kemal-controller

Kemal is awesome, but sometimes you need (or just want) a bit more structure in your web applications, kemal-controller is here to help you with that by providing a simple way to declare all your endpoints into controller classes where the method parameters will map to GET/PATCH/.../POST/URL parameters automatically.

Online documentation can be found at: https://hugopl.github.io/kemal-controller/.

Controllers are structs, so the overhead is minimal and you can still use all Kemal features as you would normally do.

struct UsersController < Kemal::Controller
  @[Get("/users")]
  def index
    "Listing all users"
  end

  @[Get("/users/:id")]
  def show(id : Int32)
    "Showing user with ID: #{id}"
  end

  @[Post("/users")]
  def create(name : String, age : Int32, description : String?))
    "Creating user with name: #{name}, age: #{age} and description: #{description}"
  end
end

Kemal-controller also supports arrays and named tuples in arguments, so you get a type safe way to handle the endpoint parameters.

struct ProductsController < Kemal::Controller
  @[Get("/products")]
  def filter(categories : Array(String), price_range : NamedTuple(min : Float64, max : Float64))
    "Filtering products in categories: #{categories.join(", ")} with price between #{price_range[:min]} and #{price_range[:max]}"
  end
end

It supports nested named tuples/arrays in any combination as well.

struct OrdersController < Kemal::Controller
  @[Post("/orders")]
  def create(items : Array(NamedTuple(id : Int32, quantity : Int32)),
             shipping_address : NamedTuple(street : String, city : String, zip : String))
    "Creating order with items: #{items.inspect} to be shipped to #{shipping_address[:street]}, #{shipping_address[:city]}, #{shipping_address[:zip]}"
  end
end

Default values aren't supported yet, meanwhile use a nilable type and handle the defaulting logic inside the method.

How the parameters are mapped?

Kemal-controller interprets the form keys almost like Rails does:

Supported types

More types may be added in the future, feel free to open an issue or a PR if you need something specific.

Enums

Enums are supported as method parameters as well, anything accepted by Enum.new or Enum.parse is recognized.

Stripping parameters

If you need to strip all parameters (like leading/trailing spaces) before they reach your controller methods, you can use the strip flag on method annotation.

To strip specific parameters use an array of symbols instead of true.

struct UsersController < Kemal::Controller
    @[Post("/users", strip: true)]
    def create(name : String, description : String?)
      "Creating user with name: '#{name}', description: '#{description}'"
    end

    @[Get("/users/edit", strip: [:email])]
    def login(email : String, password : String)
      "Logging in user with email: '#{email}'"
    end
end

Authenticated/protected routes

If you need to protect some routes with authentication you must set the auth flag to true in the method annotation and implement the authenticate! : Bool method in your controller.

If authenticate! returns false the request will be halted and no further processing will be done, status code is set to 401 (Unauthorized).

struct AdminController < Kemal::Controller
  @[Get("/admin/dashboard", auth: true)]
  def dashboard
    "Welcome to the admin dashboard!"
  end

  private def authenticate! : Bool
    if !current_user.try(&.current_user.admin?)
      redirect("/login")
      return false
    end
    true
  end
end

Printing routes

You can print all registered routes by calling the Kemal.print_routes method, useful for debugging purposes.

Kemal.config.extra_options do |parser|
  parser.on("--routes", "Show all routes") do
    Kemal.print_routes
    exit(0)
  end
end

On --routes your app will print something like:

   GET  /area51                    TestController#area51()
  POST  /array_of_named_tuples     TestController#array_of_named_tuples(items : Array(NamedTuple(name: String, age: Int32)))
   GET  /hello                     TestController#hello(name : String)
  POST  /hello                     TestController#post_hello(name : String)
   GET  /regular_kemal_route       ?

4 routes

Installation

  1. Add the dependency to your shard.yml:

    dependencies:
  kemal-controller:
    github: hugopl/kemal-controller

  2. Run shards install

Contributing

  1. Fork it (https://github.com/hugopl/kemal-controller/fork)
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request

Contributors