3 files changed, 21 insertions, 9 deletions
diff --git a/actionpack/lib/action_dispatch/http/request.rb b/actionpack/lib/action_dispatch/http/request.rb
index a1f84e5ace..a10bc3e419 100644
--- a/actionpack/lib/action_dispatch/http/request.rb
+++ b/actionpack/lib/action_dispatch/http/request.rb
@@ -20,6 +20,8 @@ module ActionDispatch
     include ActionDispatch::Http::FilterParameters
     include ActionDispatch::Http::URL
 
+    HTTP_X_REQUEST_ID = "HTTP_X_REQUEST_ID".freeze # :nodoc:
+
     autoload :Session, 'action_dispatch/request/session'
     autoload :Utils,   'action_dispatch/request/utils'
 
@@ -50,7 +52,6 @@ module ActionDispatch
       @original_fullpath = nil
       @fullpath          = nil
       @ip                = nil
-      @request_id        = nil
     end
 
     def check_path_parameters!
@@ -243,6 +244,8 @@ module ActionDispatch
       @remote_ip ||= (@env["action_dispatch.remote_ip"] || ip).to_s
     end
 
+    ACTION_DISPATCH_REQUEST_ID = "action_dispatch.request_id".freeze # :nodoc:
+
     # Returns the unique request id, which is based on either the X-Request-Id header that can
     # be generated by a firewall, load balancer, or web server or by the RequestId middleware
     # (which sets the action_dispatch.request_id environment variable).
@@ -250,11 +253,19 @@ module ActionDispatch
     # This unique ID is useful for tracing a request from end-to-end as part of logging or debugging.
     # This relies on the rack variable set by the ActionDispatch::RequestId middleware.
     def request_id
-      @request_id ||= env["action_dispatch.request_id"]
+      env[ACTION_DISPATCH_REQUEST_ID]
+    end
+
+    def request_id=(id)
+      env[ACTION_DISPATCH_REQUEST_ID] = id
     end
 
     alias_method :uuid, :request_id
 
+    def x_request_id
+      @env[HTTP_X_REQUEST_ID]
+    end
+
     # Returns the lowercase name of the HTTP server software.
     def server_software
       (@env['SERVER_SOFTWARE'] && /^([a-zA-Z]+)/ =~ @env['SERVER_SOFTWARE']) ? $1.downcase : nil
diff --git a/actionpack/lib/action_dispatch/http/response.rb b/actionpack/lib/action_dispatch/http/response.rb
index a895d1ab18..9e53a0f08b 100644
--- a/actionpack/lib/action_dispatch/http/response.rb
+++ b/actionpack/lib/action_dispatch/http/response.rb
@@ -274,7 +274,7 @@ module ActionDispatch # :nodoc:
     end
 
     # Turns the Response into a Rack-compatible array of the status, headers,
-    # and body. Allows explict splatting:
+    # and body. Allows explicit splatting:
     #
     #   status, headers, body = *response
     def to_a
diff --git a/actionpack/lib/action_dispatch/middleware/request_id.rb b/actionpack/lib/action_dispatch/middleware/request_id.rb
index b9ca524309..1555ff72af 100644
--- a/actionpack/lib/action_dispatch/middleware/request_id.rb
+++ b/actionpack/lib/action_dispatch/middleware/request_id.rb
@@ -13,22 +13,23 @@ module ActionDispatch
   # from multiple pieces of the stack.
   class RequestId
     X_REQUEST_ID = "X-Request-Id".freeze # :nodoc:
-    ACTION_DISPATCH_REQUEST_ID = "action_dispatch.request_id".freeze # :nodoc:
-    HTTP_X_REQUEST_ID = "HTTP_X_REQUEST_ID".freeze # :nodoc:
 
     def initialize(app)
       @app = app
     end
 
     def call(env)
-      env[ACTION_DISPATCH_REQUEST_ID] = external_request_id(env) || internal_request_id
-      @app.call(env).tap { |_status, headers, _body| headers[X_REQUEST_ID] = env[ACTION_DISPATCH_REQUEST_ID] }
+      req = ActionDispatch::Request.new env
+      req.request_id = make_request_id(req.x_request_id)
+      @app.call(env).tap { |_status, headers, _body| headers[X_REQUEST_ID] = req.request_id }
     end
 
     private
-      def external_request_id(env)
-        if request_id = env[HTTP_X_REQUEST_ID].presence
+      def make_request_id(request_id)
+        if request_id.presence
           request_id.gsub(/[^\w\-]/, "".freeze).first(255)
+        else
+          internal_request_id
         end
       end