Super Simple <3

require "kemal"

get "/" do
  "Hello World!"
end

Build and run!

crystal build --release src/kemal_sample.cr
./kemal_sample

Go to http://localhost:3000

Check samples for more.

Super Fast <3

Numbers speak louder than words.

Framework	Request Per Second	Avg. Response Time
Kemal (Production)	64986	170μs
Sinatra (Thin)	2274	43.82ms

These results were achieved with wrk on a Macbook Pro Late 2013. (2Ghz i7 8GB Ram OS X Yosemite)

Installation

Kemal supports Crystal 0.9.0 and up. You can add Kemal to your project by adding it to shard.yml

name: your-app

dependencies:
  kemal:
    github: sdogruyol/kemal
    branch: master

Routes

In Kemal, a route is an HTTP method paired with a URL-matching pattern. Each route is associated with a block:

  get "/" do
  .. show something ..
  end

  post "/" do
  .. create something ..
  end

  put "/" do
  .. replace something ..
  end

  patch "/" do
  .. modify something ..
  end

  delete "/" do
  .. annihilate something ..
  end

Environment

Accessing the environment (query params, body, content_type, headers, status_code) is super easy. You can use the environment returned from the block:

  # Matches /hello/kemal
  get "/hello/:name" do |env|
    name = env.params["name"]
    "Hello back to #{name}"
  end

  # Matches /resize?width=200&height=200
  get "/resize" do |env|
    width = env.params["width"]
    height = env.params["height"]
  end

  # Easily access JSON payload from the params.
  # The request content type needs to be application/json
  # The payload
  # {"name": "Serdar", "likes": ["Ruby", "Crystal"]}
  post "/json_params" do |env|
    name = env.params["name"] as String
    likes = env.params["likes"] as Array
    "#{name} likes #{likes.each.join(',')}"
  end

  # Set the content as application/json and return JSON
  get "/user.json" do |env|
    kemal = {name: "Kemal", language: "Crystal"}
    env.content_type = "application/json"
    kemal.to_json
  end

  # Add headers to your response
  get "/headers" do |env|
    env.add_header "Accept-Language", "tr"
    env.add_header "Authorization", "Token 12345"
  end

Browser Redirect

Just like other things in kemal, browser redirection is super simple as well. Use environment variable in defined route's corresponding block and call redirect on it.

  # Redirect browser
  get "/logout" do |env|
	# important stuff like clearing session etc.
	redirect "/login" # redirect to /login page
  end

Make sure to receive env as param in defined route's block or you might end-up having compile-time errors.

Middlewares

You can create your own middlewares by inheriting from HTTP::Handler

class CustomHandler < HTTP::Handler
  def call(request)
    puts "Doing some custom stuff here"
    call_next request
  end
end

Kemal.config.add_handler CustomHandler.new

Views

You can use ERB-like built-in ECR views to render files.

get '/:name' do
  render "views/hello.ecr"
end

And you should have an hello.ecr view. It will have the same context as the method.

Hello <%= env.params["name"] %>

Static Files

Kemal has built-in support for serving your static files. You need to put your static files under your /public directory.

E.g: A static file like /public/index.html will be served with the matching route /index.html.

Production / Development Mode

By default Kemal starts in developmentmode and logs to STDOUT.

You can use production mode to redirect the output to a file. By default Kemal logs the output to kemal.log.

You can start Kemal in production mode by:

./your_app -e production

Thanks

Thanks to Manas for their awesome work on Frank.

ilatif / kemal