restframework学习笔记——APIView源码解读之访问节流即控制访问频率

- 日理万妓 2023-06-21 10:29 5阅读 0赞

通过APIView中的dispatch()中执行self.initial(request, \*args, \*\*kwargs)，认证和权限判断都要经过这一步。

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
        self.perform_authentication(request)
        self.check_permissions(request)
        # 控制访问频率..........................
        self.check_throttles(request)

from rest_framework.throttling import BaseThrottle

class BaseThrottle(object):
        """ Rate throttling of requests. """
    
        def allow_request(self, request, view):
            """ Return `True` if the request should be allowed, `False` otherwise. """
            raise NotImplementedError('.allow_request() must be overridden')
    	#获取标识
        def get_ident(self, request):
            """ Identify the machine making the request by parsing HTTP_X_FORWARDED_FOR if present and number of proxies is > 0. If not use all of HTTP_X_FORWARDED_FOR if it is available, if not use REMOTE_ADDR. """
            xff = request.META.get('HTTP_X_FORWARDED_FOR')
            #获取请求的IP地址并返回
            remote_addr = request.META.get('REMOTE_ADDR')
            num_proxies = api_settings.NUM_PROXIES
    
            if num_proxies is not None:
                if num_proxies == 0 or xff is None:
                    return remote_addr
                addrs = xff.split(',')
                client_addr = addrs[-min(num_proxies, len(addrs))]
                return client_addr.strip()
    
            return ''.join(xff.split()) if xff else remote_addr
    
        def wait(self):
            """ Optionally, return a recommended number of seconds to wait before the next request. """
            return None

SimpleRateThrottle继承了BaseThrottle，并做进一步的操作

class SimpleRateThrottle(BaseThrottle):
    	cache = default_cache
        timer = time.time
        cache_format = 'throttle_%(scope)s_%(ident)s'
        scope = None
        THROTTLE_RATES = api_settings.DEFAULT_THROTTLE_RATES
    	....

1.在构造函数中先反射获取“rate”,但是SimpleRateThrottle()全局中没有；  
2.所以执行self.get\_rate()。  
3.在get\_rate()中又反射获取“scope”,“scope”在全局中为None；  
4.继续在try中执行return self.THROTTLE\_RATES\[self.scope\]，即以scope为键取值并返回，THROTTLE\_RATES在全局中为“THROTTLE\_RATES = api\_settings.DEFAULT\_THROTTLE\_RATES”，是配置文件，需要去settings.py找.  
所以，视图类需要继承SimpleRateThrottle，在视图类中自定义scope的名称scope = ‘xxx’，并且这个名称’xxx’会在配置文件中作为键，值就是你自己设置的访问频率  
REST\_FRAMEWORK = \{  
“DEFAULT\_THROTTLE\_RATES”:\{  
“xxx”: ‘5/m’,  
\}  
\}  
当你配置好scope后，get\_rate(self)就可以获取它的值，返回给self.rate,然后再由self.parse\_rate(self.rate)解析——》转下文

def __init__(self):
            if not getattr(self, 'rate', None):
                self.rate = self.get_rate()
            self.num_requests, self.duration = self.parse_rate(self.rate)
       
           
     def get_rate(self):
    	  """ Determine the string representation of the allowed request rate. """
    	  if not getattr(self, 'scope', None):
    	      msg = ("You must set either `.scope` or `.rate` for '%s' throttle" %
    	             self.__class__.__name__)
    	      raise ImproperlyConfigured(msg)
    	
    	  try:
    	      return self.THROTTLE_RATES[self.scope]
    	  except KeyError:
    	      msg = "No default throttle rate set for '%s' scope" % self.scope
    	      raise ImproperlyConfigured(msg)

获取rate后，交由parse\_rate（self,rate）处理。根据这里可以看出，我们的scope配置必须要符合它的要求，才能正确解析。解析出来频率和时间周期->(num\_requests, duration)并返回

def parse_rate(self, rate):
        """ Given the request rate string, return a two tuple of: <allowed number of requests>, <period of time in seconds> """
        #配置文件中的scope值要符合要求，例如5/m、20/h
        if rate is None:
            return (None, None)
        num, period = rate.split('/')
        num_requests = int(num)
        duration = { 's': 1, 'm': 60, 'h': 3600, 'd': 86400}[period[0]]
        return (num_requests, duration)

获取rate后继续往下，到 allow\_request(self, request, view)，其中self.key = self.get\_cache\_key(request, view)

def allow_request(self, request, view):
         """ Implement the check to see if the request should be throttled. On success calls `throttle_success`. On failure calls `throttle_failure`. """
         if self.rate is None:
             return True
    	''' get_cache_key()中啥都没写，所以需要我们自己重写，返回一个 unique cache-key，且这个unique cache-key可以被用来限制访问，例如IP地址、用户名称等等。如果此请求不用限制访问，返回None即可 '''
         self.key = self.get_cache_key(request, view)
         if self.key is None:
             return True
    	‘’‘
    	self.cache就是前面类全局中的cache = default_cache，Django内置的缓存
    	’‘’
         self.history = self.cache.get(self.key, [])
         self.now = self.timer()
    
         # Drop any requests from the history which have now passed the
         # throttle duration
         ''' 循环判断，historay列表中的最后一个和时间差对比，如果超出就pop掉。最后如果history长度小于设置的请求频率数，就不限制请求 '''
         while self.history and self.history[-1] <= self.now - self.duration:
             self.history.pop()
         if len(self.history) >= self.num_requests:
             return self.throttle_failure()
         return self.throttle_success()