`worktop/cache` POST requests

https://developers.cloudflare.com/workers/examples/cache-post-request

worktop already sets Cache-Control to private, no-cache so a good solution may be to apply POST caching when this header gets modified.

Main use case for this is to cache GraphQL queries

[lukeed]

With the changes in the next release, the above example can be consolidated into this:

import { Router } from 'worktop';
import * as Cache from 'worktop/cache';

const API = new Router;
// ...

// reusable function
const main = Cache.reply(API.run);

addEventListener('fetch', event => {
  let request = event.request;

  if (request.method !== 'POST') {
    return main(event);
  }

  let clone = request.clone();
  let key = toBodyHash(clone); // string

  // use new `key` for cache lookup
  return main(event, key);
});

[lukeed]

With the latest changes in worktop@next, this snippet (https://github.com/lukeed/worktop/issues/53#issuecomment-840825730) changes a little bit.

Now Cache.reply returns a Module.Worker definition (object), and there’s no method that does the lookup -> save sequence for you, but it’s pretty straightforward & it’s more configurable now too:

import { Router } from 'worktop';
import * as Cache from 'worktop/cache';

const API = new Router;
// ...

async function reply(req, ctx, custom) {
  let res = await Cache.lookup(custom || req);
  if (res) return res;
  
  res = await API.run(req, ctx);
  return Cache.save(custom || req, res);
} 

export default {
  fetch(req, env, ctx) {
    ctx.bindings = env;

    if (req.method === 'POST') {
      let hash = toBodyHash(clone); // string
      return reply(req, ctx, hash);
    }

    return reply(req, ctx);
  }
}