https://deno.land/x/103_early_hints

What’s not supported To reduce security and privacy implications, the HTML and Fetch living standards have some restrictions on when Early Hints can be handled. Chrome ignores Early Hints sent in the following situations to comply these specifications.

• Early Hints sent on HTTP/1.1 or earlier

https://chromium.googlesource.com/chromium/src/+/master/docs/early-hints.md#what_s-not-supported

There is currently no HTTP server in Deno that supports HTTP/2 and can send 103 Early Hints.

So this library is currently not working at all.

Let's reconsider when denoland/deno#15827 is resolved.