class Puma::Rack::Builder

def self.app(default_app = nil, &block) 

def self.app(default_app = nil, &block)
  self.new(default_app, &block).to_app
end

def self.new_from_string(builder_script, file="(rackup)") 

def self.new_from_string(builder_script, file="(rackup)")
  eval "Puma::Rack::Builder.new {\n" + builder_script + "\n}.to_app",
    TOPLEVEL_BINDING, file, 0
end

def self.parse_file(config, opts = Options.new) 

def self.parse_file(config, opts = Options.new)
  options = {}
  if config =~ /\.ru$/
    cfgfile = ::File.read(config)
    if cfgfile[/^#\\(.*)/] && opts
      options = opts.parse! $1.split(/\s+/)
    end
    cfgfile.sub!(/^__END__\n.*\Z/m, '')
    app = new_from_string cfgfile, config
  else
    require config
    app = Object.const_get(::File.basename(config, '.rb').capitalize)
  end
  [app, options]
end

def call(env) 

def call(env)
  to_app.call(env)
end

def generate_map(default_app, mapping) 

def generate_map(default_app, mapping)
  require_relative 'urlmap'
  mapped = default_app ? {'/' => default_app} : {}
  mapping.each { |r,b| mapped[r] = self.class.new(default_app, &b).to_app }
  URLMap.new(mapped)
end

def initialize(default_app = nil, &block) 

def initialize(default_app = nil, &block)
  @use, @map, @run, @warmup = [], nil, default_app, nil
  # Conditionally load rack now, so that any rack middlewares,
  # etc are available.
  begin
    require 'rack'
  rescue LoadError
  end
  instance_eval(&block) if block
end

def map(path, &block)


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

end
end
run Heartbeat
use Middleware
map '/' do
Rack::Builder.app do

The +use+ method can also be used here to specify middleware to run under a specific path:

end
end
run Heartbeat
map '/' do
Rack::Builder.app do

Creates a route within the application. 
def map(path, &block)
  @map ||= {}
  @map[path] = block
end

def run(app)

run Heartbeat

end
end
[200, { "Content-Type" => "text/plain" }, ["OK"]]
def self.call(env)
class Heartbeat

However this could also be a class:

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

The simplest form of this is a lambda object:
Takes an argument that is an object that responds to #call and returns a Rack response. 
def run(app)
  @run = app
end

def to_app 

def to_app
  app = @map ? generate_map(@run, @map) : @run
  fail "missing run or map statement" unless app
  app = @use.reverse.inject(app) { |a,e| e[a] }
  @warmup&.call app
  app
end

def use(middleware, *args, &block)

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

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

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

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

Specifies middleware to use in a stack. 
def use(middleware, *args, &block)
  if @map
    mapping, @map = @map, nil
    @use << proc { |app| generate_map app, mapping }
  end
  @use << proc { |app| middleware.new(app, *args, &block) }
end

def warmup(prc=nil, &block)

run MyApp
use SomeMiddleware

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

Takes a lambda or block that is used to warm-up the application. 
def warmup(prc=nil, &block)
  @warmup = prc || block
end