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。
其它还包括操作系统版本，浏览器类型、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。