ESP-NOW network + WiFi gateway to the Internet

The objective of this mini-project is to illustrate a communication based on the (connectionless) ESP-NOW protocol between a set of ESP32 senders and an ESP32 receiver, while configuring the receiver as a gateway to the Internet by connecting it to a WiFi router.

This mini-project was born from the observation of an erroneous implementation on the following tutorial, published by Rui and Sara on Random Nerd Tutorials:

ESP32: ESP-NOW Web Server Sensor Dashboard (ESP-NOW + Wi-Fi)

This observation led me to open a discussion on the RNT Lab forum to get the opinion of interested readers. And I'd especially like to thank Lee and Steve for taking the time to discuss the issue with me. We were finally able to identify what was wrong.

The solution was initially published on the Espressif forum by ardcp32, which I thank in passing, and which you will find here.

This mini-project is therefore intended to illustrate the right way to proceed for all readers of Random Nerd Tutorials.

You'll find here the code to be implemented on all ESP-NOW sending nodes, as well as that of the ESP-NOW receiving gateway, which is simultaneously connected to the Internet through a WiFi router.

Note that for this to work, each sender must use the same radio channel as the WiFi router. You can hard-code it, but if your router is configured to automatically switch to the least congested channel, it is best to have a routine that scans available networks and looks for the SSID of your router. This way you can easily identify the channel it is using. So I added this routine in the sender's code.