Express File Cache Middleware

middleware.v1.js

// const cachedAssetPath = ...
try {
  if (fs.existsSync(cachedAssetPath)) {
    const response = await fetch(res.locals.fetchUrl, { method: "HEAD" });

    res.locals.contentLength = response.headers.get("content-length");
    res.locals.contentType = response.headers.get("content-type");
    res.locals.buffer = fs.readFileSync(cachedAssetPath);
  } else {
    const blob = await (await fetch(res.locals.fetchUrl)).blob();
    res.locals.buffer = Buffer.from(await blob.arrayBuffer(), "binary");

    res.locals.contentType = blob.type;
    res.localscontentLength = blob.size;

    fs.writeFileSync(cachedAssetPath, res.locals.buffer);
  }

  next();
} catch (e) {
  // in case fs.writeFileSync writes partial data and fails
  if (fs.existsSync(cachedAssetPath)) {
    fs.unlinkSync(cachedAssetPath);
  }

  res.status(500).send(e.message);
}

middleware.v2.js

function encodeAssetCacheName(contentType, contentLength) {
  return Buffer.from(`${contentType}:${contentLength}`).toString("base64");
}

function decodeAssetCacheName(encodedString) {
  const decodedFileName = Buffer.from(encodedString, "base64").toString(
    "ascii"
  );
  return decodedFileName.split(":");
}

// ...

if (fs.existsSync(assetCachePath)) {
  const firstFile = fs.readdirSync(assetCachePath)[0];

  const [contentType, contentLength] = middleWare.decodeAssetCacheName(
    firstFile
  );

  res.locals.contentLength = contentLength;
  res.locals.contentType = contentType;

  res.locals.buffer = fs.readFileSync(`${assetCachePath}/${firstFile}`);
} else {
  const blob = await (await fetch(res.locals.fetchUrl)).blob();

  const fileName = middleWare.encodeAssetCacheName(blob.type, blob.size);

  res.locals.buffer = Buffer.from(await blob.arrayBuffer(), "binary");

  res.locals.contentType = blob.type;
  res.locals.contentLength = blob.size;

  fs.writeFileSync(`${assetCachePath}/${fileName}`, res.locals.buffer);
}

next();

webpack.config.js

new WorkboxWebpackPlugin.GenerateSW({
  clientsClaim: true,
  exclude: [/\.map$/, /asset-manifest\.json$/],
  importWorkboxFrom: "cdn",
  runtimeCaching: [
    {
      urlPattern: new RegExp("https://images.ctfassets.net"),
      handler: "networkFirst"
    },
    {
      urlPattern: new RegExp("https://cdn.contentful.com"),
      handler: "networkFirst"
    },
    {
      urlPattern: new RegExp("http://video.ctfassets.net"),
      handler: "networkFirst"
    }
  ],
  navigateFallback: publicUrl + "/index.html",
  navigateFallbackBlacklist: [
    // Exclude URLs starting with /_, as they're likely an API call
    new RegExp("^/_")
    // Exclude URLs containing a dot, as they're likely a resource in
    // public/ and not a SPA route
    // new RegExp("/[^/]+\\.[^/]+$")
  ]
}