Running http4s server with ZIO Env

Question

Trying to learn using ZIO library, so I decided to create a basic web service app. Idea pretty basic, use http4s lib for server and route endpoints, print "hello world" on endpoint call.

With the help of docs and examples I found, produces code:

object Main extends ManagedApp {

  type AppEnvironment = Clock with Console with HelloRepository
  type AppTask[A] = RIO[AppEnvironment, A]

  override def run(args: List[String]): ZManaged[ZEnv, Nothing, Int] = {
    val httpApp: HttpApp[AppTask] = Router[AppTask]("/" -> helloWorldService).orNotFound

    val server = ZIO.runtime[AppEnvironment].flatMap { implicit rts =>
      BlazeServerBuilder[AppTask]
        .bindHttp(8080, "0.0.0.0")
        .withHttpApp(CORS(httpApp))
        .serve
        .compile[AppTask, AppTask, ExitCode]
        .drain
    }

    (for {
      _ <- ZManaged.environment[ZEnv] >>> server.toManaged_
    } yield ())
      .foldM(err => putStrLn(s"Execution failed with: $err").as(1).toManaged_, _ => ZManaged.succeed(0))
  }

  val dsl: Http4sDsl[AppTask] = Http4sDsl[AppTask]
  import dsl._

  val helloWorldService: HttpRoutes[AppTask] = HttpRoutes.of[AppTask] {
    case GET -> Root / "hello" / name => Ok(Repo.getHello(name))
  }
}

trait HelloRepository extends Serializable {
  val helloRepository: HelloRepository.Service[Any]
}

object HelloRepository extends Serializable {
  trait Service[R] extends Serializable {
    def getHello(name: String): ZIO[R, Nothing, String]
  }
}

object Repo extends HelloRepository.Service[HelloRepository] {
  override def getHello(name: String): ZIO[HelloRepository, Nothing, String] = ZIO.succeed(s"Hello $name")
}

• I create router: Router[AppTask]("/" ...
• I create server: ZIO.runtime[AppEnvironment].flatMap ...
• Then trying to start server with ZIO enviroment, but something I am missing as this line: _ <- ZManaged.environment[ZEnv] >>> server.toManaged_ is incorected, and throws error on build: Error:(34, 39) inferred type arguments [touch.Main.AppEnvironment,Throwable,Unit] do not conform to method >>>'s type parameter bounds [R1 >: zio.ZEnv,E1,B] _ <- ZManaged.environment[ZEnv] >>> server.toManaged_

Error:(34, 39) inferred type arguments [touch.Main.AppEnvironment,Throwable,Unit] do not conform to method >>>'s type parameter bounds [R1 >: zio.ZEnv,E1,B]

Error:(34, 50) type mismatch; found : zio.ZManaged[touch.Main.AppEnvironment,Throwable,Unit] (which expands to) zio.ZManaged[zio.clock.Clock with zio.console.Console with touch.HelloRepository,Throwable,Unit] required: zio.ZManaged[R1,E1,B]

maybe someone can help me with the correct syntax? also would appriacete some explanation, or link to docs, where this is explained.

Answer 1

I would like to explain more but I don't know where you got your code sample or what your build.sbt looks like but I happen to have some http4s code lying around so I took the liberty of adding some import statements and simplifying it a bit. You can always add back the complexity I took out.

Here's what worked for me.

/tmp/http4s/test.scala

import org.http4s.implicits._
import org.http4s.server.blaze._
import org.http4s.server.Router
import org.http4s.server.middleware.CORS

import org.http4s._
import org.http4s.dsl.Http4sDsl

import zio._
import zio.clock._
import zio.console._
import zio.interop.catz._

trait HelloRepository
{
  def getHello(name: String): ZIO[AppEnvironment, Nothing, String]
}

trait AppEnvironment extends Console with Clock
{
  val helloRepository: HelloRepository
}

object Main extends App {

  type AppTask[A] = RIO[AppEnvironment, A]

  val dsl: Http4sDsl[AppTask] = Http4sDsl[AppTask]
  import dsl._

  val httpApp: HttpApp[AppTask] = Router[AppTask](
    "/" -> HttpRoutes.of[AppTask] {
      case GET -> Root / "hello" / name => Ok( ZIO.accessM[AppEnvironment](_.helloRepository.getHello(name)) )
    }
  ).orNotFound

  val program = for {
    server <- ZIO.runtime[AppEnvironment]
    .flatMap {
      implicit rts =>
        BlazeServerBuilder[AppTask]
          .bindHttp(8080, "0.0.0.0")
          .withHttpApp(CORS(httpApp))
          .serve
          .compile
          .drain
    }
  } yield server

  val runEnv = new AppEnvironment with Console.Live with Clock.Live
  {
    val helloRepository = new HelloRepository
    {
      def getHello(name: String): ZIO[AppEnvironment, Nothing, String] = ZIO.succeed(s"Hello $name")
    }
  }

  def run(args: List[String]) =
    program
      .provide(runEnv)
      .foldM(err => putStrLn(s"Execution failed with: $err") *> ZIO.succeed(1), _ => ZIO.succeed(0))
}

/tmp/http4s/build.sbt

val Http4sVersion       = "0.20.0"
val CatsVersion         = "2.0.0"
val ZioCatsVersion      = "2.0.0.0-RC3"
val ZioVersion          = "1.0.0-RC13"
val LogbackVersion      = "1.2.3"

lazy val root = (project in file("."))
  .settings(
    organization := "example",
    name := "example",
    version := "0.0.1-SNAPSHOT",
    scalaVersion := "2.12.8",
    scalacOptions ++= Seq("-Ypartial-unification"),
    libraryDependencies ++= Seq(
      "org.typelevel"              %% "cats-effect"         % CatsVersion,
      "dev.zio"                    %% "zio"                 % ZioVersion,
      "dev.zio"                    %% "zio-interop-cats"    % ZioCatsVersion,
      "org.http4s"                 %% "http4s-blaze-server" % Http4sVersion,
      "org.http4s"                 %% "http4s-dsl"          % Http4sVersion,
      "ch.qos.logback"             %  "logback-classic"     % LogbackVersion,
   ),
    addCompilerPlugin("org.spire-math" %% "kind-projector"     % "0.9.6"),
    addCompilerPlugin("com.olegpy"     %% "better-monadic-for" % "0.2.4")
  )

scalacOptions ++= Seq(
  "-deprecation",               // Emit warning and location for usages of deprecated APIs.
  "-encoding", "UTF-8",         // Specify character encoding used by source files.
  "-language:higherKinds",      // Allow higher-kinded types
  "-language:postfixOps",       // Allows operator syntax in postfix position (deprecated since Scala 2.10)
  "-feature",                   // Emit warning and location for usages of features that should be imported explicitly.
  "-Ypartial-unification",      // Enable partial unification in type constructor inference
  "-Xfatal-warnings",           // Fail the compilation if there are any warnings
)

sample execution

bash-3.2$ cd /tmp/http4s
bash-3.2$ sbt
...
sbt:example> compile
...
[info] Done compiling.
[success] Total time: 5 s, completed Oct 24, 2019 11:20:53 PM
sbt:example> run
...
[info] Running Main 
23:21:03.720 [zio-default-async-1-163838348] INFO org.http4s.blaze.channel.nio1.NIO1SocketServerGroup - Service bound to address /0:0:0:0:0:0:0:0:8080
23:21:03.725 [blaze-selector-0] DEBUG org.http4s.blaze.channel.nio1.SelectorLoop - Channel initialized.
23:21:03.732 [zio-default-async-1-163838348] INFO org.http4s.server.blaze.BlazeServerBuilder - 
  _   _   _        _ _
 | |_| |_| |_ _ __| | | ___
 | ' \  _|  _| '_ \_  _(_-<
 |_||_\__|\__| .__/ |_|/__/
             |_|
23:21:03.796 [zio-default-async-1-163838348] INFO org.http4s.server.blaze.BlazeServerBuilder - http4s v0.20.0 on blaze v0.14.0 started at http://[0:0:0:0:0:0:0:0]:8080/
23:21:11.070 [blaze-selector-1] DEBUG org.http4s.blaze.channel.nio1.SelectorLoop - Channel initialized.
23:21:11.070 [blaze-selector-1] DEBUG org.http4s.blaze.channel.nio1.NIO1HeadStage - Starting up.
23:21:11.070 [blaze-selector-1] DEBUG org.http4s.blaze.channel.nio1.NIO1HeadStage - Stage NIO1HeadStage sending inbound command: Connected
23:21:11.070 [blaze-selector-1] DEBUG org.http4s.server.blaze.Http1ServerStage$$anon$1 - Starting HTTP pipeline
23:21:11.072 [blaze-selector-1] DEBUG org.http4s.blazecore.IdleTimeoutStage - Starting idle timeout stage with timeout of 30000 ms

At this point after opening http://localhost:8080/hello/there I observed the expected output in the browser.

Hope this helps.