vaccineqr.js

/**
 * Decode and display information contained in a SMART Health Card (SHC) QR code
 * Usage: node vaccineqr.js /path/to/qrcode.png
 *
 * Required dependencies:
 *  - jimp
 *  - jsqr
 * 
 * 2021 Jacob Cook
 */

const { promises: fs } = require("fs");
const path = require("path");
const jimp = require("jimp");
const jsQR = require("jsqr");
const zlib = require("zlib");
const util = require("util");

function jwtSectionToBuffer(section) {
  return Buffer.from(section.replace("-", "+").replace("_", "/"), "base64");
}

function parseJWTSection(section) {
  return JSON.parse(jwtSectionToBuffer(section).toString("utf8"));
}

const zlibInflateRaw = util.promisify(zlib.inflateRaw);

/**
 * Reads a QR code and returns its data as a string.
 * @param {Buffer} buffer QR code image buffer in JPG/PNG/BMP format
 * @returns {Promise<string>}
 */
async function readQRCode(buffer) {
  const processed_image = await jimp.read(buffer);
  const qr = jsQR(processed_image.bitmap.data, processed_image.getWidth(), processed_image.getHeight());
  if (!qr) {
    throw new Error("QR code could not be processed");
  }
  return qr.data;
}

/**
 * Parses a SMART Health Card's raw string representation into a signed JSON Web Token.
 * @param {string} shc 
 * @returns {string}
 */
function parseSHCtoJWT(shc) {
  const data = shc.replace(/^shc:\//, "").replace(/[^0-9]/, "");
  const chars = [];
  let index = 0;
  while (index < data.length) {
    const buf = Number(data.slice(index, index + 2)) + 45;
    chars.push(String.fromCodePoint(buf));
    index += 2;
  }
  return Buffer.from(chars.join(""), "ascii").toString("utf8");
}

/**
 * Parses a JSON Web Token into its header, payload and signatures.
 * @param {string} jwt 
 */
async function parseJWT(jwt) {
  const [raw_header, raw_payload, signature] = jwt.split(".");
  const header = parseJWTSection(raw_header);

  let payload = raw_payload;
  if (header.zip === "DEF") {
    payload = await zlibInflateRaw(jwtSectionToBuffer(raw_payload));
  }
  payload = JSON.parse(payload.toString("utf8"));

  return { header, payload, signature };
}

async function main() {
  let image_path = process.argv[2];
  if (!image_path) {
    throw new Error("No image path provided");
  }
  if (image_path.startsWith(".")) {
    image_path = path.join(__dirname, image_path);
  }
  
  const raw_image = await fs.readFile(image_path);
  const shc = await readQRCode(raw_image);
  const jwt = parseSHCtoJWT(shc);
  const result = await parseJWT(jwt);
  
  console.log(JSON.stringify(result));
}

main()
  .then(() => {
    process.exit(0);
  })
  .catch((err) => {
    console.error(err);
    process.exit(1);
  });