index.js

async function handleRequest(request) {
  let url = new URL(request.url)
  // make sure you set B2_BUCKET_NAME as an environment variable

  let filename = url.pathname.substring(url.pathname.lastIndexOf('/')+1);

  let escaped_name = encodeURIComponent(filename)

  let escaped_path = url.pathname.replace(filename, escaped_name)

  url.pathname = `/file/${process.env.B2_BUCKET}${url.pathname}`

  url.hostname = 'f001.backblazeb2.com'

  let b2_path = url.toString().replace(filename, escaped_name)

  let modified = new Request(b2_path, request)

  let response = await fetch(modified, {
    cf: {
      cacheKey: request.url,
      cacheEverything: true
    }
  })

  return response
}

addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request))
})