feat(ext/http): abort event when request is cancelled

[littledivy]

Deno.serve(async (req) => {
  const { promise, resolve } = Promise.withResolvers<void>();

  req.signal.addEventListener("abort", () => {
    resolve();
  });

  await promise;

  return new Response("Ok");
});

[bartlomieju]

Very cool, have you measured the performance impact?

[littledivy]

Yep. No extra overhead unless req.signal is accessed. Even then its negligible:

Deno.serve(req => {
  req.signal.addEventListener("abort", () => {});
  return new Response("Hello");
})

divy@divy-macbook deno % wrk http://localhost:8000 # main
Running 10s test @ http://localhost:8000
  2 threads and 10 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency   102.95us   29.67us   0.94ms   78.63%
    Req/Sec    44.97k     2.99k   49.21k    70.30%
  903669 requests in 10.10s, 123.24MB read
Requests/sec:  89475.95
Transfer/sec:     12.20MB

divy@divy-macbook deno % wrk http://localhost:8000 # this PR
Running 10s test @ http://localhost:8000
  2 threads and 10 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency   103.74us   40.32us   2.33ms   88.91%
    Req/Sec    44.94k     3.92k   50.48k    68.32%
  903253 requests in 10.10s, 123.18MB read
Requests/sec:  89433.32
Transfer/sec:     12.20MB