Java 21+: Ensure simple client is closed

[ybasket]

Java 21 adds methods to close a HttpClient and also makes it implement AutoCloseable: https://bugs.openjdk.org/browse/JDK-8267140

Ideally, http4s-jdk-http-client should leverage this and expose the simple client wrapped in a Resource to ensure the client is properly closed and cleaned up after use. Not sure how this can be achieved without requiring Java 21+ though, needs research.

[armanbilge]

We can just use reflection. I don't think it would be a hot-path.

The bigger issue is that our signatures currently return F[_] instead of Resource. This would have to be a breaking change 😕

http4s-jdk-http-client/core/src/main/scala/org/http4s/jdkhttpclient/JdkHttpClient.scala

Lines 247 to 248 in 21de6a2

	def simple[F[_]](implicit F: Async[F]): F[Client[F]] =
	defaultHttpClient[F].map(apply(_))

[rossabaker]

Does it need reflection, or can it just pattern match on AutoCloseable?

Why does it need to be a breaking change instead of another constructor? The bigger problem I see is that the resource release would be a no-op on older JDK.

[armanbilge]

Does it need reflection, or can it just pattern match on AutoCloseable?

👍 smart

Why does it need to be a breaking change instead of another constructor?

You're right, it doesn't. See a prior discussion on a similar issue where we decided to break: #770 (comment).

[rossabaker]

That pattern match might require a nowarn when compiled on JDK21 for an unreachable fallback case.