RestFramework——API基本实现及dispatch基本源码剖析

基于Django实现

　　在使用RestFramework之前我们先用Django自己实现以下API。

　　API完全可以有我们基于Django自己开发，原理是给出一个接口（URL），前端向URL发送请求以获取数据。这样能实现前后端分离的效果。但Django实现的API许多功能都需要我们自己写。

URL

from django.contrib import admin
from django.conf.urls import url, include
from app01 import views
from app02 import views
 
urlpatterns = [
    url('admin/', admin.site.urls),
    url('app02/', include('app02.urls'))#路由分发
]

from app02 import views
from django.conf.urls import url
urlpatterns = [
    url('^users/', views.users),
    url('^user/(d+)', views.user),
#######FBV与CBV的分界线########
    url('^users/', views.UsersView.as_view()),
    url('^user/', views.UserView.as_view()),
]

views.py

　　FBV

from django.shortcuts import render,HttpResponse

import json

def users(request):
    response = {'code':1000,'data':None}  #code用来表示状态，比如1000代表成功，1001代表
    response['data'] = [
        {'name':'Damon','age':22},
        {'name':'Stefan','age':10},
        {'name':'Elena','age':11},
    ]
    return HttpResponse(json.dumps(response))  #返回就送字符串，前端解析

def user(request,pk):
    if request.method =='GET':
        return HttpResponse(json.dumps({'name':'Stefan','age':11}))  #返回一条数据
    elif request.method =='POST':
        return HttpResponse(json.dumps({'code':1111}))  #返回一条数据
    elif request.method =='PUT':
        pass
    elif request.method =='DELETE':
        pass

　　CBV

from django.views import View
class UsersView(View):
    def get(self,request):
        response = {'code':1000,'data':None}
        response['data'] = [
            {'name': 'Damon', 'age': 22},
            {'name': 'Stefan', 'age': 10},
            {'name': 'Elena', 'age': 11},
        ]
        return HttpResponse(json.dumps(response),stutas=200)
 
class UserView(View):
    def get(self,request,pk):
        return HttpResponse(json.dumps({'name':'haiyan','age':11}))  #返回一条数据
    def post(self,request,pk):
        return HttpResponse(json.dumps({'code':1111}))  #返回一条数据
    def put(self,request,pk):
        pass
    def delete(self,request,pk):
        pass

注：通常我们在前后端分离进行编程时会推崇使用CBV的形式，CBV的代码可读性较高。

基于RestFramework实现

安装：

pip3 install djangorestframework -i http://pypi.douban.com/simple/ --trusted-host=pypi.douban.com

　　RestFramework可以直接在Django中使用，安装完RestFramework后在Django中可以当做模块一般导入即可使用。（记得在settings.py中进行注册，如app）

URL与基于Django实现相同，这里选用CBV的形式

from app02 import views
from django.conf.urls import url
urlpatterns = [
    url('^users/', views.UsersView.as_view()),#CBV必须要有as_view()
    url('^user/', views.UserView.as_view()),
]

views.py

　　CBV

#导入rest_framework，自定义视图的类需继承APIView
from rest_framework.views import APIView
from rest_framework.response import Response
 
class TestView(APIView):
    def dispatch(self, request, *args, **kwargs):
        """
        请求到来之后，在url中执行as_view()就会执行dispatch方法，dispatch方法是APIView类中内置的，根据请求方式不同触发 get/post/put等方法。可自定制~
         
        注意：APIView中的dispatch方法有好多好多的功能
        """
        return super().dispatch(request, *args, **kwargs)
 
    def get(self, request, *args, **kwargs):
        return Response('GET请求，响应内容')
 
    def post(self, request, *args, **kwargs):
        return Response('POST请求，响应内容')
 
    def put(self, request, *args, **kwargs):
        return Response('PUT请求，响应内容')

注：重要的功都在APIView的dispatch中触发。要掌握RestFramework，必须弄懂dispatch方法做了些什么，这样我们才可以根据自己的需求进行自定制。

dispatch基本源码剖析

　　我们在继承了APIView之后就可以重写里面的方法进行自定制。此时我们需要先弄懂APIView里到底封装了哪些方法。在APIView中，最重要的就是dispatch方法。

请求在url中执行as_view()时就会触发dispatch，进入源码我们可以看到dispatch主要做了四件事：

#在APIView类中：
    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
        # 1.封装Django原始的request，使得用了framework以后的request都具有更多功能
        """
        增加的功能
            parsers=self.get_parsers(),
            authenticators=self.get_authenticators(),#获取认证相关的所有类并实例化，传入request对象
            negotiator=self.get_content_negotiator(),
            parser_context=parser_context
        """
        request = self.initialize_request(request, *args, **kwargs)
        self.request = request#将封装后的request赋值给原始request
        self.headers = self.default_response_headers  # deprecate?

        try:
            """
            2.版本处理、用户认证、权限、访问频率限制
            """
            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
            #3.执行函数get/post/put/delete
            response = handler(request, *args, **kwargs)

        except Exception as exc:
            response = self.handle_exception(exc)
        #4.对返回结果进行再次加工
        self.response = self.finalize_response(request, response, *args, **kwargs)
        return self.response

接下来我们对每一步进行具体的分析

第一步：封装request

request = self.initialize_request(request, *args, **kwargs)
#查看initialize_request做了什么
def initialize_request(self, request, *args, **kwargs):
    """
    Returns the initial request object.
    """
    parser_context = self.get_parser_context(request)

    return Request(
        request,
        parsers=self.get_parsers(),
        authenticators=self.get_authenticators(),#获取认证相关的所有类并实例化，传入request对象。优先找自己的，没有就找父类的
        negotiator=self.get_content_negotiator(),
        parser_context=parser_context
    )

1.1、我们看到request封装了一个认证的功能——获取认证相关的所有的类并实例化，看看get_authenticators()做了什么

def get_authenticators(self):
        """
        Instantiates and returns the list of authenticators that this view can use.
        """
        #返回的是对象列表[SessionAuthentication,BaseAuthentication]
        return [auth() for auth in self.authentication_classes]


#self.authentication_classes是封装有认证功能的类的列表
authentication_classes = api_settings.DEFAULT_AUTHENTICATION_CLASSES  #默认的，如果自己有会优先执行直接的

1.2、去settings.py查看默认的配置是什么

DEFAULTS = {
    # Base API policies
    'DEFAULT_AUTHENTICATION_CLASSES': (
        'rest_framework.authentication.SessionAuthentication',   #这时候就找到了他默认认证的类了，可以导入看看
        'rest_framework.authentication.BasicAuthentication'
    ),

1.3、导入SessionAutentication和BasicAuthentication查看这两个雷兜风装了什么功能

from rest_framework.authentication import SessionAuthentication
from rest_framework.authentication import BaseAuthentication

class BaseAuthentication(object):
    """
    All authentication classes should extend BaseAuthentication.
    """

    def authenticate(self, request):
        """
        Authenticate the request and return a two-tuple of (user, token).
        """
        raise NotImplementedError(".authenticate() must be overridden.")

    def authenticate_header(self, request):
        """
        Return a string to be used as the value of the `WWW-Authenticate`
        header in a `401 Unauthenticated` response, or `None` if the
        authentication scheme should return `403 Permission Denied` responses.
        """
        pass

class BasicAuthentication(BaseAuthentication):
    """
    HTTP Basic authentication against username/password.
    """
    www_authenticate_realm = 'api'

    def authenticate(self, request):
        """
        Returns a `User` if a correct username and password have been supplied
        using HTTP Basic authentication.  Otherwise returns `None`.
        """
        auth = get_authorization_header(request).split()

        if not auth or auth[0].lower() != b'basic':
            return None   #返回none不处理。让下一个处理

        if len(auth) == 1:
            msg = _('Invalid basic header. No credentials provided.')
            raise exceptions.AuthenticationFailed(msg)
        elif len(auth) > 2:
            msg = _('Invalid basic header. Credentials string should not contain spaces.')
            raise exceptions.AuthenticationFailed(msg)

        try:
            auth_parts = base64.b64decode(auth[1]).decode(HTTP_HEADER_ENCODING).partition(':')   #用partition切割冒号也包括
        except (TypeError, UnicodeDecodeError, binascii.Error):
            msg = _('Invalid basic header. Credentials not correctly base64 encoded.')
            raise exceptions.AuthenticationFailed(msg)

        userid, password = auth_parts[0], auth_parts[2]  # 返回用户和密码
        return self.authenticate_credentials(userid, password, request)

    def authenticate_credentials(self, userid, password, request=None):
        """
        Authenticate the userid and password against username and password
        with optional request for context.
        """
        credentials = {
            get_user_model().USERNAME_FIELD: userid,
            'password': password
        }
        user = authenticate(request=request, **credentials)

        if user is None:
            raise exceptions.AuthenticationFailed(_('Invalid username/password.'))

        if not user.is_active:
            raise exceptions.AuthenticationFailed(_('User inactive or deleted.'))

        return (user, None)

    def authenticate_header(self, request):
        return 'Basic realm="%s"' % self.www_authenticate_realm

1.4、简单自定制认证的类

　　我们可以看到源码中最重要的就是BasicAuthentication的authenticate方法，所以要自定制认证的类只需重写该方法即可

class MyAuthentication(BaseAuthentication):
    def authenticate(self, request):
        token = request.query_params.get('token')#登录用户有tocken字段
        obj = models.UserInfo.objects.filter(token=token).first()
        if obj:
            return (obj.username,obj)
        return None

    def authenticate_header(self, request):
        pass

第二步、版本处理、认证、权限、访问频率限制

self.initial(request, *args, **kwargs)

#查看initial方法做了什么
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.
    #2.1 处理版本信息,获取版本必须用version
    version, scheme = self.determine_version(request, *args, **kwargs)
    request.version, request.versioning_scheme = version, scheme

    # Ensure that the incoming request is permitted
    #2.2认证，将user封装到request对象中
    self.perform_authentication(request)
    #2.3 权限
    self.check_permissions(request)
    #2.4 对请求用户进行访问频率的限制
    self.check_throttles(request)

2.2.1、认证：查看perform_authentication方法，发现只是将user封装到了request中

def perform_authentication(self, request):

    request.user

2.2.2、查看request.user中都封装了什么

class Request(object):
    @property
    def user(self):
        """
        Returns the user associated with the current request, as authenticated
        by the authentication classes provided to the request.
        """
        if not hasattr(self, '_user'):
            self._authenticate()#执行用户认证
        return self._user

2.2.3、执行self._authenticate() 开始用户认证，如果验证成功后返回元组： (用户,用户Token)

    def _authenticate(self):
        """
        Attempt to authenticate the request using each authentication instance
        in turn.
        """
        #循环对象列表
        for authenticator in self.authenticators:
            try:
                # 执行每一个对象的authenticate 方法
                user_auth_tuple = authenticator.authenticate(self)
            except exceptions.APIException:
                self._not_authenticated()
                raise

            if user_auth_tuple is not None:
                self._authenticator = authenticator
                self.user, self.auth = user_auth_tuple#返回一个元组，赋给了self,就可以request.user,request.auth了
                return

        self._not_authenticated()

2.2.4、在user_auth_tuple = authenticator.authenticate(self) 进行验证，如果验证成功，执行类里的authenticatie方法。如果用户没有认证成功：self._not_authenticated()

    def _not_authenticated(self):
        """
        Set authenticator, user & authtoken representing an unauthenticated request.

        Defaults are None, AnonymousUser & None.
        """
        # 如果跳过了所有认证，默认用户和Token和使用配置文件进行设置
        self._authenticator = None

        if api_settings.UNAUTHENTICATED_USER:
            self.user = api_settings.UNAUTHENTICATED_USER()# 默认值为：匿名用户AnonymousUser
        else:
            self.user = None# None 表示跳过该认证

        if api_settings.UNAUTHENTICATED_TOKEN:
            self.auth = api_settings.UNAUTHENTICATED_TOKEN()# 默认值为：None
        else:
            self.auth = None


#默认值都可以在settings.py中进行自定制配置
REST_FRAMEWORK = {
    'UNAUTHENTICATED_USER': None,
    'UNAUTHENTICATED_TOKEN': None,
  
}

2.3.、权限控制

######check_permissions方法#######
    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():#寻找类中的get_permissions()方法
            if not permission.has_permission(request, self):#无权限则抛出异常
                self.permission_denied(
                    request, message=getattr(permission, 'message', None)
                )

######get_permissions方法#######
    def get_permissions(self):
        """
        Instantiates and returns the list of permissions that this view requires.
        """
        return [permission() for permission in self.permission_classes]#去settings.py中查是否有权限配置

2.4、对访问频率进行限制（以下简称限流）

　　限流的主要目的还是为了防爬。一个网站的最终目的是为了让人去访问的，但是有时候会有一些人工智能做一些对网站有伤害的事，这时候我们就需要进行相应的限制了。权限的分配是一种对网站的保护的限制，但有些功能（比如看新闻、看动态等）是不需要任何权限只需要进入网站就可以查看的，这时我们就需要进行相应的限流操作，区分出非人类的用户访问予以限制。

    def check_throttles(self, request):
        """
        Check if request should be throttled.
        Raises an appropriate exception if the request is throttled.
        """
        """
        循环每一个throttle对象，执行allow_request方法
        allow_request:
        返回False，说明限制访问频率
        返回True，说明不限制，通行
        可自定制
        """
        for throttle in self.get_throttles():
            if not throttle.allow_request(request, self):
                self.throttled(request, throttle.wait())#throttle.wait()表示多少秒后可再次访问

from __future__ import unicode_literals

import time

from django.core.cache import cache as default_cache
from django.core.exceptions import ImproperlyConfigured

from rest_framework.settings import api_settings


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):#唯一标识
        """
        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')#获取IP等
        num_proxies = api_settings.NUM_PROXIES#获取代理信息

        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#等待时长，可重写

class SimpleRateThrottle(BaseThrottle):
    """
    一个简单的缓存实现，只需要` get_cache_key() `。被覆盖。
    速率（请求/秒）是由视图上的“速率”属性设置的。类。该属性是一个字符串的形式number_of_requests /期。
    周期应该是：（的），“秒”，“M”，“min”，“h”，“小时”，“D”，“一天”。
    以前用于节流的请求信息存储在高速缓存中。
    A simple cache implementation, that only requires `.get_cache_key()`
    to be overridden.

    The rate (requests / seconds) is set by a `throttle` 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()#点进去看到需要些一个scope  ，2/m
        self.num_requests, self.duration = self.parse_rate(self.rate)

    def get_cache_key(self, request, view):#这个相当于是一个半成品，我们可以来补充它
        """
        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):#检测必须有scope，没有就报错了
            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)

    # 1、一进来首先执行，
    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)#2、执行get_cache_key
        if self.key is None:
            return True#不限制

        self.history = self.cache.get(self.key, [])#3、得到的key，默认是一个列表，赋值给了self.history，
                                                       # self.history可以理解为每一个ip对应的访问记录
        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)

第三步、执行函数get/post/put/delete

if request.method.lower() in self.http_method_names:#http_method_names = ['get', 'post', 'put', 'patch', 'delete', 'head', 'options', 'trace']
　　handler = getattr(self, request.method.lower(),self.http_method_not_allowed)#反射
else:
　　handler = self.http_method_not_allowed#抛出异常

第四步、对返回结果进行再次加工