ESP32 USB-to-AirPrint: give an old USB printer AirPrint and scanning with an ESP32-S3

ESP32 USB-to-AirPrint, by Xuan-Son Nguyen (ngxson), turns a USB-only printer into a wireless printer and scanner with one ESP32-S3 dev board. The board plugs into the printer's USB port, joins your Wi-Fi and presents the printer as an AirPrint printer for iPhone, iPad and Mac, a Mopria printer for Android, and an IPP printer for Linux, with no drivers or apps. Scanning works from any browser, from Image Capture or Preview on a Mac (eSCL), or with the BOOT button on the board (press to scan, press twice for a test page, hold 2 s to cancel). The firmware also serves a web app where you can print PDFs and pictures, scan, keep files in the browser and combine pages (rotate, crop, ID-card copies) into a PDF. The catch is printer support: right now the drivers are Canon PIXMA only. The MG2550S is the one model validated on a real printer; about 16 more Canon series (MG2400, MG2500, MG2900, MG3000, E460/E470, E3100, TS3100, MP230, MP250-MP280, MP490-MP495, MX340-MX420, plus iP2700, iP2800 and P200 without scanners) are listed as expected to work but untested, and the author is asking printer owners to contribute and test drivers. Hardware is an ESP32-S3 dev board with two USB-C ports; the build targets the ESP32-S3-DevKitC-1 with the N16R8 module (16 MB flash, 8 MB PSRAM). Plug the board's COM port into your computer, build once with PlatformIO to create a .env file, put your Wi-Fi name and password, printer name and hostname in it, and flash with pio run -t upload. Then plug the printer into the port labelled USB; you may need to bridge the board's USB-OTG solder jumper so it supplies 5 V, because the printer uses that line to sense the cable. MODE=debug in .env allows later updates over Wi-Fi. An SSD1315 128x64 I2C OLED (SCL GPIO41, SDA GPIO42) and extra buttons on GPIO4 and GPIO5 are optional, and the author shows a 3D-printed case. The protocols follow Gutenprint and SANE's pixma backend. MIT licensed.