Selenium WebDriver原理（二）：Selenium是如何操纵浏览器的？

前言

上一篇文章《selenium webdriver 是怎么运行的》用了一个简单的例子——搭出租车，形象地讲解selenium webdriver 是如何运行的，而这一篇文章可以理解为深入了解selenium是如何和浏览器驱动进行交互，也可以认为是乙醇老师写的《selenium是如何启动浏览器的》 文章的2.0版本 。

环境准备：

python 3.0以上
selenium 3.0以上
浏览器 Chrome
浏览器驱动 ChromeDriver
接口测试工具

小编的环境：

python 3.6.4
selenium 3.13
浏览器 ：Chrome 68
浏览器驱动： ChromeDriver 2.38
接口测试工具：python requests

首先，我们运行下述代码块

#encoding:utf8
from selenium import webdriver
import logging
logging.basicConfig(level=logging.DEBUG)
dr = webdriver.Chrome()
dr.implicitly_wait(10)
#打开深圳-逸遥 博客园首页
dr.get('https://www.cnblogs.com/snailrunning')
#定位深圳-逸遥 第一篇博文标题
el = dr.find_element_by_css_selector('.postTitle a')
#点击第一篇博文标题
el.click()

运行结果：

DEBUG:selenium.webdriver.remote.remote_connection:
POST http://127.0.0.1:4102/session 
{"capabilities": {"firstMatch": [{}], "alwaysMatch": {"browserName":     "chrome", "platformName": "any", "goog:chromeOptions": {"extensions": [], "args": []}}}, 
 "desiredCapabilities": {"browserName": "chrome", "version": "", "platform": "ANY", "goog:chromeOptions": {"extensions": [], "args": []}}}
DEBUG:selenium.webdriver.remote.remote_connection:
b'{"sessionId":"7cbbff953318267ef0089dc66f127051",
   "status":0,
   "value":{"acceptInsecureCerts":false,"acceptSslCerts":false,"applicationCacheEnabled":false,"browserConnectionEnabled":false,"browserName":"chrome","chrome":{"chromedriverVersion":"2.38.552522 (437e6fbedfa8762dec75e2c5b3ddb86763dc9dcb)","userDataDir":"C:\\Users\\lenovo\\AppData\\Local\\Temp\\scoped_dir13812_4179"},"cssSelectorsEnabled":true,"databaseEnabled":false,"handlesAlerts":true,"hasTouchScreen":false,"javascriptEnabled":true,"locationContextEnabled":true,"mobileEmulationEnabled":false,"nativeEvents":true,"networkConnectionEnabled":false,"pageLoadStrategy":"normal","platform":"Windows NT","rotatable":false,"setWindowRect":true,"takesHeapSnapshot":true,"takesScreenshot":true,"unexpectedAlertBehaviour":"","version":"68.0.3440.106","webStorageEnabled":true}}'
DEBUG:selenium.webdriver.remote.remote_connection:Finished Request

DEBUG:selenium.webdriver.remote.remote_connection:
POST 
http://127.0.0.1:4102/session/7cbbff953318267ef0089dc66f127051/timeouts/implicit_wait 
{"ms": 10000.0, "sessionId": "7cbbff953318267ef0089dc66f127051"}
DEBUG:selenium.webdriver.remote.remote_connection:
b'{"sessionId":"7cbbff953318267ef0089dc66f127051","status":0,"value":null}'
DEBUG:selenium.webdriver.remote.remote_connection:Finished Request

DEBUG:selenium.webdriver.remote.remote_connection:
POST http://127.0.0.1:4102/session/7cbbff953318267ef0089dc66f127051/url 
{"url": "https://www.cnblogs.com/snailrunning", "sessionId": "7cbbff953318267ef0089dc66f127051"}
DEBUG:selenium.webdriver.remote.remote_connection:
b'{"sessionId":"7cbbff953318267ef0089dc66f127051","status":0,"value":null}'
DEBUG:selenium.webdriver.remote.remote_connection:Finished Request

DEBUG:selenium.webdriver.remote.remote_connection:
POST 
http://127.0.0.1:4102/session/7cbbff953318267ef0089dc66f127051/element 
{"using": "css selector", "value": ".postTitle a", "sessionId": "7cbbff953318267ef0089dc66f127051"}
DEBUG:selenium.webdriver.remote.remote_connection:
b'{"sessionId":"7cbbff953318267ef0089dc66f127051","status":0,"value":{"ELEMENT":"0.3612689441010788-1"}}'
DEBUG:selenium.webdriver.remote.remote_connection:Finished Request

DEBUG:selenium.webdriver.remote.remote_connection:
POST http://127.0.0.1:4102/session/7cbbff953318267ef0089dc66f127051/element/0.3612689441010788-1/click
{"id": "0.3612689441010788-1", "sessionId": "7cbbff953318267ef0089dc66f127051"}
DEBUG:selenium.webdriver.remote.remote_connection:
b'{"sessionId":"7cbbff953318267ef0089dc66f127051","status":0,"value":null}'
DEBUG:selenium.webdriver.remote.remote_connection:Finished Request

从上述代码运行结果，我们可以得出以下结论

• 对于每个Selenium命令，都会创建一个HTTP请求并将其发送到浏览器驱动程序
• 每一个命令的执行结果都会返回给自动化代码
• ChromeDirver创建session时打开了浏览器
• Selenium代码和浏览器驱动的交互都根据ChromeDriver创建的sessionId

文章到这里，很多测试的同学看了会头晕，没关系，我们现在先根据上述返回的结果来拆解一下请求的接口和返回，以及我们通过接口工具来模拟Selenium自动化代码来操纵浏览器

1、启动浏览器接口

请求方式：post  
请求url : http://127.0.0.1:4102/session
请求body: {"capabilities": {"firstMatch": [{}], "alwaysMatch": {"browserName":     "chrome", "platformName": "any", "goog:chromeOptions": {"extensions": [], "args": []}}}, 
 "desiredCapabilities": {"browserName": "chrome", "version": "", "platform": "ANY", "goog:chromeOptions": {"extensions": [], "args": []}}}
 
返回body : b'{"sessionId":"7cbbff953318267ef0089dc66f127051",
   "status":0,
   "value":{"acceptInsecureCerts":false,"acceptSslCerts":false,"applicationCacheEnabled":false,"browserConnectionEnabled":false,"browserName":"chrome","chrome":{"chromedriverVersion":"2.38.552522 (437e6fbedfa8762dec75e2c5b3ddb86763dc9dcb)","userDataDir":"C:\\Users\\lenovo\\AppData\\Local\\Temp\\scoped_dir13812_4179"},"cssSelectorsEnabled":true,"databaseEnabled":false,"handlesAlerts":true,"hasTouchScreen":false,"javascriptEnabled":true,"locationContextEnabled":true,"mobileEmulationEnabled":false,"nativeEvents":true,"networkConnectionEnabled":false,"pageLoadStrategy":"normal","platform":"Windows NT","rotatable":false,"setWindowRect":true,"takesHeapSnapshot":true,"takesScreenshot":true,"unexpectedAlertBehaviour":"","version":"68.0.3440.106","webStorageEnabled":true}}'

1.1 开启ChomeDriver

Starting ChromeDriver 2.38.552522   开启ChromeDriver 版本号2.38.552522
(437e6fbedfa8762dec75e2c5b3ddb86763dc9dcb) on port 9515 监听的端口是9515
Only local connections are allowed. ； 只允许本地链接

1.2 构造请求

请求方式 ：POST
请求地址 ：http://localhost:9515/session
请求body ：{"capabilities": {"firstMatch": [{}], "alwaysMatch": {"browserName":     "chrome", "platformName": "any", "goog:chromeOptions": {"extensions": [], "args": []}}}, 
 "desiredCapabilities": {"browserName": "chrome", "version": "", "platform": "ANY", "goog:chromeOptions": {"extensions": [], "args": []}}}

1.3 使用python requests 向 ChromeDriver发送请求

#encoding:utf8
import requests
session_url = 'http://localhost:9515/session'
session_pars = {"capabilities": {"firstMatch": [{}], 
                      "alwaysMatch": {"browserName": "chrome",
                                      "platformName": "any", 
                                      "goog:chromeOptions": {"extensions": [], "args": []}}}, 
                "desiredCapabilities": {"browserName": "chrome", 
                             "version": "", "platform": "ANY", "goog:chromeOptions": {"extensions": [], "args": []}}}
r_session = requests.post(session_url,json=session_pars)
print(r_session.json())

此时Chrome浏览器被打开

1.4 查看返回结果

{
    "sessionId": "b2801b5dc58b15e76d0d3295b04d295c",
    "status": 0,
    "value": {
        "acceptInsecureCerts": false,
        "acceptSslCerts": false,
        "applicationCacheEnabled": false,
        "browserConnectionEnabled": false,
        "browserName": "chrome",
        "chrome": {
            "chromedriverVersion": "2.38.552522 (437e6fbedfa8762dec75e2c5b3ddb86763dc9dcb)",
            "userDataDir": "C:\Users\lenovo\AppData\Local\Temp\scoped_dir1792_5142"
        },
        "cssSelectorsEnabled": true,
        "databaseEnabled": false,
        "handlesAlerts": true,
        "hasTouchScreen": false,
        "javascriptEnabled": true,
        "locationContextEnabled": true,
        "mobileEmulationEnabled": false,
        "nativeEvents": true,
        "networkConnectionEnabled": false,
        "pageLoadStrategy": "normal",
        "platform": "Windows NT",
        "rotatable": false,
        "setWindowRect": true,
        "takesHeapSnapshot": true,
        "takesScreenshot": true,
        "unexpectedAlertBehaviour": "",
        "version": "68.0.3440.106",
        "webStorageEnabled": true
    }
}

2、打开深圳-逸遥的博客园

2.1 构造请求

请求方式 ：POST
请求地址 ：http://localhost:9515/session/:sessionId/url

注意： 上述地址中的 ":sessionId"
要用启动浏览器的请求返回结果中的sessionId的值
例如：我刚刚发送请求，启动浏览器，返回结果中"sessionId": "b2801b5dc58b15e76d0d3295b04d295c"  
然后我构造 导航到"深圳-逸遥的博客园"的请求地址
请求地址：http://localhost:9515/session/b2801b5dc58b15e76d0d3295b04d295c/url

请求body ：{"url": "https://www.cnblogs.com/snailrunning", "sessionId": "b2801b5dc58b15e76d0d3295b04d295c"}

2.2 使用python requests 向 ChromeDriver发送请求

#encoding:utf8
import requests
url = 'http://localhost:9515/session/b2801b5dc58b15e76d0d3295b04d295c/url'
pars = {"url": "https://www.cnblogs.com/snailrunning", "sessionId": "b2801b5dc58b15e76d0d3295b04d295c"}
r = requests.post(url,json=pars)
print(r.json())

浏览器打开”深圳-逸遥“的博客园

2.3 查看请求返回结果

{'sessionId': 'b2801b5dc58b15e76d0d3295b04d295c', 'status': 0, 'value': None}

3、定位”深圳-逸遥“第一篇博文的标题

3.1 构造请求

请求方式 ：POST
请求地址 ：http://localhost:9515/session/:sessionId/element

注意： 上述地址中的 ":sessionId"
要用启动浏览器的请求返回结果中的sessionId的值
例如：我刚刚发送请求，启动浏览器，返回结果中"sessionId": "b2801b5dc58b15e76d0d3295b04d295c"  
然后我构造 查找页面元素的请求地址
请求地址：http://localhost:9515/session/b2801b5dc58b15e76d0d3295b04d295c/element

请求body ：{"using": "css selector", "value": ".postTitle a", "sessionId": "b2801b5dc58b15e76d0d3295b04d295c"}

3.2 使用python requests 向 ChromeDriver发送请求

#encoding:utf8
import requests
url = 'http://localhost:9515/session/b2801b5dc58b15e76d0d3295b04d295c/element'
pars = {"using": "css selector", "value": ".postTitle a", "sessionId": "b2801b5dc58b15e76d0d3295b04d295c"}
r = requests.post(url,json=pars)
print(r.json())

3.3 查看请求返回的结果

{'sessionId': 'b2801b5dc58b15e76d0d3295b04d295c', 'status': 0, 'value': {'ELEMENT': '0.11402119390850629-1'}}

• 返回结果中的{'ELEMENT': '0.11402119390850629-1'}
• 官方文档称为：找到的元素的WebElement JSON对象，表示页面上的DOM元素，同时服务器分配给ELEMENT的值是不透明的（随机的） 这个ELEMENT的值会在针对该元素发出的所有后续命令中使用。

### 4、点击”深圳-逸遥“博客 第一篇博文的标题 4.1 构造请求 ``` 请求方式 ：POST 请求地址 ：http://localhost:9515/session/:sessionId/element/:id/click

注意： 上述地址中的 ":sessionId"
要用启动浏览器的请求返回结果中的sessionId的值
:id 要用元素定位请求后返回ELEMENT的值

例如：我刚刚发送请求，启动浏览器，返回结果中"sessionId": "b2801b5dc58b15e76d0d3295b04d295c"
元素定位,返回ELEMENT的值"0.11402119390850629-1"

然后我构造 点击页面元素的请求地址
请求地址：http://localhost:9515/session/b2801b5dc58b15e76d0d3295b04d295c/element/0.11402119390850629-1/click

请求body ：{"id": "0.11402119390850629-1", "sessionId": "b2801b5dc58b15e76d0d3295b04d295c"}

4.2  使用python requests 向 ChromeDriver发送请求 

encoding:utf8

import requests
url = 'http://localhost:9515/session/b2801b5dc58b15e76d0d3295b04d295c/element/0.11402119390850629-1/click'
pars ={"id": "0.5930642995574296-1", "sessionId": "b2801b5dc58b15e76d0d3295b04d295c"}
r = requests.post(url,json=pars)
print(r.json())

<br>

####  浏览器导航到“深圳-逸遥”首页的第一篇博文
![image](https://wx2.sinaimg.cn/mw690/6e01037bgy1fucuuhddl9j20jk0o9abt.jpg)  

4.3  查看请求返回的结果

{'sessionId': 'b2801b5dc58b15e76d0d3295b04d295c', 'status': 0, 'value': None}

<br>
#### 文章末尾再炒一下旧饭
- 对于每个Selenium命令，都会创建一个HTTP请求并将其发送到浏览器驱动程序
- 每一个命令的执行结果都会返回给自动化代码
- 响应状态代码 status 等于0 ，即表示命令执行成功
- ChromeDirver创建session时打开了浏览器
- Selenium代码和浏览器驱动的交互都根据ChromeDriver创建的sessionId

<br>

#### 附带上述操作相关的接口文档——[selenium webdriver JsonWireProtocol](https://github.com/SeleniumHQ/selenium/wiki/JsonWireProtocol)

[WebDriver JsonWireProtocol 基本术语和概念 ](https://github.com/SeleniumHQ/selenium/wiki/JsonWireProtocol#basic-terms-and-concepts)

[请求响应说明](https://github.com/SeleniumHQ/selenium/wiki/JsonWireProtocol#messages)

[启动浏览器，创建sessionId](https://github.com/SeleniumHQ/selenium/wiki/JsonWireProtocol#session-1)

[导航指定url](https://github.com/SeleniumHQ/selenium/wiki/JsonWireProtocol#post-sessionsessionidurl)

[元素定位](https://github.com/SeleniumHQ/selenium/wiki/JsonWireProtocol#sessionsessionidelement)

[元素点击操作](https://github.com/SeleniumHQ/selenium/wiki/JsonWireProtocol#sessionsessionidelementidclick)

<br>
#### 参考文章
[乙醇 - selenium是如何启动浏览器的](https://www.cnblogs.com/nbkhic/p/9249330.html)

#### 推荐阅读
[乙醇 - selenium是如何启动浏览器的](https://www.cnblogs.com/nbkhic/p/9249330.html)

[深圳-逸遥 - Selenium WebDriver原理（一）：Selenium WebDriver 是怎么工作的？](https://www.cnblogs.com/snailrunning/p/9413446.html)

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