RestFramework——API基本實現及dispatch基本源碼剖析

時間 2019-11-07

標籤 restframework api 基本實現 dispatch 源碼剖析简体版

原文原文鏈接

基於Django實現

　　在使用RestFramework以前咱們先用Django本身實現如下API。前端

　　API徹底能夠有咱們基於Django本身開發，原理是給出一個接口（URL），前端向URL發送請求以獲取數據。這樣能實現先後端分離的效果。但Django實現的API許多功能都須要咱們本身寫。django

URL編程

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'))#路由分發
]

全局路由

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

app02/urls.py

views.pyjson

　　FBV後端

from django.shortcuts import render,HttpResponse

import json

def users(request):
    response = {'code':1000,'data':None}  #code用來表示狀態，好比1000表明成功，1001表明
    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}))  #返回一條數據
    elif request.method =='POST':
        return HttpResponse(json.dumps({'code':1111}))  #返回一條數據
    elif request.method =='PUT':
        pass
    elif request.method =='DELETE':
        pass

FBV

　　CBVapi

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}))  #返回一條數據
    def post(self,request,pk):
        return HttpResponse(json.dumps({'code':1111}))  #返回一條數據
    def put(self,request,pk):
        pass
    def delete(self,request,pk):
        pass

CBV

注：一般咱們在先後端分離進行編程時會推崇使用CBV的形式，CBV的代碼可讀性較高。緩存

基於RestFramework實現

安裝：app

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

　　RestFramework能夠直接在Django中使用，安裝完RestFramework後在Django中能夠當作模塊通常導入便可使用。（記得在settings.py中進行註冊，如app）前後端分離

URL與基於Django實現相同，這裏選用CBV的形式ide

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

views.py

　　CBV

#導入rest_framework，自定義視圖的類需繼承APIView
from rest_framework.views import APIView
from rest_framework.response import Response
 
class TestView(APIView):
    def dispatch(self, request, *args, **kwargs):
        """
        請求到來以後，在url中執行as_view()就會執行dispatch方法，dispatch方法是APIView類中內置的，根據請求方式不一樣觸發 get/post/put等方法。可自定製~
         
        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請求，響應內容')
 
    def post(self, request, *args, **kwargs):
        return Response('POST請求，響應內容')
 
    def put(self, request, *args, **kwargs):
        return Response('PUT請求，響應內容')

注：重要的功都在APIView的dispatch中觸發。要掌握RestFramework，必須弄懂dispatch方法作了些什麼，這樣咱們才能夠根據本身的需求進行自定製。

dispatch基本源碼剖析

　　咱們在繼承了APIView以後就能夠重寫裏面的方法進行自定製。此時咱們須要先弄懂APIView裏到底封裝了哪些方法。在APIView中，最重要的就是dispatch方法。

請求在url中執行as_view()時就會觸發dispatch，進入源碼咱們能夠看到dispatch主要作了四件事：

#在APIView類中：
    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.封裝Django原始的request，使得用了framework之後的request都具備更多功能
        """
        增長的功能
            parsers=self.get_parsers(),
            authenticators=self.get_authenticators(),#獲取認證相關的全部類並實例化，傳入request對象
            negotiator=self.get_content_negotiator(),
            parser_context=parser_context
        """
        request = self.initialize_request(request, *args, **kwargs)
        self.request = request#將封裝後的request賦值給原始request
        self.headers = self.default_response_headers  # deprecate?

        try:
            """
            2.版本處理、用戶認證、權限、訪問頻率限制
            """
            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.執行函數get/post/put/delete
            response = handler(request, *args, **kwargs)

        except Exception as exc:
            response = self.handle_exception(exc)
        #4.對返回結果進行再次加工
        self.response = self.finalize_response(request, response, *args, **kwargs)
        return self.response

接下來咱們對每一步進行具體的分析

第一步：封裝request

request = self.initialize_request(request, *args, **kwargs)
#查看initialize_request作了什麼
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(),#獲取認證相關的全部類並實例化，傳入request對象。優先找本身的，沒有就找父類的
        negotiator=self.get_content_negotiator(),
        parser_context=parser_context
    )

1.一、咱們看到request封裝了一個認證的功能——獲取認證相關的全部的類並實例化，看看get_authenticators()作了什麼

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


#self.authentication_classes是封裝有認證功能的類的列表
authentication_classes = api_settings.DEFAULT_AUTHENTICATION_CLASSES  #默認的，若是本身有會優先執行直接的

1.二、去settings.py查看默認的配置是什麼

DEFAULTS = {
    # Base API policies
    'DEFAULT_AUTHENTICATION_CLASSES': (
        'rest_framework.authentication.SessionAuthentication',   #這時候就找到了他默認認證的類了，能夠導入看看
        'rest_framework.authentication.BasicAuthentication'
    ),

1.三、導入SessionAutentication和BasicAuthentication查看這兩個雷兜風裝了什麼功能

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

BaseAuthentication

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不處理。讓下一個處理

        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切割冒號也包括
        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]  # 返回用戶和密碼
        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

BasicAuthentication

1.四、簡單自定製認證的類

　　咱們能夠看到源碼中最重要的就是BasicAuthentication的authenticate方法，因此要自定製認證的類只需重寫該方法便可

class MyAuthentication(BaseAuthentication):
    def authenticate(self, request):
        token = request.query_params.get('token')#登陸用戶有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、版本處理、認證、權限、訪問頻率限制

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

#查看initial方法作了什麼
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 處理版本信息,獲取版本必須用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認證，將user封裝到request對象中
    self.perform_authentication(request)
    #2.3 權限
    self.check_permissions(request)
    #2.4 對請求用戶進行訪問頻率的限制
    self.check_throttles(request)

2.2.一、認證：查看perform_authentication方法，發現只是將user封裝到了request中

def perform_authentication(self, request):

    request.user

2.2.二、查看request.user中都封裝了什麼

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()#執行用戶認證
        return self._user

2.2.三、執行self._authenticate() 開始用戶認證，若是驗證成功後返回元組： (用戶,用戶Token)

    def _authenticate(self):
        """
        Attempt to authenticate the request using each authentication instance
        in turn.
        """
        #循環對象列表
        for authenticator in self.authenticators:
            try:
                # 執行每個對象的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#返回一個元組，賦給了self,就能夠request.user,request.auth了
                return

        self._not_authenticated()

2.2.四、在user_auth_tuple = authenticator.authenticate(self) 進行驗證，若是驗證成功，執行類裏的authenticatie方法。若是用戶沒有認證成功：self._not_authenticated()

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

        Defaults are None, AnonymousUser & None.
        """
        # 若是跳過了全部認證，默認用戶和Token和使用配置文件進行設置
        self._authenticator = None

        if api_settings.UNAUTHENTICATED_USER:
            self.user = api_settings.UNAUTHENTICATED_USER()# 默認值爲：匿名用戶AnonymousUser
        else:
            self.user = None# None 表示跳過該認證

        if api_settings.UNAUTHENTICATED_TOKEN:
            self.auth = api_settings.UNAUTHENTICATED_TOKEN()# 默認值爲：None
        else:
            self.auth = None


#默認值均可以在settings.py中進行自定製配置
REST_FRAMEWORK = {
    'UNAUTHENTICATED_USER': None,
    'UNAUTHENTICATED_TOKEN': None,
  
}

2.3.、權限控制

######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():#尋找類中的get_permissions()方法
            if not permission.has_permission(request, self):#無權限則拋出異常
                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中查是否有權限配置

2.四、對訪問頻率進行限制（如下簡稱限流）

　　限流的主要目的仍是爲了防爬。一個網站的最終目的是爲了讓人去訪問的，可是有時候會有一些人工智能作一些對網站有傷害的事，這時候咱們就須要進行相應的限制了。權限的分配是一種對網站的保護的限制，但有些功能（好比看新聞、看動態等）是不須要任何權限只須要進入網站就能夠查看的，這時咱們就須要進行相應的限流操做，區分出非人類的用戶訪問予以限制。

    def check_throttles(self, request):
        """
        Check if request should be throttled.
        Raises an appropriate exception if the request is throttled.
        """
        """
        循環每個throttle對象，執行allow_request方法
        allow_request:
        返回False，說明限制訪問頻率
        返回True，說明不限制，通行
        可自定製
        """
        for throttle in self.get_throttles():
            if not throttle.allow_request(request, self):
                self.throttled(request, throttle.wait())#throttle.wait()表示多少秒後可再次訪問

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):#惟一標識
        """
        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')#獲取IP等
        num_proxies = api_settings.NUM_PROXIES#獲取代理信息

        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#等待時長，可重寫

BaseThrottle

class SimpleRateThrottle(BaseThrottle):
    """
    一個簡單的緩存實現，只須要` get_cache_key() `。被覆蓋。
    速率（請求/秒）是由視圖上的「速率」屬性設置的。類。該屬性是一個字符串的形式number_of_requests /期。
    週期應該是：（的），「秒」，「M」，「min」，「h」，「小時」，「D」，「一天」。
    之前用於節流的請求信息存儲在高速緩存中。
    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()#點進去看到須要些一個scope  ，2/m
        self.num_requests, self.duration = self.parse_rate(self.rate)

    def get_cache_key(self, request, view):#這個至關因而一個半成品，咱們能夠來補充它
        """
        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):#檢測必須有scope，沒有就報錯了
            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)

    # 一、一進來首先執行，
    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)#二、執行get_cache_key
        if self.key is None:
            return True#不限制

        self.history = self.cache.get(self.key, [])#三、獲得的key，默認是一個列表，賦值給了self.history，
                                                       # self.history能夠理解爲每個ip對應的訪問記錄
        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)

SimpleRateThrottle

第三步、執行函數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#拋出異常

第四步、對返回結果進行再次加工