ky sending empty request when evaluated by PageSpeed

[gajus]

This has been one of the more confusing debugging experiences.

I will provide context as it may help others.

We tried using https://pagespeed.web.dev/ to measure our page performance.

Our website produces good Lighthouse score when tested using Lighthouse built into Chrome, but we were tipped that it is failing PageSpeed test.

Upon investigating, we discovered that PageSpeed is failing with an error

However, nothing immediately obvious surfaced as to why it would be failing, i.e. nothing in Sentry other than the request is failing.

Then we noticed that around the same time that we run PageSpeed test, our load balancer is returning 400 error.

POST /api/                                                   400 Bad Request
GET  /static/assets/GlassyContraLogo.37dd3240.webp           200 OK
POST /api/                                                   400 Bad Request

Further investigation led to discover that ky is sending an empty request to our server.

However,

• no errors are surfaced to the application
• our app worked fine when using legacy browsers (all the way down to Chrome 78)
• Ligthhouse built into browser did not produce the same behavior

The request itself is pretty simple:

const headers: Record<string, string> = {
  accept: 'application/json',
  'content-type': 'application/json',
  'x-contra-client-url': window.location.href,
  'x-contra-release-version': releaseVersion ?? '',
};

if (window.posthogSessionId) {
  headers['x-posthog-session-id'] = window.posthogSessionId;
}

const response = await ky(apiUrl, {
  body: safeStringify({
    query: operation.text,
    variables: clonedVariables,
  }),
  credentials: 'include',
  headers,
  method: 'POST',
});

const json = await response.json<GraphQLResponse>();

We ended up replacing ky with fetch and it started working again.

TLDLR something is quietly failing when PageSpeed (whatever client they are using) is running code that uses ky.

[sholladay]

Is this still happening with latest Ky?

[sholladay]

My best guess is that this is related to request.clone(), which tends to be problematic for non-browser environments.

PR #601 released in Ky 1.4.0 attempts to address this to some degree by reducing our reliance on request.clone() and hopefully that has improved the situation. Going to close this for now. Please let me know if anyone else runs into this.