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module Rack
# Rack::Builder implements a small DSL to iteratively construct Rack
# applications.
#
# Example:
#
# require 'rack/lobster'
# app = Rack::Builder.new do
# use Rack::CommonLogger
# use Rack::ShowExceptions
# map "/lobster" do
# use Rack::Lint
# run Rack::Lobster.new
# end
# end
#
# run app
#
# Or
#
# app = Rack::Builder.app do
# use Rack::CommonLogger
# run lambda { |env| [200, {'Content-Type' => 'text/plain'}, ['OK']] }
# end
#
# run app
#
# +use+ adds middleware to the stack, +run+ dispatches to an application.
# You can use +map+ to construct a Rack::URLMap in a convenient way.
class Builder
def self.parse_file(config, opts = Server::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
return app, options
end
def self.new_from_string(builder_script, file="(rackup)")
eval "Rack::Builder.new {\n" + builder_script + "\n}.to_app",
TOPLEVEL_BINDING, file, 0
end
def initialize(default_app = nil,&block)
@use, @map, @run = [], nil, default_app
instance_eval(&block) if block_given?
end
def self.app(default_app = nil, &block)
self.new(default_app, &block).to_app
end
# 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.
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
# Takes an argument that is an object that responds to #call and returns a Rack response.
# The simplest form of this is a lambda object:
#
# run lambda { |env| [200, { "Content-Type" => "text/plain" }, ["OK"]] }
#
# However this could also be a class:
#
# class Heartbeat
# def self.call(env)
# [200, { "Content-Type" => "text/plain" }, ["OK"]]
# end
# end
#
# run Heartbeat
def run(app)
@run = app
end
# Creates a route within the application.
#
# Rack::Builder.app do
# map '/' do
# run Heartbeat
# end
# end
#
# The +use+ method can also be used here to specify middleware to run under a specific path:
#
# Rack::Builder.app do
# map '/' do
# use Middleware
# run Heartbeat
# end
# end
#
# This example includes a piece of middleware which will run before requests hit +Heartbeat+.
#
def map(path, &block)
@map ||= {}
@map[path] = block
end
def to_app
app = @map ? generate_map(@run, @map) : @run
fail "missing run or map statement" unless app
@use.reverse.inject(app) { |a,e| e[a] }
end
def call(env)
to_app.call(env)
end
private
def generate_map(default_app, mapping)
mapped = default_app ? {'/' => default_app} : {}
mapping.each { |r,b| mapped[r] = self.class.new(default_app, &b) }
URLMap.new(mapped)
end
end
end
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