fix: cache mechanism for request with different headers

[alejogschwind]

closes #8752

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[benmccann]

You would need to update packages/kit/src/runtime/server/page/serialize_data.js as well

Also, I think we could probably have just a single hash computed from a combination of the headers and body

[Rich-Harris]

Thanks! Note that opts.headers can be any HeadersInit object, so if someone does this...

const headers = new Headers();
headers.append('Authorization', `Bearer ${token}`);
fetch('/blah', { headers });

...the hash will be all wrong because JSON.stringify(headers) === '{}'. The easiest solution would be along these lines (except combined with body, as @benmccann suggests):

if (opts?.headers) {
-  const headers = JSON.stringify(opts.headers);
+  const headers = [...new Headers(opts.headers)].join(',');
  selector += `[data-headers-hash="${hash(headers)}"]`;
}

[alejogschwind]

I still didn't figure out why this test is failing. I updated the hash to consider headers but it seems that the hash now it's different than the test above so maybe there is some header that I'm not considering when I hash manually.

[alejogschwind]

I found the issue, I was concatenating an ArrayBufferView + string.

To achieve this single hash computation I will need to update the hash function, I don't know if you want to do that. The other option is to concatenate the two hashes hash(headers) + hash(body)

[Rich-Harris]

thank you!