--- /dev/null
+module Rack
+ # Rack::Cascade tries an request on several apps, and returns the
+ # first response that is not 404 (or in a list of configurable
+ # status codes).
+
+ class Cascade
+ NotFound = [404, {}, []]
+
+ attr_reader :apps
+
+ def initialize(apps, catch=404)
+ @apps = []; @has_app = {}
+ apps.each { |app| add app }
+
+ @catch = {}
+ [*catch].each { |status| @catch[status] = true }
+ end
+
+ def call(env)
+ result = NotFound
+
+ @apps.each do |app|
+ result = app.call(env)
+ break unless @catch.include?(result[0].to_i)
+ end
+
+ result
+ end
+
+ def add app
+ @has_app[app] = true
+ @apps << app
+ end
+
+ def include? app
+ @has_app.include? app
+ end
+
+ alias_method :<<, :add
+ end
+end