Cache POST requests

JavaScript

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);
    }
  },
};

TypeScript

interface Env {}
export default {
  async fetch(request, env, ctx): Promise<Response> {
    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);
    }
  },
} satisfies ExportedHandler<Env>;

Python

import hashlib
from pyodide.ffi import create_proxy
from js import fetch, URL, Headers, Request, caches

async def on_fetch(request, _, ctx):
    if 'POST' in request.method:
        # Hash the request body to use it as a part of the cache key
        body = await request.clone().text()
        body_hash = hashlib.sha256(body.encode('UTF-8')).hexdigest()

        # Store the URL in cache by prepending the body's hash
        cache_url = URL.new(request.url)
        cache_url.pathname = "/posts" + cache_url.pathname + body_hash

        # Convert to a GET to be able to cache
        headers = Headers.new(dict(request.headers).items())
        cache_key = Request.new(cache_url.toString(), method='GET', headers=headers)

        # Find the cache key in the cache
        cache = caches.default
        response = await cache.match(cache_key)

        # Otherwise, fetch response to POST request from origin
        if response is None:
            response = await fetch(request)
            ctx.waitUntil(create_proxy(cache.put(cache_key, response.clone())))

        return response

    return fetch(request)