How to compose an effect with an Http4s HttpRoutes?

Question

I have an http4s HttpRoutes and a task in my effect type (ZIO, if that matters). The effect is side-effecting and returns no value. I want to compose the two together, creating a new HttpRoutes that will run the effect before any matching route in the HttpRoutes.

import zio.Task

val httpRoutes: HttpRoutes[Task] = ...
val effect: Task[Unit] = ...

val combined: HttpRoutes[Task] = ???

How do I combine the HttpRoutes and the effect together?

Answer 1

Naive implementation according to https://http4s.org/v0.21/middleware

works for me

@accessible
trait HttpServer {
  def bindHttp: UIO[Server[Task]]
}

object HttpServer {
  def make(
    httpRoutes: HttpRoutes[Task],
    cpuPool: ExecutionContext@Id("zio.cpu"),
  ) = {
    for {
      implicit0(rts: Runtime[Any]) <- ZIO.runtime[Any].toManaged_
      combined = Kleisli { (req: Request[Task]) =>
        val effect: Task[Unit] = Task.effectTotal(println("123"))
        OptionT.liftF(effect).flatMap { _ =>
          httpRoutes(req)
        }
      }
      srv <- BlazeServerBuilder[Task](cpuPool)
        .withHttpApp(combined.orNotFound)
        .bindHttp(host = "0.0.0.0")
        .resource
        .toManaged
    } yield new HttpServer {
      val bindHttp = IO.succeed(srv)
    }
  }
}