Railsで作ったJSONをRackでHTMLにする

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RailsやiOS、HTML5の情報を発信中!! → http://qiita.com/teams/frogapps

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RailsでiOSなどのアプリ用のサーバを作ると、JSONを出力するAPIを作ることになると思います。

そのJSON APIを使って、HTMLをレンダリングするRackモジュールを作ってみました。

これを使うことで、Railsがモデルとコントローラ層、Rackでビュー層という風に別れます。
Railsのビューより機能は劣りますが、A/Bテストを仕込むなど、なにか手を加えたいときには全体が把握しやすく、Railsのバージョンにも依存しなくなるというメリットがあります。

json_render.rb

=begin
# This file is used by Rack-based servers to start the application.

require ::File.expand_path('../config/environment',  __FILE__)
require './lib/json_render'
use JSONRender,
  :routes => {
    %r|/test/(\w+)$| => {
      :json => "/home/\\1.json",
      :erb => Proc.new do
        ['erb/home.1.html.erb', 'erb/home.2.html.erb'][rand(2)]
      end
    },
    %r|^/$| => {
      :json => "/home.json",
      :erb => 'erb/index.html.erb'
    }
  }

run JsonRenderTest::Application
=end

require 'erubis'
require 'net/http'

class JSONRender
  def initialize(app, options)
    @app, @routes = app, options[:routes]
    @templates = {}
  end

  def call(env)
    path_info = env['PATH_INFO']
    key, settings = @routes.find do |path, settings|
      path_info.match(path)
    end.to_a
    return @app.call(env) unless key

    # get json data from specific path
    settings_json = settings[:json]
    settings_json = settings_json.call(env) if settings_json.is_a?(Proc)
    json_path = path_info.gsub(key, settings_json)
    status, headers, response = @app.call(env.update('PATH_INFO' => json_path))
    return [status, headers, response] if [Net::HTTPNotModified].include?(status)
    response.close if response.respond_to?(:close)

    if status / 100 == 2
      # render data
      erb_path = settings[:erb]
      erb_path = erb_path.call(env) if erb_path.is_a?(Proc)
      response = render(erb_path, JSON.parse(response.is_a?(Hash) ? response.first : response.body))

      # Set new Content-Length, if it was set before we mutated the response body
      if headers['Content-Length']
        length = response.to_ary.inject(0) { |len, part| len + Rack::Utils::bytesize(part) }
        headers['Content-Length'] = length.to_s
      end

      headers['Content-Type'] = 'text/html'
    end
    [status, headers, response]
  end

  def render(erb_file, params)
    erb_file = File.expand_path(erb_file)
    template = @templates[erb_file]
    if !template || template[:timestamp] != File.mtime(erb_file)
      erb = Erubis::Eruby.new(File.read(erb_file))
      template = {:erb => erb, :timestamp => File.mtime(erb_file)}
      @templates[erb_file] = template
    end
    [template[:erb].evaluate(params)]
  end
end