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Cache POST requests

Cache POST requests using the Cache API.
export default {
async fetch(request, env, ctx) {
async function sha256(message) {
// encode as UTF-8
const msgBuffer = await new TextEncoder().encode(message);
// hash the message
const hashBuffer = await crypto.subtle.digest('SHA-256', msgBuffer);
// convert bytes to hex string
return [...new Uint8Array(hashBuffer)]
.map((b) => b.toString(16).padStart(2, '0'))
.join('');
}
try {
if (request.method.toUpperCase() === 'POST') {
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);
ctx.waitUntil(cache.put(cacheKey, response.clone()));
}
return response;
}
return fetch(request);
} catch (e) {
return new Response('Error thrown ' + e.message);
}
},
};
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 bytes to hex string
return [...new Uint8Array(hashBuffer)].map(b => b.toString(16).padStart(2, '0')).join('');
}
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));
}
});