Add class Diversipub::RackApp

diversipub.gemspec

@@ -41,6 +41,7 @@ Gem::Specification.new do |spec|
 
   spec.executables = spec.files.grep(%r{\Aexe/}) { |f| File.basename f }
 
+  spec.add_runtime_dependency 'rack',    '~> 2.2', '>= 2.2.7'
   spec.add_runtime_dependency 'sinatra', '~> 3.0', '>= 3.0.6'
 
   spec.add_development_dependency 'pry',  '~> 0.14'

lib/diversipub.rb

@@ -1,7 +1,9 @@
 # frozen_string_literal: true
 
+require 'rack'
 require 'sinatra/base'
 
 require_relative 'diversipub/main'
+require_relative 'diversipub/rack_app'
 require_relative 'diversipub/sinatra_app'
 require_relative 'diversipub/version'

lib/diversipub/rack_app.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+module Diversipub
+  ##
+  # Rack web application.
+  #
+  class RackApp
+    def initialize(sinatra_app)
+      @sinatra_app = sinatra_app
+    end
+
+    def call(env)
+      to_app.call env
+    end
+
+    def to_app
+      @to_app ||= builder.to_app
+    end
+
+  private
+
+    def builder
+      @builder ||= Rack::Builder.new.tap do |builder|
+        builder.run @sinatra_app
+      end
+    end
+  end
+end