Django Rest Framework源码剖析(二)-----权限

一、简介

在已经解读过了：

dispatch()

def dispatch(self, request, *args, **kwargs):
        """
        `.dispatch()` is pretty much the same as Django's regular dispatch,
        but with extra hooks for startup, finalize, and exception handling.
        """
        self.args = args
        self.kwargs = kwargs
        #对原始request进行加工，丰富了一些功能
        #Request(
        #     request,
        #     parsers=self.get_parsers(),
        #     authenticators=self.get_authenticators(),
        #     negotiator=self.get_content_negotiator(),
        #     parser_context=parser_context
        # )
        #request(原始request,[BasicAuthentications对象，])
        #获取原生request,request._request
        #获取认证类的对象，request.authticators
        #1.封装request
        request = self.initialize_request(request, *args, **kwargs)
        self.request = request
        self.headers = self.default_response_headers  # deprecate?

        try:
            #2.认证
            self.initial(request, *args, **kwargs)

            # Get the appropriate handler method
            if request.method.lower() in self.http_method_names:
                handler = getattr(self, request.method.lower(),
                                  self.http_method_not_allowed)
            else:
                handler = self.http_method_not_allowed

            response = handler(request, *args, **kwargs)

        except Exception as exc:
            response = self.handle_exception(exc)

        self.response = self.finalize_response(request, response, *args, **kwargs)
        return self.response

2.执行inital方法，initial方法中执行perform_authentication则开始进行认证

 def initial(self, request, *args, **kwargs):
        """
        Runs anything that needs to occur prior to calling the method handler.
        """
        self.format_kwarg = self.get_format_suffix(**kwargs)

        # Perform content negotiation and store the accepted info on the request
        neg = self.perform_content_negotiation(request)
        request.accepted_renderer, request.accepted_media_type = neg

        # Determine the API version, if versioning is in use.
        version, scheme = self.determine_version(request, *args, **kwargs)
        request.version, request.versioning_scheme = version, scheme

        # Ensure that the incoming request is permitted
        #4.实现认证
        self.perform_authentication(request)
        #5.权限判断
        self.check_permissions(request)
        self.check_throttles(request)

3.当执行完perform_authentication方法认证通过时候，这时候就进入了本篇文章主题--权限(check_permissions方法)，下面是check_permissions方法源码：

    def check_permissions(self, request):
        """
        Check if the request should be permitted.
        Raises an appropriate exception if the request is not permitted.
        """
        for permission in self.get_permissions():   #循环对象get_permissions方法的结果，如果自己没有，则去父类寻找，
            if not permission.has_permission(request, self): #判断每个对象中的has_permission方法返回值（其实就是权限判断），这就是为什么我们需要对权限类定义has_permission方法
                self.permission_denied(                       
                    request, message=getattr(permission, 'message', None) #返回无权限信息，也就是我们定义的message共有属性
                )

4.从上源码中我们可以看出，perform_authentication方法中循环get_permissions结果，并逐一判断权限，所以需要分析get_permissions方法返回结果，以下是get_permissions方法源码：

 def get_permissions(self):
        """
        Instantiates and returns the list of permissions that this view requires.
        """
        return [permission() for permission in self.permission_classes]  #与权限一样采用列表生成式获取每个认证类对象

5.get_permissions方法中寻找权限类是通过self.permission_class字段寻找，和认证类一样默认该字段在全局也有配置，如果我们视图类中已经定义，则使用我们自己定义的类。

class APIView(View):

    # The following policies may be set at either globally, or per-view.
    renderer_classes = api_settings.DEFAULT_RENDERER_CLASSES
    parser_classes = api_settings.DEFAULT_PARSER_CLASSES
    authentication_classes = api_settings.DEFAULT_AUTHENTICATION_CLASSES
    throttle_classes = api_settings.DEFAULT_THROTTLE_CLASSES
    permission_classes = api_settings.DEFAULT_PERMISSION_CLASSES  #权限控制
    content_negotiation_class = api_settings.DEFAULT_CONTENT_NEGOTIATION_CLASS
    metadata_class = api_settings.DEFAULT_METADATA_CLASS
    versioning_class = api_settings.DEFAULT_VERSIONING_CLASS

6.承接check_permissions方法，当认证类中的has_permission()方法返回false时(也就是认证不通过)，则执行self.permission_denied(),以下是self.permission_denied()源码：

    def permission_denied(self, request, message=None):
        """
        If request is not permitted, determine what kind of exception to raise.
        """
        if request.authenticators and not request.successful_authenticator:
            raise exceptions.NotAuthenticated()
        raise exceptions.PermissionDenied(detail=message) # 如果定义了message属性，则抛出属性值

7.认证不通过，则至此django rest framework的权限源码到此结束，相对于认证源码简单一些。

四、内置权限验证类

django rest framework 提供了内置的权限验证类，其本质都是定义has_permission()方法对权限进行验证：

#路径：rest_framework.permissions
##基本权限验证
class BasePermission(object)

##允许所有
class AllowAny(BasePermission)

##基于django的认证权限，官方示例
class IsAuthenticated(BasePermission):

##基于django admin权限控制
class IsAdminUser(BasePermission)

##也是基于django admin
class IsAuthenticatedOrReadOnly(BasePermission)
.....

五、总结

1.使用方法：

• 继承BasePermission类(推荐)
• 重写has_permission方法
• has_permission方法返回True表示有权访问，False无权访问

2.配置：

###全局使用
REST_FRAMEWORK = {
   #权限
    "DEFAULT_PERMISSION_CLASSES":['API.utils.permission.MyPremission'],
}

##单一视图使用,为空代表不做权限验证
permission_classes = [MyPremission,] 


###优先级
单一视图>全局配置