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Cache POST requests

Cache POST requests using the Cache API.

async function sha256(message) {  // encode as UTF-8  const msgBuffer = new TextEncoder().encode(message)
  // hash the message  const hashBuffer = await crypto.subtle.digest("SHA-256", msgBuffer)
  // convert ArrayBuffer to Array  const hashArray = Array.from(new Uint8Array(hashBuffer))
  // convert bytes to hex string  const hashHex = hashArray.map(b => ("00" + b.toString(16)).slice(-2)).join("")  return hashHex}
async function handlePostRequest(event) {  const request = event.request  const body = await request.clone().text()
  // Hash the request body to use it as a part of the cache key  const hash = await sha256(body)  const cacheUrl = new URL(request.url)
  // Store the URL in cache by prepending the body's hash  cacheUrl.pathname = "/posts" + cacheUrl.pathname + hash
  // Convert to a GET to be able to cache  const cacheKey = new Request(cacheUrl.toString(), {    headers: request.headers,    method: "GET",  })
  const cache = caches.default
  // Find the cache key in the cache  let response = await cache.match(cacheKey)
  // Otherwise, fetch response to POST request from origin  if (!response) {    response = await fetch(request)    event.waitUntil(cache.put(cacheKey, response.clone()))  }  return response}
addEventListener("fetch", event => {  try {    const request = event.request    if (request.method.toUpperCase() === "POST")      return event.respondWith(handlePostRequest(event))    return event.respondWith(fetch(request))  } catch (e) {    return event.respondWith(new Response("Error thrown " + e.message))  }})