Table of Contents

Web of Things at FOSDEM 2026

Quick start

Advanced: HTTP API

Web of Things is a set of standards for Internet of Things use cases. At the Matrix Hackathon and FOSDEM 2026, I brought the following hardware. They support support Web of Things via HTTP and Websockets.

Receipt printer

Current status: Ready

URLs

Code examples (images)

Bash: 

curl -X POST \
  -H "Content-Type: application/json" \
  --data "{\"image\":\"$(base64 image.png | tr -d '\n')\"}" \
  https://wot-why.jaller.de/receipt-printers-for-events/photo/actions/print-photo

Or in NodeJS / Bun / Deno: 

import { readFile } from "node:fs/promise";
 
const image = await readFile("image.png");
const response = await fetch("https://wot-why.jaller.de/receipt-printers-for-events/photo/actions/print-photo", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    image: image.toString("base64"),
  }),
});
 
if (!response.ok) {
  throw Error(`Failed to queue print job. HTTP ${response.status}`);
}

Code examples (text)

Bash: 

curl -X POST \
  --header "Content-Type: application/json" \
  --data '{"text":"Hello World!"}' \
  https://wot-why.jaller.de/receipt-printers-for-events/text/actions/print-text

Or in NodeJS / Bun / Deno: 

const response = await fetch("https://wot-why.jaller.de/receipt-printers-for-events/text/actions/print-text", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    text: "Hello World!",
  }),
});
 
if (!response.ok) {
  throw Error(`Failed to queue print job. HTTP ${response.status}`);
}

E-paper screen

Current status: Ready at https://wot-wrench.chrpaul.de/#try=https://wot.chrpaul.de/image-storage/LDN3dJE3vu

URLs

Use these URLs to test your scripts. They will not display anything on the screen, but the Thing has a preview property.

Use this URL to HTTP PUT an image onto the screen.

Code Examples

To upload a local PNG file image.png via a Bash: 

curl -X PUT \
  -H "Content-Type: application/json" \
  --data "\"$(base64 image.png | tr -d '\n')\"" \
  https://wot.chrpaul.de/image-storage/fosdem/properties/image

Or in NodeJS / Bun / Deno:

Have a look at this demo project: https://codeberg.org/jaller94/wot-fosdem-demo 

import { readFile } from "node:fs/promise";
 
const image = await readFile("image.png");
const response = await fetch("https://wot.chrpaul.de/image-storage/fosdem/properties/image", {
  method: "PUT",
  headers: {
    "Content-Type": "application/json",
  },
  body: JSON.stringify(image.toString("base64")),
});
 
if (!response.ok) {
  throw Error(`Failed to upload image. HTTP ${response.status}`);
}

Dithering

Images will be resized and dithered automatically. However, if you want full control over the result, you can send images in the right resolution using only the supported color palette.

For TypeScript, I recommend using my fork of dither-me-this. It supports custom color palettes which is optimal for the e-paper screens. Previously, I used my fork of canvas-dither. Its API is easier and more mature, but it only supports 1-bit dithering. It's most suitable for the receipt printer.