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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))
}
})