selenium-webdriver(python) (十四) -- webdriver原理

原创

虫师blog 2023-11-03 09:42:06 ©著作权

文章标签 chrome 服务器输入框 文章分类 Python 后端开发

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之前看乙醇视频中提到，selenium 的ruby 实现有一个小后门，在代码中加上$DEBUG=1 ，再运行脚本的过程中，就可以看到客户端请求的信息与服务器端返回的数据；觉得这个功能很强大，可以帮助理解webdriver的运行原理。

后来查了半天，python并没有提供这样一个方便的后门，不过我们可以通过代理的方式获得这些交互信息；

一、需要安装java 虚拟机与selenium-server-standalone ，参考《selenium + python自动化测试环境搭建》第7、8操作：

二、通过下面命令启动服务：

C:\selenium>java -jar selenium-server-standalone-2.33.0.jar

在命令结尾加 >d:\log.txt 可以将命令信息存入文件，但信息很少。

然后运行下面的自动化脚本：

#coding = utf-8

import time
from selenium import webdriver
from selenium.webdriver.common.desired_capabilities import DesiredCapabilities

driver = webdriver.Remote(desired_capabilities=DesiredCapabilities.CHROME)
driver.get("http://www.youdao.com")
driver.find_element_by_name("q").send_keys("hello")
driver.find_element_by_name("q").send_keys("key.ENTER")

driver.close()

webdriver原理：

1. WebDriver 启动目标浏览器，并绑定到指定端口。该启动的浏览器实例，做为web driver的remote server。

2. Client 端通过CommandExcuter 发送HTTPRequest 给remote server 的侦听端口（通信协议： the webriver wire protocol）

3. Remote server 需要依赖原生的浏览器组件（如：IEDriver.dll,chromedriver.exe），来转化转化浏览器的native调用。

查看命令提示符下的运行日志：

咋一看很乱，慢慢分析一下就发现很有意思！结合上面的脚本分析

---------------------------------------------------------------------------------------
启动代理进入监听状态
C:\selenium>java -jar selenium-server-standalone-2.33.0.jar
八月 22, 2013 10:19:48 上午 org.openqa.grid.selenium.GridLauncher main
INFO: Launching a standalone server
10:19:48.734 INFO - Java: Oracle Corporation 23.21-b01
10:19:48.734 INFO - OS: Windows XP 5.1 x86
10:19:48.734 INFO - v2.33.0, with Core v2.33.0. Built from revision 4e90c97
10:19:48.843 INFO - RemoteWebDriver instances should connect to: http://127.0.0.
1:4444/wd/hub
10:19:48.843 INFO - Version Jetty/5.1.x
10:19:48.843 INFO - Started HttpContext[/selenium-server/driver,/selenium-server
/driver]
10:19:48.843 INFO - Started HttpContext[/selenium-server,/selenium-server]
10:19:48.843 INFO - Started HttpContext[/,/]
10:19:48.890 INFO - Started org.openqa.jetty.jetty.servlet.ServletHandler@176343
e
10:19:48.890 INFO - Started HttpContext[/wd,/wd]
10:19:48.906 INFO - Started SocketListener on 0.0.0.0:4444
10:19:48.906 INFO - Started org.openqa.jetty.jetty.Server@388c74
--------------------------------------------------------------------------------------

创建新session 
10:20:38.593 INFO - Executing: [new session: {platform=ANY, javascriptEnabled=tr
ue, browserName=chrome, version=}] at URL: /session)
10:20:38.593 INFO - Creating a new session for Capabilities [{platform=ANY, java
scriptEnabled=true, browserName=chrome, version=}]   

webdrivr通过GET方式发送请求
[0.921][INFO]: received Webriver request: GET /status  

向webdrver返回响应，返回码200表示成功
[0.921][INFO]: sending Webriver response: 200 {
   "sessionId": "",
   "status": 0,
   "value": {
      "build": {
         "version": "alpha"
      },
      "os": {
         "arch": "x86",
         "name": "Windows NT",
         "version": "5.1 SP3"
      }
   }
}

webdriver 再次以POST方式发送请求，并启动浏览器相关信息
[0.984][INFO]: received Webriver request: POST /session {
   "desiredCapabilities": {
      "browserName": "chrome",
      "javascriptEnabled": true,
      "platform": "ANY",
      "version": ""
   }
}
[0.984][INFO]: Launching chrome: "C:\ocuments and Settings\Administrator\Local S
ettings\Application ata\Google\Chrome\Application\chrome.exe" --remote-debugging
-port=4223 --no-first-run --enable-logging --logging-level=1 --user-data-dir="C:
\OCUME~1\AMINI~1\LOCALS~1\Temp\scoped_dir1808_7550" --load-extension="C:\OCUME~1
\AMINI~1\LOCALS~1\Temp\scoped_dir1808_26821\internal" --ignore-certificate-error
s data:text/html;charset=utf-8,
[1.773][INFO]: sending Webriver response: 303

webdriver再次以GET方法请求，这附加上了session的信息
[1.778][INFO]: received Webriver request: GET /session/32b33aa585ccbbf7ba7853588
2852af3

服务器先对sesssionID进行解析，确认是selenium调用的以及要访问的网址，
[1.779][INFO]: sending Webriver response: 200 {
   "sessionId": "32b33aa585ccbbf7ba78535882852af3",
   "status": 0,
   "value": {
      "acceptSslCerts": true,
      "applicationCacheEnabled": false,
      "browserConnectionEnabled": false,
      "browserName": "chrome",
      "chrome": {
         "chromedriverVersion": "2.0"
      },
      "cssSelectorsEnabled": true,
      "databaseEnabled": true,
      "handlesAlerts": true,
      "javascriptEnabled": true,
      "locationContextEnabled": true,
      "nativeEvents": true,
      "platform": "Windows NT",
      "rotatable": false,
      "takesScreenshot": true,
      "version": "27.0.1453.116",
      "webStorageEnabled": true
   }
}
10:20:40.640 INFO - Done: /session
10:20:40.640 INFO - Executing: org.openqa.selenium.remote.server.handler.GetSess
ionCapabilities@14cf7a1 at URL: /session/ac5b2c71-5b1a-469e-814c-fdd09a2061fc)
10:20:40.640 INFO - Done: /session/ac5b2c71-5b1a-469e-814c-fdd09a2061fc
10:20:40.656 INFO - Executing: [get: http://www.youdao.com] at URL: /session/ac5
b2c71-5b1a-469e-814c-fdd09a2061fc/url)

webdriver正试向服务器请求youdao网站
[1.820][INFO]: received Webriver request: POST /session/32b33aa585ccbbf7ba785358
82852af3/url {
   "url": "http://www.youdao.com"
}
[1.822][INFO]: waiting for pending navigations...
[1.829][INFO]: done waiting for pending navigations
[2.073][INFO]: waiting for pending navigations...
[2.900][INFO]: done waiting for pending navigations

获得服务器数据的应答
[2.900][INFO]: sending Webriver response: 200 {
   "sessionId": "32b33aa585ccbbf7ba78535882852af3",
   "status": 0,
   "value": null
}
10:20:41.734 INFO - Done: /session/ac5b2c71-5b1a-469e-814c-fdd09a2061fc/url
--------------------------------------------------------------------------------------
下面接着发送定位输入框的信息
10:20:41.734 INFO - Executing: [find element: By.name: q] at URL: /session/ac5b2
c71-5b1a-469e-814c-fdd09a2061fc/element)
[2.905][INFO]: received Webriver request: POST /session/32b33aa585ccbbf7ba785358
82852af3/element {
   "using": "name",
   "value": "q"
}
[2.905][INFO]: waiting for pending navigations...
[2.905][INFO]: done waiting for pending navigations
[2.922][INFO]: waiting for pending navigations...
[2.922][INFO]: done waiting for pending navigations

得到服务器应答
[2.922][INFO]: sending Webriver response: 200 {
   "sessionId": "32b33aa585ccbbf7ba78535882852af3",
   "status": 0,
   "value": {
      "ELEMENT": "0.19427558477036655:1"
   }
}
10:20:41.765 INFO - Done: /session/ac5b2c71-5b1a-469e-814c-fdd09a2061fc/element
10:20:41.765 INFO - Executing: [send keys: 0 org.openqa.selenium.support.events.
EventFiringWebDriver$EventFiringWebElement@a8215ba9, [h, e, l, l, o]] at URL: /s
ession/ac5b2c71-5b1a-469e-814c-fdd09a2061fc/element/0/value)

向定位到的输入框写入hello
[2.936][INFO]: received Webriver request: POST /session/32b33aa585ccbbf7ba785358
82852af3/element/0.19427558477036655:1/value {
   "id": "0.19427558477036655:1",
   "value": [ "h", "e", "l", "l", "o" ]
}
[2.936][INFO]: waiting for pending navigations...
[2.936][INFO]: done waiting for pending navigations
[3.002][INFO]: waiting for pending navigations...
[3.002][INFO]: done waiting for pending navigations
[3.002][INFO]: sending Webriver response: 200 {
   "sessionId": "32b33aa585ccbbf7ba78535882852af3",
   "status": 0,
   "value": null
}
10:20:41.843 INFO - Done: /session/ac5b2c71-5b1a-469e-814c-fdd09a2061fc/element/
0/value

再次发送定位输入框的请求
10:20:41.843 INFO - Executing: [find element: By.name: q] at URL: /session/ac5b2
c71-5b1a-469e-814c-fdd09a2061fc/element)
[3.006][INFO]: received Webriver request: POST /session/32b33aa585ccbbf7ba785358
82852af3/element {
   "using": "name",
   "value": "q"
}
[3.006][INFO]: waiting for pending navigations...
[3.006][INFO]: done waiting for pending navigations
[3.016][INFO]: waiting for pending navigations...
[3.016][INFO]: done waiting for pending navigations
[3.016][INFO]: sending Webriver response: 200 {
   "sessionId": "32b33aa585ccbbf7ba78535882852af3",
   "status": 0,
   "value": {
      "ELEMENT": "0.19427558477036655:1"
   }
}
10:20:41.859 INFO - Done: /session/ac5b2c71-5b1a-469e-814c-fdd09a2061fc/element
10:20:41.859 INFO - Executing: [send keys: 0 org.openqa.selenium.support.events.
EventFiringWebDriver$EventFiringWebElement@a8215ba9, [k, e, y, ., E, N, T, E, R]
] at URL: /session/ac5b2c71-5b1a-469e-814c-fdd09a2061fc/element/0/value)

对定位的到的输入框发送回车（ENTER）事件请求
[3.021][INFO]: received Webriver request: POST /session/32b33aa585ccbbf7ba785358
82852af3/element/0.19427558477036655:1/value {
   "id": "0.19427558477036655:1",
   "value": [ "k", "e", "y", ".", "E", "N", "T", "E", "R" ]
}
[3.021][INFO]: waiting for pending navigations...
[3.021][INFO]: done waiting for pending navigations
[3.064][INFO]: waiting for pending navigations...
[3.064][INFO]: done waiting for pending navigations
[3.064][INFO]: sending Webriver response: 200 {
   "sessionId": "32b33aa585ccbbf7ba78535882852af3",
   "status": 0,
   "value": null
}
10:20:41.906 INFO - Done: /session/ac5b2c71-5b1a-469e-814c-fdd09a2061fc/element/
0/value
10:20:41.906 INFO - Executing: [close window] at URL: /session/ac5b2c71-5b1a-469
e-814c-fdd09a2061fc/window)
[3.068][INFO]: received Webriver request: ELETE /session/32b33aa585ccbbf7ba78535
882852af3/window
[WARNING:chrome_desktop_impl.cc(88)] chrome detaches, user should take care of d
irectory:C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\scoped_dir1808_7550 and C:\DOCUME~1\
ADMINI~1\LOCALS~1\Temp\scoped_dir1808_26821
[5.318][INFO]: sending Webriver response: 200 {
   "sessionId": "32b33aa585ccbbf7ba78535882852af3",
   "status": 0,
   "value": null
}
10:20:44.156 INFO - Done: /session/ac5b2c71-5b1a-469e-814c-fdd09a2061fc/window

request 请求 / response应答

一次请求会对应一次应答

POST/GET 是请求(request)两种类型；关于两种请求方式的类别参考其它资料

200 、203是 HTTP请求返回的状态码，200表示成功；

sessionid ：每一个访问服务器的客户端，都要先得到服务器端分配的一个sessionid ，就像通行证一样，只有得到sessionid的客户端才能向服务器请求想要的数据。

URL、字符类型等非常详细的记录。熟悉HTTP ，了解TCP 的三次握手四次挥手，相信你对浏览器的交互与webdriver原理会有更深入的认识。