config.ru

require 'rack'

# Modified version of TryStatic, from rack-contrib
# https://github.com/rack/rack-contrib/blob/master/lib/rack/contrib/try_static.rb

# Serve static files under a `build` directory:
# - `/` will try to serve your `build/index.html` file
# - `/foo` will try to serve `build/foo` or `build/foo.html` in that order
# - missing files will try to serve build/404.html or a tiny default 404 page

module Rack
  class TryStatic
    def initialize(app, options)
      @app = app
      @try = ['', *options.delete(:try)]
      @static = ::Rack::Static.new(lambda { [404, {}, []] }, options)
    end

    def call(env)
      orig_path = env['PATH_INFO']
      found = nil

      @try.each do |path|
        resp = @static.call(env.merge!({'PATH_INFO' => orig_path + path}))
        break if 404 != resp[0] && found = resp
      end

      found or @app.call(env.merge!('PATH_INFO' => orig_path))
    end
  end
end

# Serve files from the build directory
use Rack::TryStatic,
root: 'build',
urls: %w[/],
try: ['.html', 'index.html', '/index.html']

run lambda{ |env|
  four_oh_four_page = File.expand_path("../build/404/index.html",
  __FILE__)
  [ 404, { 'Content-Type'  => 'text/html'}, [
  File.read(four_oh_four_page) ]]
}