如何处理 python WebDriver 中零星的 BadStatusLine、CannotSendRequest 错误

Question

自从我们开始在 jenkins 中运行 selenium UI 测试以来，我们注意到测试期间出现的错误频率虽然很小但很烦人。我们在看似随机的 selenium 操作（单击、退出、访问等）上收到 BadStatusLine 和 CannotSendRequest 错误。

它们通常看起来像：

  File "/usr/lib/python2.7/unittest/case.py", line 327, in run
    testMethod()
  File "/home/jenkins/workspace/Create and Upload Functional Testing/shapeways/test_suite/Portal/CreateAndUpload/TestUploadWhenNotLoggedIn_ExpectLoginModal.py", line 22, in runTest
    self.dw.visit(ShapewaysUrlBuilder.build_model_upload_url())
  File "/home/jenkins/workspace/Create and Upload Functional Testing/webdriver/webdriverwrapper/WebDriverWrapper.py", line 212, in visit
    return self.execute_and_handle_webdriver_exceptions(lambda: _visit(url))
  File "/home/jenkins/workspace/Create and Upload Functional Testing/webdriver/webdriverwrapper/WebDriverWrapper.py", line 887, in execute_and_handle_webdriver_exceptions
    return function_to_execute()
  File "/home/jenkins/workspace/Create and Upload Functional Testing/webdriver/webdriverwrapper/WebDriverWrapper.py", line 212, in <lambda>
    return self.execute_and_handle_webdriver_exceptions(lambda: _visit(url))
  File "/home/jenkins/workspace/Create and Upload Functional Testing/webdriver/webdriverwrapper/WebDriverWrapper.py", line 205, in _visit
    return self.driver.get(url)
  File "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/remote/webdriver.py", line 185, in get
    self.execute(Command.GET, {'url': url})
  File "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/remote/webdriver.py", line 171, in execute
    response = self.command_executor.execute(driver_command, params)
  File "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/remote/remote_connection.py", line 349, in execute
    return self._request(command_info[0], url, body=data)
  File "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/remote/remote_connection.py", line 380, in _request
    resp = self._conn.getresponse()
  File "/usr/lib/python2.7/httplib.py", line 1030, in getresponse
    response.begin()
  File "/usr/lib/python2.7/httplib.py", line 407, in begin
    version, status, reason = self._read_status()
  File "/usr/lib/python2.7/httplib.py", line 371, in _read_status
    raise BadStatusLine(line)

这个特殊情况来自以下堆栈：

• 硒==2.44.0
• python==2.7.3
• 火狐==34.0
• 詹金斯
• xvfb（使用 jenkins 插件进行无头显示器）

尽管我们已经看到这些错误在 firefox/selenium 的许多不同版本排列中一直出现。

我运行了一个 tcpdump 来捕获在 BadStatusLine 错误出现之前发送的实际请求并得到以下信息。

    POST /hub/session/ab64574a-4a17-447a-b2e8-5b0f5ed5e923/url HTTP/1.1 
    Host: 127.0.0.1:41246
    Accept-Encoding: identity Content-Length: 102
    Connection: keep-alive
    Content-type: application/json;charset="UTF-8"
    POST: /hub/session/ab64574a-4a17-447a-b2e8-5b0f5ed5e923/url
    Accept: application/json
    User-Agent: Python http auth

    {"url": "http://example.com/login", "sessionId": "ab64574a-4a17-447a-b2e8-5b0f5ed5e923"}

响应返回 0 个字节。所以 BadStatusLine 是由空响应引起的，这是有道理的。

问题是，为什么 selenium 的服务器会返回一个空响应。如果服务器死了，我们不会得到 ConnectionError 或类似的东西吗？

Answer 1

有一段时间，我没有重现，也不知道原因是什么。我终于能够通过运行来重现：

import requests
import json

while True:

  requests.post('http://127.0.0.1/hub/session/', data=json.dumps({"url": "http://example.com/login", "sessionId": "ab64574a-4a17-447a-b2e8-5b0f5ed5e923"}))

在运行时，我退出了浏览器并收到了 BadStatusLine 错误！当我再次尝试发出该请求时，我得到了预期的“ConnectionError”，你会从任何死服务器上看到它。

所以，我怀疑会发生什么，当浏览器被发送终止信号时，在其关闭期间有一个短暂的窗口，仍然会返回任何响应，但只有 0 个字节。这就是为什么您会为基本相同的问题（浏览器死机）获得不同类型的异常。原来我们有一个 cron 在后台杀死我们的浏览器。