selenium webdriver 执行原理
selenium webdriver源码结构
Python版的源码结构，只看webdriver相关
selenium-master\py\selenium\webdriver\remote 下的文件
|-- command.py 命令相关
|-- errorhandler.py 错误处理
|-- file_detector.py 文件标识
|-- mobile.py 手机相关
|-- remote_connection.py 远程连接driver 服务端
|-- switch_to.py 切换alert相关
|-- utils.py 公用类
|-- webdriver.py webdriver客户端
|-- webelement.py 解析dom元素
|-- __init__.py
启动流程：
1.一般是初始化一个webdriver实例，以chrome driver 为例看源码可知chrome driver 都是继承remotedriver的，如下代码所示
class WebDriver(RemoteWebDriver):
"""
Controls the ChromeDriver and allows you to drive the browser.
You will need to download the ChromeDriver executable from
http://chromedriver.storage.googleapis.com/index.html
"""
def __init__(self, executable_path="chromedriver", port=DEFAULT_PORT,
options=None, service_args=None,
desired_capabilities=None, service_log_path=DEFAULT_SERVICE_LOG_PATH,
chrome_options=None, service=None, keep_alive=True):
"""
Creates a new instance of the chrome driver.
Starts the service and then creates new instance of chrome driver.
:Args:
- executable_path - Deprecated: path to the executable. If the default is used it assumes the executable is in the $PATH
- port - Deprecated: port you would like the service to run, if left as 0, a free port will be found.
- options - this takes an instance of ChromeOptions
- service_args - Deprecated: List of args to pass to the driver service
- desired_capabilities - Deprecated: Dictionary object with non-browser specific
capabilities only, such as "proxy" or "loggingPref".
- service_log_path - Deprecated: Where to log information from the driver.
- keep_alive - Whether to configure ChromeRemoteConnection to use HTTP keep-alive.
"""
#检查各个参数
if executable_path != 'chromedriver':
warnings.warn('executable_path has been deprecated, please pass in a Service object',
DeprecationWarning, stacklevel=2)
if desired_capabilities is not None:
warnings.warn('desired_capabilities has been deprecated, please pass in a Service object',
DeprecationWarning, stacklevel=2)
if port != DEFAULT_PORT:
warnings.warn('port has been deprecated, please pass in a Service object',
DeprecationWarning, stacklevel=2)
self.port = port
if service_log_path != DEFAULT_SERVICE_LOG_PATH:
warnings.warn('service_log_path has been deprecated, please pass in a Service object',
DeprecationWarning, stacklevel=2)
if chrome_options:
warnings.warn('use options instead of chrome_options',
DeprecationWarning, stacklevel=2)
options = chrome_options
if options is None:
# desired_capabilities stays as passed in
if desired_capabilities is None:
desired_capabilities = self.create_options().to_capabilities()
else:
if desired_capabilities is None:
desired_capabilities = options.to_capabilities()
else:
desired_capabilities.update(options.to_capabilities())
if service:
self.service = service
else:
#在本地启动webdriver，port如果没指定则为随机端口
self.service = Service(
executable_path,
port=port,
service_args=service_args,
log_path=service_log_path)
self.service.start()
try:
#RemoteWebDriver 初始化
RemoteWebDriver.__init__(
self,
command_executor=ChromeRemoteConnection(
remote_server_addr=self.service.service_url,
keep_alive=keep_alive),
desired_capabilities=desired_capabilities)
except Exception:
self.quit()
raise
self._is_remote = False
接着看RemoteWebDriver 源码：
class WebDriver(object):
"""
Controls a browser by sending commands to a remote server.
This server is expected to be running the WebDriver wire protocol
as defined at
https://github.com/SeleniumHQ/selenium/wiki/JsonWireProtocol
:Attributes:
- session_id - String ID of the browser session started and controlled by this WebDriver.
- capabilities - Dictionary of effective capabilities of this browser session as returned
by the remote server. See https://github.com/SeleniumHQ/selenium/wiki/DesiredCapabilities
- command_executor - remote_connection.RemoteConnection object used to execute commands.
- error_handler - errorhandler.ErrorHandler object used to handle errors.
"""
_web_element_cls = WebElement
def __init__(self, command_executor='http://127.0.0.1:4444/wd/hub',
desired_capabilities=None, browser_profile=None, proxy=None,
keep_alive=True, file_detector=None, options=None):
"""
Create a new driver that will issue commands using the wire protocol.
:Args:
- command_executor - Either a string representing URL of the remote server or a custom
remote_connection.RemoteConnection object. Defaults to 'http://127.0.0.1:4444/wd/hub'.
- desired_capabilities - A dictionary of capabilities to request when
starting the browser session. Required parameter.
- browser_profile - A selenium.webdriver.firefox.firefox_profile.FirefoxProfile object.
Only used if Firefox is requested. Optional.
- proxy - A selenium.webdriver.common.proxy.Proxy object. The browser session will
be started with given proxy settings, if possible. Optional.
- keep_alive - Whether to configure remote_connection.RemoteConnection to use
HTTP keep-alive. Defaults to True.
- file_detector - Pass custom file detector object during instantiation. If None,
then default LocalFileDetector() will be used.
- options - instance of a driver options.Options class
"""
capabilities = {}
if options is not None:
capabilities = options.to_capabilities()
if desired_capabilities is not None:
if not isinstance(desired_capabilities, dict):
raise WebDriverException("Desired Capabilities must be a dictionary")
else:
capabilities.update(desired_capabilities)
self.command_executor = command_executor
if type(self.command_executor) is bytes or isinstance(self.command_executor, str):
#初始化一个webdriver的连接
self.command_executor = RemoteConnection(command_executor, keep_alive=keep_alive)
self._is_remote = True
self.session_id = None
self.capabilities = {}
self.error_handler = ErrorHandler()
self.start_client()
self.start_session(capabilities, browser_profile)
self._switch_to = SwitchTo(self)
self._mobile = Mobile(self)
self.file_detector = file_detector or LocalFileDetector()
........
2.webdriver实例化之后可以调用其方法，以 find_element_by_id讲解
def find_element_by_id(self, id_):
"""Finds an element by id.
:Args:
- id\\_ - The id of the element to be found.
:Returns:
- WebElement - the element if it was found
:Raises:
- NoSuchElementException - if the element wasn't found
:Usage:
::
element = driver.find_element_by_id('foo')
"""
return self.find_element(by=By.ID, value=id_)
#主要是这个方法
def find_element(self, by=By.ID, value=None):
.....
return self.execute(Command.FIND_ELEMENT, {
'using': by,
'value': value})['value']
#command.py中的所有命令
STATUS = "status"
NEW_SESSION = "newSession"
GET_ALL_SESSIONS = "getAllSessions"
DELETE_SESSION = "deleteSession"
NEW_WINDOW = "newWindow"
CLOSE = "close"
QUIT = "quit"
GET = "get"
GO_BACK = "goBack"
GO_FORWARD = "goForward"
REFRESH = "refresh"
ADD_COOKIE = "addCookie"
GET_COOKIE = "getCookie"
GET_ALL_COOKIES = "getCookies"
DELETE_COOKIE = "deleteCookie"
DELETE_ALL_COOKIES = "deleteAllCookies"
FIND_ELEMENT = "findElement"
FIND_ELEMENTS = "findElements"
FIND_CHILD_ELEMENT = "findChildElement"
FIND_CHILD_ELEMENTS = "findChildElements"
CLEAR_ELEMENT = "clearElement"
CLICK_ELEMENT = "clickElement"
SEND_KEYS_TO_ELEMENT = "sendKeysToElement"
SEND_KEYS_TO_ACTIVE_ELEMENT = "sendKeysToActiveElement"
SUBMIT_ELEMENT = "submitElement"
UPLOAD_FILE = "uploadFile"
GET_CURRENT_WINDOW_HANDLE = "getCurrentWindowHandle"
W3C_GET_CURRENT_WINDOW_HANDLE = "w3cGetCurrentWindowHandle"
GET_WINDOW_HANDLES = "getWindowHandles"
W3C_GET_WINDOW_HANDLES = "w3cGetWindowHandles"
GET_WINDOW_SIZE = "getWindowSize"
W3C_GET_WINDOW_SIZE = "w3cGetWindowSize"
......
#执行方法
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_id
params = self._wrap_value(params)
#具体执行
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 success
return {'success': 0, 'value': None, 'sessionId': self.session_id}
#execute
def execute(self, command, params):
"""
Send a command to the remote server.
Any path subtitutions required for the URL mapped to the command should be
included in the command parameters.
:Args:
- command - A string specifying the command to execute.
- params - A dictionary of named parameters to send with the command as
its JSON payload.
"""
command_info = self._commands[command]
assert command_info is not None, 'Unrecognised command %s' % command
path = 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)
# _request
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 = None
if body and method != 'POST' and method != 'PUT':
body = None
if self.keep_alive:
#self._conn就是remote_connection 对象
resp = self._conn.request(method, url, body=body, headers=headers)
statuscode = resp.status
else:
http = urllib3.PoolManager(timeout=self._timeout)
resp = http.request(method, url, body=body, headers=headers)
.....
#remote_connection
def __init__(self, remote_server_addr, keep_alive=False, resolve_ip=True):
# Attempt to resolve the hostname and get an IP address.
self.keep_alive = keep_alive
parsed_url = parse.urlparse(remote_server_addr)
if parsed_url.hostname and resolve_ip:
port = parsed_url.port or None
if parsed_url.scheme == "https":
ip = parsed_url.hostname
elif port and not common_utils.is_connectable(port, parsed_url.hostname):
ip = None
LOGGER.info('Could not connect to port {} on host '
'{}'.format(port, parsed_url.hostname))
else:
ip = common_utils.find_connectable_ip(parsed_url.hostname,
port=port)
if ip:
netloc = ip
if parsed_url.port:
netloc = common_utils.join_host_port(netloc,
parsed_url.port)
if parsed_url.username:
auth = parsed_url.username
if parsed_url.password:
auth += ':%s' % parsed_url.password
netloc = '%s@%s' % (auth, netloc)
remote_server_addr = parse.urlunparse(
(parsed_url.scheme, netloc, parsed_url.path,
parsed_url.params, parsed_url.query, parsed_url.fragment))
else:
LOGGER.info('Could not get IP address for host: %s' %
parsed_url.hostname)
#webdriver的地址
self._url = remote_server_addr
if keep_alive:
self._conn = urllib3.PoolManager(timeout=self._timeout)
#命令对应的请求
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:
...
由以上代码可知，当操作元素时，其实是发操作对应的请求给webdriver服务端，然后服务端操作浏览器，并且返回响应给客户端。
