diff --git a/lib/faraday.rb b/lib/faraday.rb
index 0f9dfd367..03153f8e7 100644
--- a/lib/faraday.rb
+++ b/lib/faraday.rb
@@ -2,6 +2,8 @@
 require 'cgi'
 require 'set'
 require 'forwardable'
+require 'faraday/middleware_registry'
+require 'faraday/dependency_loader'
 
 # This is the main namespace for Faraday.
 #
@@ -147,126 +149,6 @@ def self.default_connection_options=(options)
     Timer = Timeout
   end
 
-  # Adds the ability for other modules to register and lookup
-  # middleware classes.
-  module MiddlewareRegistry
-    # Register middleware class(es) on the current module.
-    #
-    # @param autoload_path [String] Middleware autoload path
-    # @param mapping [Hash{Symbol => Module, Symbol, Array<Module, Symbol, String>}] Middleware mapping from a lookup symbol to a reference to the middleware. - Classes can be expressed as:
-    #           - a fully qualified constant
-    #           - a Symbol
-    #           - a Proc that will be lazily called to return the former
-    #           - an array is given, its first element is the constant or symbol,
-    #             and its second is a file to `require`.
-    # @return [void]
-    #
-    # @example Lookup by a constant
-    #
-    #   module Faraday
-    #     class Whatever
-    #       # Middleware looked up by :foo returns Faraday::Whatever::Foo.
-    #       register_middleware :foo => Foo
-    #     end
-    #   end
-    #
-    # @example Lookup by a symbol
-    #
-    #   module Faraday
-    #     class Whatever
-    #       # Middleware looked up by :bar returns Faraday::Whatever.const_get(:Bar)
-    #       register_middleware :bar => :Bar
-    #     end
-    #   end
-    #
-    # @example Lookup by a symbol and string in an array
-    #
-    #   module Faraday
-    #     class Whatever
-    #       # Middleware looked up by :baz requires 'baz' and returns Faraday::Whatever.const_get(:Baz)
-    #       register_middleware :baz => [:Baz, 'baz']
-    #     end
-    #   end
-    #
-    def register_middleware(autoload_path = nil, mapping = nil)
-      if mapping.nil?
-        mapping = autoload_path
-        autoload_path = nil
-      end
-      middleware_mutex do
-        @middleware_autoload_path = autoload_path if autoload_path
-        (@registered_middleware ||= {}).update(mapping)
-      end
-    end
-
-    # Unregister a previously registered middleware class.
-    #
-    # @param key [Symbol] key for the registered middleware.
-    def unregister_middleware(key)
-      @registered_middleware.delete(key)
-    end
-
-    # Lookup middleware class with a registered Symbol shortcut.
-    #
-    # @param key [Symbol] key for the registered middleware.
-    # @return [Class] a middleware Class.
-    # @raise [Faraday::Error] if given key is not registered
-    #
-    # @example
-    #
-    #   module Faraday
-    #     class Whatever
-    #       register_middleware :foo => Foo
-    #     end
-    #   end
-    #
-    #   Faraday::Whatever.lookup_middleware(:foo)
-    #   # => Faraday::Whatever::Foo
-    #
-    def lookup_middleware(key)
-      load_middleware(key) ||
-        raise(Faraday::Error.new("#{key.inspect} is not registered on #{self}"))
-    end
-
-    def middleware_mutex(&block)
-      @middleware_mutex ||= begin
-        require 'monitor'
-        Monitor.new
-      end
-      @middleware_mutex.synchronize(&block)
-    end
-
-    def fetch_middleware(key)
-      defined?(@registered_middleware) && @registered_middleware[key]
-    end
-
-    def load_middleware(key)
-      value = fetch_middleware(key)
-      case value
-      when Module
-        value
-      when Symbol, String
-        middleware_mutex do
-          @registered_middleware[key] = const_get(value)
-        end
-      when Proc
-        middleware_mutex do
-          @registered_middleware[key] = value.call
-        end
-      when Array
-        middleware_mutex do
-          const, path = value
-          if root = @middleware_autoload_path
-            path = "#{root}/#{path}"
-          end
-          require(path)
-          @registered_middleware[key] = const
-        end
-        load_middleware(key)
-      end
-    end
-  end
-
   require_libs "utils", "options", "connection", "rack_builder", "parameters",
     "middleware", "adapter", "request", "response", "upload_io", "error"
 
diff --git a/lib/faraday/adapter.rb b/lib/faraday/adapter.rb
index 78cbf1026..11147fec4 100644
--- a/lib/faraday/adapter.rb
+++ b/lib/faraday/adapter.rb
@@ -1,7 +1,10 @@
 module Faraday
   # Base class for all Faraday adapters. Adapters are
   # responsible for fulfilling a Faraday request.
-  class Adapter < Middleware
+  class Adapter
+    extend MiddlewareRegistry
+    extend DependencyLoader
+
     CONTENT_LENGTH = 'Content-Length'.freeze
 
     register_middleware File.expand_path('../adapter', __FILE__),
@@ -31,13 +34,14 @@ def inherited(subclass)
     self.supports_parallel = false
 
     def initialize(app = nil, opts = {}, &block)
-      super(app)
+      @app = lambda { |env| env.response }
       @connection_options = opts
       @config_block = block
     end
 
     def call(env)
       env.clear_body if env.needs_body?
+      env.response = Response.new
     end
 
     private
@@ -50,6 +54,9 @@ def save_response(env, status, body, headers = nil, reason_phrase = nil)
         response_headers.update headers unless headers.nil?
         yield(response_headers) if block_given?
       end
+
+      env.response.finish(env) unless env.parallel?
+      env.response
     end
   end
 end
diff --git a/lib/faraday/dependency_loader.rb b/lib/faraday/dependency_loader.rb
new file mode 100644
index 000000000..c46960207
--- /dev/null
+++ b/lib/faraday/dependency_loader.rb
@@ -0,0 +1,27 @@
+module Faraday
+  module DependencyLoader
+    attr_accessor :load_error
+    private :load_error=
+
+    # Executes a block which should try to require and reference dependent libraries
+    def dependency(lib = nil)
+      lib ? require(lib) : yield
+    rescue LoadError, NameError => error
+      self.load_error = error
+    end
+
+    def new(*)
+      raise "missing dependency for #{self}: #{load_error.message}" unless loaded?
+      super
+    end
+
+    def loaded?
+      load_error.nil?
+    end
+
+    def inherited(subclass)
+      super
+      subclass.send(:load_error=, self.load_error)
+    end
+  end
+end
diff --git a/lib/faraday/middleware.rb b/lib/faraday/middleware.rb
index c45d51ade..c1468bd37 100644
--- a/lib/faraday/middleware.rb
+++ b/lib/faraday/middleware.rb
@@ -1,34 +1,7 @@
 module Faraday
   class Middleware
     extend MiddlewareRegistry
-
-    class << self
-      attr_accessor :load_error
-      private :load_error=
-    end
-
-    self.load_error = nil
-
-    # Executes a block which should try to require and reference dependent libraries
-    def self.dependency(lib = nil)
-      lib ? require(lib) : yield
-    rescue LoadError, NameError => error
-      self.load_error = error
-    end
-
-    def self.new(*)
-      raise "missing dependency for #{self}: #{load_error.message}" unless loaded?
-      super
-    end
-
-    def self.loaded?
-      load_error.nil?
-    end
-
-    def self.inherited(subclass)
-      super
-      subclass.send(:load_error=, self.load_error)
-    end
+    extend DependencyLoader
 
     def initialize(app = nil)
       @app = app
diff --git a/lib/faraday/middleware_registry.rb b/lib/faraday/middleware_registry.rb
new file mode 100644
index 000000000..26625e7d7
--- /dev/null
+++ b/lib/faraday/middleware_registry.rb
@@ -0,0 +1,121 @@
+module Faraday
+  # Adds the ability for other modules to register and lookup
+  # middleware classes.
+  module MiddlewareRegistry
+    # Register middleware class(es) on the current module.
+    #
+    # @param autoload_path [String] Middleware autoload path
+    # @param mapping [Hash{Symbol => Module, Symbol, Array<Module, Symbol, String>}] Middleware mapping from a lookup symbol to a reference to the middleware. - Classes can be expressed as:
+    #           - a fully qualified constant
+    #           - a Symbol
+    #           - a Proc that will be lazily called to return the former
+    #           - an array is given, its first element is the constant or symbol,
+    #             and its second is a file to `require`.
+    # @return [void]
+    #
+    # @example Lookup by a constant
+    #
+    #   module Faraday
+    #     class Whatever
+    #       # Middleware looked up by :foo returns Faraday::Whatever::Foo.
+    #       register_middleware :foo => Foo
+    #     end
+    #   end
+    #
+    # @example Lookup by a symbol
+    #
+    #   module Faraday
+    #     class Whatever
+    #       # Middleware looked up by :bar returns Faraday::Whatever.const_get(:Bar)
+    #       register_middleware :bar => :Bar
+    #     end
+    #   end
+    #
+    # @example Lookup by a symbol and string in an array
+    #
+    #   module Faraday
+    #     class Whatever
+    #       # Middleware looked up by :baz requires 'baz' and returns Faraday::Whatever.const_get(:Baz)
+    #       register_middleware :baz => [:Baz, 'baz']
+    #     end
+    #   end
+    #
+    def register_middleware(autoload_path = nil, mapping = nil)
+      if mapping.nil?
+        mapping = autoload_path
+        autoload_path = nil
+      end
+      middleware_mutex do
+        @middleware_autoload_path = autoload_path if autoload_path
+        (@registered_middleware ||= {}).update(mapping)
+      end
+    end
+
+    # Unregister a previously registered middleware class.
+    #
+    # @param key [Symbol] key for the registered middleware.
+    def unregister_middleware(key)
+      @registered_middleware.delete(key)
+    end
+
+    # Lookup middleware class with a registered Symbol shortcut.
+    #
+    # @param key [Symbol] key for the registered middleware.
+    # @return [Class] a middleware Class.
+    # @raise [Faraday::Error] if given key is not registered
+    #
+    # @example
+    #
+    #   module Faraday
+    #     class Whatever
+    #       register_middleware :foo => Foo
+    #     end
+    #   end
+    #
+    #   Faraday::Whatever.lookup_middleware(:foo)
+    #   # => Faraday::Whatever::Foo
+    #
+    def lookup_middleware(key)
+      load_middleware(key) ||
+        raise(Faraday::Error.new("#{key.inspect} is not registered on #{self}"))
+    end
+
+    def middleware_mutex(&block)
+      @middleware_mutex ||= begin
+        require 'monitor'
+        Monitor.new
+      end
+      @middleware_mutex.synchronize(&block)
+    end
+
+    def fetch_middleware(key)
+      defined?(@registered_middleware) && @registered_middleware[key]
+    end
+
+    def load_middleware(key)
+      value = fetch_middleware(key)
+      case value
+      when Module
+        value
+      when Symbol, String
+        middleware_mutex do
+          @registered_middleware[key] = const_get(value)
+        end
+      when Proc
+        middleware_mutex do
+          @registered_middleware[key] = value.call
+        end
+      when Array
+        middleware_mutex do
+          const, path = value
+          if root = @middleware_autoload_path
+            path = "#{root}/#{path}"
+          end
+          require(path)
+          @registered_middleware[key] = const
+        end
+        load_middleware(key)
+      end
+    end
+  end
+end
diff --git a/lib/faraday/rack_builder.rb b/lib/faraday/rack_builder.rb
index d6fb077a5..7c3448a22 100644
--- a/lib/faraday/rack_builder.rb
+++ b/lib/faraday/rack_builder.rb
@@ -47,7 +47,7 @@ def ==(other)
         end
       end
 
-      def build(app)
+      def build(app = nil)
         klass.new(app, *@args, &@block)
       end
     end
@@ -160,19 +160,14 @@ def build_response(connection, request)
     def app
       @app ||= begin
         lock!
-        to_app(lambda { |env|
-          response = Response.new
-          env.response = response
-          response.finish(env) unless env.parallel?
-          response
-        })
+        to_app
       end
     end
 
-    def to_app(inner_app)
+    def to_app
       # last added handler is the deepest and thus closest to the inner app
       # adapter is always the last one
-      (@handlers + [@adapter]).reverse.inject(inner_app) { |app, handler| handler.build(app) }
+      (@handlers).reverse.inject(@adapter.build) { |app, handler| handler.build(app) }
     end
 
     def ==(other)