django 处理请求

本文基于 django runsever

• 入口
  • 执行 python manage.py runserver
    • 调用 django.core.management.commands.runserver.Command.handle
    • 文件 runserver.py(django/core/management/commands/runserver.py)
• 启动 TCP server
  • 从上面 handle 会进入 django.core.servers.basehttp.run

# 其中 server_cls 为 WSGIServer
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:
        # ThreadingMixIn.daemon_threads indicates how threads will behave on an
        # abrupt shutdown; like quitting the server by the user or restarting
        # by the auto-reloader. True means the server will not wait for thread
        # termination before it quits. This will make auto-reloader faster
        # and will prevent the need to kill the server manually if a thread
        # isn't terminating correctly.
        httpd.daemon_threads = True
    # wsgi_handler 为 settings.WSGI_APPLICATION 一般为 product_name/wsgi.py 中的 application
    httpd.set_app(wsgi_handler) # httpd_cls.application = application 在后面 get_app 方法中会获取到
    httpd.serve_forever()

• 进入 server_forever

# socketserver.BaseServer.serve_forever
    def serve_forever(self, poll_interval=0.5):
        """Handle one request at a time until shutdown.

        Polls for shutdown every poll_interval seconds. Ignores
        self.timeout. If you need to do periodic tasks, do them in
        another thread.
        """
        self.__is_shut_down.clear()
        try:
            # XXX: Consider using another file descriptor or connecting to the
            # socket to wake this up instead of polling. Polling reduces our
            # responsiveness to a shutdown request and wastes cpu at all other
            # times.
            with _ServerSelector() as selector:
                selector.register(self, selectors.EVENT_READ)

                while not self.__shutdown_request:
                    ready = selector.select(poll_interval)
                    # bpo-35017: shutdown() called during select(), exit immediately.
                    if self.__shutdown_request:
                        break
                    if ready:
                        self._handle_request_noblock()

                    self.service_actions()
        finally:
            self.__shutdown_request = False
            self.__is_shut_down.set()

• 接下来进入 self._handle_request_noblock()

# socketserver.BaseServer._handle_request_noblock
    def _handle_request_noblock(self):
        """Handle one request, without blocking.

        I assume that selector.select() has returned that the socket is
        readable before this function was called, so there should be no risk of
        blocking in get_request().
        """
        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)

其中 request, client_address = self.get_request(), 这时候 request 还只是一个 socket 对象

# socketserver.TCPServer.get_request
    def get_request(self):
        """Get the request and client address from the socket.

        May be overridden.

        """
        return self.socket.accept()

• 处理请求 self.process_request(request, client_address)

# socketserver.BaseServer.process_request
    def process_request(self, request, client_address):
        """Call finish_request.

        Overridden by ForkingMixIn and ThreadingMixIn.

        """
        self.finish_request(request, client_address)
        self.shutdown_request(request)

• 完成一个 request self.finish_request(request, client_address)

# socketserver.BaseServer.finish_request
    def finish_request(self, request, client_address):
        """Finish one request by instantiating RequestHandlerClass."""
        self.RequestHandlerClass(request, client_address, self)

其中 RequestHandlerClass 为 WSGIRequestHandler (django.core.servers.basehttp.WSGIRequestHandler)

注意: 这时候 request 还只是一个 socket 对象 <class 'socket.socket'>

• 实例化 handler socketserver.BaseRequestHandler

# socketserver.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()

其中 self.handle

# django.core.servers.basehttp.WSGIRequestHandler.handle
    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 (socket.error, AttributeError):
            pass

• 从请求中获取信息 self.handle_one_request()

# django.core.servers.basehttp.WSGIRequestHandler.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())  # 对应上面的 set_app

其中 ServerHandler 实例化中没有做特殊的操作

# django.core.servers.basehttp.ServerHandler
pass

run

# wsgiref.handlers.BaseHandler.run
# application 则是上面的 get_app 拿到的结果
    def run(self, application):
        """Invoke the application"""
        # Note to self: don't move the close()!  Asynchronous servers shouldn't
        # call close() from finish_response(), so if you close() anywhere but
        # the double-error branch here, you'll break asynchronous servers by
        # prematurely closing.  Async servers must return from 'run()' without
        # closing if there might still be output to iterate over.
        try:
            self.setup_environ()
            self.result = application(self.environ, self.start_response)
            self.finish_response()
        except:
            try:
                self.handle_error()
            except:
                # If we get an error handling an error, just give up already!
                self.close()
                raise   # ...and let the actual server figure it out.

调用 handler 的 __call__

• 上面的 application 其实就是 product/wsgi.py 中的 application 最终拿到的是 WSGIHandler 的一个实例

# django.core.handlers.wsgi.WSGIHandler
class WSGIHandler(base.BaseHandler):
    request_class = WSGIRequest

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.load_middleware()

    def __call__(self, environ, start_response):
        set_script_prefix(get_script_name(environ))
        signals.request_started.send(sender=self.__class__, environ=environ) # 发送 request_started 信号
        request = self.request_class(environ) # 实例化 WSGIRequest 得到 django 中 view 中真实的 request
        response = self.get_response(request) # 获取 response 会进入 middleware

        response._handler_class = self.__class__

        status = '%d %s' % (response.status_code, response.reason_phrase)
        response_headers = list(response.items())
        for c in response.cookies.values():
            response_headers.append(('Set-Cookie', c.output(header='')))
        start_response(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

• 实例化 Request

# django.core.handlers.wsgi.WSGIRequest
pass

• 获取 response

# django.core.handlers.base.BaseHandler.get_response
    def get_response(self, request):
        """Return an HttpResponse object for the given HttpRequest."""
        # Setup default url resolver for this thread
        set_urlconf(settings.ROOT_URLCONF)

        response = self._middleware_chain(request)

        response._closable_objects.append(request)

        # If the exception handler returns a TemplateResponse that has not
        # been rendered, force it to be rendered.
        if not getattr(response, 'is_rendered', True) and callable(getattr(response, 'render', None)):
            response = response.render()

        if response.status_code >= 400:
            log_response(
                '%s: %s', response.reason_phrase, request.path,
                response=response,
                request=request,
            )

        return response

接着回到 run

• 关注下 self.finish_response()

# wsgiref.handlers.BaseHandler.finish_response
    def finish_response(self):
        """Send any iterable data, then close self and the iterable

        Subclasses intended for use in asynchronous servers will
        want to redefine this method, such that it sets up callbacks
        in the event loop to iterate over the data, and to call
        'self.close()' once the response is finished.
        """
        try:
            if not self.result_is_file() or not self.sendfile():
                for data in self.result:
                    self.write(data)
                self.finish_content()
        finally:
            self.close()

# 其中  self.write
# wsgiref.handlers.BaseHandler.write
    def write(self, data):
        """'write()' callable as specified by PEP 3333"""

        assert type(data) is bytes, \
            "write() argument must be a bytes instance"

        if not self.status:
            raise AssertionError("write() before start_response()")

        elif not self.headers_sent:
            # Before the first output, send the stored headers
            self.bytes_sent = len(data)    # make sure we know content-length
            self.send_headers()
        else:
            self.bytes_sent += len(data)

        # XXX check Content-Length and truncate if too many bytes written?
        self._write(data)
        self._flush()

# 其中 self._write
# wsgiref.handlers.SimpleHandler._write
    def _write(self,data):
        result = self.stdout.write(data)
        if result is None or result == len(data):
            return
        from warnings import warn
        warn("SimpleHandler.stdout.write() should not do partial writes",
            DeprecationWarning)
        while True:
            data = data[result:]
            if not data:
                break
            result = self.stdout.write(data)

# 其中 result = self.stdout.write(data)
    def write(self, b):
        self._sock.sendall(b)
        with memoryview(b) as view:
            return view.nbytes