add support for action dispatch request id generation

lib/rack/timeout/core.rb

@@ -43,7 +43,9 @@ def ms(k)   # helper method used for formatting values in milliseconds
       :timed_out, # This request has run for too long and we're raising a timeout error in it
       :completed, # We're done with this request (also set after having timed out a request)
       ]
-    ENV_INFO_KEY = "rack-timeout.info" # key under which each request's RequestDetails instance is stored in its env.
+    ENV_INFO_KEY = "rack-timeout.info".freeze # key under which each request's RequestDetails instance is stored in its env.
+    HTTP_X_REQUEST_ID = "HTTP_X_REQUEST_ID".freeze # key where request id is stored if generated by upstream client/proxy
+    ACTION_DISPATCH_REQUEST_ID = "action_dispatch.request_id".freeze # key where request id is stored if generated by action dispatch
 
     # helper methods to read timeout properties. Ensure they're always positive numbers or false. When set to false (or 0), their behaviour is disabled.
     def read_timeout_property value, default
@@ -75,7 +77,7 @@ def initialize(app, service_timeout:nil, wait_timeout:nil, wait_overtime:nil, se
     RT = self # shorthand reference
     def call(env)
       info      = (env[ENV_INFO_KEY] ||= RequestDetails.new)
-      info.id ||= env["HTTP_X_REQUEST_ID"] || SecureRandom.hex
+      info.id ||= env[HTTP_X_REQUEST_ID] || env[ACTION_DISPATCH_REQUEST_ID] || SecureRandom.uuid
 
       time_started_service = Time.now                      # The wall time the request started being processed by rack
       ts_started_service   = fsecs                         # The monotonic time the request started being processed by rack

lib/rack/timeout/rails.rb

@@ -3,6 +3,11 @@
 class Rack::Timeout::Railtie < Rails::Railtie
   initializer("rack-timeout.prepend") do |app|
     next if Rails.env.test?
-    app.config.middleware.insert_before Rack::Runtime, Rack::Timeout
+
+    if defined?(ActionDispatch::RequestId)
+      app.config.middleware.insert_after(ActionDispatch::RequestId, Rack::Timeout)
+    else
+      app.config.middleware.insert_before(Rack::Runtime, Rack::Timeout)
+    end
   end
-end
+end