readme.md

Expected Output

When running without errors it outputs something like the following to stdout:

IpInfo(X1.X2.X3.X4)

Equivalent in JavaScript

fetch("https://jsonip.com", {headers: { "Accept": "application/json" }})
  .catch(err => { status: err })
  .then(resp => resp.json())
  .then(console.log)

Except that this JS doesn't check the form of the JSON returned conforms to the expected structure.

In async/await code structure it would be like this:

const onFailure = err => { status: err }
const resp = await fetch("https://jsonip.com", {headers: { "Accept": "application/json" }}).catch(onFailure)
const json = resp.json()
console.log(json)

Again there is not decoding the response body to check it has the structure the client expects.

Equivalent in TypeScript with response body structure checking

import * as t from 'io-ts'

const IpInfo = t.type({
  status: t.number
})

type IpInfo = t.TypeOf<typeof IpInfo>

const onFailure = err => { status: err }
const resp = await fetch("https://jsonip.com", {headers: { "Accept": "application/json" }}).catch(onFailure)
const json = resp.json()
const result = IpInfo.decode(json)
console.log(result)

build.sbt

scalaVersion := "3.1.0"
libraryDependencies ++= Seq(
  "io.circe"      %% "circe-generic"       % "0.14.1",
  "org.http4s"    %% "http4s-client"       % "1.0.0-M30",
  "org.scastie"   %% "runtime-scala"       % "1.0.0-SNAPSHOT",
  "org.typelevel" %% "cats-core"           % "2.7.0",
  "org.http4s"    %% "http4s-core"         % "1.0.0-M30",
  "org.http4s"    %% "http4s-blaze-client" % "1.0.0-M30",
  "org.http4s"    %% "http4s-circe"        % "1.0.0-M30",
  "org.typelevel" %% "cats-effect"         % "3.3.3"
)

HttpClient.scala

import cats.effect.{IO, IOApp, ExitCode}
import io.circe.generic.auto._
import org.http4s.Status._
import org.http4s.blaze.client.BlazeClientBuilder
import org.http4s.circe._
import org.http4s.client.Client
import org.http4s.syntax.all._

sealed trait IpResult
case class IpInfo(ip: String) extends IpResult
case class IpError(status: Int) extends IpResult

object HttpClient extends IOApp {
  def runClient(client: Client[IO]): IO[IpResult] =
    client.get(uri"https://jsonip.com") {
      case Successful(body) => body.decodeJson[IpInfo]
      case resp             => IO.pure(IpError(resp.status.code))
    }
  
  override def run(args: List[String]) =
    BlazeClientBuilder[IO].resource.use(runClient).flatMap(IO.println).as(ExitCode.Success)
}