前言

Selenium是一個用于Web應用程序自動化測試工具。Selenium測試直接運行在瀏覽器中，就像真正的用戶在操作一樣。支持的瀏覽器包括IE（7, 8, 9, 10, 11），Mozilla Firefox，Safari，Google Chrome，Opera等。

主要功能包括：測試與瀏覽器的兼容性——測試你的應用程序看是否能夠很好得工作在不同瀏覽器和操作系統之上。

測試系統功能——創建回歸測試檢驗軟件功能和用戶需求。支持自動錄制動作和自動生成 .Net、Java、Perl等不同語言的測試腳本(這里主要是針對selenium ide)

一、selenium歷程

04年，誕生了Selenium Core，Selenium Core是基于瀏覽器并且采用JavaScript編程語言的測試工具，運行在瀏覽器的安全沙箱中，設計理念是將待測試產品、Selenium Core和測試腳本均部署到同一臺服務器上來完成自動化測試的工作。

05年，Selenium RC誕生，就是selenium1 ，這個時候，Selenium Core其實是Selenium RC的核心。

Selenium RC讓待測試產品、Selenium Core和測試腳本三者分散在不同的服務器上。（測試腳本只關心將HTTP請求發送到指定的URL上，selenium本身不需要關心HTTP請求由于什么程序編程語言編寫而成）

Selenium RC包括兩部分：一個是Selenium RC Server，一個是提供各種編程語言的客戶端驅動來編寫測試腳本

07年，Webdriver誕生，WebDriver的設計理念是將端到端測試與底層具體的測試工具分隔離，并采用設計模式Adapter適配器來達到目標。WebDriver的API組織更多的是面向對象。

08/09年，selenium2誕生，selenium2其實是selenium rc和webdriver的合并，合并的根本原因是相互補充各自的缺點

09年，selenium3誕生，這個版本剔除了selenium rc ， 主要由 selenium webdriver和selenium Grid組成， 我們日常使用的其實就是selenium webdriver，至于selenium grid是一個分布式實現自動化測試的工具

那么今天我們就要說說selenium3(selenium webdriver)的工作原理，下面簡稱selenium(以上具體時間可能不太準確，我也是通過網絡資料了解到的，拋磚引玉^-^)

二、selenium原理

我們使用Selenium實現自動化測試，主要需要3個東西

1.測試腳本，可以是python，java編寫的腳本程序（也可以叫做client端）

2.瀏覽器驅動, 這個驅動是根據不同的瀏覽器開發的，不同的瀏覽器使用不同的webdriver驅動程序且需要對應相應的瀏覽器版本，比如：geckodriver.exe(chrome)

3.瀏覽器，目前selenium支持市面上大多數瀏覽器，如：火狐，谷歌，IE等

三、selenium腳本

先看一個簡單的代碼

""" from selenium import webdriverdr = webdriver.Chrome() # 打開瀏覽器

執行上述代碼，我們會發現程序打開了Chrome瀏覽器(前提：你已經正確配置了chrome的驅動和對應版本)

那么selenium是如何實現這個過程的呢？ok，我們今天就通過分析源碼的方式來理解selenium的工作原理

四、源碼分析

查看weddriver源碼(按住Ctrl鍵，鼠標點擊Chrome)

C:\Python36\Lib\site-packages\selenium\webdriver\chrome\webdriver.py

1 class WebDriver(RemoteWebDriver):2 """3 Controls the ChromeDriver and allows you to drive the browser.4 5 You will need to download the ChromeDriver executable from6 http://chromedriver.storage.googleapis.com/index.html7 """8 9 def __init__(self, executable_path="chromedriver", port=0, 10 options=None, service_args=None, 11 desired_capabilities=None, service_log_path=None, 12 chrome_options=None, keep_alive=True): 13 """ 14 Creates a new instance of the chrome driver. 15 16 Starts the service and then creates new instance of chrome driver. 17 18 :Args: 19 - executable_path - path to the executable. If the default is used it assumes the executable is in the $PATH 20 - port - port you would like the service to run, if left as 0, a free port will be found. 21 - options - this takes an instance of ChromeOptions 22 - service_args - List of args to pass to the driver service 23 - desired_capabilities - Dictionary object with non-browser specific 24 capabilities only, such as "proxy" or "loggingPref". 25 - service_log_path - Where to log information from the driver. 26 - chrome_options - Deprecated argument for options 27 - keep_alive - Whether to configure ChromeRemoteConnection to use HTTP keep-alive. 28 """ 29 if chrome_options: 30 warnings.warn('use options instead of chrome_options', 31 DeprecationWarning, stacklevel=2) 32 options = chrome_options 33 34 if options is None: 35 # desired_capabilities stays as passed in 36 if desired_capabilities is None: 37 desired_capabilities = self.create_options().to_capabilities() 38 else: 39 if desired_capabilities is None: 40 desired_capabilities = options.to_capabilities() 41 else: 42 desired_capabilities.update(options.to_capabilities()) 43 44 self.service = Service( 45 executable_path, 46 port=port, 47 service_args=service_args, 48 log_path=service_log_path) 49 self.service.start() 50 51 try: 52 RemoteWebDriver.__init__( 53 self, 54 command_executor=ChromeRemoteConnection( 55 remote_server_addr=self.service.service_url, 56 keep_alive=keep_alive), 57 desired_capabilities=desired_capabilities) 58 except Exception: 59 self.quit() 60 raise 61 self._is_remote = False

通過源碼中的44-49行發現，初始化了一個service對象，然后調用了start()方法，那么我們繼續看下一49行的start()方法到底實現了什么功能？

C:\Python36\Lib\site-packages\selenium\webdriver\common\service.py

1 def start(self):2 """3 Starts the Service.4 5 :Exceptions:6 - WebDriverException : Raised either when it can't start the service7 or when it can't connect to the service8 """9 try: 10 cmd = [self.path] 11 cmd.extend(self.command_line_args()) 12 self.process = subprocess.Popen(cmd, env=self.env, 13 close_fds=platform.system() != 'Windows', 14 stdout=self.log_file, 15 stderr=self.log_file, 16 stdin=PIPE) 17 except TypeError: 18 raise 19 except OSError as err: 20 if err.errno == errno.ENOENT: 21 raise WebDriverException( 22 "'%s' executable needs to be in PATH. %s" % ( 23 os.path.basename(self.path), self.start_error_message) 24 ) 25 elif err.errno == errno.EACCES: 26 raise WebDriverException( 27 "'%s' executable may have wrong permissions. %s" % ( 28 os.path.basename(self.path), self.start_error_message) 29 ) 30 else: 31 raise 32 except Exception as e: 33 raise WebDriverException( 34 "The executable %s needs to be available in the path. %s\n%s" % 35 (os.path.basename(self.path), self.start_error_message, str(e))) 36 count = 0 37 while True: 38 self.assert_process_still_running() 39 if self.is_connectable(): 40 break 41 count += 1 42 time.sleep(1) 43 if count == 30: 44 raise WebDriverException("Can not connect to the Service %s" % self.path)

我們發現9-16行其實就是執行了一個cmd命令，命令的作用就是啟動了chromedriver.exeChrome瀏覽器的驅動程序

這里我們需要注意一點: 下載的瀏覽器驅動一定要配置到環境變量中，或者放到python的根目錄下，便于程序在執行驅動的時候查找

這個過程和我們手動啟動瀏覽器驅動是一樣的效果，類似下面的結果

啟動驅動程序后，綁定端口號9515，且只允許本地訪問這個服務，其實我們可以查看一下我們本地電腦任務管理器，確實開啟了一個服務進程程序

第一步工作我們已經知道了執行測試腳本webdriver.Chrome()會自動執行chromedriver.exe驅動程序，然后開啟一個進程

五、如何打開瀏覽器

我們繼續看源碼 C:\Python36\Lib\site-packages\selenium\webdriver\chrome\webdriver.py 的51-57行代碼，調用了父類RemoteWebDriver 的初始化方法，我們看這個方法做了什么事？

C:\Python36\Lib\site-packages\selenium\webdriver\remote\webdriver.py

1 class WebDriver(object):2 """3 Controls a browser by sending commands to a remote server.4 This server is expected to be running the WebDriver wire protocol5 as defined at6 https://github.com/SeleniumHQ/selenium/wiki/JsonWireProtocol7 8 :Attributes:9 - session_id - String ID of the browser session started and controlled by this WebDriver. 10 - capabilities - Dictionaty of effective capabilities of this browser session as returned 11 by the remote server. See https://github.com/SeleniumHQ/selenium/wiki/DesiredCapabilities 12 - command_executor - remote_connection.RemoteConnection object used to execute commands. 13 - error_handler - errorhandler.ErrorHandler object used to handle errors. 14 """ 15 16 _web_element_cls = WebElement 17 18 def __init__(self, command_executor='http://127.0.0.1:4444/wd/hub', 19 desired_capabilities=None, browser_profile=None, proxy=None, 20 keep_alive=False, file_detector=None, options=None): 21 """ 22 Create a new driver that will issue commands using the wire protocol. 23 24 :Args: 25 - command_executor - Either a string representing URL of the remote server or a custom 26 remote_connection.RemoteConnection object. Defaults to 'http://127.0.0.1:4444/wd/hub'. 27 - desired_capabilities - A dictionary of capabilities to request when 28 starting the browser session. Required parameter. 29 - browser_profile - A selenium.webdriver.firefox.firefox_profile.FirefoxProfile object. 30 Only used if Firefox is requested. Optional. 31 - proxy - A selenium.webdriver.common.proxy.Proxy object. The browser session will 32 be started with given proxy settings, if possible. Optional. 33 - keep_alive - Whether to configure remote_connection.RemoteConnection to use 34 HTTP keep-alive. Defaults to False. 35 - file_detector - Pass custom file detector object during instantiation. If None, 36 then default LocalFileDetector() will be used. 37 - options - instance of a driver options.Options class 38 """ 39 capabilities = {} 40 if options is not None: 41 capabilities = options.to_capabilities() 42 if desired_capabilities is not None: 43 if not isinstance(desired_capabilities, dict): 44 raise WebDriverException("Desired Capabilities must be a dictionary") 45 else: 46 capabilities.update(desired_capabilities) 47 if proxy is not None: 48 warnings.warn("Please use FirefoxOptions to set proxy", 49 DeprecationWarning, stacklevel=2) 50 proxy.add_to_capabilities(capabilities) 51 self.command_executor = command_executor 52 if type(self.command_executor) is bytes or isinstance(self.command_executor, str): 53 self.command_executor = RemoteConnection(command_executor, keep_alive=keep_alive) 54 self._is_remote = True 55 self.session_id = None 56 self.capabilities = {} 57 self.error_handler = ErrorHandler() 58 self.start_client() 59 if browser_profile is not None: 60 warnings.warn("Please use FirefoxOptions to set browser profile", 61 DeprecationWarning, stacklevel=2) 62 self.start_session(capabilities, browser_profile) 63 self._switch_to = SwitchTo(self) 64 self._mobile = Mobile(self) 65 self.file_detector = file_detector or LocalFileDetector()

這里有一行最重要的代碼，62行self.start_session(capabilities, browser_profile) 這個方法，繼續看一下這個方法的源碼做了什么工作

1 def start_session(self, capabilities, browser_profile=None):2 """3 Creates a new session with the desired capabilities.4 5 :Args:6 - browser_name - The name of the browser to request.7 - version - Which browser version to request.8 - platform - Which platform to request the browser on.9 - javascript_enabled - Whether the new session should support JavaScript. 10 - browser_profile - A selenium.webdriver.firefox.firefox_profile.FirefoxProfile object. Only used if Firefox is requested. 11 """ 12 if not isinstance(capabilities, dict): 13 raise InvalidArgumentException("Capabilities must be a dictionary") 14 if browser_profile: 15 if "moz:firefoxOptions" in capabilities: 16 capabilities["moz:firefoxOptions"]["profile"] = browser_profile.encoded 17 else: 18 capabilities.update({'firefox_profile': browser_profile.encoded}) 19 w3c_caps = _make_w3c_caps(capabilities) 20 parameters = {"capabilities": w3c_caps, 21 "desiredCapabilities": capabilities} 22 response = self.execute(Command.NEW_SESSION, parameters) 23 if 'sessionId' not in response: 24 response = response['value'] 25 self.session_id = response['sessionId'] 26 self.capabilities = response.get('value') 27 28 # if capabilities is none we are probably speaking to 29 # a W3C endpoint 30 if self.capabilities is None: 31 self.capabilities = response.get('capabilities') 32 33 # Double check to see if we have a W3C Compliant browser 34 self.w3c = response.get('status') is None 35 self.command_executor.w3c = self.w3c

分析這部分源碼可以發現22行是向地址localhost:9515/session發送了一個post請求，參數是json格式的，然后返回特定的響應信息給程序(這里主要就是新建了一個sessionid)，最終打開了瀏覽器

ok，打開瀏覽器的操作完成了

六、如何執行對應操作

查看C:\Python36\Lib\site-packages\selenium\webdriver\chrome\webdriver.py源碼(第一個源碼中的51-57行)

51 try: 52 RemoteWebDriver.__init__( 53 self, 54 command_executor=ChromeRemoteConnection( 55 remote_server_addr=self.service.service_url, 56 keep_alive=keep_alive), 57 desired_capabilities=desired_capabilities)

點擊ChromeRemoteConnection查看一下源碼

1 from selenium.webdriver.remote.remote_connection import RemoteConnection2 3 4 class ChromeRemoteConnection(RemoteConnection):5 6 def __init__(self, remote_server_addr, keep_alive=True):7 RemoteConnection.__init__(self, remote_server_addr, keep_alive)8 self._commands["launchApp"] = ('POST', '/session/$sessionId/chromium/launch_app')9 self._commands["setNetworkConditions"] = ('POST', '/session/$sessionId/chromium/network_conditions') 10 self._commands["getNetworkConditions"] = ('GET', '/session/$sessionId/chromium/network_conditions') 11 self._commands['executeCdpCommand'] = ('POST', '/session/$sessionId/goog/cdp/execute')

第7行訪問的是localhost:9515/session地址，第8-11行，定義了一些和我們使用的瀏覽器(chrome)特有的接口地址，我們再看一下父類RemoteConnection里面源碼

C:\Python36\Lib\site-packages\selenium\webdriver\remote\remote_connection.py:RemoteConnection

1 self._commands = {2 Command.STATUS: ('GET', '/status'),3 Command.NEW_SESSION: ('POST', '/session'),4 Command.GET_ALL_SESSIONS: ('GET', '/sessions'),5 Command.QUIT: ('DELETE', '/session/$sessionId'),6 Command.GET_CURRENT_WINDOW_HANDLE:7 ('GET', '/session/$sessionId/window_handle'),8 Command.W3C_GET_CURRENT_WINDOW_HANDLE:9 ('GET', '/session/$sessionId/window'),10 Command.GET_WINDOW_HANDLES:11 ('GET', '/session/$sessionId/window_handles'),12 Command.W3C_GET_WINDOW_HANDLES:13 ('GET', '/session/$sessionId/window/handles'),14 Command.GET: ('POST', '/session/$sessionId/url'),15 Command.GO_FORWARD: ('POST', '/session/$sessionId/forward'),16 Command.GO_BACK: ('POST', '/session/$sessionId/back'),17 Command.REFRESH: ('POST', '/session/$sessionId/refresh'),18 Command.EXECUTE_SCRIPT: ('POST', '/session/$sessionId/execute'),19 Command.W3C_EXECUTE_SCRIPT:20 ('POST', '/session/$sessionId/execute/sync'),21 Command.W3C_EXECUTE_SCRIPT_ASYNC:22 ('POST', '/session/$sessionId/execute/async'),23 Command.GET_CURRENT_URL: ('GET', '/session/$sessionId/url'),24 Command.GET_TITLE: ('GET', '/session/$sessionId/title'),25 Command.GET_PAGE_SOURCE: ('GET', '/session/$sessionId/source'),26 Command.SCREENSHOT: ('GET', '/session/$sessionId/screenshot'),27 Command.ELEMENT_SCREENSHOT: ('GET', '/session/$sessionId/element/$id/screenshot'),28 Command.FIND_ELEMENT: ('POST', '/session/$sessionId/element'),29 Command.FIND_ELEMENTS: ('POST', '/session/$sessionId/elements'),30 Command.W3C_GET_ACTIVE_ELEMENT: ('GET', '/session/$sessionId/element/active'),31 Command.GET_ACTIVE_ELEMENT:32 ('POST', '/session/$sessionId/element/active'),33 Command.FIND_CHILD_ELEMENT:34 ('POST', '/session/$sessionId/element/$id/element'),35 Command.FIND_CHILD_ELEMENTS:36 ('POST', '/session/$sessionId/element/$id/elements'),37 Command.CLICK_ELEMENT: ('POST', '/session/$sessionId/element/$id/click'),38 Command.CLEAR_ELEMENT: ('POST', '/session/$sessionId/element/$id/clear'),39 Command.SUBMIT_ELEMENT: ('POST', '/session/$sessionId/element/$id/submit'),40 Command.GET_ELEMENT_TEXT: ('GET', '/session/$sessionId/element/$id/text'),41 Command.SEND_KEYS_TO_ELEMENT:42 ('POST', '/session/$sessionId/element/$id/value'),43 Command.SEND_KEYS_TO_ACTIVE_ELEMENT:44 ('POST', '/session/$sessionId/keys'),45 Command.UPLOAD_FILE: ('POST', "/session/$sessionId/file"),46 Command.GET_ELEMENT_VALUE:47 ('GET', '/session/$sessionId/element/$id/value'),48 Command.GET_ELEMENT_TAG_NAME:49 ('GET', '/session/$sessionId/element/$id/name'),50 Command.IS_ELEMENT_SELECTED:51 ('GET', '/session/$sessionId/element/$id/selected'),52 Command.SET_ELEMENT_SELECTED:53 ('POST', '/session/$sessionId/element/$id/selected'),54 Command.IS_ELEMENT_ENABLED:55 ('GET', '/session/$sessionId/element/$id/enabled'),56 Command.IS_ELEMENT_DISPLAYED:57 ('GET', '/session/$sessionId/element/$id/displayed'),58 Command.GET_ELEMENT_LOCATION:59 ('GET', '/session/$sessionId/element/$id/location'),60 Command.GET_ELEMENT_LOCATION_ONCE_SCROLLED_INTO_VIEW:61 ('GET', '/session/$sessionId/element/$id/location_in_view'),62 Command.GET_ELEMENT_SIZE:63 ('GET', '/session/$sessionId/element/$id/size'),64 Command.GET_ELEMENT_RECT:65 ('GET', '/session/$sessionId/element/$id/rect'),66 Command.GET_ELEMENT_ATTRIBUTE:67 ('GET', '/session/$sessionId/element/$id/attribute/$name'),68 Command.GET_ELEMENT_PROPERTY:69 ('GET', '/session/$sessionId/element/$id/property/$name'),70 Command.GET_ALL_COOKIES: ('GET', '/session/$sessionId/cookie'),71 Command.ADD_COOKIE: ('POST', '/session/$sessionId/cookie'),72 Command.GET_COOKIE: ('GET', '/session/$sessionId/cookie/$name'),73 Command.DELETE_ALL_COOKIES:74 ('DELETE', '/session/$sessionId/cookie'),75 Command.DELETE_COOKIE:76 ('DELETE', '/session/$sessionId/cookie/$name'),77 Command.SWITCH_TO_FRAME: ('POST', '/session/$sessionId/frame'),78 Command.SWITCH_TO_PARENT_FRAME: ('POST', '/session/$sessionId/frame/parent'),79 Command.SWITCH_TO_WINDOW: ('POST', '/session/$sessionId/window'),80 Command.CLOSE: ('DELETE', '/session/$sessionId/window'),81 Command.GET_ELEMENT_VALUE_OF_CSS_PROPERTY:82 ('GET', '/session/$sessionId/element/$id/css/$propertyName'),83 Command.IMPLICIT_WAIT:84 ('POST', '/session/$sessionId/timeouts/implicit_wait'),85 Command.EXECUTE_ASYNC_SCRIPT: ('POST', '/session/$sessionId/execute_async'),86 Command.SET_SCRIPT_TIMEOUT:87 ('POST', '/session/$sessionId/timeouts/async_script'),88 Command.SET_TIMEOUTS:89 ('POST', '/session/$sessionId/timeouts'),90 Command.DISMISS_ALERT:91 ('POST', '/session/$sessionId/dismiss_alert'),92 Command.W3C_DISMISS_ALERT:93 ('POST', '/session/$sessionId/alert/dismiss'),94 Command.ACCEPT_ALERT:95 ('POST', '/session/$sessionId/accept_alert'),96 Command.W3C_ACCEPT_ALERT:97 ('POST', '/session/$sessionId/alert/accept'),98 Command.SET_ALERT_VALUE:99 ('POST', '/session/$sessionId/alert_text'), 100 Command.W3C_SET_ALERT_VALUE: 101 ('POST', '/session/$sessionId/alert/text'), 102 Command.GET_ALERT_TEXT: 103 ('GET', '/session/$sessionId/alert_text'), 104 Command.W3C_GET_ALERT_TEXT: 105 ('GET', '/session/$sessionId/alert/text'), 106 Command.SET_ALERT_CREDENTIALS: 107 ('POST', '/session/$sessionId/alert/credentials'), 108 Command.CLICK: 109 ('POST', '/session/$sessionId/click'), 110 Command.W3C_ACTIONS: 111 ('POST', '/session/$sessionId/actions'), 112 Command.W3C_CLEAR_ACTIONS: 113 ('DELETE', '/session/$sessionId/actions'), 114 Command.DOUBLE_CLICK: 115 ('POST', '/session/$sessionId/doubleclick'), 116 Command.MOUSE_DOWN: 117 ('POST', '/session/$sessionId/buttondown'), 118 Command.MOUSE_UP: 119 ('POST', '/session/$sessionId/buttonup'), 120 Command.MOVE_TO: 121 ('POST', '/session/$sessionId/moveto'), 122 Command.GET_WINDOW_SIZE: 123 ('GET', '/session/$sessionId/window/$windowHandle/size'), 124 Command.SET_WINDOW_SIZE: 125 ('POST', '/session/$sessionId/window/$windowHandle/size'), 126 Command.GET_WINDOW_POSITION: 127 ('GET', '/session/$sessionId/window/$windowHandle/position'), 128 Command.SET_WINDOW_POSITION: 129 ('POST', '/session/$sessionId/window/$windowHandle/position'), 130 Command.SET_WINDOW_RECT: 131 ('POST', '/session/$sessionId/window/rect'), 132 Command.GET_WINDOW_RECT: 133 ('GET', '/session/$sessionId/window/rect'), 134 Command.MAXIMIZE_WINDOW: 135 ('POST', '/session/$sessionId/window/$windowHandle/maximize'), 136 Command.W3C_MAXIMIZE_WINDOW: 137 ('POST', '/session/$sessionId/window/maximize'), 138 Command.SET_SCREEN_ORIENTATION: 139 ('POST', '/session/$sessionId/orientation'), 140 Command.GET_SCREEN_ORIENTATION: 141 ('GET', '/session/$sessionId/orientation'), 142 Command.SINGLE_TAP: 143 ('POST', '/session/$sessionId/touch/click'), 144 Command.TOUCH_DOWN: 145 ('POST', '/session/$sessionId/touch/down'), 146 Command.TOUCH_UP: 147 ('POST', '/session/$sessionId/touch/up'), 148 Command.TOUCH_MOVE: 149 ('POST', '/session/$sessionId/touch/move'), 150 Command.TOUCH_SCROLL: 151 ('POST', '/session/$sessionId/touch/scroll'), 152 Command.DOUBLE_TAP: 153 ('POST', '/session/$sessionId/touch/doubleclick'), 154 Command.LONG_PRESS: 155 ('POST', '/session/$sessionId/touch/longclick'), 156 Command.FLICK: 157 ('POST', '/session/$sessionId/touch/flick'), 158 Command.EXECUTE_SQL: 159 ('POST', '/session/$sessionId/execute_sql'), 160 Command.GET_LOCATION: 161 ('GET', '/session/$sessionId/location'), 162 Command.SET_LOCATION: 163 ('POST', '/session/$sessionId/location'), 164 Command.GET_APP_CACHE: 165 ('GET', '/session/$sessionId/application_cache'), 166 Command.GET_APP_CACHE_STATUS: 167 ('GET', '/session/$sessionId/application_cache/status'), 168 Command.CLEAR_APP_CACHE: 169 ('DELETE', '/session/$sessionId/application_cache/clear'), 170 Command.GET_NETWORK_CONNECTION: 171 ('GET', '/session/$sessionId/network_connection'), 172 Command.SET_NETWORK_CONNECTION: 173 ('POST', '/session/$sessionId/network_connection'), 174 Command.GET_LOCAL_STORAGE_ITEM: 175 ('GET', '/session/$sessionId/local_storage/key/$key'), 176 Command.REMOVE_LOCAL_STORAGE_ITEM: 177 ('DELETE', '/session/$sessionId/local_storage/key/$key'), 178 Command.GET_LOCAL_STORAGE_KEYS: 179 ('GET', '/session/$sessionId/local_storage'), 180 Command.SET_LOCAL_STORAGE_ITEM: 181 ('POST', '/session/$sessionId/local_storage'), 182 Command.CLEAR_LOCAL_STORAGE: 183 ('DELETE', '/session/$sessionId/local_storage'), 184 Command.GET_LOCAL_STORAGE_SIZE: 185 ('GET', '/session/$sessionId/local_storage/size'), 186 Command.GET_SESSION_STORAGE_ITEM: 187 ('GET', '/session/$sessionId/session_storage/key/$key'), 188 Command.REMOVE_SESSION_STORAGE_ITEM: 189 ('DELETE', '/session/$sessionId/session_storage/key/$key'), 190 Command.GET_SESSION_STORAGE_KEYS: 191 ('GET', '/session/$sessionId/session_storage'), 192 Command.SET_SESSION_STORAGE_ITEM: 193 ('POST', '/session/$sessionId/session_storage'), 194 Command.CLEAR_SESSION_STORAGE: 195 ('DELETE', '/session/$sessionId/session_storage'), 196 Command.GET_SESSION_STORAGE_SIZE: 197 ('GET', '/session/$sessionId/session_storage/size'), 198 Command.GET_LOG: 199 ('POST', '/session/$sessionId/log'), 200 Command.GET_AVAILABLE_LOG_TYPES: 201 ('GET', '/session/$sessionId/log/types'), 202 Command.CURRENT_CONTEXT_HANDLE: 203 ('GET', '/session/$sessionId/context'), 204 Command.CONTEXT_HANDLES: 205 ('GET', '/session/$sessionId/contexts'), 206 Command.SWITCH_TO_CONTEXT: 207 ('POST', '/session/$sessionId/context'), 208 Command.FULLSCREEN_WINDOW: 209 ('POST', '/session/$sessionId/window/fullscreen'), 210 Command.MINIMIZE_WINDOW: 211 ('POST', '/session/$sessionId/window/minimize') 212 }

這個類里面定義了所有的selenium操作需要的接口地址(這些接口地址全部封裝在瀏覽器驅動程序中)，那么所有的瀏覽器操作就是通過訪問這些接口來實現的

其中 Command.GET: ('POST', '/session/$sessionId/url') 這個地址就是實現訪問一個網址的url ，我們先記錄一下后面有用

ok，所有的操作對應接口地址我們知道了，那么又怎樣執行這些接口來達到在瀏覽器上實現各種操作呢？繼續看緊接著接口地址定義下面的源碼

1 def execute(self, command, params):2 """3 Send a command to the remote server.4 5 Any path subtitutions required for the URL mapped to the command should be6 included in the command parameters.7 8 :Args:9 - command - A string specifying the command to execute. 10 - params - A dictionary of named parameters to send with the command as 11 its JSON payload. 12 """ 13 command_info = self._commands[command] 14 assert command_info is not None, 'Unrecognised command %s' % command 15 path = string.Template(command_info[1]).substitute(params) 16 if hasattr(self, 'w3c') and self.w3c and isinstance(params, dict) and 'sessionId' in params: 17 del params['sessionId'] 18 data = utils.dump_json(params) 19 url = '%s%s' % (self._url, path) 20 return self._request(command_info[0], url, body=data) 21 22 def _request(self, method, url, body=None): 23 """ 24 Send an HTTP request to the remote server. 25 26 :Args: 27 - method - A string for the HTTP method to send the request with. 28 - url - A string for the URL to send the request to. 29 - body - A string for request body. Ignored unless method is POST or PUT. 30 31 :Returns: 32 A dictionary with the server's parsed JSON response. 33 """ 34 LOGGER.debug('%s %s %s' % (method, url, body)) 35 36 parsed_url = parse.urlparse(url) 37 headers = self.get_remote_connection_headers(parsed_url, self.keep_alive) 38 resp = None 39 if body and method != 'POST' and method != 'PUT': 40 body = None 41 42 if self.keep_alive: 43 resp = self._conn.request(method, url, body=body, headers=headers) 44 45 statuscode = resp.status 46 else: 47 http = urllib3.PoolManager(timeout=self._timeout) 48 resp = http.request(method, url, body=body, headers=headers) 49 50 statuscode = resp.status 51 if not hasattr(resp, 'getheader'): 52 if hasattr(resp.headers, 'getheader'): 53 resp.getheader = lambda x: resp.headers.getheader(x) 54 elif hasattr(resp.headers, 'get'): 55 resp.getheader = lambda x: resp.headers.get(x) 56 57 data = resp.data.decode('UTF-8') 58 try: 59 if 300 <= statuscode < 304: 60 return self._request('GET', resp.getheader('location')) 61 if 399 < statuscode <= 500: 62 return {'status': statuscode, 'value': data} 63 content_type = [] 64 if resp.getheader('Content-Type') is not None: 65 content_type = resp.getheader('Content-Type').split(';') 66 if not any([x.startswith('image/png') for x in content_type]): 67 68 try: 69 data = utils.load_json(data.strip()) 70 except ValueError: 71 if 199 < statuscode < 300: 72 status = ErrorCode.SUCCESS 73 else: 74 status = ErrorCode.UNKNOWN_ERROR 75 return {'status': status, 'value': data.strip()} 76 77 # Some of the drivers incorrectly return a response 78 # with no 'value' field when they should return null. 79 if 'value' not in data: 80 data['value'] = None 81 return data 82 else: 83 data = {'status': 0, 'value': data} 84 return data 85 finally: 86 LOGGER.debug("Finished Request") 87 resp.close()

可以看到主要是通過execute方法調用_request方法通過urilib3標準庫向服務器發送對應操作請求地址，進而實現了瀏覽器各種操作

有人會問打開瀏覽器和操作瀏覽器實現各種動作是怎么關聯的呢？

其實，打開瀏覽器也是發送請求，請求會返回一個sessionid，后面操作的各種接口地址，你也會發現接口地址中存在一個變量$sessionid，那么不難猜測打開瀏覽器和操作瀏覽器就是用過sessionid關聯到一起，達到在同一個瀏覽器中做操作

第二步在瀏覽其上實現各種操作原理也完成了

七、模擬selenium

現在我們可以通過下面的一段代碼查看一下打開瀏覽器和訪問我的博客首頁的請求參數是什么樣子的

""" from selenium import webdriver import logginglogging.basicConfig(level=logging.DEBUG) # 打印源碼中的日志 dr = webdriver.Chrome() # 打開瀏覽器 driver.get("https://www.cnblogs.com/linuxchao/") # 訪問我的博客首頁

輸出日志信息

DEBUG:selenium.webdriver.remote.remote_connection:POST http://127.0.0.1:55695/session {"capabilities": {"firstMatch": [{}], "alwaysMatch": {"browserName": "chrome", "platformName": "any", "goog:chromeOptions": {"extensions": [], "args": []}}}, "desiredCapabilities": {"browserName": "chrome", "version": "", "platform": "ANY", "goog:chromeOptions": {"extensions": [], "args": []}}} DEBUG:urllib3.connectionpool:Starting new HTTP connection (1): 127.0.0.1 DEBUG:urllib3.connectionpool:http://127.0.0.1:55695 "POST /session HTTP/1.1" 200 830 DEBUG:selenium.webdriver.remote.remote_connection:Finished Request DEBUG:selenium.webdriver.remote.remote_connection:POST http://127.0.0.1:51006/session/09d52393b7dfcb45b8bb9101885ce206/url {"url": "https://www.cnblogs.com/linuxchao/", "sessionId": "09d52393b7dfcb45b8bb9101885ce206"} DEBUG:urllib3.connectionpool:http://127.0.0.1:51006 "POST /session/09d52393b7dfcb45b8bb9101885ce206/url HTTP/1.1" 200 72 DEBUG:selenium.webdriver.remote.remote_connection:Finished Request Process finished with exit code 0

通過執行結果就很明顯明白selenium執行的過程了，程序告訴RemoteWebDriver打開一個瀏覽器(發送post請求，帶上請求參數)，然后再向remote server發送執行瀏覽器動作的請求

那么為了更加深入理解selenium實現自動化測試的過程，我們可以自己編寫程序模擬一下打開瀏覽器然后控制瀏覽器訪問我的博客地址的操作過程

首先我們需要保持瀏覽器的驅動程序打開狀態，然后編寫如下代碼并執行

""" import requests# 請求地址(打開瀏覽器) driver_url = 'http://localhost:9515/session' # 打開瀏覽器的請求參數 driver_value = {"capabilities":{"firstMatch": [{}],"alwaysMatch":{"browserName":"chrome","platformName": "any","goog:chromeOptions":{"extensions": [], "args": []}}},"desiredCapabilities":{"browserName":"chrome","version": "","platform": "ANY","goog:chromeOptions": {"extensions": [],"args": []}}} # 發送求清 response_session = requests.post(driver_url, json = driver_value) print(response_session.json()) # 訪問我的博客的請求地址 （這個地址是我們上面記錄的地址） url = 'http://localhost:9515/session/'+response_session.json()['sessionId']+'/url' # 訪問我的博客的請求參數 value = {"url": "https://www.cnblogs.com/linuxchao/", "sessionId": response_session.json()['sessionId']} response_blog = requests.post(url = url,json = value) print(response_blog.json())

執行結果

{'sessionId': '25144efef880dcce53e4e6f60c342e9d', 'status': 0, 'value': {'acceptInsecureCerts': False, 'acceptSslCerts': False, 'applicationCacheEnabled': False, 'browserConnectionEnabled': False, 'browserName': 'chrome', 'chrome': {'chromedriverVersion': '2.39.562718 (9a2698cba08cf5a471a29d30c8b3e12becabb0e9)', 'userDataDir': 'C:\\Users\\v-xug\\AppData\\Local\\Temp\\scoped_dir9944_25238'}, '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': '75.0.3770.100', 'webStorageEnabled': True}} {'sessionId': '25144efef880dcce53e4e6f60c342e9d', 'status': 0, 'value': None}Process finished with exit code 0

上面的返回信息中最重要的信息是'sessionId': '25144efef880dcce53e4e6f60c342e9d'，從代碼中你也可以看到訪問我的博客地址的url是使用這個參數拼接的，因為打開瀏覽器后，后面所有的操作都是基于這個sessionid的

你還會看到Chrome瀏覽器被打開，且打開了我的博客地址https://www.cnblogs.com/linuxchao/，這就是selenium原理的一個過程了

八、最后

前面的代碼你看不懂，也沒關系，我們再來敘述一下selenium工作的過程

1.selenium client(python等語言編寫的自動化測試腳本)初始化一個service服務，通過Webdriver啟動瀏覽器驅動程序chromedriver.exe

2.通過RemoteWebDriver向瀏覽器驅動程序發送HTTP請求，瀏覽器驅動程序解析請求，打開瀏覽器，并獲得sessionid，如果再次對瀏覽器操作需攜帶此id

3.打開瀏覽器，綁定特定的端口，把啟動后的瀏覽器作為webdriver的remote server

3.打開瀏覽器后，所有的selenium的操作(訪問地址，查找元素等)均通過RemoteConnection鏈接到remote server，然后使用execute方法調用_request方法通過urlib3向remote server發送請求

4.瀏覽器通過請求的內容執行對應動作

5.瀏覽器再把執行的動作結果通過瀏覽器驅動程序返回給測試腳本

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