Django之DRF源码分析（四）---频率认证组件

核心源码

    def check_throttles(self, request):
        """
        Check if request should be throttled.
        Raises an appropriate exception if the request is throttled.
        """
        for throttle in self.get_throttles():
            if not throttle.allow_request(request, self):
                self.throttled(request, throttle.wait())

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

    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_cache_key(self, request, view):
        # 这里需要我们在定义 频率类的时候 重写该方法，返回的是访问者的ip，并放在缓存中
        """
        Should return a unique cache-key which can be used for throttling.
        Must be overridden.

        May return `None` if the request should not be throttled.
        """
        raise NotImplementedError('.get_cache_key() must be overridden')

    def get_rate(self):
        """
        Determine the string representation of the allowed request rate.
        确认允许请求的频率的字符串表达形式
        """
        # 去继承SimpleRateThrottle的类的对象中 反射 scope ，如果存在，则不执行，如果不存在执行if
        if not getattr(self, 'scope', None):
            msg = ("You must set either `.scope` or `.rate` for '%s' throttle" %
                   self.__class__.__name__)
            raise ImproperlyConfigured(msg)

        try:
            # 根据我配置的scope 去 settings.py 中的 REST_FRAMEWORK 中去获取DEFAULT_THROTTLE_RATES 中的值  这里我配置的是 "qzk":"3/m"
            return self.THROTTLE_RATES[self.scope]
        except KeyError:
            msg = "No default throttle rate set for '%s' scope" % self.scope
            raise ImproperlyConfigured(msg)

    def parse_rate(self, rate):
        """
        Given the request rate string, return a two tuple of:
        <allowed number of requests>, <period of time in seconds>
        """
        if rate is None:
            return (None, None)
        # 通过"/" 做切分，解压赋值给 num,period
        num, period = rate.split('/')
        # 将num 转成数字类型的整型
        num_requests = int(num)
        # 此时 period = 字符串 “m” 或 “minute”
        # duration 是在 下面的 字典中的映射关系中取第{...}["m"]
        # period[0] 表示 在字符串中取第一个字符（索引0）
        duration = {'s': 1, 'm': 60, 'h': 3600, 'd': 86400}[period[0]]
        # 此时返回的 num_reuqets=3   duration=60
        return (num_requests, duration)

    def allow_request(self, request, view):
        """
        Implement the check to see if the request should be throttled.

        On success calls `throttle_success`.
        验证通过 调用 throttle_success
        On failure calls `throttle_failure`.
        验证失败 调用 `throttle_failure`
        """
        if self.rate is None:
            return True
		# 这里的self.key 获取的值是  访问者的 ip（存在缓存中），我们在自己写的频率类中重写了该方法，这个方法返回时很么我们就以什么做过滤的 key
        self.key = self.get_cache_key(request, view)
        # 如果获取不到ip 则返回none
        if self.key is None:
            return True
		# 根据ip 获取 self.cache缓存中的 value---> [ctime2,ctime1]
        self.history = self.cache.get(self.key, [])  # self.history 就是当前访客的访问时间列表
        # 获取当前时间
        self.now = self.timer()

        # Drop any requests from the history which have now passed the
        # throttle duration
        # 如果 当前访客的时间列表不为空（有值） 并且 最后一个值 <= 当前时间-你设定的时间范围（60）
        while self.history and self.history[-1] <= self.now - self.duration:
            self.history.pop()  # 将时间列表中的最后一个pop弹栈出去（删除）
        if len(self.history) >= self.num_requests:  # 如果列表的长度 >= 你设置的次数（3）
            return self.throttle_failure()   # 返回 False
        return self.throttle_success()  # 返回True

    def throttle_success(self):
        """
        Inserts the current request's timestamp along with the key
        into the cache.
        """
        self.history.insert(0, self.now)  # 将当前时间 插入到时间列表的头部
        self.cache.set(self.key, self.history, self.duration)  #
        return True

    def throttle_failure(self):
        """
        Called when a request to the API has failed due to throttling.
        """
        return False

    def wait(self):
        """
        Returns the recommended next request time in seconds.
        """
        if self.history:
            remaining_duration = self.duration - (self.now - self.history[-1])
        else:
            remaining_duration = self.duration

        available_requests = self.num_requests - len(self.history) + 1
        if available_requests <= 0:
            return None

        return remaining_duration / float(available_requests)

BaseThrottle 类

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')

    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.
        """
        # 获取 请求头中的扩展头
        xff = request.META.get('HTTP_X_FORWARDED_FOR')
        # 获取 ip地址
        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

"""频率部分源码执行流程"""
'''
	先写一个频率校验的类（继承SimpleRateThrottle） ---> 在该类中 配置 scope参数---> 重写 get_cache_key 方法 并返回self.get_ident(request)---->在需要校验的类中配置 该校验类

	执行步骤：
		1.APIView
		2.---->dispatch
		3.---->self.initial(request, *args, **kwargs)
		4.---->self.check_throttles(request)
		5.---->throttle.allow_request(request, self)
		6.---->self.get_cache_key(request, view)(自己重写的)（返回的是ip）
		7.---->self.cache.get(self.key, []) 根据ip获取当前ip的 时间列表
		8.---->需要用到参数（self.rate，self.num_requests，self.duration）在类实例化的时已经执行了如下代码（__init__）：
				8.1--> self.rate = self.get_rate()-->self.THROTTLE_RATES[self.scope]
					-->api_settings.DEFAULT_THROTTLE_RATES(配置文件中找)
					这里 self.rate  ---> 是前面配置的 'qzk':'3/m'
				8.2-->self.num_requests, self.duration = self.parse_rate(self.rate)
					这里 self.num_requests 是设定的访问限制次数（3）
						self.duration  是访问的时间限制（60）
		9.----> 通过如上数据，并进行一通逻辑判断， 返回
        		True：——> 执行throttle_success：
        					self.history.insert(0, self.now)  # 把当前访问时间添加到时间列表
        					# 再将 key,history,duration 在 {} 中更新
        					self.cache.set(self.key, self.history, self.duration)
                False ：--->  执行throttle_failure ，返回 Ture
'''