Ruby on Rails 5.2 - NoMethodError（nil:NilClass 的未定义方法“主机”）：答案

【问题标题】：Ruby on Rails 5.2 - NoMethodError (undefined method `host' for nil:NilClass):Ruby on Rails 5.2 - NoMethodError（nil:NilClass 的未定义方法“主机”）：
【发布时间】：2020-12-30 11:20:24
【问题描述】：

我有一个在 Ruby 2.6.6 上运行的 Ruby on Rails 5.2 应用程序，路径如下：/api/popups 它给了我 500 内部服务器错误。

在生产日志中，我看到以下消息：

Started GET "/api/popups" for IP at 2020-12-30 11:12:30 +0000
INFO -- : [e7a305ff-9d4d-4c83-9572-9ea0708e8f69] Processing by controller2#index as HTML
INFO -- : [e7a305ff-9d4d-4c83-9572-9ea0708e8f69] Completed 500 Internal Server Error in 3ms (ActiveRecord: 0.0ms)
FATAL -- : [e7a305ff-9d4d-4c83-9572-9ea0708e8f69]   
FATAL -- : [e7a305ff-9d4d-4c83-9572-9ea0708e8f69] NoMethodError (undefined method `host' for nil:NilClass):
FATAL -- : [e7a305ff-9d4d-4c83-9572-9ea0708e8f69]   
FATAL -- : [e7a305ff-9d4d-4c83-9572-9ea0708e8f69] app/controllers/concerns/controller1.rb:14:in `popups_for_domain'
[e7a305ff-9d4d-4c83-9572-9ea0708e8f69] app/controllers/controller2.rb:5:in `index'

controller2.rb 索引（第 5 行）如下所示：

def index
    popups = popups_for_domain.includes(:popup_template, :color_schema, :target_sets)
end

controller1.rb 第 14 行包含：

def popups_for_domain
    return @popups_for_domain if @popups_for_domain
    referer_domain = Addressable::URI.parse(request.referer).host.gsub(/^w{3}\./i, '')
    @popups_for_domain = Popup.where(domain: referer_domain)
end

错误从这一行指向主机函数：referer_domain = Addressable::URI.parse(request.referer).host.gsub(/^w{3}\./i, '')

那里出了什么问题，我该如何解决？谢谢。

【问题讨论】：

标签： ruby-on-rails ruby ruby-on-rails-5 ruby-on-rails-5.2 ruby-on-rails-5.1

【解决方案1】：

Addressabel::URI.parse returns nil 当 URL 解析为 nil 或 false 时。这意味着——至少有时——你没有request.referer，你也需要处理这些情况。

这样的事情可能对你有用：

def popups_for_domain
  return @popups_for_domain if @popups_for_domain
  return unless request.referer      

  referer_domain = Addressable::URI.parse(request.referer).host.gsub(/^w{3}\./i, '')
  @popups_for_domain = Popup.where(domain: referer_domain)

结束

【讨论】：

【解决方案2】：

根据：https://stackoverflow.com/a/6880668/1564840

request.referrer 在最终用户时/可能为空：

- entered the site URL in browser address bar itself.
- visited the site by a browser-maintained bookmark.
- visited the site as first page in the window/tab.
- clicked a link in an external application.
- switched from a https URL to a http URL.
- switched from a https URL to a different https URL.
- has security software installed (antivirus/firewall/etc) which strips the referrer from all requests.
- is behind a proxy which strips the referrer from all requests.
- visited the site programmatically (like, curl) without setting the referrer header (searchbots!).

在我的例子中，我直接在浏览器中调用了 API url，这就是缺少引用者的原因。

【讨论】：