内容摘要：
1、Selenium 1 原理
(1).测试用例（Testcase）通过Client Lib的接口向Selenium Server发送Http请求，要求和Selenium Server建立连接。
为什么要通过发送Http请求控制Selenium Server而不采用其他方式呢？从上文可以看出，Selenium Server是一个独立的中间服务器（确切地说是代理服务器），它可以架设在其他机器上！所以测试案例通过发送HTTP请求去控制Selenium Server是很正常的。
(2).Selenium Server的Launcher启动浏览器，把Selenium Core加载入浏览器页面当中，并把浏览器的代理设置为Selenium Server的Http Proxy。
(3).测试案例通过Client Lib的接口向Selenium Server发送Http请求，Selenium Server对请求进行解析，然后通过Http Proxy发送JS命令通知Selenium Core执行操作浏览器的动作。
(4).Selenium Core接收到指令后，执行操作。
(5).浏览器收到新的页面请求信息（因为在(4)中，Selenium Core的操作可能引发新的页面请求），于是发送Http请求，请求新的Web页面。
由于Selenium Server在启动浏览器时做了手脚，所以Selenium Server会接收到所有由它启动的浏览器发送的请求。
(6).Selenium Server接收到浏览器的发送的Http请求后，自己重组Http请求，获取对应的Web页面。
(7).Selenium Server的Http Proxy把接收的Web页面返回给浏览器。
2、WebDriver
WebDriver 提供了一堆用于查找和维护页面元素（DOM元素）的接口，以此方式来控制浏览器行为。目前已纳入W3C管理。
https://www.w3.org/TR/webdriver/
2.1 Webdriver 组件
在WebDriver协议里，包括local,remote,Intermidary,endpoint等概念：
·Local End：代表了WebDriver通信的客户端，通常情况下，是由一些特定语言基于通信协议组成的一套Client API。
·Remote End：remote是在通信协议的服务端。用于处理Client请求并作出响应。它包括两大类：
Intermidary node：intermidary 通常是代理，它实现了local，并代理了remote。
Endpoint ：endpoint 才是实际上的remote 端的处理的地方。和Java Web开发中的action、Webservice中的endpoint是类似的概念。
Webdriver 的通信协议是基于HTTP的以命令（command）方式组织的各种请求。WebDriver在处理一个命令时，可能会使browser执行一系列的操作。上面图中，webdriver server就是remote end，WebDriver Client就是local end。
2.2 WebDriver 协议
2.2.1 Remote End 处理流程
在local end与remote end的连接建立后，Remote End会做如下处理：
1、根据HTTP协议读取一个完整的HTTP请求，并封装成request对象。
2、根据http request method, url对请求进行匹配，找到相应的endpoint。
3、如果匹配到了error ，就发送一个error给local end，然后step 1。
4、使用sessionid进行session匹配
5、如果匹配失败（session 列表里找不到与sessionid相关联的session），响应一个error，然后step 1。
6、如果是post请求，以json方式解析requet body。如果解析成功，但并不是一个对象，或者解析失败，响应一个error给Local。然后step 1。
7、等待浏览器导航完毕
8、响应结果
2.2.2 Commands & Endpoints & 请求路由
为了控制browser的行为，提供了一系列的command，大体可以分为几类：
1）Session管理（remote 与local之间的session）
2）浏览器URL导航
3）浏览器窗口管理
4）DOM元素管理
5）JS脚本执行
6）Cookie管理
7）Alert
8）截屏
9）一些操作例如（键盘，鼠标，批处理等）
Remote在接收到这些命令时，会进行Endpoint匹配。匹配时是根据URL、http method。
他们的对应关系是：
|
Method |
URI Template |
Command |
|
POST |
/session |
|
|
DELETE |
/session/{session id} |
|
|
GET |
/status |
|
|
GET |
/session/{session id}/timeouts |
|
|
POST |
/session/{session id}/timeouts |
|
|
POST |
/session/{session id}/url |
|
|
GET |
/session/{session id}/url |
|
|
POST |
/session/{session id}/back |
|
|
POST |
/session/{session id}/forward |
|
|
POST |
/session/{session id}/refresh |
|
|
GET |
/session/{session id}/title |
|
|
GET |
/session/{session id}/window |
|
|
DELETE |
/session/{session id}/window |
|
|
POST |
/session/{session id}/window |
|
|
GET |
/session/{session id}/window/handles |
|
|
POST |
/session/{session id}/frame |
|
|
POST |
/session/{session id}/frame/parent |
|
|
GET |
/session/{session id}/window/rect |
|
|
POST |
/session/{session id}/window/rect |
|
|
POST |
/session/{session id}/window/maximize |
|
|
POST |
/session/{session id}/window/minimize |
|
|
POST |
/session/{session id}/window/fullscreen |
|
|
GET |
/session/{session id}/element/active |
|
|
POST |
/session/{session id}/element |
|
|
POST |
/session/{session id}/elements |
|
|
POST |
/session/{session id}/element/{element id}/element |
|
|
POST |
/session/{session id}/element/{element id}/elements |
|
|
GET |
/session/{session id}/element/{element id}/selected |
|
|
GET |
/session/{session id}/element/{element id}/attribute/{name} |
|
|
GET |
/session/{session id}/element/{element id}/property/{name} |
|
|
GET |
/session/{session id}/element/{element id}/css/{property name} |
|
|
GET |
/session/{session id}/element/{element id}/text |
|
|
GET |
/session/{session id}/element/{element id}/name |
|
|
GET |
/session/{session id}/element/{element id}/rect |
|
|
GET |
/session/{session id}/element/{element id}/enabled |
|
|
POST |
/session/{session id}/element/{element id}/click |
|
|
POST |
/session/{session id}/element/{element id}/clear |
|
|
POST |
/session/{session id}/element/{element id}/value |
|
|
GET |
/session/{session id}/source |
|
|
POST |
/session/{session id}/execute/sync |
|
|
POST |
/session/{session id}/execute/async |
|
|
GET |
/session/{session id}/cookie |
|
|
GET |
/session/{session id}/cookie/{name} |
|
|
POST |
/session/{session id}/cookie |
|
|
DELETE |
/session/{session id}/cookie/{name} |
|
|
DELETE |
/session/{session id)/cookie |
|
|
POST |
/session/{session id}/actions |
|
|
DELETE |
/session/{session id}/actions |
|
|
POST |
/session/{session id}/alert/dismiss |
|
|
POST |
/session/{session id}/alert/accept |
|
|
GET |
/session/{session id}/alert/text |
|
|
POST |
/session/{session id}/alert/text |
|
|
GET |
/session/{session id}/screenshot |
|
|
GET |
/session/{session id}/element/{element id}/screenshot |
2.2.3 错误消息
从上面的流程里，有多次提到发现error时，回发一个error。而实际上返回的错误需要包括
|
{ Error: // 错误码 Message://错误信息 Stacktrace:// 发生错误时的stack } |
下面是各种错误的描述：
|
Error Code |
HTTP Status |
JSON Error Code |
Description |
|
element click intercepted |
400 |
element click intercepted |
The Element Click command could not be completed because the element receiving the events is obscuring the element that was requested clicked. |
|
element not selectable |
400 |
element not selectable |
An attempt was made to select an element that cannot be selected. |
|
element not interactable |
400 |
element not interactable |
A command could not be completed because the element is notpointer- or keyboard interactable. |
|
insecure certificate |
400 |
insecure certificate |
Navigation caused the user agent to hit a certificate warning, which is usually the result of an expired or invalid TLS certificate. |
|
invalid argument |
400 |
invalid argument |
The arguments passed to a command are either invalid or malformed. |
|
invalid cookie domain |
400 |
invalid cookie domain |
An illegal attempt was made to set a cookie under a different domain than the current page. |
|
invalid coordinates |
400 |
invalid coordinates |
The coordinates provided to an interactions operation are invalid. |
|
invalid element state |
400 |
invalid element state |
A command could not be completed because the element is in an invalid state, e.g. attempting to click an element that is no longer attached to the document. |
|
invalid selector |
400 |
invalid selector |
Argument was an invalid selector. |
|
invalid session id |
404 |
invalid session id |
Occurs if the given session id is not in the list of active sessions, meaning the session either does not exist or that it’s not active. |
|
javascript error |
500 |
javascript error |
An error occurred while executing JavaScript supplied by the user. |
|
move target out of bounds |
500 |
move target out of bounds |
The target for mouse interaction is not in the browser’s viewport and cannot be brought into that viewport. |
|
no such alert |
400 |
no such alert |
An attempt was made to operate on a modal dialog when one was not open. |
|
no such cookie |
404 |
no such cookie |
No cookie matching the given path name was found amongst the associated cookies of the current browsing context’sactive document. |
|
no such element |
404 |
no such element |
An element could not be located on the page using the given search parameters. |
|
no such frame |
400 |
no such frame |
A command to switch to a frame could not be satisfied because the frame could not be found. |
|
no such window |
400 |
no such window |
A command to switch to a window could not be satisfied because the window could not be found. |
|
script timeout |
408 |
script timeout |
A script did not complete before its timeout expired. |
|
session not created |
500 |
session not created |
A new session could not be created. |
|
stale element reference |
400 |
stale element reference |
A command failed because the referenced element is no longer attached to the DOM. |
|
timeout |
408 |
timeout |
An operation did not complete before its timeout expired. |
|
unable to set cookie |
500 |
unable to set cookie |
A command to set a cookie’s value could not be satisfied. |
|
unable to capture screen |
500 |
unable to capture screen |
A screen capture was made impossible. |
|
unexpected alert open |
500 |
unexpected alert open |
A modal dialog was open, blocking this operation. |
|
unknown command |
404 |
unknown command |
A command could not be executed because the remote end is not aware of it. |
|
unknown error |
500 |
unknown error |
An unknown error occurred in the remote end while processing the command. |
|
unknown method |
405 |
unknown method |
The requested command matched a known URL but did not match an method for that URL. |
|
unsupported operation |
500 |
unsupported operation |
Indicates that a command that should have executed properly cannot be supported for some reason. |
2.3 WebDriver 配置
为了支持各个浏览器，自然要由各个浏览器厂商来实现这一套协议。各个厂商的浏览器毕竟不同，各有各自的一些特性等。为了更好的支持各个浏览器，各个厂商可以在创建Session时，指定一些自定义的配置。
一些标准的配置有：
|
Capability |
Key |
Value Type |
Description |
|
Browser name |
"browserName" |
string |
Identifies the user agent. |
|
Browser version |
"browserVersion" |
string |
Identifies the version of the user agent. |
|
Platform name |
"platformName" |
string |
Identifies the operating system of the endpoint node. |
|
Accept insecure TLS certificates |
"acceptInsecureCerts" |
boolean |
Indicates whether untrusted and self-signed TLS certificates are implicitly trusted onnavigation for the duration of the session. |
|
Page load strategy |
"pageLoadStrategy" |
string |
Defines the current session’spage load strategy. |
|
Proxy configuration |
"proxy" |
JSONObject |
Defines the current session’sproxy configuration. |
|
Window dimensioning/positioning |
"setWindowRect" |
boolean |
Indicates whether the remote end supports all of thecommands in Resizing and Positioning Windows. |
|
"timeouts" |
JSONObject |
Describes the timeouts imposed on certain session operations. |
|
|
Unhandled prompt behavior |
"unhandledPromptBehavior" |
string |
Describes the current session’s user prompt handler. |
除此之外，各个厂商可以自定义自己的配置。
具体有哪些配置，可以参考：
https://github.com/SeleniumHQ/selenium/wiki/DesiredCapabilities
整理后的配置参见：http://www.cnblogs.com/f1194361820/p/7419522.html
3、Selenium 2
Selenium 2 = WebDriver + Selenium1
只需要将Selenium 1 中的RC Server ，RC Client替换成 WebDriver ，就成了Selenium2的结构。