Simple Webrick server

serve.rb

#!/usr/bin/env ruby

require 'webrick'

class Servlet < WEBrick::HTTPServlet::FileHandler
  PORT = 4200
  INDEX_FILE = 'index.html'
  ROOT_PATH = File.expand_path(__dir__) # Folder of current file

  def do_GET(request, response)
    if readable_file_exists?(request.path)
      super(request, response) # Default handling with correct content types
    else
      response.content_type = 'text/html'
      response.body = File.read(full_path(INDEX_FILE))
    end
  end

  private

  def readable_file_exists?(path)
    File.readable?(full_path(path)) && File.file?(full_path(path))
  end

  def full_path(path)
    File.join(ROOT_PATH, path)
  end
end

server = WEBrick::HTTPServer.new(Port: Servlet::PORT)
server.mount '/', Servlet, Servlet::ROOT_PATH

trap("INT") { server.shutdown }
server.start