從0開始刻淺談 Rails 的運作魔法 - Day 08 Controller Debug

今天我們來加點 debug 機制吧

用 Rack Environment debug

step 1 印出環境變數

我們在 a_quote 中把 Rack env 這個東西印出來看看

# quotation/app/controllers/quotes_controller.rb
class QuotesController < Rainbow::Controller
  def a_quote
    "You Only Live Once, " +
    "hang on to your dreams." +
    "\n<pre>\n#{env}\n</pre>"
  end
end

step 2 重新載入伺服器

1	rackup -p 3001

昨天有稍微說明 Rack env 本身是個 hash
裡面會包含 HTTP Request、Rack 參數、其他資訊

當 Rack 傳送 Request 出去後
Application 會收到下面這包資料並進行處理

Rails 的 routes 會顯示 Method 對應到的 Controller#action
當 Controller 的 action 是使用 Post 方法時
Rack 會去這包資料中找 REQUEST_METHOD 是否為 Post

{"rack.version"=>[1, 6], "rack.errors"=>#>>, "rack.multithread"=>true, "rack.multiprocess"=>false, "rack.run_once"=>false, "rack.url_scheme"=>"http", "SCRIPT_NAME"=>"", "QUERY_STRING"=>"", "SERVER_PROTOCOL"=>"HTTP/1.1", "SERVER_SOFTWARE"=>"puma 5.6.4 Birdie's Version", "GATEWAY_INTERFACE"=>"CGI/1.2", "REQUEST_METHOD"=>"GET", "REQUEST_PATH"=>"/quotes/a_quote", "REQUEST_URI"=>"/quotes/a_quote", "HTTP_VERSION"=>"HTTP/1.1", "HTTP_HOST"=>"localhost:3001", "HTTP_CONNECTION"=>"keep-alive", "HTTP_SEC_CH_UA"=>"\"Chromium\";v=\"104\", \" Not A;Brand\";v=\"99\", \"Google Chrome\";v=\"104\"", "HTTP_SEC_CH_UA_MOBILE"=>"?0", "HTTP_SEC_CH_UA_PLATFORM"=>"\"macOS\"", "HTTP_UPGRADE_INSECURE_REQUESTS"=>"1", "HTTP_USER_AGENT"=>"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/104.0.0.0 Safari/537.36", "HTTP_ACCEPT"=>"text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9", "HTTP_SEC_FETCH_SITE"=>"none", "HTTP_SEC_FETCH_MODE"=>"navigate", "HTTP_SEC_FETCH_USER"=>"?1", "HTTP_SEC_FETCH_DEST"=>"document", "HTTP_ACCEPT_ENCODING"=>"gzip, deflate, br", "HTTP_ACCEPT_LANGUAGE"=>"zh-TW,zh;q=0.9,en-US;q=0.8,en;q=0.7", "HTTP_COOKIE"=>"__profilin=p%3Dt; 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Debugging Exceptions

還記得 exception 嗎？
當運算結果出現例外情況時，就會印出錯誤訊息

這時候我們就可以用 begin / rescue / end 來解圍

step 1 在 a_quote 中印出環境變數

class QuotesController < Rainbow::Controller
  def a_quote
    "You Only Live Once, " +
      "hang on to your dreams." +
      "\n<pre>\n#{env}\n</pre>"
  end

  def exception
    raise "It's a bad one!"
  end
end

step 2 重新執行 rackup

1	> rackup -p 3001

在 development 時，你可以設定 ENV[‘RACK_ENV’] 來避免這個狀況

但其實還有更簡單的方法，就是加上 begin / rescue / end

額外設定錯誤

啟動 rackup 到 http://localhost:3001
有發現它壞掉了嗎？
我們用 begin / rescue / end 來修好它！

step 1 建立一個 404頁面

這邊採用 Rails 404頁面的 HTML

<!DOCTYPE html>
<html>
  <head>
      <title>The page you were looking for doesn't exist (404)</title>
      <meta name="viewport" content="width=device-width,initial-scale=1">
      <style>
        .rails-default-error-page {
            background-color: #EFEFEF;
            color: #2E2F30;
            text-align: center;
            font-family: arial, sans-serif;
            margin: 0;
        }

        .rails-default-error-page div.dialog {
            width: 95%;
            max-width: 33em;
            margin: 4em auto 0;
        }

        .rails-default-error-page div.dialog > div {
            border: 1px solid #CCC;
            border-right-color: #999;
            border-left-color: #999;
            border-bottom-color: #BBB;
            border-top: #B00100 solid 4px;
            border-top-left-radius: 9px;
            border-top-right-radius: 9px;
            background-color: white;
            padding: 7px 12% 0;
            box-shadow: 0 3px 8px rgba(50, 50, 50, 0.17);
        }

        .rails-default-error-page h1 {
            font-size: 100%;
            color: #730E15;
            line-height: 1.5em;
        }

        .rails-default-error-page div.dialog > p {
            margin: 0 0 1em;
            padding: 1em;
            background-color: #F7F7F7;
            border: 1px solid #CCC;
            border-right-color: #999;
            border-left-color: #999;
            border-bottom-color: #999;
            border-bottom-left-radius: 4px;
            border-bottom-right-radius: 4px;
            border-top-color: #DADADA;
            color: #666;
            box-shadow: 0 3px 8px rgba(50, 50, 50, 0.17);
        }
      </style>
  </head>
  <body class="rails-default-error-page">
    <div class="dialog">
      <div>
        <h1>The page you were looking for doesn't exist.</h1>
        <p>You may have mistyped the address or the page may have moved.</p>
      </div>
      <p>If you are the application owner check the logs for more information.</p>
    </div>
  </body>
</html>

step 2 調整 call 方法

# rainbow/lib/rainbow.rb
module Rainbow
  class Error < StandardError; end
  # Your code goes here...
  class Application
    def call(env)
      if env['PATH_INFO'] == '/favicon.ico'
        return 
        [ 404, {'Content-Type' => 'text/html'}, [] ]
      end

      begin
        klass, act = get_controller_and_action(env)
        controller = klass.new(env)
        text = controller.send(act)
        [ 200, {'Content-Type' => 'text/html'}, [text] ]
      rescue 
        # 找不到 Controller 及 action 時執行
        # 找到 html 檔案
        errors_page = File.read(File.expand_path("../../404.html", __FILE__)) 
        # 設定 Rack
        [ 400, {'Content-Type' => 'text/html'}, [errors_page] ]
      end
    end
  end

step 3 quotation 重啟 rackup

1	> rackup -p 3001

進到 http://localhost:3001 出現 404 頁面就是設定成功囉

參考文獻
https://www.rubyguides.com/2019/06/ruby-rescue-exceptions/
https://stackoverflow.com/questions/10168436/how-do-i-turn-off-exceptions-in-a-rack-app
https://apidock.com/ruby/File/expand_path/class
https://stackoverflow.com/questions/3863781/ruby-rack-mounting-a-simple-web-server-that-reads-index-html-as-default

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