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Version: ZIO 2.x

Getting Started

ZIO HTTP is a powerful library that is used to build highly performant HTTP-based services and clients using functional scala and ZIO and uses Netty as its core.

ZIO HTTP has powerful functional domains which help in creating, modifying, composing apps easily. Let's start with the HTTP domain.

The first step when using ZIO HTTP is creating an HTTP app.


Http is a domain that models HTTP apps using ZIO and works over any request and response types. Http Domain provides different constructors to create HTTP apps, Http.text, Http.html, Http.fromFile, Http.fromData, Http.fromStream, Http.fromEffect.

Creating a "Hello World" app

Creating an HTTP app using ZIO Http is as simple as given below, this app will always respond with "Hello World!"

import zio.http._

val app = Http.text("Hello World!")

An application can be made using any of the available operators on zio.Http. In the above program for any Http request, the response is always "Hello World!".


For handling routes, Http Domain has a collect method that, accepts different requests and produces responses. Pattern matching on the route is supported by the framework. The example below shows how to create routes:

import zio.http._

val app = Http.collect[Request] {
case Method.GET -> !! / "fruits" / "a" => Response.text("Apple")
case Method.GET -> !! / "fruits" / "b" => Response.text("Banana")

You can create typed routes as well. The below example shows how to accept count as Int only:

import zio.http._

val app = Http.collect[Request] {
case Method.GET -> !! / "Apple" / int(count) => Response.text(s"Apple: $count")

Pattern matching on route is supported by the framework


Apps can be composed using operators in Http:

  • Using the ++ operator. The way it works is, if none of the routes match in a, then the control is passed on to the b app:
 import zio.http._

val a = Http.collect[Request] { case Method.GET -> !! / "a" => Response.ok }
val b = Http.collect[Request] { case Method.GET -> !! / "b" => Response.ok }

val app = a ++ b
  • Using the <> operator. The way it works is, if a fails, then the control is passed on to the b app:
import zio.http._

val a = Error("SERVER_ERROR"))
val b = Http.text("OK")

val app = a <> b

ZIO Integration

For creating effectful apps, you can use collectZIO and wrap Response with UIO to produce ZIO effect value.

val app = Http.collectZIO[Request] {
case Method.GET -> !! / "hello" => UIO(Response.text("Hello World"))

Accessing the Request

To access the request use @ as it binds a matched pattern to a variable and can be used while creating a response:

import zio.http._

val app = Http.collectZIO[Request] {
case req @ Method.GET -> !! / "fruits" / "a" =>
UIO(Response.text("URL:" + req.url.path.asString + " Headers: " + req.getHeaders))
case req @ Method.POST -> !! / "fruits" / "a" =>


Since Http is a function of the form A => ZIO[R, Option[E], B] to test it you can simply call an Http like a function:

import zio.test._
import zio.http._

object Spec extends DefaultRunnableSpec {

def spec = suite("http")(
test("should be ok") {
val app = Http.ok
val req = Request()

When we call the app with the request it calls the apply method of Http via zio.test package


Socket is functional domain in ZIO HTTP. It provides constructors to create socket apps. A socket app is an app that handles WebSocket connections.

Creating a socket app

Socket app can be created by using Socket constructors. To create a socket app, you need to create a socket that accepts WebSocketFrame and produces ZStream of WebSocketFrame. Finally, we need to convert socketApp to Response using toResponse, so that we can run it like any other HTTP app.
The below example shows a simple socket app, we are using collect which returns a stream with WebsSocketTextFrame "BAR" on receiving WebsSocketTextFrame "FOO".

import zio.socket._

private val socket = Socket.collect[WebSocketFrame] { case WebSocketFrame.Text("FOO") =>

private val app = Http.collectZIO[Request] {
case Method.GET -> !! / "greet" / name => UIO(Response.text(s"Greetings {$name}!"))
case Method.GET -> !! / "ws" => socket.toResponse


As we have seen how to create HTTP apps, the only thing left is to run an HTTP server and serve requests. ZIO HTTP provides a way to set configurations for your server. The server can be configured according to the leak detection level, request size, address etc.

Starting an HTTP App

To launch our app, we need to start the server on a port. The below example shows a simple HTTP app that responds with empty content and a 200 status code, deployed on port 8090 using Server.start.

import zio.http._
import zio.http.Server
import zio._

object HelloWorld extends App {
val app = Http.ok

override def run(args: List[String]): URIO[zio.ZEnv, ExitCode] =
Server.start(8090, app).exitCode