--- /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
+ attr_reader :apps
+
+ def initialize(apps, catch=404)
+ @apps = apps
+ @catch = [*catch]
+ end
+
+ def call(env)
+ status = headers = body = nil
+ raise ArgumentError, "empty cascade" if @apps.empty?
+ @apps.each { |app|
+ begin
+ status, headers, body = app.call(env)
+ break unless @catch.include?(status.to_i)
+ end
+ }
+ [status, headers, body]
+ end
+
+ def add app
+ @apps << app
+ end
+
+ def include? app
+ @apps.include? app
+ end
+
+ alias_method :<<, :add
+ end
+end