Python Django原始碼執行過程解析

2022-08-20 18:00:14

一、Django執行順序

WSGI會不斷監聽使用者端傳送來的請求
先經過中介軟體進行分析驗證處理
然後經過url分發與驗證
檢視層進行處理
再經過中介軟體進行分析驗證處理
返回響應內容

1.啟動

1.1 命令列啟動(測試伺服器)

命令列結論：其在第二步utility.execute()函數會根據命令列引數，分發給不同的類進行處理

在manange.py裡面execute_from_command_line(sys.argv)進入關鍵程式碼

def main():
    os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'testDjango.settings')
    try:
        from django.core.management import execute_from_command_line
    except ImportError as exc:
		---
    execute_from_command_line(sys.argv)

2.execute_from_command_line函數裡面其範例化 ManagementUtility類然後執行utility.execute()函數 [
2.1. 此函數是專門用來分析引數的，例如python manage.py runserver、python manage.py help
2.2 其會通過分析額外新增的引數選擇要使用的類或者函數，類或者函數對應著djangocoremanagementcommands裡面的類

def execute_from_command_line(argv=None):
    utility = ManagementUtility(argv)
    utility.execute()

3.從self.fetch_command(subcommand).run_from_argv(self.argv)[約第413行]
3.1 self.fetch_command(subcommand)，這個函數返回了runserver.Command物件（可以自行深入檢視），之後執行該Command父類別裡面的run_from_argv函數

 def execute(self):
			---
        if subcommand == 'help':
			---
        elif subcommand == 'version' or self.argv[1:] == ['--version']:
            sys.stdout.write(django.get_version() + 'n')
        elif self.argv[1:] in (['--help'], ['-h']):
            sys.stdout.write(self.main_help_text() + 'n')
        else:
            self.fetch_command(subcommand).run_from_argv(self.argv)

4.從run_from_argv函數self.execute(*args, **cmd_options)進入
4.1 當前類也有這個execute函數，但是由於繼承關係（此時的self也指向Command類），子類如果已經存在該函數會覆蓋執行，execute是在子類 Command類中（之後由於super還會到父類別裡面）[約第354行]

    def run_from_argv(self, argv):
        self._called_from_command_line = True
        parser = self.create_parser(argv[0], argv[1])
        options = parser.parse_args(argv[2:])
        cmd_options = vars(options)

        args = cmd_options.pop('args', ())
        handle_default_options(options)
        try:
            self.execute(*args, **cmd_options)
        except CommandError as e:
			---

5.execute函數執行output = self.handle(*args, **options)[約第398行]跳進子類runserver.Command類的handle函數
5.1 此時位於Command類的父類別裡面的execute，因為super().execute(*args, **options) #繼承下來父類別

    def handle(self, *args, **options):
        if not settings.DEBUG and not settings.ALLOWED_HOSTS:
            raise CommandError('You must set settings.ALLOWED_HOSTS if DEBUG is False.')
        self.use_ipv6 = options['use_ipv6']
        if self.use_ipv6 and not socket.has_ipv6:
            raise CommandError('Your Python does not support IPv6.')
        self._raw_ipv6 = False
        if not options['addrport']:
        	---
        else:
           	---
        if not self.addr:
            self.addr = self.default_addr_ipv6 if self.use_ipv6 else self.default_addr
            self._raw_ipv6 = self.use_ipv6
        self.run(**options)

6.handle 函數最後一行，從 self.run(**options) 進入

    def run(self, **options):
        use_reloader = options['use_reloader']

        if use_reloader:
            autoreload.run_with_reloader(self.inner_run, **options)
        else:
            self.inner_run(None, **options)

7.從def inner_run(self, *args, **options)再執行run函數

    def inner_run(self, *args, **options):
    		---
        try:
            handler = self.get_handler(*args, **options)
            run(self.addr, int(self.port), handler,
                ipv6=self.use_ipv6, threading=threading, server_cls=self.server_cls)
        except OSError as e:
          	 ---

8.最後啟動服務，此時跳到django.core.servers.basehttp.py的run函數
8.1 httpd_cls = type('WSGIServer', (socketserver.ThreadingMixIn, server_cls), {}) 這一步特別重要，其涉及到較長的繼承關係，2.監聽-4.1這一環節會介紹到

def run(addr, port, wsgi_handler, ipv6=False, threading=False, server_cls=WSGIServer):
    server_address = (addr, port)
    if threading:
        httpd_cls = type('WSGIServer', (socketserver.ThreadingMixIn, server_cls), {})
    else:
        httpd_cls = server_cls
    httpd = httpd_cls(server_address, WSGIRequestHandler, ipv6=ipv6)
    if threading:
        httpd.daemon_threads = True
    httpd.set_app(wsgi_handler)
    httpd.serve_forever()

總結流程：

解析執行 python manage.py 所提供的引數，例如: help
載入所有的app
根據引數找到相對應的命令管理工具
檢查埠、ipv4檢測、ipv6檢測、埠是否佔用、執行緒檢查
orm物件檢查表是否建立
最後啟動python Lib庫中的WSGIServer

2.監聽

解釋：WSGI開啟後，不間斷的監聽外界的請求

快速閱讀：下面寫的比較麻煩，最快了解監聽和到中介軟體前的經過就是去讀 1 、12.1 和 13

2.1 runserver(測試伺服器)

1.runserver成功開啟後，關鍵的一步是httpd.serve_forever()，其使得進入監聽即一個死迴圈

def run(addr, port, wsgi_handler, ipv6=False, threading=False, server_cls=WSGIServer):
	---
    httpd.set_app(wsgi_handler)
    httpd.serve_forever()

2.在serve_forever()函數裡面執行，當ready有值時，表示有請求發來，然後進入self._handle_request_noblock()

    def serve_forever(self, poll_interval=0.5):
        self.__is_shut_down.clear()
        try:
            with _ServerSelector() as selector:
                selector.register(self, selectors.EVENT_READ)
                while not self.__shutdown_request:
                    ready = selector.select(poll_interval)
                    if self.__shutdown_request:
                        break
                    if ready:
                        self._handle_request_noblock()

                    self.service_actions()
		---

3.從self._handle_request_noblock()正常請求將進入self.process_request(request, client_address)

    def _handle_request_noblock(self):
        try:
            request, client_address = self.get_request()
        except OSError:
            return
        if self.verify_request(request, client_address):
            try:
                self.process_request(request, client_address)
            except Exception:
                self.handle_error(request, client_address)
                self.shutdown_request(request)
            except:
                self.shutdown_request(request)
                raise
        else:
            self.shutdown_request(request)

4.從self.process_request(request, client_address)進入來到了ThreadingMixIn.process_request
4.1 此時，如果沒有搞清楚此時的self是誰，就搞不明白為什麼進入到ThreadingMixIn.process_request，而不是其它的process_request，這時候就關聯到上面提到的httpd_cls = type('WSGIServer', (socketserver.ThreadingMixIn, server_cls), {})
4.2 type的用法是動態的建立類，此時httpd_cls 是一個新類，裡面分別繼承了ThreadingMixIn和server_cls對應得WSGIServer，這時就不難理解為什麼找的是ThreadingMixIn.process_request

    def process_request(self, request, client_address):
        """Start a new thread to process the request."""
        t = threading.Thread(target = self.process_request_thread,
                             args = (request, client_address))
        t.daemon = self.daemon_threads
        if not t.daemon and self.block_on_close:
            if self._threads is None:
                self._threads = []
            self._threads.append(t)
        t.start()

5.在def process_request(self, request, client_address)裡面的t = threading.Thread(target = self.process_request_thread,args = (request, client_address))實際呼叫了self.process_request_thread，但是等t.start()才會真正執行

    def process_request_thread(self, request, client_address):
        """Same as in BaseServer but as a thread.

        In addition, exception handling is done here.

        """
        try:
            self.finish_request(request, client_address)
        except Exception:
            self.handle_error(request, client_address)
        finally:
            self.shutdown_request(request)

6.從def process_request_thread(self, request, client_address)進入，self.finish_request(request, client_address)，繼續完成請求
6.1 這時候又需要回顧之前的程式碼，因為self.RequestHandlerClass不是已經有的類，而是初始化的時候賦值，其值變為了某個類
6.2 這個過程就在1.啟動-8裡面的httpd = httpd_cls(server_address, WSGIRequestHandler, ipv6=ipv6)，此時的httpd_cls是type動態建立的，繼承了ThreadingMixIn和server_cls對應得WSGIServer，範例化時會執行def __init__方法，其關鍵執行了self.RequestHandlerClass = RequestHandlerClass

class BaseServer:
    timeout = None

    def __init__(self, server_address, RequestHandlerClass):
        """Constructor.  May be extended, do not override."""
        self.server_address = server_address
        self.RequestHandlerClass = RequestHandlerClass
        self.__is_shut_down = threading.Event()
        self.__shutdown_request = False

    def finish_request(self, request, client_address):
        self.RequestHandlerClass(request, client_address, self)
        # self.RequestHandlerClass等同於self.WSGIRequestHandler

7.從self.RequestHandlerClass(request, client_address, self)，即去WSGIRequestHandler類裡面初始化，根據一層層繼承關係，只要最老類BaseRequestHandler有初始化方法

class BaseRequestHandler:
    def __init__(self, request, client_address, server):
        self.request = request
        self.client_address = client_address
        self.server = server
        self.setup()
        try:
            self.handle()
        finally:
            self.finish()

從def __init__(self, request, client_address, server):進入self.handle()
8.1 此時的self.handle()，根據繼承關係，其就在最小子類WSGIRequestHandler裡面

    def handle(self):
        self.close_connection = True
        self.handle_one_request()
        while not self.close_connection:
            self.handle_one_request()
        try:
            self.connection.shutdown(socket.SHUT_WR)
        except (AttributeError, OSError):
            pass

9.從def handle(self)進入self.handle_one_request()

    def handle_one_request(self):
        """Copy of WSGIRequestHandler.handle() but with different ServerHandler"""
        self.raw_requestline = self.rfile.readline(65537)
        if len(self.raw_requestline) > 65536:
            self.requestline = ''
            self.request_version = ''
            self.command = ''
            self.send_error(414)
            return

        if not self.parse_request():  # An error code has been sent, just exit
            return

        handler = ServerHandler(
            self.rfile, self.wfile, self.get_stderr(), self.get_environ()
        )
        handler.request_handler = self      # backpointer for logging & connection closing
        handler.run(self.server.get_app())

10.從def handle_one_request(self)進入handler.run(self.server.get_app())
10.1 注意此時handler為ServerHandler範例化物件，run方法存在它的最大父類別BaseHandler裡面
10.2 此時handler.run(self.server.get_app())執行了self.server.get_app()，其返回django.contrib.staticfiles.handlers.StaticFilesHandler，handler.run把其當引數傳遞了過去

    def run(self, application):
        try:
            self.setup_environ()
            self.result = application(self.environ, self.start_response)
            self.finish_response()
        except (ConnectionAbortedError, BrokenPipeError, ConnectionResetError):

            return
        except:
			---

11.從def run(self, application)進入self.result = application(self.environ, self.start_response)，其中application是django.contrib.staticfiles.handlers.StaticFilesHandler
11.1 其中self.application已經初始化了是WSGIHandler

class StaticFilesHandler(StaticFilesHandlerMixin, WSGIHandler):
    def __init__(self, application):
        self.application = application
        self.base_url = urlparse(self.get_base_url())
        super().__init__()

    def __call__(self, environ, start_response):
        if not self._should_handle(get_path_info(environ)):
            return self.application(environ, start_response)
        return super().__call__(environ, start_response)

12.進入後執行def __call__(self, environ, start_response)方法，進入return self.application(environ, start_response)，此時self.application已經初始化了是WSGIHandler
12.1 request = self.request_class(environ)獲取到使用者請求的url後面就開始設定runserver啟動時候載入的url； response = self.get_response(request)獲取使用者url對應的響應準備開始往檢視轉

    def __call__(self, environ, start_response):
        set_script_prefix(get_script_name(environ))
        signals.request_started.send(sender=self.__class__, environ=environ)
        request = self.request_class(environ)
        response = self.get_response(request)
		---

13.進入response = self.get_response(request)，結束，再下一步就要開始中介軟體的進行

    def get_response(self, request):
        set_urlconf(settings.ROOT_URLCONF)
        response = self._middleware_chain(request)
        response._resource_closers.append(request.close)
        if response.status_code >= 400:
            log_response(
                '%s: %s', response.reason_phrase, request.path,
                response=response,
                request=request,
            )
        return response

3.中介軟體的執行

解釋：中介軟體的執行需要聯絡著上面執行過程，這個過程是一個遞迴的過程，下面介紹的五個函數是中介軟體命名規則對應得內容

process_request()：完成請求物件的建立，但使用者存取的網址尚未與網站的路由地址匹配。
process_view()：完成使用者存取的網址與路由地址的匹配，但尚未執行檢視函數。
process_exception()：在執行檢視函數的期間發生異常，比如程式碼異常，主動丟擲404異常等。
process_response()：完成檢視函數的執行，但尚未將響應內容返回瀏覽器
process_template_response()：預設不執行，在檢視函數完成操作後呼叫，除非檢視函數返回的response中有render方法(幾乎不會用，可以忽略)

1.遞迴的進入階段：迴圈進行下面的程式碼（此程式碼位置djangocorehandlersexception.py）

1.1 此處出現process_request()和process_response()

        @wraps(get_response)
        def inner(request):
            try:
                response = get_response(request) # 此進入迴圈
            except Exception as exc:
                response = response_for_exception(request, exc)
            return response
        return inner

    def __call__(self, request):
        # Exit out to async mode, if needed
        if asyncio.iscoroutinefunction(self.get_response):
            return self.__acall__(request)
        response = None
        if hasattr(self, 'process_request'):
            response = self.process_request(request) # 進行中介軟體的process_request步驟
        response = response or self.get_response(request) # 此進入迴圈
        if hasattr(self, 'process_response'):
            response = self.process_response(request, response) # 此是遞迴後執行的
        return response

2.遞迴的結束準備回傳：進行下面的程式碼（此程式碼位置djangocorehandlersbase.py）
2.1 此處出現process_view()、process_template_response()和process_exception()

進入檢視的關鍵函數：

callback, callback_args, callback_kwargs = self.resolve_request(request) # callback即對於檢視函數url匹配到對應的view函數
for middleware_method in self._view_middleware_view_middleware裡面放著所有的process_view()函數（初始化時載入的）， process_view()正是在該程式碼下面的環節迴圈執行
response = wrapped_callback(request, *callback_args, **callback_kwargs) 回撥函數傳參，並返回試圖函數響應。
沿著這個路徑連續進入兩次，就到了後面講到的as_view裡面（此內容是專門檢視處理的前的關鍵步驟）
response = self.process_exception_by_middleware(e, request)對應process_exception()
self._template_response_middleware 迴圈載入模板中介軟體

 def _get_response(self, request):
        response = None
        callback, callback_args, callback_kwargs = self.resolve_request(request)
        for middleware_method in self._view_middleware:
            response = middleware_method(request, callback, callback_args, callback_kwargs)
            if response:
                break
        if response is None:
            wrapped_callback = self.make_view_atomic(callback) # 找到檢視函數
            # If it is an asynchronous view, run it in a subthread.
            if asyncio.iscoroutinefunction(wrapped_callback):
                wrapped_callback = async_to_sync(wrapped_callback)
            try:
                response = wrapped_callback(request, *callback_args, **callback_kwargs)
            except Exception as e:
                response = self.process_exception_by_middleware(e, request)
                if response is None:
                    raise
        self.check_response(response, callback)
        if hasattr(response, 'render') and callable(response.render):
            for middleware_method in self._template_response_middleware:
                response = middleware_method(request, response)
                self.check_response(
                    response,
                    middleware_method,
                    name='%s.process_template_response' % (
                        middleware_method.__self__.__class__.__name__,
                    )
                )
            try:
                response = response.render()
            except Exception as e:
                response = self.process_exception_by_middleware(e, request)
                if response is None:
                    raise
        return response

3.遞迴的結束回傳：迴圈進行下面的程式碼

        @wraps(get_response)
        def inner(request):
            try:
                response = get_response(request) # 此進入迴圈
            except Exception as exc:
                response = response_for_exception(request, exc)
            return response
        return inner

    def __call__(self, request):
        # Exit out to async mode, if needed
        if asyncio.iscoroutinefunction(self.get_response):
            return self.__acall__(request)
        response = None
        if hasattr(self, 'process_request'):
            response = self.process_request(request) 
        response = response or self.get_response(request) # 此進入迴圈
        if hasattr(self, 'process_response'):
            response = self.process_response(request, response) # 進行中介軟體的process_response步驟
        return response

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