Class: Rack::Builder

Load the given file as a rackup file, treating the contents as if specified inside a Builder block.

Ignores content in the file after __END__, so that use of __END__ will not result in a syntax error.

Example config.ru file:

$ cat config.ru

use Rack::ContentLength
require './app.rb'
run App

Evaluate the given builder_script string in the context of a Builder block, returning a ::Rack application.

Parse the given config file to get a ::Rack application.

If the config file ends in .ru, it is treated as a rackup file and the contents will be treated as if specified inside a Builder block.

If the config file does not end in .ru, it is required and ::Rack will use the basename of the file to guess which constant will be the ::Rack application to run.

Examples:

Rack::Builder.parse_file('config.ru')
# Rack application built using Rack::Builder.new

Rack::Builder.parse_file('app.rb')
# requires app.rb, which can be anywhere in Ruby's
# load path. After requiring, assumes App constant
# is a Rack application

Rack::Builder.parse_file('./my_app.rb')
# requires ./my_app.rb, which should be in the
# process's current directory.  After requiring,
# assumes MyApp constant is a Rack application

Freeze the app (set using run) and all middleware instances when building the application in to_app.

Generate a URLMap instance by generating new ::Rack applications for each map block in this instance.

Creates a route within the application. Routes under the mapped path will be sent to the ::Rack application specified by run inside the block. Other requests will be sent to the default application specified by run outside the block.

class App
  def call(env)
    [200, {'content-type' => 'text/plain'}, ["Hello World"]]
  end
end

class Heartbeat
  def call(env)
    [200, { "content-type" => "text/plain" }, ["OK"]]
  end
end

app = Rack::Builder.app do
  map '/heartbeat' do
    run Heartbeat.new
  end
  run App.new
end

run app

The #use method can also be used inside the block to specify middleware to run under a specific path:

app = Rack::Builder.app do
  map '/heartbeat' do
    use Middleware
    run Heartbeat.new
  end
  run App.new
end

This example includes a piece of middleware which will run before /heartbeat requests hit Heartbeat.

Note that providing a path of / will ignore any default application given in a #run statement outside the block.

Takes a block or argument that is an object that responds to #call and returns a ::Rack response.

You can use a block:

run do |env|
  [200, { "content-type" => "text/plain" }, ["Hello World!"]]
end

You can also provide a lambda:

run lambda { |env| [200, { "content-type" => "text/plain" }, ["OK"]] }

You can also provide a class instance:

class Heartbeat
  def call(env)
   [200, { "content-type" => "text/plain" }, ["OK"]]
  end
end

run Heartbeat.new

Return the ::Rack application generated by this instance.

Specifies middleware to use in a stack.

class Middleware
  def initialize(app)
    @app = app
  end

  def call(env)
    env["rack.some_header"] = "setting an example"
    @app.call(env)
  end
end

use Middleware
run lambda { |env| [200, { "content-type" => "text/plain" }, ["OK"]] }

All requests through to this application will first be processed by the middleware class. The #call method in this example sets an additional environment key which then can be referenced in the application if required.

Takes a lambda or block that is used to warm-up the application. This block is called before the ::Rack application is returned by to_app.

warmup do |app|
  client = Rack::MockRequest.new(app)
  client.get('/')
end

use SomeMiddleware
run MyApp