Use external Rack adapter

faraday.gemspec

@@ -22,6 +22,7 @@ Gem::Specification.new do |spec| # rubocop:disable Metrics/BlockLength
   spec.add_dependency 'faraday-net_http', '~> 1.0'
   spec.add_dependency 'faraday-net_http_persistent', '~> 1.1'
   spec.add_dependency 'faraday-patron', '~> 1.0'
+  spec.add_dependency 'faraday-rack', '~> 1.0'
   spec.add_dependency 'multipart-post', '>= 1.2', '< 3'
   spec.add_dependency 'ruby2_keywords', '>= 0.0.4'
 

lib/faraday.rb

@@ -36,6 +36,7 @@
 require 'faraday/net_http'
 require 'faraday/net_http_persistent'
 require 'faraday/patron'
+require 'faraday/rack'
 
 # This is the main namespace for Faraday.
 #

lib/faraday/adapter.rb

@@ -11,8 +11,7 @@ class Adapter
 
     register_middleware File.expand_path('adapter', __dir__),
                         test: [:Test, 'test'],
-                        typhoeus: [:Typhoeus, 'typhoeus'],
-                        rack: [:Rack, 'rack']
+                        typhoeus: [:Typhoeus, 'typhoeus']
 
     # This module marks an Adapter as supporting parallel requests.
     module Parallelism

lib/faraday/autoload.rb

@@ -59,8 +59,7 @@ class Adapter
     extend AutoloadHelper
     autoload_all 'faraday/adapter',
                  Typhoeus: 'typhoeus',
-                 Test: 'test',
-                 Rack: 'rack'
+                 Test: 'test'
   end
 
   # Request represents a single HTTP request for a Faraday adapter to make.