Running http4s server with ZIO Env - scala

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.