IoT API cloud in between. You can send messages directly to your Wi-Fi chips and this guide will show you how to do that.

This quick start guide describes how to use Husarnet VPN Client software library on ESP32 Wi-Fi microcontrollers and how to configure a network using Husarnet Dashboard in a few easy steps.

system architecture

Sections IV and V contain two demo project: basic and advanced. After finishing this quick start guide you will know not only how to connect your ESP32 and Linux computer together, but also how to usefull such a connection could be!

I. Create a network#

Log in to Husarnet Dashboard, click [Create network] button, name your network and click [Create] button.

create network

II. Get a join code#

Click [Add element] button, select [join code] tab and copy your join code which looks something like this:


find joincode

III. Configure Arduino IDE environment#

1. Install Arduino IDE#

First, download and install Arduino IDE.

2. Add ESP32 boards (powered by Husarnet)#

Open Arduino IDE and install the fork of Arduino core for the ESP32 by following these steps:

  • go to File -> Preferences
  • in a field Additional Board Manager URLs paste this link:

Board Manager URL

  • go to Tools -> Board: ... -> Boards Manager ...
  • Search for esp32-husarnet by Husarion
  • Click install button

ESP32 board install

3. Select ESP32 dev board:#

  • go to Tools -> Board
  • select ESP32 Dev Module under ESP32 Arduino (Husarnet) section

IV. Demo no. 1 (basic)#

We created a simple "hello world" demo for ESP32 and Husarnet. To run it you will need the following:

  • ESP32 dev board
  • laptop running Linux

It looks like this: ESP32 board is sending

Hello world! 1
Hello world! 2
Hello world! 3

over the internet using Husarnet VPN to a computer with a very basic server running on 8002 port and written in Python3.

Both client and server code is available on GitHub

ESP32 client code#

Create and open a new folder called husarnet-esp32-minimal and paste the code presented bellow to the husarnet-esp32-minimal.ino file (remember to replace wifi-ssid-1 and wifi-pass-for-ssid-1 by your Wi-Fi credentials and also replace a joincode by your own obtained in section II):

#include <WiFi.h>
#include <Husarnet.h>
// WiFi credentials
const char* ssid = "wifi-ssid-1";
const char* password = "wifi-pass-for-ssid-1";
// Husarnet credentials
const char* hostName = "esp32basic";
const char* husarnetJoinCode = "fc94:b01d:1803:8dd8:b293:5c7d:7639:932a/xxxxxxxxxxxxxxxxxxxxxx";
const char* dashboardURL = "default";
// Hostname of your laptop hosting a server
const char* laptopHostname = "mylaptop1";
void setup()
/* Connect to WiFi */
Serial.printf("Connecting to %s", ssid);
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {
Serial.printf("done\r\nlocal IP: %s", WiFi.localIP());
/* Start Husarnet */
Husarnet.join(husarnetJoinCode, hostName);
void loop()
HusarnetClient client;
uint8_t buf[100];
int buf_s = 0;
int cnt = 0;
/* Try to connect to a server on port 8002 on your laptop */
if (!client.connect(laptopHostname, 8002)) {
Serial.printf("connection to \"%s\" failed\r\n", laptopHostname);
/* While connected send "Hello world!" + counter value */
while(client.connected()) {
buf_s = sprintf ((char*)buf, "Hello world! %d\r\n", cnt++);
Serial.printf("sending: %s\r\n", (char*)buf);

Then build the project. Build project

And upload the code to your ESP32.

Python server code#

First, connect your Linux laptop to the same Husarnet network as ESP32. Follow getting started guide for Linux to see how to install Husarnet Client app and connect your laptop to the Husarnet network.

Create a file and paste this code:

import socket
with socket.socket(socket.AF_INET6, socket.SOCK_STREAM) as s:
s.bind((socket.gethostname(), 8002))
conn, addr = s.accept()
with conn:
print('Connected by', addr)
while True:
data = conn.recv(1024)
if not data: break

Then open a linux terminal in the same location where the python project is located and execute:

python3 ./
use IPv6 in your programs

Husarnet runs on top of both IPv4 and IPv6 networks but creates only IPv6 overlay network on top.

If you want to connect your existing code over the internet remember to change all settings to use IPv6 network like socket.AF_INET6 in the example above.

Read if you face errors during project build
  1. In some configurations you may face issues with other existing Wi-Fi libraries. The simplest way to fix that is to remove ...

V. Demo no. 2 (advanced)#

Demo no. 1 was really basic. Now let's create something that could be a good starting point for a real IoT project working on ESP32 board and Husarnet!

Here is a list of improvements:

  • use websockets that are very handy to handle communication in JavaScript and Python code
  • use JSON for data serialization and to provide elegant API
  • host simple web server on the ESP32
  • create a Python3 script that will save data in the SQLite database
  • make ESP32 to act as a server, not as a client

Typical IoT devices act only as clients connected to a central server with a static IP address:

Old IoT

Husarnet allows you to have a completely new approach to creating your own internet connected devices. They can act both as a server and as a client even with no static and public IP needed.

Thanks to that approach your sensors can be running the whole time with no additional server needed and you can connect, from a level of your laptop, to them directly over the internet whenever you want. That gives you much lower latency (comparing to central server based approach, especially if your devices are in near networks) and makes your IoT network configuration much simpler.

Old IoT

ESP32 client code#

At first, clone husarnet-esp32-default project from GitHub containging the following files:

  • husarnet-esp32-default.ino with a main code
  • html.h and default_js.h header files containging c-string tables with HTML and JS code of a server hosted by ESP32
  • lut.cpp and lut.h - library to generate fake data. Replace this with the real sensor data after finishing this quick start guide.

There is also a python folder containing a code that will be executed on your laptop side.

1. Install ArduinoJson and arduinoWebSockets libarty in Arduino IDE#

Install ArduinoJson library:

  • open Tools -> Manage Libraries...
  • search for ArduinoJson
  • click install button

Install arduinoWebSockets library (Husarnet fork):

  • download as a ZIP file (this is Husarnet compatible fork of arduinoWebSockets by Links2004 (Markus) )
  • open Sketch -> Include Library -> Add .ZIP Library ...
  • choose file that you just downloaded and click open button

2. Add your own Wi-Fi and Husarnet credentials#

in husarnet-esp32-default.ino file replace wifi-ssid-1 and wifi-pass-for-ssid-1 with your Wi-Fi credentials and also replace a joincode by your own, obtained in section II):

#include <WiFi.h>
#include <WiFiMulti.h>
#include <Husarnet.h>
#include <WebSocketsServer.h>
#include <WebServer.h>
#include <ArduinoJson.h>
#include "time.h"
#include "lut.h"
/* =============== config section start =============== */
#define HTTP_PORT 8000
#define WEBSOCKET_PORT 8001
#if __has_include("credentials.h")
#include "credentials.h"
// WiFi credentials
#define NUM_NETWORKS 2
const char* ssidTab[NUM_NETWORKS] = {
const char* passwordTab[NUM_NETWORKS] = {
// Husarnet credentials
const char* hostName = "esp32basic";
const char* husarnetJoinCode = "fc94:b01d:1803:8dd8:b293:5c7d:7639:932a/xxxxxxxxxxxxxxxxxxxxxx";
const char* dashboardURL = "default";
/* =============== config section end =============== */
// NTP settings
const char* ntpServer = "";
const long gmtOffset_sec = 3600;
const int daylightOffset_sec = 3600;
// HTTP server on port 8000
WebServer server(HTTP_PORT);
// websocket server on port 8001
WebSocketsServer webSocket = WebSocketsServer(WEBSOCKET_PORT);
// you can provide credentials to multiple WiFi networks
WiFiMulti wifiMulti;
// JSON documents
StaticJsonDocument<100> jsonDocRx; // {"set_output":"sine"}
StaticJsonDocument<200> jsonDocTx; // {"timestamp":1000000000, "output_type":"sine", "value":129}
// global variable to store a current waveform type to be sent over websocket
String modeName = "sine"; //"square", "triangle", "none"
SemaphoreHandle_t sem = NULL;
// HTML and JS files for HTTP server on port 8000
const char* html =
#include "html.h"
const char* default_js =
#include "default_js.h"
// get local time - synchronisation with NTP server
bool getTime(time_t& rawtime) {
struct tm timeinfo;
if (!getLocalTime(&timeinfo)) {
Serial.println("Failed to obtain time");
return 0;
} else {
rawtime = mktime(&timeinfo);
return 1;
void onWebSocketEvent(uint8_t num, WStype_t type, uint8_t* payload, size_t length) {
switch (type) {
Serial.printf("[%u] Disconnected\r\n", num);
case WStype_CONNECTED:
Serial.printf("\r\n[%u] Connection from Husarnet \r\n", num);
case WStype_TEXT:
Serial.printf("[%u] Text: %s\r\n", num, (char*)payload);
auto error = deserializeJson(jsonDocRx, payload);
if (!error) {
if (jsonDocRx["set_output"]) {
String output = jsonDocRx["set_output"];
if ( (output == "sine") || (output == "triangle") || (output == "square") || (output == "none")) {
modeName = output;
case WStype_BIN:
case WStype_ERROR:
case WStype_FRAGMENT:
void onHttpReqFunc() {
server.sendHeader("Connection", "close");
server.send(200, "text/html", html);
void taskWifi( void * parameter );
void taskStatus( void * parameter );
void setup()
sem = xSemaphoreCreateMutex();
xSemaphoreTake(sem, ( TickType_t)portMAX_DELAY);
taskWifi, /* Task function. */
"taskWifi", /* String with name of task. */
20000, /* Stack size in bytes. */
NULL, /* Parameter passed as input of the task */
1, /* Priority of the task. */
NULL); /* Task handle. */
taskStatus, /* Task function. */
"taskStatus", /* String with name of task. */
20000, /* Stack size in bytes. */
NULL, /* Parameter passed as input of the task */
1, /* Priority of the task. */
NULL); /* Task handle. */
void taskWifi( void * parameter ) {
uint8_t stat = WL_DISCONNECTED;
/* Configure Wi-Fi */
for (int i = 0; i < NUM_NETWORKS; i++) {
wifiMulti.addAP(ssidTab[i], passwordTab[i]);
Serial.printf("WiFi %d: SSID: \"%s\" ; PASS: \"%s\"\r\n", i, ssidTab[i], passwordTab[i]);
while (stat != WL_CONNECTED) {
stat =;
Serial.printf("WiFi status: %d\r\n", (int)stat);
Serial.printf("WiFi connected\r\n", (int)stat);
Serial.printf("IP address: ");
/* Start Husarnet */
Husarnet.join(husarnetJoinCode, hostName);
/* Configure connection to the NTP server (get accurate time for timestamps) */
configTime(gmtOffset_sec, daylightOffset_sec, ntpServer);
/* Start websocket server */
/* Confgiure HTTP server */
server.on("/", HTTP_GET, onHttpReqFunc);
server.on("/index.html", HTTP_GET, onHttpReqFunc);
server.on("/default.js", HTTP_GET, []() {
server.sendHeader("Connection", "close");
server.send(200, "application/javascript", default_js);
xSemaphoreGive( sem );
xSemaphoreGive( sem );
while (1) {
// loop to handle websocket server and HTTP server
while (WiFi.status() == WL_CONNECTED) {
if (xSemaphoreTake(sem, ( TickType_t)0) == pdTRUE ) {
xSemaphoreGive( sem );
Serial.printf("WiFi disconnected, reconnecting\r\n");
stat =;
Serial.printf("WiFi status: %d\r\n", (int)stat);
void taskStatus( void * parameter )
time_t currentTime;
while (1) {
if (xSemaphoreTake(sem, ( TickType_t)portMAX_DELAY) == pdTRUE ) {
if (getTime(currentTime)) {
String output;
jsonDocTx["timestamp"] = currentTime;
jsonDocTx["output_type"] = modeName;
jsonDocTx["value"] = getLutVal(modeName);
serializeJson(jsonDocTx, output);
// if websocket connection is opened send JSON like {"timestamp":1000000000, "output_type":"sine", "value":129}
if (webSocket.sendTXT(0, output)) {
xSemaphoreGive( sem );
Serial.print(F("Sending: "));
} else {
xSemaphoreGive( sem );
void loop()
Serial.printf("[RAM: %d]\r\n", esp_get_free_heap_size());

Web page hosted by ESP32#

After you upload a code to your ESP32 board, you should be able to access a web page hosted by ESP32 from a level of a web browser (on a laptop in the same Husarnet network).

You can just use a hostname in the URL: http://esp32basic:8000, where esp32basic is a Husarnet hostname of your ESP32 board, and 8000 is a port on which HTTP server is available.

Another option is to use Husarnet IPv6 address of your ESP32 board in the URL (you can find it in Husarnet Dashboard): http://[fc94:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx]:8000/.

web UI ESP32

Python server code#

First, connect your Linux laptop to the same Husarnet network as ESP32. Follow getting started guide for Linux to see how to install Husarnet Client app and connect your laptop to the Husarnet network.

In the husarnet-esp32-default repository there is a Python folder containing file

import sqlite3
import asyncio
import websockets
import argparse
import json
from sqlite3 import Error
conn = None
cur = None
sql_insert = "INSERT INTO exampledb (timestamp, output_type, value) VALUES (?, ?, ?);"
async def mainfunc():
uri = "ws://" + args.hostname + ":8001"
print("connecting: " + uri)
async with websockets.connect(uri) as websocket:
tx_msg = json.dumps({"set_output":args.outputType})
await websocket.send(tx_msg)
while True:
rx_msg = await websocket.recv()
rx_json = json.loads(rx_msg)
cur.execute(sql_insert, (rx_json["timestamp"],rx_json["output_type"],rx_json["value"]))
if __name__ == '__main__':
parser = argparse.ArgumentParser()
parser.add_argument("hostname", nargs='?', default="esp32basic")
parser.add_argument("outputType", nargs='?', default="sine")
args = parser.parse_args()
print("hostname: ", args.hostname)
print("outputType: ", args.outputType)
conn = sqlite3.connect("./exampledb.db")
print("sqlite version: " + sqlite3.version)
cur = conn.cursor()
cur.execute("CREATE TABLE IF NOT EXISTS exampledb (timestamp, output_type, value)")
except Error as e:
except KeyboardInterrupt:
print("\r\nReceived exit, exiting")
print("\r\nClose database connection")
if conn:

Then open a linux terminal in the same location where the python project is located and execute:

python3 ./

In the code we're trying to connect to a websocket port 8001 served by the ESP32 board under a defaul URL: ws://esp32basic:8001. If connection is established, we send a name of a waveform to be generated by ESP32 and then store each received fake sensor data in exampledb.db (created by Python program if not existing).

That's all. Installing and using Husarnet VPN Client library for ESP32 is very simple. Basically it works just like standard Arduino core for ESP32 repository, but instead of <WiFiClient.h> and <WiFiServer.h> libraries (that are still available) you need to use<HusarnetClient.h> and <HusarnetServer.h> libraries provied by Husarnet.


There is a simple way to quickly port probably most of libraries available for ESP32 board that use <WiFiClient.h> and <WiFiServer.h> standard libraries.

Just open library files (both .cpp and .h) and replace each occurence of:

  • WiFiClient string by HusarnetClient string
  • WiFiServer string by HusarnetServer string

Your Husarnet connected devices see each other like they were in the same LAN network even if one of them is a microcontroller and other is Linux computer.

Just be aware that the servers and client you are using must support IPv6 (as Husarnet is an IPv6 overlay network) - for example, you have to listen on "::", not "".

Python2 issues with Arduino IDE and ESP32#

install python2#

ESP32 CORE for ESP32 uses python2. In the Ubuntu 20.04 you have only python3 installed. To install python2 and setup that as a default "python" run those commands in the terminal

$ sudo apt install python2

The command:

$ sudo update-alternatives --list python

will return:


To set whether default 'python' should be python2 or python3 run those commands:

$ sudo update-alternatives --install /usr/bin/python python /usr/bin/python2 1
$ sudo update-alternatives --install /usr/bin/python python /usr/bin/python3 2
$ sudo update-alternatives --config python

To check your default 'python' version execute:

$ python -V

This guide is based on

install python "serial" module:#

When you first build you project probably you can see the error message like this:

Traceback (most recent call last):
File "/home/user1/.arduino15/packages/esp32-husarnet/hardware/esp32/1.2.1/tools/esptool/", line 37, in <module>
import serial
ImportError: No module named serial
Multiple libraries were found for "WiFi.h"
Used: /home/user1/.arduino15/packages/esp32-husarnet/hardware/esp32/1.2.1/libraries/WiFi
Not used: /opt/arduino-1.8.13/libraries/WiFi
exit status 1
Error compiling for board ESP32 Dev Module.

At first you will need to install python pip. The process is described here:

Install python2 "serial" module execute the following command:

$ python -m pip install pyserial

To access serial port as a normal user you will probably need to change tty group:

$ sudo usermod -a -G tty username
$ sudo usermod -a -G dialout username

and then logout and login. If it doesn't help try with:

sudo chown username /dev/ttyUSB0

More resources:#