Django开发：wsgi源码分析

我不是女神ヾ 2023-02-13 05:45 131阅读 0赞

# 入口 #

看源码，找到程序的入口是第一步，很简单，我们怎么启动django来着

python manage.py runserver 8000

好了，就它manage.py，我们来看看它里面都干了些啥（读源码不必面面俱到，找到关键代码即可）

#!/usr/bin/env python
    import os
    import sys
    
    if __name__ == "__main__":
        os.environ.setdefault("DJANGO_SETTINGS_MODULE", "Winston_crm.settings")
        try:
            from django.core.management import execute_from_command_line
        except ImportError:
            # The above import may fail for some other reason. Ensure that the
            # issue is really that Django is missing to avoid masking other
            # exceptions on Python 2.
            try:
                import django
            except ImportError:
                raise ImportError(
                    "Couldn't import Django. Are you sure it's installed and "
                    "available on your PYTHONPATH environment variable? Did you "
                    "forget to activate a virtual environment?"
                )
            raise
        execute_from_command_line(sys.argv)

找到关键代码`execute_from_command_line(sys.argv)`，进入到里面：

def execute_from_command_line(argv=None):
        """Run a ManagementUtility."""
        # 调用当前文件中的类ManagementUtility产生对象，这个类就在该函数的上方，一找就能找到
        utility = ManagementUtility(argv)
        # 调用类ManagementUtility中的方法execute
        utility.execute()

关键代码`utility.execute()` ，去类`ManagementUtility`中可以找到，该方法特别长，就不列举了，一连串`if`条件就是判断参数是否合法

进入到`execute()`方法中

def execute(self):
        """ Given the command-line arguments, figure out which subcommand is being run, create a parser appropriate to that command, and run it. """
        # 获取命令行输入第一个参数,如果没有则为help
        try:
            subcommand = self.argv[1]
        except IndexError:
            subcommand = 'help'  # Display help if no arguments were given.
    
        # Preprocess options to extract --settings and --pythonpath.
        # These options could affect the commands that are available, so they
        # must be processed early.
        # 添加命令说明
        parser = CommandParser(usage='%(prog)s subcommand [options] [args]', add_help=False, allow_abbrev=False)
        parser.add_argument('--settings')
        parser.add_argument('--pythonpath')
        parser.add_argument('args', nargs='*')  # catch-all
        try:
            # 解析后面的参数，options:Namespace(args=[],pythonpath=None,settings=None)
            options, args = parser.parse_known_args(self.argv[2:])
            # 如果options中的pythonpath或者settings有，则使用传入的路径与文件
            handle_default_options(options)
        except CommandError:
            pass  # Ignore any option errors at this point.
        # 当是django-admin输入时没有配置文件此时会报错，
        # 如果是已经生产的项目则可以导入配置文件中已经配置的应用
        try:
            settings.INSTALLED_APPS
        except ImproperlyConfigured as exc:
            self.settings_exception = exc
        except ImportError as exc:
            self.settings_exception = exc
    
        if settings.configured:
            # Start the auto-reloading dev server even if the code is broken.
            # The hardcoded condition is a code smell but we can't rely on a
            # flag on the command class because we haven't located it yet.
            # 如果不是runserver并且没有关闭自动重载功能，则执行以下函数
            if subcommand == 'runserver' and '--noreload' not in self.argv:
                try:
                    # 调用自动检测文件是否修改如果修改则自动重新启动Django服务
                    autoreload.check_errors(django.setup)()
                except Exception:
                    # The exception will be raised later in the child process
                    # started by the autoreloader. Pretend it didn't happen by
                    # loading an empty list of applications.
                    apps.all_models = defaultdict(OrderedDict)
                    apps.app_configs = OrderedDict()
                    apps.apps_ready = apps.models_ready = apps.ready = True
    
                    # Remove options not compatible with the built-in runserver
                    # (e.g. options for the contrib.staticfiles' runserver).
                    # Changes here require manually testing as described in
                    # #27522.
                    _parser = self.fetch_command('runserver').create_parser('django', 'runserver')
                    _options, _args = _parser.parse_known_args(self.argv[2:])
                    for _arg in _args:
                        self.argv.remove(_arg)
    
            # In all other cases, django.setup() is required to succeed.
            else:
                # 初始化Django环境
                django.setup()
        # 检测是否是自动完成
        self.autocomplete()
        # 如果解析命令为help
        if subcommand == 'help':
            if '--commands' in args:
                # 打印出help命令
                sys.stdout.write(self.main_help_text(commands_only=True) + '\n')
            # 如果输入参数为空
            elif not options.args:
                sys.stdout.write(self.main_help_text() + '\n')
            else:
                # 针对某个命令打印相应命令的帮助信息
                self.fetch_command(options.args[0]).print_help(self.prog_name, options.args[0])
        # Special-cases: We want 'django-admin --version' and
        # 'django-admin --help' to work, for backwards compatibility.
        # 如果输入的命令是打印版本信息
        elif subcommand == 'version' or self.argv[1:] == ['--version']:
            # 则输出当前Django的版本
            sys.stdout.write(django.get_version() + '\n')
        # 如果输入参数中包括了--help -h 则打印帮助信息
        elif self.argv[1:] in (['--help'], ['-h']):
            sys.stdout.write(self.main_help_text() + '\n')
        else:
            # 如果命令行输入单个命令，则寻找该命令，然后执行输入的参数
            self.fetch_command(subcommand).run_from_argv(self.argv)

首先使用命令行工具创建django项目和应用，此时使用的命令为startproject,startapp,该两个命令比较相似，实现的功能都是讲django/conf目录下的project\_template和app\_template两个模板进行一定数据的渲染后生成一个完整的项目到指定目录下。假如当前执行的参数为django-admin startapp testapp，此时就会执行到`self.fetch_command(subcommand).run_from_argv(self.argv)`，链式调用，我们一点一点来看； 先看`fetch_command(subcommand)`，即`fetch_command('runserver')`,就在类`ManagementUtility`中往上翻可以找到该方法，进入其中：

def fetch_command(self, subcommand): # 执行命令行输入的具体命令
        """ Try to fetch the given subcommand, printing a message with the appropriate command called from the command line (usually "django-admin" or "manage.py") if it can't be found. """
        # Get commands outside of try block to prevent swallowing exceptions
        # get_comands()会返回一个字典
        commands = get_commands() # 获取所有支持的命令
        try:
        # app_name = commands[subcommand]取值操作即app_name='django.core' 
            app_name = commands[subcommand] # 获取命令名称所在的路径或者实例
        except KeyError:
            if os.environ.get('DJANGO_SETTINGS_MODULE'):
                # If `subcommand` is missing due to misconfigured settings, the
                # following line will retrigger an ImproperlyConfigured exception
                # (get_commands() swallows the original one) so the user is
                # informed about it.
                settings.INSTALLED_APPS
            else:
                sys.stderr.write("No Django settings specified.\n")
            possible_matches = get_close_matches(subcommand, commands)
            sys.stderr.write('Unknown command: %r' % subcommand)
            if possible_matches:
                sys.stderr.write('. Did you mean %s?' % possible_matches[0])
            sys.stderr.write("\nType '%s help' for usage.\n" % self.prog_name)
            sys.exit(1)
        if isinstance(app_name, BaseCommand):# 判断app_name是否是基本命令的实例，还是命令的路径
            # If the command is already loaded, use it directly.
            klass = app_name
        else:
        # klass = load_command_class(app_name, subcommand)
        # 即klass = load_command_class('django.core' ，’runserver‘)，
        # 自己去看很简单，klass=django.core.management.commands.runserver.Command类
            klass = load_command_class(app_name, subcommand) # 如果是路径则导入该命令
        return klass # 将命令的实例化对象返回

`self.fetch_command`是利用django内置的命令管理工具去匹配到具体的模块，例如`self.fetch_command(subcommand)`其实就相当于是`self.fetch_command('runserver')`，它最终找到了==`django.contrib.staticfiles.management.commands.runserver.Command`==这个命令工具。  
django中的命令工具代码组织采用的是策略模式+接口模式，也就是说`django.core.management.commands`这个目录下面存在各种命令工具，每个工具下面都有一个`Command`接口，当匹配到`'runserver'`时调用`'runserver'`命令工具的`Command`接口，当匹配到`'migrate'`时调用`'migrate'`命令工具的`Command`接口。

好啦，此时我们得知`self.fetch_command(subcommand)`得到的是类`Command`，好多人就在这懵逼了，接下来链式调用应该去找`run_from_argv(self.argv)`了，但是在`Command`类中怎么也找不到，傻了吧，去`Command`的父类`BaseCommand`里找啊

def run_from_argv(self, argv):
            """ Set up any environment changes requested (e.g., Python path and Django settings), then run this command. If the command raises a ``CommandError``, intercept it and print it sensibly to stderr. If the ``--traceback`` option is present or the raised ``Exception`` is not ``CommandError``, raise it. """
            self._called_from_command_line = True # 从命令行调入标识
            parser = self.create_parser(argv[0], argv[1])# 创建帮助的说明
    
            options = parser.parse_args(argv[2:])# 解析输入的参数
            cmd_options = vars(options)
            # Move positional args out of options to mimic legacy optparse
            args = cmd_options.pop('args', ())
            handle_default_options(options)# 调用命令行输入的配置文件
            try:
                self.execute(*args, **cmd_options)# 调用execute方法
            except Exception as e:
                if options.traceback or not isinstance(e, CommandError):
                    raise
    
                # SystemCheckError takes care of its own formatting.
                if isinstance(e, SystemCheckError):
                    self.stderr.write(str(e), lambda x: x)
                else:
                    self.stderr.write('%s: %s' % (e.__class__.__name__, e))
                sys.exit(1)
            finally:
                try:
                    connections.close_all()# 关闭所有的数据库连接
                except ImproperlyConfigured:
                    # Ignore if connections aren't setup at this point (e.g. no
                    # configured settings).
                    pass

`run_from_argv`的作用是初始化中间件、启动服务，也就是拉起`wsgi`(但实际上并不是由它来直接完成，而是由后续很多其他代码来完成)，直观上看它应该是`runserver.Command`对象的一个方法，但实际上要稍微更复杂一些，因为没有列出关联代码，所以在下一个代码块中进行说明。

关键代码`self.execute(*args, **cmd_options)`,注意了，这个`execute`应该去`Command`类里找啊，因为该`self`是`Command`类的对象啊，让我们回到`Command`类中，找`execute`

这里有个坑，我找了好久都没找到`Command`类的入口，原来藏在`runserver.py`中：

django/core/management/commands/runserver.py # Command类所在文件

class Command(BaseCommand):
        help = "Starts a lightweight Web server for development."
    
        # Validation is called explicitly each time the server is reloaded.
        requires_system_checks = False
        stealth_options = ('shutdown_message',)
    
        default_addr = '127.0.0.1'
        default_addr_ipv6 = '::1'
        default_port = '8000'# 默认启动服务监听的端口
        protocol = 'http'
        server_cls = WSGIServer
    
        def add_arguments(self, parser):  # 创建帮助信息
            parser.add_argument(
                'addrport', nargs='?',
                help='Optional port number, or ipaddr:port'
            )
            parser.add_argument(
                '--ipv6', '-6', action='store_true', dest='use_ipv6',
                help='Tells Django to use an IPv6 address.',
            )
            parser.add_argument(
                '--nothreading', action='store_false', dest='use_threading',
                help='Tells Django to NOT use threading.',
            )
            parser.add_argument(
                '--noreload', action='store_false', dest='use_reloader',
                help='Tells Django to NOT use the auto-reloader.',
            )
    
        def execute(self, *args, **options):# 调用处理方法
            if options['no_color']:# 检查是否需要更改文字颜色
                # We rely on the environment because it's currently the only
                # way to reach WSGIRequestHandler. This seems an acceptable
                # compromise considering `runserver` runs indefinitely.
                os.environ["DJANGO_COLORS"] = "nocolor"
            # super().execute(*args, **options)会去父类BaseCommand中找到excute方法，
            # 该方法中的关键代码为output = self.handle(*args, **options)，
            # 该self是Command类的对象，所以接着去Command类中找到handle方法
            super().execute(*args, **options)# 调用父类的执行方法
    
        def get_handler(self, *args, **options):
            """Return the default WSGI handler for the runner."""
            return get_internal_wsgi_application()
    
        def handle(self, *args, **options):# 调用处理方法
            # 检查是否是debug模式，如果不是则ALLOWED_HOSTS不能为空
            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']
            # 检查输入参数中是否是ipv6格式，检查当前python是否支持ipv6
            if self.use_ipv6 and not socket.has_ipv6:
                raise CommandError('Your Python does not support IPv6.')
            self._raw_ipv6 = False
            # 如果输入参数中没有输入端口则使用默认的端口
            if not options['addrport']:
                self.addr = ''
                self.port = self.default_port
            # 检查匹配的ip格式
            else:
                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'])
                # 找出匹配的数据
                self.addr, _ipv4, _ipv6, _fqdn, self.port = m.groups()
                # 检查端口是否为数字
                if not self.port.isdigit():
                    raise CommandError("%r is not a valid port number." % self.port)
                # 检查解析出的地址是否合法的ipv6地址
                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)
            # 如果没有输入ip地址则使用默认的地址
            if not self.addr:
                self.addr = self.default_addr_ipv6 if self.use_ipv6 else self.default_addr
                self._raw_ipv6 = self.use_ipv6
            # 运行，调用run方法
            self.run(**options)
    
        def run(self, **options):
            """Run the server, using the autoreloader if needed."""
            # 根据配置是否自动加载，如果没有输入则default=True 
            use_reloader = options['use_reloader']
            # 当开启了自动加载时，则调用自动启动运行
            if use_reloader:
                autoreload.run_with_reloader(self.inner_run, **options)
            # 如果没有开启文件更新自动重启服务功能则直接运行
            else:
                self.inner_run(None, **options)
    
        def inner_run(self, *args, **options):
            # If an exception was silenced in ManagementUtility.execute in order
            # to be raised in the child process, raise it now.
            autoreload.raise_last_exception()
            # 是否开启多线程模式，当不传入时则默认为多线程模式运行
            threading = options['use_threading']
            # 'shutdown_message' is a stealth option.
            shutdown_message = options.get('shutdown_message', '')
            # 打印停止服务信息
            quit_command = 'CTRL-BREAK' if sys.platform == 'win32' else 'CONTROL-C'
    
            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.
            # 检查是否migrations是否与数据库一致
            self.check_migrations()
            # 获取当前时间
            now = datetime.now().strftime('%B %d, %Y - %X')
            # 解析当前时间
            self.stdout.write(now)
            # 打印时间等信息
            self.stdout.write((
                "Django version %(version)s, using settings %(settings)r\n"
                "Starting development server at %(protocol)s://%(addr)s:%(port)s/\n"
                "Quit the server with %(quit_command)s.\n"
            ) % { 
                "version": self.get_version(),
                "settings": settings.SETTINGS_MODULE,
                "protocol": self.protocol,
                "addr": '[%s]' % self.addr if self._raw_ipv6 else self.addr,
                "port": self.port,
                "quit_command": quit_command,
            })
    
            try:
                # 获取信息处理的handler,默认返回wsgi
                handler = self.get_handler(*args, **options)
                # 调用run方法
                run(self.addr, int(self.port), handler,
                    ipv6=self.use_ipv6, threading=threading, server_cls=self.server_cls)
            except socket.error as e:
                # Use helpful error messages instead of ugly tracebacks.
                ERRORS = { 
                    errno.EACCES: "You don't have permission to access that port.",
                    errno.EADDRINUSE: "That port is already in use.",
                    errno.EADDRNOTAVAIL: "That IP address can't be assigned to.",
                }
                try:
                    error_text = ERRORS[e.errno]
                except KeyError:
                    error_text = e
                self.stderr.write("Error: %s" % error_text)
                # Need to use an OS exit because sys.exit doesn't work in a thread
                os._exit(1)
            except KeyboardInterrupt:
                if shutdown_message:
                    self.stdout.write(shutdown_message)
                sys.exit(0)

执行无异常的话，最终都要定位到一个run方法，该方法就在本文件开头位置导入过

from django.core.servers.basehttp import (
        WSGIServer, get_internal_wsgi_application, run,
    )

截止到该部分，`Command`类实际上就是一个初始化过程，全部都为`'runserver'`服务，虽然很多代码我没有列出来，但是它确实做了一些，例如参数解析、端口指定检测、ipv4检测、ipv6检测、端口是否占用、线程检查、文件改动检测自动重启服务等工作。

接下来我把注意力放在`django.core.servers.basehttp`下的`run`函数上，代码如下

# 形参wsgi_handler的值为StaticFilesHandler
    # run方法主要是知会各个对象启动wsgi服务
    def run(addr, port, wsgi_handler, ipv6=False, threading=False, server_cls=WSGIServer):
        # 服务监听的地址和端口
        server_address = (addr, port)
        # 如果是多线程运行
        if threading:
            # 调用内置元类type创建一个类WSGIServer，该类继承了
            #(socketserver.ThreadingMixIn, WSGIServer),去代码块WSGIServer类中查看它本身只继承
            # wsgiref.simple_server.WSGIServer、object这两个类，通过type重新创建一下是给
            #类WSGIServer强行添加了一个爹socketserver.ThreadingMixIn,这么做的意义是每次调用类
            #WSGIServer的时候都会单独启用一个线程来处理，说完了WSGIServer的第一个基类，
            #我们再来说它的第二个基类WSGIServer完整的继承家族
            """ django.core.servers.basehttp.WSGIServer wsgiref.simple_server.WSGIServer、 socketserver.ThreadingMixIn http.server.HTTPServer socketserver.TCPServer socketserver.BaseServer object """
            # httpd_cls这个变量被定义完成之后，由于大量的继承关系，它其实已经不单纯的属于django，
            # 它是一个传统意义上的WSGI服务对象了。
            httpd_cls = type('WSGIServer', (socketserver.ThreadingMixIn, server_cls), { })
        else:
            httpd_cls = server_cls
        # 实例化该类，它是WSGI服务器与django之间相互通信的唯一枢纽通道，也就是说，
        # 当WSGI服务对象收到socket请求后，会将这个请求传递给django的WSGIRequestHandler
        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.
            # 等到子线程执行完成
            httpd.daemon_threads = True
        # 是将django.contrib.staticfiles.handlers.StaticFilesHandler 传递给
        # WSGIServer当作一个application，当WSGIServer收到网络请求后，可以将数据分发给
        # django.core.servers.basehttp.WSGIRequestHandler，最终由
        # django.core.servers.basehttp.WSGIRequestHandler将数据传递给
        # application(即：django.contrib.staticfiles.handlers.StaticFilesHandler)
        httpd.set_app(wsgi_handler)
        # 启动非堵塞网络监听服务。
        httpd.serve_forever()

总结：综上所述其实都是在为启动django服务而做准备，大致内容如下

1.  解析运行 python manage.py 所提供的参数，例如: runserver.
2.  根据参数 找到相对应的 命令管理工具。
3.  加载所有的app。
4.  检查端口、ipv4检测、ipv6检测、端口是否占用、线程检查、orm对象检查(表是否创建)。
5.  实例化WSGIRequestHandler，并且将它注册到python Lib库中的WSGIServer中。
6.  最后启动python Lib库中的WSGIServer

`httpd.serve_forever`调用的是`socketserver.BaseServer.serve_forever`方法(关于`socketserver`的源码解析[点击这里][Link 1]，下面我直接说流程，原理不再累述)。

1.  `socketserver.BaseServer.serve_forever`方法采用了`selector`网络模型进行等待数据，每0.5秒遍历一次文件描述符，当有数据进来时，`ready`变量会是一个`socket`请求对象，这时会将后续工作转交给`self._handler_request_noblock`方法(即：`socketserver.BaseServer._handler_request_noblock`)去处理。
2.  `socketserver.BaseServer._handler_request_noblock`方法基本没做什么事情(`self.verify_request`压根就没有检查任何东西)，直接就把后续工作转交给 `socketserver.BaseServer.process_request` 方法。
3.  `socketserver.BaseServer.process_request`也没做什么事情，直接就将后续工作转交给`socketserver.BaseServer.finish_request`方法，只不过在最后加了一条关闭请求的命令。
4.  `socketserver.BaseServer.finish_request`也没做什么事情，直接就将后续工作转交给`socketserver.BaseServer.RequestHandlerClass`。
5.  `socketserver.BaseServer.RequestHandlerClass`是由上一节`httpd = httpd_cls(server_address, WSGIRequestHandler, ipv6=ipv6)`传递过来的参数`django.core.servers.basehttp.WSGIRequestHandler`。 也就是说当执行`self.RequestHandler(request, client_address, self)`时等同于执行`django.core.servers.basehttp.WSGIRequestHandler(request, client_address, self)`。

`serve_forever`就是开启了一个`while`来无限监听网络层的`scoket`请求，当一条请求过来时，就层层转交到`django.core.servers.basehttp.WSGIRequestHandler`代码如下

class WSGIRequestHandler(simple_server.WSGIRequestHandler):
        protocol_version = 'HTTP/1.1'
    
        def address_string(self):
            # Short-circuit parent method to not call socket.getfqdn
            return self.client_address[0]
    
        def log_message(self, format, *args):
            extra = { 
                'request': self.request,
                'server_time': self.log_date_time_string(),
            }
            if args[1][0] == '4':
                # 0x16 = Handshake, 0x03 = SSL 3.0 or TLS 1.x
                if args[0].startswith('\x16\x03'):
                    extra['status_code'] = 500
                    logger.error(
                        "You're accessing the development server over HTTPS, but "
                        "it only supports HTTP.\n", extra=extra,
                    )
                    return
    
            if args[1].isdigit() and len(args[1]) == 3:
                status_code = int(args[1])
                extra['status_code'] = status_code
    
                if status_code >= 500:
                    level = logger.error
                elif status_code >= 400:
                    level = logger.warning
                else:
                    level = logger.info
            else:
                level = logger.info
    
            level(format, *args, extra=extra)
    
        def get_environ(self):
            # Strip all headers with underscores in the name before constructing
            # the WSGI environ. This prevents header-spoofing based on ambiguity
            # between underscores and dashes both normalized to underscores in WSGI
            # env vars. Nginx and Apache 2.4+ both do this as well.
            for k in self.headers:
                if '_' in k:
                    del self.headers[k]
    
            return super().get_environ()
    
        def handle(self): # 关键代码
            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
    
        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())

方法`handle`，至于如何调用到它，需要从`WSGIRequestHandler`的实例化说起，上面我们提到当执行`self.RequestHandler(request, client_address, self)`时等同于执行`django.core.servers.basehttp.WSGIRequestHandler(request, client_address, self)`，而`WSGIRequestHandler`的继承的父类们如下：

1. django.core.servers.basehttp.WSGIRequestHandler
    2. wsgiref.simple_server.WSGIRequestHandler
    3. http.server.BaseHTTPRequestHandler
    4. socketserver.StreamRequestHandler
    5. socketserver.BaseRequestHandler
    6. object

实例化类`WSGIRequestHandler`时发现它并没有`__init__`和`__call__`方法，需要去父类中找，最终在`socketserver.BaseRequestHandler`中找到，它调用了`self.hande`方法，注意`self.handle`并不是直接调用`BaseRequestHandler`中的`handle`，根据对象属性的查找关系，会去`django.core.servers.basehttp.WSGIRequestHandler`类中找，找到了`handle`，其实是相当于回调了`handle`，代码如下

def handle(self):
        self.close_connection = True
        self.handle_one_request()
        while not self.close_connection:
            self.handle_one_request() # 关键代码
        try:
            self.connection.shutdown(socket.SHUT_WR)
        except (socket.error, AttributeError):
            pass

关键代码：`self.handle_one_request()`直接在当前类中找到，代码如下

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
        # 实例化了ServerHandler对象
        handler = ServerHandler(
            self.rfile, self.wfile, self.get_stderr(), self.get_environ()
        )
        # 将django.contrib.staticfiles.handlers.StaticFilesHandler转交给ServerHandler去运行，
        # 而ServerHandler对象并没有run方法，去它的父类们中去找
        handler.request_handler = self      # backpointer for logging & connection closing
        handler.run(self.server.get_app())

`run`方法位置：

1、django.core.servers.basehttp.ServerHandler
    2、wsgiref.simple_server.ServerHandler
    3、wsgiref.handlers.SimpleHandler
    4、wsgiref.handlers.BaseHandler # 在此处找到run方法
    5、object

进入`run`方法：

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)# 关键代码
                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.

关键代码：`application(self.environ, self.start_response)`也就相当于是`django.contrib.staticfiles.handlers.StaticFilesHandler.__call__(self.environ, lf.start_response)`。

进入到`StaticFilesHandler`类中：

class StaticFilesHandler(WSGIHandler): # django专门用来处理静态文件的类
        """ WSGI middleware that intercepts calls to the static files directory, as defined by the STATIC_URL setting, and serves those files. """
        # May be used to differentiate between handler types (e.g. in a
        # request_finished signal)
        handles_files = True
    
        def __init__(self, application):
            self.application = application
            # 解析配置的静态文件路径
            self.base_url = urlparse(self.get_base_url())
            super().__init__()
    
        def load_middleware(self):
            # Middleware are already loaded for self.application; no need to reload
            # them for self.
            pass
    
        def get_base_url(self):
            # 检查静态文件相关配置是否正确
            utils.check_settings()
            # 返回配置中的静态文件
            return settings.STATIC_URL
    
        def _should_handle(self, path):
            """ Check if the path should be handled. Ignore the path if: * the host is provided as part of the base_url * the request's path isn't under the media path (or equal) """
            # 路径是否以静态路径开头，并且配置文件没有给出静态文件的Host
            return path.startswith(self.base_url[2]) and not self.base_url[1]
    
        def file_path(self, url):
            """ Return the relative path to the media file on disk for the given URL. """
            # 获取文件的相对路径
            relative_url = url[len(self.base_url[2]):]
            return url2pathname(relative_url)
    
        def serve(self, request):
            """Serve the request path."""
            # 启动server处理静态文件
            return serve(request, self.file_path(request.path), insecure=True)
    
        def get_response(self, request):
            from django.http import Http404
            # 如果是静态文件路径则使用server处理
            if self._should_handle(request.path):
                try:
                    return self.serve(request)
                except Http404 as e:
                    return response_for_exception(request, e)
            return super().get_response(request)
    
        def __call__(self, environ, start_response):
            # 先判断请求url是否是静态文件路径
            if not self._should_handle(get_path_info(environ)):
                # 如果不是静态文件路径，则正常处理
                return self.application(environ, start_response) # 关键代码
            # 如果是静态文件路径则调用父方法处理
            return super().__call__(environ, start_response)

`self.application(environ, start_response)` ，先说`self.application`是个啥呢，可以看到在该类的`__init__`方法中执行了一个`self.application = application`，那它的值到底是啥呢？

读源码的窍门在于读一点记录一点，遇到看不懂的变量打印一下值看一下即可，最好不要重复回头，那样只会让你更晕，例如我们用管理用户（修改django源码需要权限）修改文件`django.contrib.staticfiles.handlers.StaticFilesHandler`加一行打印代码

def __init__(self, application):
        self.application = application
        print('django源码打印--->self.application值为',self.application) # 打印
        self.base_url = urlparse(self.get_base_url())
        super().__init__()

然后重启django可以看到`self.application`的值为`<django.core.handlers.wsgi.WSGIHandler object at 0x106cf0278>`，去查看类`django.core.handlers.wsgi.WSGIHandler` 的实例化发现加载了中间件`self.load_middleware()`,至此我们完成分析如何从`wsgi`服务到将`url`请求信息转交给django，剩下的就是django的内部流程啦，我们有机会再继续剖析吧

另外补充：可以用同样的手法查看`envion`变量，该变量非常重要，`http`协议的请求信息都被放入了`environ`变量中。我们分析流程中的`WSGIServer`类主要用于处理`socket`请求和对接`WSGIRequestHandler`，`WSGIRequestHandler`类主要针对`environ`进行预处理和对接`WSGIServerHandler`，而`ServerHandler`类则主要用于执行应用程序(`application`)和返回响应给`WSGIServer`

[Link 1]: https://blog.csdn.net/qq_35289736/article/details/103793720