fetch() cancels with an AbortSignal, does res.json() too?-CodePudding

I understand the workflow of cancelling an ongoing request with AbortSignal, which is to pass it to the options:

const res = await fetch('/endpoint', { signal });
const data = await res.json();

However, what happens if the signal is cancelled after the request itself has finished, but before the data has been parsed? Like this:

const res = await fetch('/endpoint', { signal });
// Cancel signal here
const data = await res.json();

My tests in Firefox, Chrome and Safari show that it will be properly cancelled and throw during that res.json(), but is it the official behavior?

const log = (...text) => document.body.insertAdjacentHTML('beforeend', `${text.join(' ')}<br />`);

(async () => {
  try {
    const controller = new AbortController();
    const signal = controller.signal;

    const res = await fetch('https://swapi.dev/api/films/2/', { signal });
    log('Request:', signal.aborted);
    controller.abort();
    log('Before:', signal.aborted);
    const data = await res.json();
    log('After:', signal.aborted);
  } catch (error) {
    log('Cancelled:', error.name);
  }
})();

// Request: false
// Before: true
// Cancelled: AbortError

From the output we can see it properly throws on res.json(), it never reaches the After step, and it's thrown with an AbortError.

CodePudding user response：

Yes, that's the official behavior. json() (and friends) consume the response's body. And as per step 10 of https://fetch.spec.whatwg.org/#dom-global-fetch that body can end up in an aborted state due to a signal. In that case, json() (and friends) will essentially rethrow.