使用Open-URI来获取XML，以及在远程URL不能返回/超时的情况下的最佳做法？ [英] Using Open-URI to fetch XML and the best practice in case of problems with a remote url not returning/timing out?

问题描述

目前的代码只要没有远程错误就可以工作：

Current code works as long as there is no remote error:

def get_name_from_remote_url
      cstr = "http://someurl.com"
      getresult = open(cstr, "UserAgent" => "Ruby-OpenURI").read
      doc = Nokogiri::XML(getresult)
      my_data = doc.xpath("/session/name").text
      #  => 'Fred' or 'Sam' etc
      return my_data
end

但是，如果远程URL超时或什么也不返回？例如，我如何检测并返回nil？

But, what if the remote URL times out or returns nothing? How I detect that and return nil, for example?

而且，Open-URI是否提供了一种方法来定义放弃之前等待多久？在用户等待响应时调用此方法，那么我们如何在放弃之前设置最大时间间隔，并告诉用户对不起，我们尝试访问的远程服务器现在不可用？

And, does Open-URI give a way to define how long to wait before giving up? This method is called while a user is waiting for a response, so how do we set a max timeoput time before we give up and tell the user "sorry the remote server we tried to access is not available right now"?

推荐答案

Open-URI方便，但易用性意味着他们正在删除对其他HTTP客户端的大量配置详细信息的访问像Net :: HTTP允许。

Open-URI is convenient, but that ease of use means they're removing the access to a lot of the configuration details the other HTTP clients like Net::HTTP allow.

这取决于你使用的是什么版本的Ruby。对于1.8.7，您可以使用超时模块。从文档：

It depends on what version of Ruby you're using. For 1.8.7 you can use the Timeout module. From the docs:

require 'timeout'
begin
status = Timeout::timeout(5) {
  getresult = open(cstr, "UserAgent" => "Ruby-OpenURI").read
}
rescue Timeout::Error => e
  puts e.to_s
end

然后检查getresult的长度看看你是否有任何内容：

Then check the length of getresult to see if you got any content:

if (getresult.empty?)
  puts "got nothing from url"
end

如果您使用的是Ruby 1.9.2，可以添加 ：read_timeout => open（）方法中的 选项。

If you are using Ruby 1.9.2 you can add a :read_timeout => 10 option to the open() method.

此外，您的代码可以收紧，并更灵活。这将让您传递URL或默认值到当前使用的URL。另请参阅Nokogiri的 NodeSet 文档，了解 xpath ， / ， css 和 at ，％， at_css ， at_xpath / p>

Also, your code could be tightened up and made a bit more flexible. This will let you pass in a URL or default to the currently used URL. Also read Nokogiri's NodeSet docs to understand the difference between xpath, /, css and at, %, at_css, at_xpath:

def get_name_from_remote_url(cstr = 'http://someurl.com')
  doc = Nokogiri::XML(open(cstr, 'UserAgent' => 'Ruby-OpenURI'))

  # xpath returns a nodeset which has to be iterated over
  # my_data = doc.xpath('/session/name').text #  => 'Fred' or 'Sam' etc  

  # at returns a single node
  doc.at('/session/name').text
end

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