CBS-Mobile-App/download-fonts.js

/**
 * Fetches the app's font files into assets/fonts/.
 *
 * ── WHY THIS SCRIPT IS THE WAY IT IS ────────────────────────────────────────
 * An earlier version pointed at a Nunito URL that had died and piped whatever
 * came back straight into the .ttf without looking at the HTTP status. So it
 * wrote GitHub's 404 page into every font file — 300KB HTML documents with a
 * .ttf extension.
 *
 * Nothing complained. React Native does not validate a font asset: Android
 * silently falls back to Roboto, so the app rendered in the system font while
 * appearing to have a typeface of its own. That is the failure this script now
 * refuses to repeat:
 *
 *   - a non-2xx response aborts instead of being written to disk;
 *   - every extracted file is checked for the TrueType magic number
 *     (0x00010000) before it is kept;
 *   - a file that fails either check is deleted, and the script exits non-zero.
 *
 * ── WHERE INTER COMES FROM ──────────────────────────────────────────────────
 * Inter's static TTFs are not committed to its repository; they ship only in
 * the release zip. So this downloads the release once and extracts the five
 * weights from `extras/ttf/`. The zip is read with Node's own zlib — there is
 * no unzip dependency to install.
 *
 * ── WHY THE FILENAMES MATTER ────────────────────────────────────────────────
 * iOS resolves `fontFamily` against the PostScript name while Android resolves
 * it against the asset filename, so the two only agree if the file is named
 * after the PostScript name. Inter's release files already are —
 * `Inter-SemiBold.ttf` has the PostScript name `Inter-SemiBold` — so they are
 * kept exactly as shipped. Do not rename them.
 *
 * After running this, re-link and rebuild — the files have to be inside the
 * binary, so a Metro reload alone will not pick them up:
 *
 *   node download-fonts.js
 *   npx react-native-asset
 *   npx react-native run-android
 */

/* eslint-disable no-undef -- A Node build script, not app code: the project's
   ESLint environment is React Native and does not declare Node globals. */

const fs = require('fs');
const https = require('https');
const path = require('path');
const zlib = require('zlib');

const INTER_ZIP = 'https://github.com/rsms/inter/releases/download/v4.1/Inter-4.1.zip';

const fonts = ['Inter-Regular.ttf', 'Inter-Medium.ttf', 'Inter-SemiBold.ttf', 'Inter-Bold.ttf', 'Inter-ExtraBold.ttf'];


const dir = path.join(__dirname, 'assets', 'fonts');

if (!fs.existsSync(dir)) {
  fs.mkdirSync(dir, { recursive: true });
}

/** Buffers the body so nothing reaches disk until the status has been checked. */
const fetch = (url, redirects = 0) =>
  new Promise((resolve, reject) => {
    if (redirects > 5) {
      reject(new Error('too many redirects'));
      return;
    }

    https
      .get(url, (response) => {
        const { statusCode, headers } = response;

        if (statusCode === 301 || statusCode === 302 || statusCode === 307 || statusCode === 308) {
          response.resume();
          fetch(headers.location, redirects + 1).then(resolve, reject);
          return;
        }

        if (statusCode !== 200) {
          response.resume();
          reject(new Error(`HTTP ${statusCode}`));
          return;
        }

        const chunks = [];
        response.on('data', (chunk) => chunks.push(chunk));
        response.on('end', () => resolve(Buffer.concat(chunks)));
        response.on('error', reject);
      })
      .on('error', reject);
  });

/**
 * Pulls one file out of a zip by its basename, via the central directory.
 * Handles the two methods a release zip uses: stored (0) and deflate (8).
 */
const extract = (zip, basename) => {
  const eocd = zip.lastIndexOf(Buffer.from([0x50, 0x4b, 0x05, 0x06]));

  if (eocd < 0) {
    throw new Error('not a zip archive');
  }

  const entries = zip.readUInt16LE(eocd + 10);
  let cursor = zip.readUInt32LE(eocd + 16);

  for (let i = 0; i < entries; i += 1) {
    const method = zip.readUInt16LE(cursor + 10);
    const compressedSize = zip.readUInt32LE(cursor + 20);
    const nameLength = zip.readUInt16LE(cursor + 28);
    const extraLength = zip.readUInt16LE(cursor + 30);
    const commentLength = zip.readUInt16LE(cursor + 32);
    const localHeader = zip.readUInt32LE(cursor + 42);
    const name = zip.toString('utf8', cursor + 46, cursor + 46 + nameLength);

    if (name.endsWith(`extras/ttf/${basename}`)) {
      const dataStart =
        localHeader + 30 + zip.readUInt16LE(localHeader + 26) + zip.readUInt16LE(localHeader + 28);
      const data = zip.subarray(dataStart, dataStart + compressedSize);

      if (method === 0) {
        return data;
      }
      if (method === 8) {
        return zlib.inflateRawSync(data);
      }
      throw new Error(`unsupported zip method ${method}`);
    }

    cursor += 46 + nameLength + extraLength + commentLength;
  }

  throw new Error('not found in the release zip');
};

/**
 * A TrueType file opens with sfntVersion 0x00010000. `OTTO` would be an
 * OpenType/CFF font, which React Native on Android will not load, and anything
 * else — an HTML error page, most likely — is not a font at all.
 */
const isTrueType = (buffer) => buffer.length > 4 && buffer.readUInt32BE(0) === 0x00010000;

const run = async () => {
  let zip;

  try {
    zip = await fetch(INTER_ZIP);
  } catch (error) {
    console.error(`  FAILED   ${INTER_ZIP}  — ${error.message}`);
    process.exitCode = 1;
    return;
  }

  let failed = 0;

  for (const font of fonts) {
    const dest = path.join(dir, font);

    try {
      const body = extract(zip, font);

      if (!isTrueType(body)) {
        const magic = body.length > 4 ? body.readUInt32BE(0).toString(16) : 'empty';
        throw new Error(`not a TrueType file (magic 0x${magic}, ${body.length} bytes)`);
      }

      fs.writeFileSync(dest, body);
      console.log(`  ok       ${font}  (${body.length} bytes)`);
    } catch (error) {
      failed += 1;
      // Leave nothing half-written behind: a stale or truncated file here is
      // exactly what caused the silent fallback this script exists to prevent.
      fs.rmSync(dest, { force: true });
      console.error(`  FAILED   ${font}  — ${error.message}`);
    }
  }

  if (failed > 0) {
    console.error(`\n${failed} font(s) could not be extracted. Do not build with fonts missing.`);
    process.exitCode = 1;
    return;
  }

  console.log('\nAll fonts downloaded and verified.');
  console.log('Next: npx react-native-asset  &&  npx react-native run-android');
};

void run();