webdriver协议

何为协议？协议就是客户端和服务器规定好的通信方式。
web driver协议规定了某一个操作（比如find_element_by_id），客户端需要向服务器的哪个路由（其实是通过command来定义的接口地址）接口发送怎样的数据格式以及响应的数据。
协议是抽象类，只规定了有哪些操作和怎样的数据格式，没有具体的实现，具体的实现是由不同的服务器来实现的，比如浏览器驱动、appium服务器，相同的操作对不同的服务器来说调用的接口和传递的参数是相同的，因为这是协议规定的；然而具体的实现是由服务器特定的功能决定的，浏览器驱动是用来操作浏览器的，appium是用来操作手机设备的，具体实现肯定是不同。

appium

appium扩展了selenium，它可以用selenium所有的接口，因为appium服务器也具体实现了其功能，所以可以兼容使用（服务器接口和接收的参数由协议规定）。

selenium/appium怎么向服务器发送请求

这一切都发动自selenium webdriver类中的execute这个方法

    def execute(self, driver_command, params=None):"""Sends a command to be executed by a command.CommandExecutor.:Args:- driver_command: The name of the command to execute as a string.- params: A dictionary of named parameters to send with the command.:Returns:The command's JSON response loaded into a dictionary object."""if self.session_id is not None:if not params:params = {'sessionId': self.session_id}elif 'sessionId' not in params:params['sessionId'] = self.session_idparams = self._wrap_value(params)response = self.command_executor.execute(driver_command, params)if response:self.error_handler.check_response(response)response['value'] = self._unwrap_value(response.get('value', None))return response# If the server doesn't send a response, assume the command was# a successreturn {'success': 0, 'value': None, 'sessionId': self.session_id}

其中调用了command_executor.execute方法

    def execute(self, command, params):"""Send a command to the remote server.Any path subtitutions required for the URL mapped to the command should beincluded in the command parameters.:Args:- command - A string specifying the command to execute.- params - A dictionary of named parameters to send with the command asits JSON payload."""command_info = self._commands[command]assert command_info is not None, 'Unrecognised command %s' % commandpath = string.Template(command_info[1]).substitute(params)if hasattr(self, 'w3c') and self.w3c and isinstance(params, dict) and 'sessionId' in params:del params['sessionId']data = utils.dump_json(params)url = '%s%s' % (self._url, path)return self._request(command_info[0], url, body=data)

    def _request(self, method, url, body=None):"""Send an HTTP request to the remote server.:Args:- method - A string for the HTTP method to send the request with.- url - A string for the URL to send the request to.- body - A string for request body. Ignored unless method is POST or PUT.:Returns:A dictionary with the server's parsed JSON response."""LOGGER.debug('%s %s %s' % (method, url, body))parsed_url = parse.urlparse(url)headers = self.get_remote_connection_headers(parsed_url, self.keep_alive)resp = Noneif body and method != 'POST' and method != 'PUT':body = Noneif self.keep_alive:resp = self._conn.request(method, url, body=body, headers=headers)statuscode = resp.statuselse:http = urllib3.PoolManager(timeout=self._timeout)resp = http.request(method, url, body=body, headers=headers)statuscode = resp.statusif not hasattr(resp, 'getheader'):if hasattr(resp.headers, 'getheader'):resp.getheader = lambda x: resp.headers.getheader(x)elif hasattr(resp.headers, 'get'):resp.getheader = lambda x: resp.headers.get(x)data = resp.data.decode('UTF-8')try:if 300 <= statuscode < 304:return self._request('GET', resp.getheader('location'))if 399 < statuscode <= 500:return {'status': statuscode, 'value': data}content_type = []if resp.getheader('Content-Type') is not None:content_type = resp.getheader('Content-Type').split(';')if not any([x.startswith('image/png') for x in content_type]):try:data = utils.load_json(data.strip())except ValueError:if 199 < statuscode < 300:status = ErrorCode.SUCCESSelse:status = ErrorCode.UNKNOWN_ERRORreturn {'status': status, 'value': data.strip()}# Some of the drivers incorrectly return a response# with no 'value' field when they should return null.if 'value' not in data:data['value'] = Nonereturn dataelse:data = {'status': 0, 'value': data}return datafinally:LOGGER.debug("Finished Request")resp.close()

最终发送请求的是_request这个方法。
在selenium webdriver中的execute中最后用_unwrap_value包装了下返回的响应，放在了response['value']中。

看看服务器路由接口的定义

self._commands = {Command.STATUS: ('GET', '/status'),Command.NEW_SESSION: ('POST', '/session'),Command.GET_ALL_SESSIONS: ('GET', '/sessions'),Command.QUIT: ('DELETE', '/session/$sessionId'),Command.GET_CURRENT_WINDOW_HANDLE:('GET', '/session/$sessionId/window_handle'),Command.W3C_GET_CURRENT_WINDOW_HANDLE:('GET', '/session/$sessionId/window'),Command.GET_WINDOW_HANDLES:('GET', '/session/$sessionId/window_handles'),Command.W3C_GET_WINDOW_HANDLES:('GET', '/session/$sessionId/window/handles'),Command.GET: ('POST', '/session/$sessionId/url'),Command.GO_FORWARD: ('POST', '/session/$sessionId/forward'),Command.GO_BACK: ('POST', '/session/$sessionId/back'),Command.REFRESH: ('POST', '/session/$sessionId/refresh'),Command.EXECUTE_SCRIPT: ('POST', '/session/$sessionId/execute'),Command.W3C_EXECUTE_SCRIPT:('POST', '/session/$sessionId/execute/sync'),Command.W3C_EXECUTE_SCRIPT_ASYNC:('POST', '/session/$sessionId/execute/async'),Command.GET_CURRENT_URL: ('GET', '/session/$sessionId/url'),Command.GET_TITLE: ('GET', '/session/$sessionId/title'),Command.GET_PAGE_SOURCE: ('GET', '/session/$sessionId/source'),Command.SCREENSHOT: ('GET', '/session/$sessionId/screenshot'),Command.ELEMENT_SCREENSHOT: ('GET', '/session/$sessionId/element/$id/screenshot'),Command.FIND_ELEMENT: ('POST', '/session/$sessionId/element'),Command.FIND_ELEMENTS: ('POST', '/session/$sessionId/elements'),Command.W3C_GET_ACTIVE_ELEMENT: ('GET', '/session/$sessionId/element/active'),Command.GET_ACTIVE_ELEMENT:('POST', '/session/$sessionId/element/active'),Command.FIND_CHILD_ELEMENT:('POST', '/session/$sessionId/element/$id/element'),Command.FIND_CHILD_ELEMENTS:('POST', '/session/$sessionId/element/$id/elements'),Command.CLICK_ELEMENT: ('POST', '/session/$sessionId/element/$id/click'),Command.CLEAR_ELEMENT: ('POST', '/session/$sessionId/element/$id/clear'),Command.SUBMIT_ELEMENT: ('POST', '/session/$sessionId/element/$id/submit'),Command.GET_ELEMENT_TEXT: ('GET', '/session/$sessionId/element/$id/text'),Command.SEND_KEYS_TO_ELEMENT:('POST', '/session/$sessionId/element/$id/value'),Command.SEND_KEYS_TO_ACTIVE_ELEMENT:('POST', '/session/$sessionId/keys'),Command.UPLOAD_FILE: ('POST', "/session/$sessionId/file"),Command.GET_ELEMENT_VALUE:('GET', '/session/$sessionId/element/$id/value'),Command.GET_ELEMENT_TAG_NAME:('GET', '/session/$sessionId/element/$id/name'),Command.IS_ELEMENT_SELECTED:('GET', '/session/$sessionId/element/$id/selected'),Command.SET_ELEMENT_SELECTED:('POST', '/session/$sessionId/element/$id/selected'),Command.IS_ELEMENT_ENABLED:('GET', '/session/$sessionId/element/$id/enabled'),Command.IS_ELEMENT_DISPLAYED:('GET', '/session/$sessionId/element/$id/displayed'),Command.GET_ELEMENT_LOCATION:('GET', '/session/$sessionId/element/$id/location'),Command.GET_ELEMENT_LOCATION_ONCE_SCROLLED_INTO_VIEW:('GET', '/session/$sessionId/element/$id/location_in_view'),Command.GET_ELEMENT_SIZE:('GET', '/session/$sessionId/element/$id/size'),Command.GET_ELEMENT_RECT:('GET', '/session/$sessionId/element/$id/rect'),Command.GET_ELEMENT_ATTRIBUTE:('GET', '/session/$sessionId/element/$id/attribute/$name'),Command.GET_ELEMENT_PROPERTY:('GET', '/session/$sessionId/element/$id/property/$name'),Command.GET_ALL_COOKIES: ('GET', '/session/$sessionId/cookie'),Command.ADD_COOKIE: ('POST', '/session/$sessionId/cookie'),Command.GET_COOKIE: ('GET', '/session/$sessionId/cookie/$name'),Command.DELETE_ALL_COOKIES:('DELETE', '/session/$sessionId/cookie'),Command.DELETE_COOKIE:('DELETE', '/session/$sessionId/cookie/$name'),Command.SWITCH_TO_FRAME: ('POST', '/session/$sessionId/frame'),Command.SWITCH_TO_PARENT_FRAME: ('POST', '/session/$sessionId/frame/parent'),Command.SWITCH_TO_WINDOW: ('POST', '/session/$sessionId/window'),Command.CLOSE: ('DELETE', '/session/$sessionId/window'),Command.GET_ELEMENT_VALUE_OF_CSS_PROPERTY:('GET', '/session/$sessionId/element/$id/css/$propertyName'),Command.IMPLICIT_WAIT:('POST', '/session/$sessionId/timeouts/implicit_wait'),Command.EXECUTE_ASYNC_SCRIPT: ('POST', '/session/$sessionId/execute_async'),Command.SET_SCRIPT_TIMEOUT:('POST', '/session/$sessionId/timeouts/async_script'),Command.SET_TIMEOUTS:('POST', '/session/$sessionId/timeouts'),Command.DISMISS_ALERT:('POST', '/session/$sessionId/dismiss_alert'),Command.W3C_DISMISS_ALERT:('POST', '/session/$sessionId/alert/dismiss'),Command.ACCEPT_ALERT:('POST', '/session/$sessionId/accept_alert'),Command.W3C_ACCEPT_ALERT:('POST', '/session/$sessionId/alert/accept'),Command.SET_ALERT_VALUE:('POST', '/session/$sessionId/alert_text'),Command.W3C_SET_ALERT_VALUE:('POST', '/session/$sessionId/alert/text'),Command.GET_ALERT_TEXT:('GET', '/session/$sessionId/alert_text'),Command.W3C_GET_ALERT_TEXT:('GET', '/session/$sessionId/alert/text'),Command.SET_ALERT_CREDENTIALS:('POST', '/session/$sessionId/alert/credentials'),Command.CLICK:('POST', '/session/$sessionId/click'),Command.W3C_ACTIONS:('POST', '/session/$sessionId/actions'),Command.W3C_CLEAR_ACTIONS:('DELETE', '/session/$sessionId/actions'),Command.DOUBLE_CLICK:('POST', '/session/$sessionId/doubleclick'),Command.MOUSE_DOWN:('POST', '/session/$sessionId/buttondown'),Command.MOUSE_UP:('POST', '/session/$sessionId/buttonup'),Command.MOVE_TO:('POST', '/session/$sessionId/moveto'),Command.GET_WINDOW_SIZE:('GET', '/session/$sessionId/window/$windowHandle/size'),Command.SET_WINDOW_SIZE:('POST', '/session/$sessionId/window/$windowHandle/size'),Command.GET_WINDOW_POSITION:('GET', '/session/$sessionId/window/$windowHandle/position'),Command.SET_WINDOW_POSITION:('POST', '/session/$sessionId/window/$windowHandle/position'),Command.SET_WINDOW_RECT:('POST', '/session/$sessionId/window/rect'),Command.GET_WINDOW_RECT:('GET', '/session/$sessionId/window/rect'),Command.MAXIMIZE_WINDOW:('POST', '/session/$sessionId/window/$windowHandle/maximize'),Command.W3C_MAXIMIZE_WINDOW:('POST', '/session/$sessionId/window/maximize'),Command.SET_SCREEN_ORIENTATION:('POST', '/session/$sessionId/orientation'),Command.GET_SCREEN_ORIENTATION:('GET', '/session/$sessionId/orientation'),Command.SINGLE_TAP:('POST', '/session/$sessionId/touch/click'),Command.TOUCH_DOWN:('POST', '/session/$sessionId/touch/down'),Command.TOUCH_UP:('POST', '/session/$sessionId/touch/up'),Command.TOUCH_MOVE:('POST', '/session/$sessionId/touch/move'),Command.TOUCH_SCROLL:('POST', '/session/$sessionId/touch/scroll'),Command.DOUBLE_TAP:('POST', '/session/$sessionId/touch/doubleclick'),Command.LONG_PRESS:('POST', '/session/$sessionId/touch/longclick'),Command.FLICK:('POST', '/session/$sessionId/touch/flick'),Command.EXECUTE_SQL:('POST', '/session/$sessionId/execute_sql'),Command.GET_LOCATION:('GET', '/session/$sessionId/location'),Command.SET_LOCATION:('POST', '/session/$sessionId/location'),Command.GET_APP_CACHE:('GET', '/session/$sessionId/application_cache'),Command.GET_APP_CACHE_STATUS:('GET', '/session/$sessionId/application_cache/status'),Command.CLEAR_APP_CACHE:('DELETE', '/session/$sessionId/application_cache/clear'),Command.GET_NETWORK_CONNECTION:('GET', '/session/$sessionId/network_connection'),Command.SET_NETWORK_CONNECTION:('POST', '/session/$sessionId/network_connection'),Command.GET_LOCAL_STORAGE_ITEM:('GET', '/session/$sessionId/local_storage/key/$key'),Command.REMOVE_LOCAL_STORAGE_ITEM:('DELETE', '/session/$sessionId/local_storage/key/$key'),Command.GET_LOCAL_STORAGE_KEYS:('GET', '/session/$sessionId/local_storage'),Command.SET_LOCAL_STORAGE_ITEM:('POST', '/session/$sessionId/local_storage'),Command.CLEAR_LOCAL_STORAGE:('DELETE', '/session/$sessionId/local_storage'),Command.GET_LOCAL_STORAGE_SIZE:('GET', '/session/$sessionId/local_storage/size'),Command.GET_SESSION_STORAGE_ITEM:('GET', '/session/$sessionId/session_storage/key/$key'),Command.REMOVE_SESSION_STORAGE_ITEM:('DELETE', '/session/$sessionId/session_storage/key/$key'),Command.GET_SESSION_STORAGE_KEYS:('GET', '/session/$sessionId/session_storage'),Command.SET_SESSION_STORAGE_ITEM:('POST', '/session/$sessionId/session_storage'),Command.CLEAR_SESSION_STORAGE:('DELETE', '/session/$sessionId/session_storage'),Command.GET_SESSION_STORAGE_SIZE:('GET', '/session/$sessionId/session_storage/size'),Command.GET_LOG:('POST', '/session/$sessionId/log'),Command.GET_AVAILABLE_LOG_TYPES:('GET', '/session/$sessionId/log/types'),Command.CURRENT_CONTEXT_HANDLE:('GET', '/session/$sessionId/context'),Command.CONTEXT_HANDLES:('GET', '/session/$sessionId/contexts'),Command.SWITCH_TO_CONTEXT:('POST', '/session/$sessionId/context'),Command.FULLSCREEN_WINDOW:('POST', '/session/$sessionId/window/fullscreen'),Command.MINIMIZE_WINDOW:('POST', '/session/$sessionId/window/minimize')}

上面这些command只是selenium中的，appium还有自己增加的command
在appium中的webdriver类中有_addCommands这个方法，这个方法会遍历所有的父类，只要父类也有_addCommands方法，则执行一遍，所以appium初始化后的command会更多，接口也就更多，这也就是说其扩展了selenium。

    def _addCommands(self):# call the overridden command binders from all mixin classesfor mixin_class in filter(lambda x: x is not self.__class__, self.__class__.__mro__):if hasattr(mixin_class, self._addCommands.__name__):getattr(mixin_class, self._addCommands.__name__, None)(self)self.command_executor._commands[Command.TOUCH_ACTION] = \('POST', '/session/$sessionId/touch/perform')self.command_executor._commands[Command.MULTI_ACTION] = \('POST', '/session/$sessionId/touch/multi/perform')self.command_executor._commands[Command.GET_CURRENT_PACKAGE] = \('GET', '/session/$sessionId/appium/device/current_package')self.command_executor._commands[Command.SET_IMMEDIATE_VALUE] = \('POST', '/session/$sessionId/appium/element/$id/value')self.command_executor._commands[Command.LAUNCH_APP] = \('POST', '/session/$sessionId/appium/app/launch')self.command_executor._commands[Command.CLOSE_APP] = \('POST', '/session/$sessionId/appium/app/close')self.command_executor._commands[Command.END_TEST_COVERAGE] = \('POST', '/session/$sessionId/appium/app/end_test_coverage')self.command_executor._commands[Command.RESET] = \('POST', '/session/$sessionId/appium/app/reset')self.command_executor._commands[Command.OPEN_NOTIFICATIONS] = \('POST', '/session/$sessionId/appium/device/open_notifications')self.command_executor._commands[Command.REPLACE_KEYS] = \('POST', '/session/$sessionId/appium/element/$id/replace_value')self.command_executor._commands[Command.GET_SETTINGS] = \('GET', '/session/$sessionId/appium/settings')self.command_executor._commands[Command.UPDATE_SETTINGS] = \('POST', '/session/$sessionId/appium/settings')self.command_executor._commands[Command.LOCATION_IN_VIEW] = \('GET', '/session/$sessionId/element/$id/location_in_view')self.command_executor._commands[Command.CLEAR] = \('POST', '/session/$sessionId/element/$id/clear')

小节

1. 协议是抽象类，只规定了操作、接口和传参数据格式。
2. appium扩展了selenium，appium服务器也实现了selenium的接口功能，只是实现方式不同，当然也有appium特有的功能接口（web不具备的，手机具备的特有功能）。
3. 所有的操作在客户端，最终都通过execute方法来请求服务器，并封装响应。