Caching POST Requests

function uint8ArrayToHex(arr) {
  return Array.prototype.map.call(arr, (x) => (('0' + x.toString(16)).slice(-2))).join('');
}

// The SHA-256 signature digest.
async function sha256(message) {
  const msgBuffer = new TextEncoder().encode(message);
  const hashBuffer = await crypto.subtle.digest('SHA-256', msgBuffer);

  return uint8ArrayToHex(new Uint8Array(hashBuffer));
}

async function fetchContent(event, cacheKey) {
  const cache = caches.default;

  // If the resource is not found in the cache, fetch the resource from the origin server and cache the resource.
  const response = await fetch(event.request);

  // Add the Cache-Control field to the response header and specify the cache duration.
  response.headers.set('Cache-Control', 's-maxage=10');
  event.waitUntil(cache.put(cacheKey, response.clone()));

  // Add an identifier indicating that the resource is not found in the cache to the response header.
  response.headers.append('x-edgefunctions-cache', 'miss');

  return response;
}

async function handleRequest(event) {
  const request = event.request;
  const body = await request.clone().text();

  // // Calculate the hash value based on the request body.
  const hash = await sha256(body);

  // Use the hash value that is calculated based on the request body as a part of the cache key.
  const cacheKey = `${request.url}${hash}`;

  const cache = caches.default;

  try {
    // Fetch the associated response content from the cache.
    let response = await cache.match(cacheKey);

    if (!response) {
        return fetchContent(event, cacheKey);
    }

    // Add an identifier indicating that the resource is found in the cache to the response header.
    response.headers.append('x-edgefunctions-cache', 'hit');

    return response;
  } catch (error) {
    await cache.delete(cacheKey);
    // If the cache duration of the resource times out or the resource is not found in the cache, re-fetch the remote resource.
    return fetchContent(event, cacheKey);
  }

  return response;
}

addEventListener('fetch', (event) => {
  try {
    const request = event.request;
    // Process a POST request.
    if (request.method.toUpperCase() === 'POST') {
      return event.respondWith(handleRequest(event));
    }
    // Non-POST request.
    return event.respondWith(fetch(request));
  } catch (e) {
    return event.respondWith(new Response('Error thrown ' + e.message));
  }
});