| 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