Http4s X-Request-Id middleware

RequestIdMiddleware.scala

import java.util.UUID

import org.http4s.{Header, Http, Request, Response}
import cats.data.Kleisli
import cats.effect.Sync
import cats.implicits._
import org.http4s.syntax.string._

/**
  * Propagate a `X-Request-Id` header to the response, generate a UUID
  * when the `X-Request-Id` header is unset.
  * https://devcenter.heroku.com/articles/http-request-id
  */
object RequestIdMiddleware {

  def apply[G[_], F[_]](http: Http[G, F])(implicit G: Sync[G]): Http[G, F] =
    Kleisli[G, Request[F], Response[F]] { req =>
      for {
        header <- req.headers.get("X-Request-ID".ci) match {
          case None => G.delay[Header](Header("X-Request-ID", UUID.randomUUID().toString))
          case Some(header) => G.pure[Header](header)
        }
        response <- http(req.putHeaders(header))
      } yield response.putHeaders(header)
    }
}