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# frozen_string_literal: true
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
# https://stackoverflow.com/questions/2223882/whats-the-difference-between-utf-8-and-utf-8-without-bom
UTF_8_BOM = '\xef\xbb\xbf'
# 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 Rack::Builder block, using the given
# options.
#
# 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.
# The options given will be ignored in this case.
#
# 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
# # contains 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 contains Rack application
def self.parse_file(config, opts = Server::Options.new)
if config.end_with?('.ru')
return self.load_file(config, opts)
else
require config
app = Object.const_get(::File.basename(config, '.rb').split('_').map(&:capitalize).join(''))
return app, {}
end
end
# Load the given file as a rackup file, treating the
# contents as if specified inside a Rack::Builder block.
#
# Treats the first comment at the beginning of a line
# that starts with a backslash as options similar to
# options passed on a rackup command line.
#
# 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
#
# #\ -p 9393
#
# use Rack::ContentLength
# require './app.rb'
# run App
def self.load_file(path, opts = Server::Options.new)
options = {}
cfgfile = ::File.read(path)
cfgfile.slice!(/\A#{UTF_8_BOM}/) if cfgfile.encoding == Encoding::UTF_8
if cfgfile[/^#\\(.*)/] && opts
warn "Parsing options from the first comment line is deprecated!"
options = opts.parse! $1.split(/\s+/)
end
cfgfile.sub!(/^__END__\n.*\Z/m, '')
app = new_from_string cfgfile, path
return app, options
end
# Evaluate the given +builder_script+ string in the context of
# a Rack::Builder block, returning a Rack application.
def self.new_from_string(builder_script, file = "(rackup)")
# We want to build a variant of TOPLEVEL_BINDING with self as a Rack::Builder instance.
# We cannot use instance_eval(String) as that would resolve constants differently.
binding, builder = TOPLEVEL_BINDING.eval('Rack::Builder.new.instance_eval { [binding, self] }')
eval builder_script, binding, file
builder.to_app
end
# Initialize a new Rack::Builder instance. +default_app+ specifies the
# default application if +run+ is not called later. If a block
# is given, it is evaluted in the context of the instance.
def initialize(default_app = nil, &block)
@use, @map, @run, @warmup, @freeze_app = [], nil, default_app, nil, false
instance_eval(&block) if block_given?
end
# Create a new Rack::Builder instance and return the Rack application
# generated from it.
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
ruby2_keywords(:use) if respond_to?(:ruby2_keywords, true)
# 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
# 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
def warmup(prc = nil, &block)
@warmup = prc || block
end
# 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.
#
# Rack::Builder.app do
# map '/heartbeat' do
# run Heartbeat
# end
# run App
# end
#
# The +use+ method can also be used inside the block to specify middleware to run under a specific path:
#
# Rack::Builder.app do
# map '/heartbeat' do
# use Middleware
# run Heartbeat
# end
# run App
# 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.
def map(path, &block)
@map ||= {}
@map[path] = block
end
# Freeze the app (set using run) and all middleware instances when building the application
# in to_app.
def freeze_app
@freeze_app = true
end
# Return the Rack application generated by this instance.
def to_app
app = @map ? generate_map(@run, @map) : @run
fail "missing run or map statement" unless app
app.freeze if @freeze_app
app = @use.reverse.inject(app) { |a, e| e[a].tap { |x| x.freeze if @freeze_app } }
@warmup.call(app) if @warmup
app
end
# Call the Rack application generated by this builder instance. Note that
# this rebuilds the Rack application and runs the warmup code (if any)
# every time it is called, so it should not be used if performance is important.
def call(env)
to_app.call(env)
end
private
# Generate a URLMap instance by generating new Rack applications for each
# map block in this instance.
def generate_map(default_app, mapping)
mapped = default_app ? { '/' => default_app } : {}
mapping.each { |r, b| mapped[r] = self.class.new(default_app, &b).to_app }
URLMap.new(mapped)
end
end
end
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