trot

Trot is an Elixir web micro-framework based on Plug and Cowboy. The goal of Trot is to make common patterns in Plug easier to use, particularly when writing APIs, without sacrificing flexibility.

Usage

Add Trot as a dependency to your mix.exs file and update your applications list to include it.

defp deps do
      [{:trot, github: "hexedpackets/trot"}]
    end

    def application do
      [applications: [:trot]]
    end

The following configuration options are supported by the server:

config :trot, :port, 4000: port to listen on for incoming HTTP requests. Defaults to “4000”.

config :trot, :router, MyApp.Router: module to route requests to. Defaults to “Trot.NotFound”.

config :trot, :heartbeat, "/heartbeat": path to setup a heartbeat route. This will always return 200 with a body of “OK”. Defaults to “/heartbeat”.

Finally, put use Trot.Router to the top of your module. This will add route macros and setup the plug pipeline at compile time.

Routes

Routes are specified using one of the HTTP method macros: get/3, post/3, put/3, patch/3, delete/3, options/3. The first argument is a the path to route to, the second (optional) argument is a keyword list of any options to match against, and the last argument is the block of code to execute. Examples are below.

If @path_root is specified, it will be prefixed to all routes in that module.

Routes can be setup in different modules and imported into the main router with the import_routes/1 macro, which takes a module name as the only argument. Note that ordering matters as normal Elixir pattern matching rules apply to imported routes.

A default 404 response can be enabled by putting import_routes Trot.NotFound or use Trot.NotFound at the end of the module.

Responses

All of the following are valid return values from handlers and will be parsed into full HTTP responses:

• String of response body
• Status code, either numeric or an atom from Plug.Conn.Status
• {code, body}
• {code, body, headers}
• JSONable object
• {code, object}
• {code, object, headers}
• {:redirect, location}
• {:badrpc, error}
• %Plug.Conn{}

Example router application

defmodule SoLoMoApp.Router do
      use Trot.Router

      # Returns an empty body with a status code of 400
      get "/bad" do
        :bad_request
      end

      # Sets the status code to 200 with a text body
      get "/text" do
        "Thank you for your question."
      end

      # Redirect the incoming request
      get "/text/body", headers: ["x-text-type": "question"] do
        {:redirect, "/text"}
      end

      # Sets the status code to 201 with a text body
      get "/text/body" do
        {201, "optimal tip-to-tip efficiency"}
      end

      # Sets status code to 200 with a JSON-encoded body
      get "/json" do
        %{"hyper" => "social"}
      end

      # Pattern match part of the path into a variable
      get "/presenter/:name" do
        "The presenter is #{name}"
      end

      import_routes Trot.NotFound
    end

Templating

To add templating in a router, add use Trot.Template and set @template_root to the top-level directory containing your templates. By default, @template_root is “templates/“.

Trot can be used to render EEx templates (the default engine include with Elixir), HAML templates through Calliope, or a combination of both. When the application is compiled a render_template/2 function is generated for every template under @template_root. render_template/2 expects the name of the template relative to @template_root as the first argument and a keyword list of variables to assign as the second argument.

When MIX_ENV=prod all of templates are loaded and pre-compiled for faster rendering.

Example app using templates

defmodule PiedPiper do
      use Trot.Router
      use Trot.Template
      @template_root "templates/root"

      get "/compression/pied_piper" do
        render_template("compression_results.html.eex", [weissman_score: 5.2])
      end

      get "/compression/nucleus" do
        render_template("compression_results.html.haml", [weissman_score: 2.89])
      end
    end

    # compression_results.html.eex
    <html><body>Pied piper has a Weissman Score of <%= @weissman_score %></body></html>

    # compression_results.html.haml
    %html
      %body Nucleaus has a Weissman Score of <%= @weissman_score %>

API versioning

Adding use Trot.Versioning to your module will enable API version parsing and pattern matching. The first part of the path for all requests in the module is assumed to be the version. It is parsed into the conn[:assigns] dictionary, making it easy to access. Routes can also be configured to only match a particular version.

Example versioned app

defmodule Nucleus do
      use Trot.Router
      use Trot.Versioning

      get "/version" do
        conn.assigns[:version]
      end

      get "/current", version: "v1" do
        :ok
      end

      get "/current" do
        :bad_request
      end
    end

In the above example, “/v1/version” will return “v1” as the response body. A request to “/v1/current” will return a 200 but “/v2/current” will return a 400.