Quick Start

Note: To run examples, please make sure that the flag -Ypartial-unification
is enabled in your compiler options (i.e scalacOptions += "-Ypartial-unification" in sbt). This is enabled by default in the giter8 template.

Getting started with http4s is easy. Let’s materialize an http4s skeleton project from its giter8 template:

$ sbt -sbt-version 1.1.1 new http4s/http4s.g8

Follow the prompts. For every step along the way, a default value is provided in brackets.

name of your project.
the organization you publish under. It’s common practice on the JVM to make this a domain you own, in reverse order (i.e., TLD first). io.github.username is also a fine choice.
by default, your organization followed by the project name.
the version of SBT for your generated project.
the version of Scala for your generated project.
defaults to the latest stable release of http4s. See the versions page for other suggestions.
the version of Logback for logging in your generated project.

At the end of the process, you’ll see:

Template applied in ./quickstart

In addition to sbt build machinery, a Scala source files are generated:

$ cd quickstart
$ find . -name '*.scala'

HelloWorldService.scala defines a runnable class by extending StreamApp[IO]. A StreamApp[IO] must define a method stream(args: List[String], requestShutdown: IO[Unit]) which acts the entry point to your application. That method starts blaze, http4s’ native server backend.

The route method defines a simple HttpService that responds to GET /hello/$USERNAME with a JSON greeting. Let’s try it:

$ sbt run

Depending on the state of your Ivy cache, several dependencies will download. This is a good time to grab a beverage. When you come back, you should see a line similar to this:

264 [run-main-0] INFO org.http4s.blaze.channel.nio1.NIO1SocketServerGroup - Service bound to address /

This indicates that blaze is running our service on port 8080. Let’s try out the hello world service with curl:

$ curl -i http://localhost:8080/hello/world
HTTP/1.1 200 OK
Content-Type: application/json; charset=UTF-8
Date: Thu, 01 Dec 2016 05:05:24 GMT
Content-Length: 26

{"message":"Hello, world"}

To shut down your server, simply press ^C in your console. Note that when running interactive SBT, ^C will kill the SBT process. For rapid application development, you may wish to add the sbt-revolver plugin to your project and starting the server from the SBT prompt with re-start.

With just a few commands, we have a fully functional app for creating a simple JSON service.