在上面提到了django内部的資料流轉,那麼就順便說說request在django内部流轉,最終生成response。下面這幅圖就很好說明了資料處理過程。
1. 使用者在浏覽器輸入url時,浏覽器會生成請求封包通過 OSI七層網絡模型 發給服務
2. 請求到達伺服器時,先通過 wsgi協定 将http請求資料轉化為python請求對象
3. 請求到達request 中間件,中間件對request請求做預處理檢查,如果檢查不通過則直接傳回 response,否則進入下一步
4. 到達django路由系統,找到對應的視圖函數
5. 視圖函數通過ORM通路底層資料,并進行相應處理傳回response
OSI七層網絡模型
當使用者在浏覽器輸入網址時,浏覽器會将資料封裝成請求資料包括請求頭和請求體(應用層),經過轉換、壓縮、加密,請求資料被轉化成 message封包(表示層),在伺服器和用戶端建立會話連接配接(會話層)。
(傳輸層)解封message封包後得到segment資料段,根據tcp頭或udp頭(源端口和目的端口,傳輸資料序号)進行傳輸。(網絡層)解封上層資料後得到packet網絡包,根據目的ip和源ip進行路由轉發。在每段路由轉發過程,(資料鍊路層)資料包繼續被解封成frame資料幀,并根據以太網資料進行節點對節點之間的傳輸。此時,(實體層)資料将會以bit比特流方式傳輸。
到達目的位址後,資料将會像上述逆序封裝。最終伺服器收到request請求資料
小知識點:
非官方語言,僅小故事記憶
1. 三步握手建立連接配接
某天,A想打電話給B,但又怕影響到B工作。于是,
- A發了條SYN短信給B:我想打電話給你,可以嗎
- B回複ACK資訊:剛才的資訊已經收到了,并約定SYN通信
- A回複ACK資訊:收到,到時間聯系。
2. 四步揮手斷開連接配接
兩人聊了一段時間,A想挂斷電話。
- A發送FIN:我沒有要說的了,挂斷吧
- B發送ACK:我知道了,我還有幾句要說的
- B巴拉巴拉說了一通後,回複FIN、ACK:好了,我們結束通話吧
- A回複ACK:好,我挂斷了
wsgi協定
WSGI協定(web server gateway interface)是一種通信協定,主要包括兩部分:
- server: 從用戶端接收請求,将request轉發給application,将application傳回的response傳回給用戶端
- application: 接收由server轉發的request,并将處理結果傳回給server
uWSGI和gunicorn1是實作了wsgi server協定的伺服器,django,flask是實作了wsgi application協定的web架構, 可以根據項目實際情況搭配使用。
那麼,我就以gunicorn+django為例說明:
當我們建立django項目時,
python manage.py startproject HelloWorld
可以檢視項目目錄
$ tree
| -- HelloWorld
| | -- __init__.py
| | -- settings.py
| | -- urls.py
| | -- wsgi.py
| -- manage.py
啟動django項目時,執行指令
gunicorn HelloWorld.wsgi
此時,gunicorn 建立起 WSGI 伺服器,并與HelloWorld.wsgi application建立連結。
application 源碼解析
class WSGIHandler(base.BaseHandler):
request_class = WSGIRequest
def __init__(self, *args, **kwargs):
super(WSGIHandler, self).__init__(*args, **kwargs)
# 加載中間件
self.load_middleware()
def __call__(self, environ, start_response):
# 設定環境變量資訊,如DJANGO_SETTINGS_MODULE
set_script_prefix(get_script_name(environ))
# 請求處理前發送資訊
signals.request_started.send(sender=self.__class__, environ=environ)
# 初始化request 對象
request = self.request_class(environ)
# 處理request,生成response(通過中間件處理)
response = self.get_response(request)
response._handler_class = self.__class__
# response資料處理
status = '%d %s' % (response.status_code, response.reason_phrase)
response_headers = [(str(k), str(v)) for k, v in response.items()]
for c in response.cookies.values():
response_headers.append((str('Set-Cookie'), str(c.output(header=''))))
# server提供的回調方法,将響應的header和status傳回給server
start_response(force_str(status), response_headers)
if getattr(response, 'file_to_stream', None) is not None and environ.get('wsgi.file_wrapper'):
response = environ['wsgi.file_wrapper'](response.file_to_stream)
return response
- 雖然django本身也提供了runserver來啟動wsgi server,但這種啟動方式是單程序的。我更推薦使用了uwsgi\gunicorn\Apache等方式啟動服務,實作使用者請求資料處理和應用業務邏輯處理隔離開。同時,uwsgi\gunicorn\Apache還有高并發,高性能,多程序處理的優勢。
中間件資料處理
中間件是介于request處理和response傳回之間的一道處理過程,将請求資料處理和業務邏輯分離。
源碼分析
在加載中間件load_middleware時,我們可以看到下述代碼:
if hasattr(mw_instance, 'process_request'):
self._request_middleware.append(mw_instance.process_request)
if hasattr(mw_instance, 'process_view'):
self._view_middleware.append(mw_instance.process_view)
if hasattr(mw_instance, 'process_template_response'):
self._template_response_middleware.insert(0, mw_instance.process_template_response)
if hasattr(mw_instance, 'process_response'):
self._response_middleware.insert(0, mw_instance.process_response)
if hasattr(mw_instance, 'process_exception'):
self._exception_middleware.insert(0, mw_instance.process_exception)
這意味着中間件可以預定義5個函數: process_request 請求預處理、process_view 視圖預處理、process_template_response 模闆渲染處理、process_response 響應處理、 process_exception 異常處理
在這裡要注意: 前兩個請求函數順序處理,後三個響應函數逆序處理。
def get_response(self, request):
urlconf = settings.ROOT_URLCONF
urlresolvers.set_urlconf(urlconf)
resolver = urlresolvers.get_resolver(urlconf)
response_is_rendered = False
try:
response = None
# 執行process_request函數,若傳回response直接中斷後續中間件的處理
for middleware_method in self._request_middleware:
response = middleware_method(request)
if response:
break
if response is None:
if hasattr(request, 'urlconf'):
urlconf = request.urlconf
urlresolvers.set_urlconf(urlconf)
resolver = urlresolvers.get_resolver(urlconf)
# 處理url請求
resolver_match = resolver.resolve(request.path_info)
# callback: 處理request的python函數 callback_args: 位置參數 callback_kwargs: 關鍵字參數字典
callback, callback_args, callback_kwargs = resolver_match
request.resolver_match = resolver_match
# 執行 process_view 函數,同樣傳回response,則中斷後續中間件處理
for middleware_method in self._view_middleware:
response = middleware_method(request, callback, callback_args, callback_kwargs)
if response:
break
# 進入 callback 函數,執行業務邏輯;執行報錯進入process_exception函數處理
if response is None:
wrapped_callback = self.make_view_atomic(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:
if isinstance(callback, types.FunctionType): # FBV
view_name = callback.__name__
else: # CBV
view_name = callback.__class__.__name__ + '.__call__'
raise ValueError("The view %s.%s didn't return an HttpResponse object. It returned None instead."
% (callback.__module__, view_name))
# 當response對象有 render 方法時,才會調用
if hasattr(response, 'render') and callable(response.render):
for middleware_method in self._template_response_middleware:
response = middleware_method(request, response)
# Complain if the template response middleware returned None (a common error).
if response is None:
raise ValueError(
"%s.process_template_response didn't return an "
"HttpResponse object. It returned None instead."
% (middleware_method.__self__.__class__.__name__))
# response 渲染處理
try:
response = response.render()
except Exception as e:
response = self.process_exception_by_middleware(e, request)
response_is_rendered = True
except http.Http404 as exc:
logger.warning('Not Found: %s', request.path,
extra={
'status_code': 404,
'request': request
})
if settings.DEBUG:
response = debug.technical_404_response(request, exc)
else:
response = self.get_exception_response(request, resolver, 404, exc)
except PermissionDenied as exc:
logger.warning(
'Forbidden (Permission denied): %s', request.path,
extra={
'status_code': 403,
'request': request
})
response = self.get_exception_response(request, resolver, 403, exc)
except MultiPartParserError as exc:
logger.warning(
'Bad request (Unable to parse request body): %s', request.path,
extra={
'status_code': 400,
'request': request
})
response = self.get_exception_response(request, resolver, 400, exc)
except SuspiciousOperation as exc:
# The request logger receives events for any problematic request
# The security logger receives events for all SuspiciousOperations
security_logger = logging.getLogger('django.security.%s' %
exc.__class__.__name__)
security_logger.error(
force_text(exc),
extra={
'status_code': 400,
'request': request
})
if settings.DEBUG:
return debug.technical_500_response(request, *sys.exc_info(), status_code=400)
response = self.get_exception_response(request, resolver, 400, exc)
except SystemExit:
# Allow sys.exit() to actually exit. See tickets #1023 and #4701
raise
except: # Handle everything else.
# Get the exception info now, in case another exception is thrown later.
signals.got_request_exception.send(sender=self.__class__, request=request)
response = self.handle_uncaught_exception(request, resolver, sys.exc_info())
try:
# 執行 process_response 函數
for middleware_method in self._response_middleware:
response = middleware_method(request, response)
# Complain if the response middleware returned None (a common error).
if response is None:
raise ValueError(
"%s.process_response didn't return an "
"HttpResponse object. It returned None instead."
% (middleware_method.__self__.__class__.__name__))
response = self.apply_response_fixes(request, response)
except:
signals.got_request_exception.send(sender=self.__class__, request=request)
response = self.handle_uncaught_exception(request, resolver, sys.exc_info())
response._closable_objects.append(request)
if not response_is_rendered and callable(getattr(response, 'render', None)):
response = response.render()
# 傳回 response 對象
return response
總結
- gunicorn較uwsgi配置簡單,易上手,且響應速度快。但uwsgi功能強大,穩定性強,吞吐量大 ↩︎