Django Rest Framework源码剖析(三)-----频率控制

一、简介

承接上篇文章Django Rest Framework源码剖析(二)-----权限，当服务的接口被频繁调用，导致资源紧张怎么办呢？当然或许有很多解决办法，比如：负载均衡、提高服务器配置、通过代理限制访问频率等，但是django rest framework自身就提供了访问频率的控制，可以从代码本身做控制。

二、频率控制内部原理概述

django rest framework 中频率控制基本原理基于访问次数和时间，通过计算实现，当然我们也可以自己定义频率控制方法。基本原理如下：

启用频率，DRF内部会有一个字典记录来访者的IP，以及访问时间最近几（通过配置）次的访问时间，这样确保每次列表中最后一个元素都是该用户请求的最早时间，形式如下：

{
IP1:[第三次请求时间，第二次请求时间,第一次请求时间,],
IP2:[第二次请求时间,第一次请求时间,],
.....
}

举例说明，比如我现在配置了5秒内只能访问2次，每次请求到达频率控制时候先判断请求者IP是否已经在这个请求字典中，若存在，在判断用户请求5秒内的请求次数，若次数小于等于2，则允许请求，若大于2，则超过频率，不允许请求。

关于请求频率的的算法（以5秒内最多访问两次为例）：

1.首先删除掉列表里5秒之前的请求，循环判断当前请求时间和最早请求时间之差记作t1，若t1大于5则代表列表中最早的请求已经在5秒外了，删除掉，继续判断倒数第二个请求，直到t1小于5.

2.当确保请求列表中只有5秒内请求时候，接着判断其请求次数(列表长度)，若长度大于2，则证明超过5秒内访问超过2次了，则不允许，否则，通过并将此次访问时间插入到列表最前面，作为最新访问时间。

三、基本使用

同样，先来了解下频率控制的使用方法，后面在分析源码

1.在utils目录下新建立文件，throttle.py,添加频率控制为每分钟只能访问5次

#!/usr/bin/env python3
#_*_ coding:utf-8 _*_
#Author:wd
from rest_framework.throttling import SimpleRateThrottle

class VisitThrottle(SimpleRateThrottle):
    """5秒内最多访问三次"""
    scope = "WD"  #settings配置文件中的key,用于获取配置的频率

    def get_cache_key(self, request, view):
        return self.get_ident(request)

2.settings.py中配置全局频率控制

REST_FRAMEWORK = {
    #频率控制配置
    "DEFAULT_THROTTLE_CLASSES":['utils.throttle.VisitThrottle'],   #全局配置，
    "DEFAULT_THROTTLE_RATES":{
        'WD':'5/m',         #速率配置每分钟不能超过5次访问，WD是scope定义的值，

    }
}

urls.py

from django.conf.urls import url
from django.contrib import admin
from app01 import views

urlpatterns = [

    url(r'^api/v1/auth', views.AuthView.as_view()),
    url(r'^api/v1/order', views.OrderView.as_view()),
]

models.py

from django.db import models

class UserInfo(models.Model):
    user_type_choice = (
        (1,"普通用户"),
        (2,"会员"),
    )
    user_type = models.IntegerField(choices=user_type_choice)
    username = models.CharField(max_length=32,unique=True)
    password = models.CharField(max_length=64)


class UserToken(models.Model):
    user = models.OneToOneField(to=UserInfo)
    token = models.CharField(max_length=64)

订单视图

class OrderView(APIView):
    '''查看订单'''
    from utils.permissions import MyPremission
    authentication_classes = [Authentication,]    #添加认证
    permission_classes = [MyPremission,]           #添加权限控制
    def get(self,request,*args,**kwargs):
        #request.user
        #request.auth
        ret = {'code':1000,'msg':"你的订单已经完成",'data':"买了一个mac"}
        return JsonResponse(ret,safe=True)

使用postman验证如下图，可以看到频率限制已经起作用了。

四、频率控制源码剖析

在前面几篇文章中已经分析了DRF的认证、权限源码，频率控制也一样也从APIView的dispatch方法说起，参考注解：

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:
            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check_throttles则开始频率控制

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
        #2.实现认证
        self.perform_authentication(request)
        #3.权限判断
        self.check_permissions(request)
        #4.频率限制
        self.check_throttles(request)    

3.下面是check_throttles源码，与认证、权限一样采用列表对象方式，通过判断allow_request方法返回值判断频率是否通过

  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(): #循环频率控制类结果
            if not throttle.allow_request(request, self): #判断其中的allow_requestf返回结果，true则频率通过，否则返回等待多少秒可以访问
                self.throttled(request, throttle.wait())

4.get_throttles方法，采用列表生成式生成频率控制对象，与认证、权限一直

    def get_throttles(self):
        """
        Instantiates and returns the list of throttles that this view uses.
        """
        return [throttle() for throttle in self.throttle_classes] #列表生成式生成控制频率对象列表

5.self.throttle_classes属性获取

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     #频率控制全局配置
    permission_classes = api_settings.DEFAULT_PERMISSION_CLASSES
    content_negotiation_class = api_settings.DEFAULT_CONTENT_NEGOTIATION_CLASS
    metadata_class = api_settings.DEFAULT_METADATA_CLASS
    versioning_class = api_settings.DEFAULT_VERSIONING_CLASS

6.通过以上分析，知道了频率控制是通过判断每个类中的allow_request放法的返回值来判断频率是否通过，下面我们来看看我们所使用的SimpleRateThrottle怎么实现的,分析部分请看注解：

SimpleRateThrottle类源码：

class SimpleRateThrottle(BaseThrottle):
    """
    A simple cache implementation, that only requires `.get_cache_key()`
    to be overridden.

    The rate (requests / seconds) is set by a `rate` attribute on the View
    class.  The attribute is a string of the form 'number_of_requests/period'.

    Period should be one of: ('s', 'sec', 'm', 'min', 'h', 'hour', 'd', 'day')

    Previous request information used for throttling is stored in the cache.
    """
    cache = default_cache  # 存放请求时间，类似与示例中的大字典，这里使用的是django的缓存
    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):
 # 获取请求的key标识，必须要有否则会报错，这里可以重写，使用用户的用户名、或其他作为key，在示例中使用的get_ident方法用户获取用户IP作为key
        """
        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):   # 获取配置文件的配置速率
        """
        Determine the string representation of the allowed request rate.
        """
        if not getattr(self, 'scope', None):  # 通过获取共有属性scope来获取配置的速率
            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)

    def parse_rate(self, rate):  # 格式化速率
        """
        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)
        num, period = rate.split('/')  # 分离字符串
        num_requests = int(num)
        duration = {'s': 1, 'm': 60, 'h': 3600, 'd': 86400}[period[0]]  # 转换时间为数字，示例配置的5/m，m转为60秒
        return (num_requests, duration)

    def allow_request(self, request, view):   #  判断请求的速率是否通过
        """
        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

        self.key = self.get_cache_key(request, view)
        if self.key is None:
            return True

        self.history = self.cache.get(self.key, [])
        self.now = self.timer()

        # Drop any requests from the history which have now passed the
        # throttle duration
        while self.history and self.history[-1] <= self.now - self.duration:   # 频率判断实现原理，已经举例进行了说明
            self.history.pop()
        if len(self.history) >= self.num_requests:
            return self.throttle_failure()
        return self.throttle_success()

    def throttle_success(self):       # 频率通过返回true
        """
        Inserts the current request's timestamp along with the key
        into the cache.
        """
        self.history.insert(0, self.now)
        self.cache.set(self.key, self.history, self.duration)
        return True

    def throttle_failure(self):    # 不通过返回false
        """
        Called when a request to the API has failed due to throttling.
        """
        return False

    def wait(self):               # 返回等待时间
        """
        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)

get_ident方法源码，该方法用于获取请求的IP：

    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')
        remote_addr = request.META.get('REMOTE_ADDR')
        #这里request是封装以后的requst，django原生的是request._request.META 这样也可以获取
        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

五、内置频率控制类

DRF内置了多种频率控制类提供我们使用，其核心原理都是通过判断request_allow方法返回值来判断频率是否通过，通过wait方法返回等待时间。

1.BaseThrottle:最基本的频率控制需要重写allow_request方法和wait方法

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.
        """
        xff = request.META.get('HTTP_X_FORWARDED_FOR')
        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

2.SimpleRateThrottle:示例中已经使用，并对源码和原理进行了分析。

class SimpleRateThrottle(BaseThrottle):
    """
    A simple cache implementation, that only requires `.get_cache_key()`
    to be overridden.

    The rate (requests / seconds) is set by a `rate` attribute on the View
    class.  The attribute is a string of the form 'number_of_requests/period'.

    Period should be one of: ('s', 'sec', 'm', 'min', 'h', 'hour', 'd', 'day')

    Previous request information used for throttling is stored in the cache.
    """
    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):
        """
        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.
        """
        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)

    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)
        num, period = rate.split('/')
        num_requests = int(num)
        duration = {'s': 1, 'm': 60, 'h': 3600, 'd': 86400}[period[0]]
        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`.
        On failure calls `throttle_failure`.
        """
        if self.rate is None:
            return True

        self.key = self.get_cache_key(request, view)
        if self.key is None:
            return True

        self.history = self.cache.get(self.key, [])
        self.now = self.timer()

        # Drop any requests from the history which have now passed the
        # throttle duration
        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()

    def throttle_success(self):
        """
        Inserts the current request's timestamp along with the key
        into the cache.
        """
        self.history.insert(0, self.now)
        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)

3.AnonRateThrottle：匿名用户频率控制

class AnonRateThrottle(SimpleRateThrottle):
    """
    Limits the rate of API calls that may be made by a anonymous users.

    The IP address of the request will be used as the unique cache key.
    """
    scope = 'anon'

    def get_cache_key(self, request, view):
        if request.user.is_authenticated:
            return None  # Only throttle unauthenticated requests.

        return self.cache_format % {
            'scope': self.scope,
            'ident': self.get_ident(request)
        }

4.UserRateThrottle:基于SimpleRateThrottle，对用户的频率控制

class UserRateThrottle(SimpleRateThrottle):
    """
    Limits the rate of API calls that may be made by a given user.

    The user id will be used as a unique cache key if the user is
    authenticated.  For anonymous requests, the IP address of the request will
    be used.
    """
    scope = 'user'

    def get_cache_key(self, request, view):
        if request.user.is_authenticated:
            ident = request.user.pk
        else:
            ident = self.get_ident(request)

        return self.cache_format % {
            'scope': self.scope,
            'ident': ident
        }

六、自定义频率控制

自定义频率控制无非实现request_allow方法和wait方法，你可以根据实际需求来定制你的频率控制，下面是示例：

from rest_framework.throttling import BaseThrottle
import time

REQUEST_RECORD = {}  # 访问记录，可使用nosql数据库


class VisitThrottle(BaseThrottle):
    '''60s内最多能访问5次'''

    def __init__(self):
        self.history = None

    def allow_request(self, request, view):
        # 获取用户ip (get_ident)
        remote_addr = self.get_ident(request)
        ctime = time.time()

        if remote_addr not in REQUEST_RECORD:
            REQUEST_RECORD[remote_addr] = [ctime, ]  # 保持请求的时间，形式{ip:[时间,]}
            return True  # True表示可以访问
        # 获取当前ip的历史访问记录
        history = REQUEST_RECORD.get(remote_addr)
       
        self.history = history

       
        while history and history[-1] < ctime - 60:
            # while循环确保每列表中是最新的60秒内的请求
            
            history.pop()
        # 访问记录小于5次，将本次请求插入到最前面，作为最新的请求
        if len(history) < 5:
            history.insert(0, ctime)
            return True

    def wait(self):
        '''返回等待时间'''
        ctime = time.time()
        return 60 - (ctime - self.history[-1])

七、总结

1.使用方法：

• 继承BaseThrottle类
• 重写request_allow方法和wait方法，request_allow方法返回true代表通过，否则拒绝，wait返回等待的时间

2.配置

###全局使用

REST_FRAMEWORK = {
    #频率控制配置
    "DEFAULT_THROTTLE_CLASSES":['utils.throttle.VisitThrottle'],   #全局配置，
    "DEFAULT_THROTTLE_RATES":{
        'WD':'5/m',         #速率配置每分钟不能超过5次访问，WD是scope定义的值

    }
}

##单一视图使用
throttle_classes = [VisitThrottle,]

##优先级
单一视图>全局