config.ru

# encoding: utf-8
ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../Gemfile', __FILE__)
require 'bundler/setup' if File.exist?(ENV['BUNDLE_GEMFILE'])
require 'rack/contrib'

require File.expand_path("../rack_try_static", __FILE__)

use Rack::ResponseHeaders do |headers|
  headers['Content-Type'] = 'text/html; charset=utf-8' if headers['Content-Type'] == 'text/html'
end
use Rack::Deflater
use Rack::StaticCache, urls: ["/images", "/stylesheets", "/javascripts", "/fonts"], root: "build"
use ::Rack::TryStatic,
  root: "build",
  urls: ["/"],
  try: [".html", "index.html", "/index.html"]

run lambda { [404, {"Content-Type" => "text/plain"}, ["File not found!"]] }

rack_try_static.rb

# encoding: utf-8

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
    end
  end
end