轉:Django 原始碼閱讀(一):概覽從入口到請求到響應
轉載:Django 原始碼閱讀(一):概覽從入口到請求到響應————作者:hongweipeng
起步
在我研究完 django 的自動載入機制後,有了閱讀 django 原始碼的想法。那就看看吧,也不知道能堅持到什麼地方。我閱讀的版本也是我正在使用的 1.10.5 版本,算是比較新的了。
一般執行 django 程式都是通過: python manage.py runserver 開始的,那我們就從這個入口開始。
入口檔案
manage.py 檔案裡只有簡單的幾行程式碼:
#!/usr/bin/env python import os import sys if __name__ == "__main__": # 將settings模組設定到環境變數中 os.environ.setdefault("DJANGO_SETTINGS_MODULE", "webui.settings") from django.core.management import execute_from_command_line # 執行命令 execute_from_command_line(sys.argv)
在設定環境變數之後,命令引數的列表傳到了 execute_from_command_line 中:
def execute_from_command_line(argv=None):
"""
A simple method that runs a ManagementUtility.
"""
utility = ManagementUtility(argv)
utility.execute()
命令管理工具
命令引數又傳到了 ManagementUtility 類中:
class ManagementUtility(object): def __init__(self, argv=None): self.argv = argv or sys.argv[:] self.prog_name = os.path.basename(self.argv[0]) self.settings_exception = None
prog_name 就是 manage.py。例項化後呼叫了 execute() 方法,在這個方法中,會對命令引數進行處理。當解析的的命令是 runserver 時,會有兩條路,第一個是會自動重灌的路線,通過 autoreload.check_errors(django.setup)() 代理完成。另一個路線是引數中有 --noreload 時,就用 django.setup() 來啟動服務。
如果不是 runserver 而是其他命令,那麼會對命令引數 self.argv[1] 進行判斷,包括錯誤處理,是否是 help ,是否是 version ,根據不同的情況展示不同的資訊。
最重要的是最後一句,即前面的情況都不是,就進入 self.fetch_command(subcommand).run_from_argv(self.argv) ,這邊分兩步,一步是獲取執行命令所需要的類,其次是將命令引數作為引數傳遞給執行函式執行:
def fetch_command(self, subcommand):
commands = get_commands()
try:
app_name = commands[subcommand]
except KeyError:
sys.exit(1)
if isinstance(app_name, BaseCommand):
# If the command is already loaded, use it directly.
klass = app_name
else:
klass = load_command_class(app_name, subcommand)
return klass
get_commands() 是返回是一個命令與模組對映作用的字典:
{
"makemessages": "django.core",
"makemigrations": "django.core",
"migrate": "django.core",
"runserver": "django.contrib.staticfiles",
"startapp": "django.core",
"startproject": "django.core",
"createsuperuser": "django.contrib.auth"
...
}
動態載入模組
模組是通過 load_command_class 來動態載入的:
def load_command_class(app_name, name):
module = import_module('%s.management.commands.%s' % (app_name, name))
return module.Command()
如執行 runserver 命令的模組就是 django.contrib.staticfiles.management.commands.runserver 返回該模組中定義的 Command 類的例項。獲得例項後呼叫了 run_from_argv(self.argv) :
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:]) # Namespace(addrport=None, ...) 返回一個Namespace的例項
cmd_options = vars(options) # 物件轉成字典
# Move positional args out of options to mimic legacy optparse
args = cmd_options.pop('args', ())
handle_default_options(options) # 設定預設引數
try:
self.execute(*args, **cmd_options) # 異常捕獲包裹的execute
except Exception as e:
sys.exit(1)
finally:
connections.close_all()
設定請求控制代碼
在 execute 中會做一些設定引數的錯誤檢查,然後設定控制代碼:
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']:
self.addr = '' # 預設地址
self.port = self.default_port # 預設埠
else: # 如果設定了ip地址和埠號,用正則匹配出來
m = re.match(naiveip_re, options['addrport'])
if m is None:
raise CommandError('"%s" is not a valid port number '
'or address:port pair.' % options['addrport'])
self.addr, _ipv4, _ipv6, _fqdn, self.port = m.groups()
if not self.port.isdigit():
raise CommandError("%r is not a valid port number." % self.port)
if self.addr:
if _ipv6:
self.addr = self.addr[1:-1]
self.use_ipv6 = True
self._raw_ipv6 = True
elif self.use_ipv6 and not _fqdn:
raise CommandError('"%s" is not a valid IPv6 address.' % self.addr)
if not self.addr:
self.addr = '::1' if self.use_ipv6 else '127.0.0.1' #如果沒有設定ip地址使用127.0.0.1代替
self._raw_ipv6 = self.use_ipv6
self.run(**options) # 執行命令
run 方法主要時呼叫了 inner_run(*args, **options) 這個方法:
def inner_run(self, *args, **options):
threading = options['use_threading']
# 'shutdown_message' is a stealth option.
shutdown_message = options.get('shutdown_message', '')
quit_command = 'CTRL-BREAK' if sys.platform == 'win32' else 'CONTROL-C'
# 輸出基礎資訊
self.stdout.write("Performing system checks...\n\n")
self.check(display_num_errors=True)
# Need to check migrations here, so can't use the
# requires_migrations_check attribute.
self.check_migrations()
now = datetime.now().strftime('%B %d, %Y - %X')
if six.PY2:
now = now.decode(get_system_encoding())
self.stdout.write(now)
self.stdout.write((
"Django version %(version)s, using settings %(settings)r\n"
"Starting development server at http://%(addr)s:%(port)s/\n"
"Quit the server with %(quit_command)s.\n"
) % {
"version": self.get_version(),
"settings": settings.SETTINGS_MODULE,
"addr": '[%s]' % self.addr if self._raw_ipv6 else self.addr,
"port": self.port,
"quit_command": quit_command,
})
try:
# 獲取處理 http 的控制代碼
handler = self.get_handler(*args, **options)
run(self.addr, int(self.port), handler,
ipv6=self.use_ipv6, threading=threading)
except socket.error as e:
os._exit(1)
except KeyboardInterrupt:
if shutdown_message:
self.stdout.write(shutdown_message)
sys.exit(0)
這部分除了有熟悉的資訊輸出外,重要的是這個控制代碼:
def get_handler(self, *args, **options):
"""
Returns the default WSGI handler for the runner.
"""
return get_internal_wsgi_application()
get_handler 函式最終會返回一個 WSGIHandler 的例項。WSGIHandler 類只實現了 def __call__(self, environ, start_response) , 使它本身能夠成為 WSGI 中的應用程式, 並且實現 __call__ 能讓類的行為跟函式一樣。
def run(addr, port, wsgi_handler, ipv6=False, threading=False):
server_address = (addr, port)
if threading:
httpd_cls = type(str('WSGIServer'), (socketserver.ThreadingMixIn, WSGIServer), {})
else:
httpd_cls = WSGIServer
httpd = httpd_cls(server_address, WSGIRequestHandler, ipv6=ipv6)
if threading:
httpd.daemon_threads = True
httpd.set_app(wsgi_handler)
httpd.serve_forever()
這是一個標準的 wsgi 實現。httpd_cls 是 WSGIServer 類,最終的例項化方法在父類 SocketServer 中的 TCPServer 和 BaseServer 中。包括初始化執行緒,初始化網路控制代碼,像下面的 __is_shut_down 和 __shutdown_request 都是在其中初始化的。
處理請求
def serve_forever(self, poll_interval=0.5):
"""
處理一個 http 請求直到關閉
"""
#__is_shut_down為一個初始化的threading.Event()的控制代碼,用於執行緒間通訊
self.__is_shut_down.clear() #.clear()將標識設定為false
try:
with _ServerSelector() as selector:
selector.register(self, selectors.EVENT_READ)
while not self.__shutdown_request:
# 下面的函式就是一個封裝好了的select函式,超時時間 0.5 s
ready = selector.select(poll_interval)
if ready:
self._handle_request_noblock()
self.service_actions()
finally:
self.__shutdown_request = False
self.__is_shut_down.set() #將標識設定為true
當發現有請求後,就呼叫 _handle_request_noblock 進行處理:
def _handle_request_noblock(self):
try:
# 返回請求控制代碼,客戶端地址,get_request()中呼叫了self.socket.accept()來實現客戶端的連線
request, client_address = self.get_request()
except OSError:
return
if self.verify_request(request, client_address): # 驗證請求合法性
try:
#真正的處理連線請求的地方,呼叫了self.finish_request(request, client_address)
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)
在 finish_request 函式返回 django.core.servers.basehttp.WSGIRequestHandler 的例項,其父類 BaseHTTPRequestHandler 類中有對 http 包解包的過程,從其父類的初始化:
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()
響應請求
可以看出,會回撥 handle() 函式,也就是子類 WSGIRequestHandler 覆蓋的方法:
def handle(self):
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
#傳入的引數,讀,寫,錯誤,環境變數。在其父類SimpleHandler中進行了初始化,並且打開了多執行緒和多程序選項
handler = ServerHandler(
self.rfile, self.wfile, self.get_stderr(), self.get_environ()
)
handler.request_handler = self
handler.run(self.server.get_app())
handler.run(self.server.get_app()) 中就是呼叫之前設定控制代碼的 WSGIHandler 類:
class WSGIHandler(base.BaseHandler):
request_class = WSGIRequest
def __init__(self, *args, **kwargs):
super(WSGIHandler, self).__init__(*args, **kwargs)
self.load_middleware()
def __call__(self, environ, start_response):
...
response = self.get_response(request)
response._handler_class = self.__class__
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=''))))
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
就有一個 response 響應返回啦。