Ajax跨域、Json跨域、Socket跨域和Canvas跨域等同源策略限制的解

发布时间：2020-12-15 21:36:50 所属栏目：百科来源：网络整理

导读：同源是指相同的协议、域名、端口，三者都相同才属于同域。不符合上述定义的请求，则称为跨域。相信每个开发人员都曾遇到过跨域请求的情况，虽然情况不一样，但问题的本质都可以归为浏览器出于安全考虑下的同源策略的限制。跨域的情形有很多，最常见的有Aja

同源是指相同的协议、域名、端口，三者都相同才属于同域。不符合上述定义的请求，则称为跨域。

相信每个开发人员都曾遇到过跨域请求的情况，虽然情况不一样，但问题的本质都可以归为浏览器出于安全考虑下的同源策略的限制。

跨域的情形有很多，最常见的有Ajax跨域、Socket跨域和Canvas跨域。下面列举一些我们常见的跨域情形下，某些浏览器控制台给出的错误提示：

FireFox下的提示：

已阻止交叉源请求：同源策略不允许读取***上的远程资源。可以将资源移动到相同的域名上或者启用 CORS 来解决这个问题。

Canvas跨域Chrome下的提示：

UncaughtSecurityError:Failedto execute'getImageData'on'CanvasRenderingContext2D':Thecanvas has been taintedbycross-origin data.

或：

Imagefrom origin 'http://js.xx.com' has been blocked from loading by Cross-OriginResource Sharing policy: No 'Access-Control-Allow-Origin' header is present onthe requested resource. Origin 'http://act.xx.com' is therefore not allowedaccess.

网上有许多解决跨域的方法，大体上有这几种：

1）document.domain+iframe的设置

2）动态创建script

3）利用iframe和location.hash

4）window.name实现的跨域数据传输

5）使用HTML5 postMessage

6）利用flash

7）通过代理，js访问代理，代理转到不同的域

http://developer.yahoo.com/javascript/howto-proxy.html

8）Jquery JSONP(不能成为真正的Ajax，本质上仍是动态创建script)

http://www.cnblogs.com/chopper/archive/2012/03/24/2403945.html

9）跨域资源共享（CORS）这是HTML5跨域问题的标准解决方案

说明：方案1~方案6见Rain Man所写的文章《JavaScript跨域总结与解决办法》

http://www.cnblogs.com/rainman/archive/2011/02/20/1959325.html

下面主要就我总结的几种解决跨域的方法，展开说一下。

1）绕开跨域。

适用情形是：动静分离。

example1.com域名下的页面中跨域请求是以JavaScript内联方式实现的，而请求的目标静态资源是放在example2.com域名下，这时可以将执行跨域请求的JavaScript代码块独立出来，放到example2.com上，而example1.com页面通过外联方式引入该静态域名下的js文件。这样，js与请求的图片等资源都在example2.com下，即可正常访问到。这种方法其实是一种巧妙避开跨域的方法。

2）后台抓取克隆图片。

适用情形：动静不分离（两个域名均运行访问静态资源）。

example1.com请求example2.com下的资源图片，可以使用PHP抓取图片并在example2.com下生成一份，这样就可以间接访问到example1.com的静态资源。

html模板示例代码：

$("#scratchpad").wScratchPad({ //刮刮卡示例，当前域名http://act.xxx.com

width:283,

height:154,51); font-family:Arial; font-size:14px; line-height:26px"> //color: "#a9a9a7",51); font-family:Arial; font-size:14px; line-height:26px"> image2:"imgdata.php?url=http://js.xxx.com/static/activity/sq/guagua315/images/card_inner.jpg",51); font-family:Arial; font-size:14px; line-height:26px"> scratchMove:function() {

}

});

xi=newXMLHttpRequest();

xi.open("GET","imgdata.php?url="+yourImageURL,true);

xi.send();

xi.onreadystatechange=function() {

if(xi.readyState==4&& xi.status==200) {

img=Image;

img.onload=function(){

ctx.drawImage(img,0,canvas.width,canvas.height);

}

img.src=xi.responseText;

}

PHP处理代码：

<?php//imgdata.php

$url=$_GET['url'];

$img =file_get_contents($url);

$imgname = substr(strrchr($url,"/"),1);

file_put_contents($fn,$img);

echo $imgname;

上述代码在当前php目录下生成了克隆生成了一张图片。

3）后台程序设置Access-Control-Allow-Origin

适用情形：Ajax获取跨域接口的JSON数据。

example1.com请求example2.com的数据接口，则需要在example2.com的数据接口添加跨域访问授权。

PHP程序中开始出添加header('HeaderName:HeaderValue'); 这样的header标记：

header('Access-Control-Allow-Origin:*');

4）修改服务器配置启用CORS

适用情形：跨域访问静态资源。

Access-Control-Allow-Origin是什么作用呢？用于授权资源的跨站访问。比如,静态资源图片都放在example2.com 域名下,如果在返回的头中没有设置 Access-Control-Allow-Origin,那么别的域是没有权限外链你的图片的。

要实现CORS跨域，服务端需要这个一个流程，图片引自html5rocks，附图如下

a.对于简单请求，如GET，只需要在HTTP Response后添加Access-Control-Allow-Origin。

b.对于非简单请求，比如POST、PUT、DELETE等，浏览器会分两次应答。第一次preflight（method: OPTIONS），主要验证来源是否合法，并返回允许的Header等。第二次才是真正的HTTP应答。所以服务器必须处理OPTIONS应答。

这里是一个nginx启用CORS的参考配置示例http://enable-cors.org/server_nginx.html。代码：

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 #
 #ACORS(Cross-OriginResouceSharing)configfornginx
 #
 #==Purpose
 #ThisnginxconfigurationenablesCORSrequestsinthefollowingway:
 #-enablesCORSjustfororiginsonawhitelistspecifiedbyaregularexpression
 #-CORSpreflightrequest(OPTIONS)arerespondedimmediately
 #-Access-Control-Allow-Credentials=trueforGETandPOSTrequests
 #-Access-Control-Max-Age=20days,tominimizerepetitiveOPTIONSrequests
 #-varioussuperluoussettingstoaccommodatenonconformantbrowsers
 #
 #==CommentonechoingAccess-Control-Allow-Origin
 #HowdoyouallowCORSrequestsonlyfromcertaindomains?Thelast
 #publishedW3Ccandidaterecommendationstatesthatthe
 #Access-Control-Allow-Originheadercanincludealistoforigins.
 #(See:http://www.w3.org/TR/2013/CR-cors-20130129/#access-control-allow-origin-response-header)
 #However,browsersdonotsupportthiswellanditlikelywillbe
 #droppedfromthespec(see,http://www.rfc-editor.org/errata_search.php?rfc=6454&eid=3249).
 #Theusualworkaroundisfortheservertokeepawhitelistof
 #acceptableorigins(asaregularexpression),matchtherequest's
 #Originheaderagainstthelist,andechobackthematchedvalue.
 #(Yesyoucanuse'*'toacceptalloriginsbutthisistooopenand
 #preventsusing'Access-Control-Allow-Credentials:true',whichis
 #neededforHTTPBasicAccessauthentication.)
 #==Commentonspec
 #CommentsbelowareallbasedonmyreadingoftheCORSspecasof
 #2013-Jan-29(http://www.w3.org/TR/2013/CR-cors-20130129/),the
 #XMLHttpRequestspec(
 #http://www.w3.org/TR/2012/WD-XMLHttpRequest-20121206/),and
 #experimentationwithlatestversionsofFirefox,Chrome,Safariat
 #thatpointintime.
 #==Changelog
 #sharedat:https://gist.github.com/algal/5480916
 #basedon:https://gist.github.com/alexjs/4165271
 
 location/{
 #iftherequestincludedanOrigin:headerwithanoriginonthewhitelist,
 #thenitissomekindofCORSrequest.
 
 #specifically,thisexampleallowCORSrequestsfrom
 #scheme:httporhttps
 #authority:anyauthorityendingin".mckinsey.com"
 #port:nothing,or:
 if($http_origin~*(https?://[^/]*.mckinsey.com(:[0-9]+)?)$){
 set$cors"true";
 }
 #Nginxdoesn'tsupportnestedIfstatements,soweusestring
 #concatenationtocreateaflagforcompoundconditions
 #OPTIONSindicatesaCORSpre-flightrequest
 if($request_method='OPTIONS'){
 set$cors"${cors}options";
 #non-OPTIONSindicatesanormalCORSrequest
 if($request_method='GET'){
 set$cors"${cors}get";
 }
 if($request_method='POST'){
 set$cors"${cors}post";
 #ifit'saGETorPOST,setthestandardCORSresponsesheader
 if($cors="trueget"){
 #Tellsthebrowserthisoriginmaymakecross-originrequests
 #(Here,weechotherequestingorigin,whichmatchedthewhitelist.)
 add_header'Access-Control-Allow-Origin'"$http_origin";
 #Tellsthebrowseritmayshowtheresponse,whenXmlHttpRequest.withCredentials=true.
 add_header'Access-Control-Allow-Credentials''true';
 ##TellthebrowserwhichresponseheaderstheJScansee,besidesthe"simpleresponseheaders"
 #add_header'Access-Control-Expose-Headers''myresponseheader';
 if($cors="truepost"){
 #ifit'sOPTIONS,thenit'saCORSpreflightrequestsorespondimmediatelywithnoresponsebody
 if($cors="trueoptions"){
 #Tellsthebrowserthisoriginmaymakecross-originrequests
 #(Here,whichmatchedthewhitelist.)
 add_header'Access-Control-Allow-Origin'"$http_origin";
 #inapreflightresponse,tellsbrowserthesubsequentactualrequestcanincludeusercredentials(e.g.,cookies)
 add_header'Access-Control-Allow-Credentials''true';
 #Returnspecialpreflightinfo
 #Tellbrowsertocachethispre-flightinfofor20days
 add_header'Access-Control-Max-Age'1728000;
 #TellbrowserwerespondtoGET,POST,OPTIONSinnormalCORSrequests.
 #Notofficiallyneededbutstillincludedtohelpnon-conformingbrowsers.
 #OPTIONSshouldnotbeneededhere,sincethefieldisused
 #toindicatemethodsallowedfor"actualrequest"notthe
 #preflightrequest.
 #GET,POSTalsoshouldnotbeneeded,sincethe"simple
 #methods"GET,HEADareincludedbydefault.
 #Weshouldonlyneedthisheaderfornon-simplerequests
 #methods(e.g.,DELETE),orcustomrequestmethods(e.g.,XMODIFY)
 add_header'Access-Control-Allow-Methods''GET,OPTIONS';
 #Tellbrowserweaccepttheseheadersintheactualrequest
 #Adynamic,wide-openconfigwouldjustechobackalltheheaders
 #listedinthepreflightrequest's
 #Access-Control-Request-Headers.
 #subsetofAccess-Control-Request-Headersheaderswhichare
 #allowedforthisresource.
 #Thisstatic,fairlyopenconfigjustreturnsahardcodedsetof
 #headersthatcoversmanycases,includingsomeheadersthat
 #areofficiallyunnecessarybutactuallyneededtosupport
 #non-conformingbrowsers
 #Commentonsomeparticularheadersbelow:
 #Authorization--practicallyandofficiallyneededtosupport
 #requestsusingHTTPBasicAccessauthentication.BrowserJS
 #canuseHTTPBAauthenticationwithanXmlHttpRequestobject
 #reqbycalling
 #req.withCredentials=true,248)"> #req.setRequestHeader('Authorization','Basic'+window.btoa(theusername+':'+thepassword))
 #Counterintuitively,theusernameandpasswordfieldson
 #XmlHttpRequest#opencannotbeusedtosettheauthorization
 #fieldautomaticallyforCORSrequests.
 #Content-Type--thisisa"simpleheader"onlywhenit's
 #valueiseitherapplication/x-www-form-urlencoded,248)"> #multipart/form-data,ortext/plain;andinthatcaseitdoes
 #notofficiallyneedtobeincluded.But,ifyourbrowser
 #codesetsthecontenttypeasapplication/json,forexample,
 #thenthatmakestheheadernon-simple,andthenyourserver
 #mustdeclarethatitallowstheContent-Typeheader.
 #Accept,Accept-Language,Content-Language--thesearethe
 #"simpleheaders"andtheyareofficiallynever
 #required.Practically,possiblyrequired.
 #Origin--logically,shouldnotneedtobeexplicitly
 #required,sinceit'simplicitlyrequiredbyallof
 #CORS.officially,itisunclearifitisrequiredor
 #forbidden!practically,probablyrequiredbyexisting
 #browsers(GeckodoesnotrequestitbutWebKitdoes,so
 #WebKitmightchokeifit'snotreturnedback).
 #User-Agent,DNT--officially,shouldnotberequired,as
 #theycannotbesetas"authorrequestheaders".practically,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important"> #mayberequired.
 #MyComment:
 #Thespecsarecontradictory,orelsejustconfusingtome,248)"> #inhowtheydescribecertainheadersasrequiredbyCORSbut
 #forbiddenbyXmlHttpRequest.TheCORSspecsaysthebrowser
 #issupposedtosetAccess-Control-Request-Headerstoinclude
 #only"authorrequestheaders"(section7.1.5).Andthenthe
 #serverissupposedtouseAccess-Control-Allow-Headersto
 #echobackthesubsetofthosewhichisallowed,tellingthe
 #browserthatitshouldnotcontinueandperformtheactual
 #requestifitincludesadditionalheaders(section7.1.5,248)"> #step8).Sothisimpliesthebrowserclientcodemusttake
 #caretoincludeallnecessaryheadersasauthorrequest
 #headers.
 #However,thespecforXmlHttpRequest#setRequestHeader
 #(section4.6.2)providesalonglistofheaderswhichthe
 #thebrowserclientcodeisforbiddentoset,includingfor
 #instanceOrigin,DNT(donottrack),User-Agent,etc..This
 #isunderstandable:theseareallheadersthatwewantthe
 #browseritselftocontrol,sothatmaliciousbrowserclient
 #codecannotspoofthemandforinstancepretendtobefroma
 #differentorigin,etc..
 #ButifXmlHttpRequestforbidsthebrowserclientcodefrom
 #settingthese(aspertheXmlHttpRequestspec),thenthey
 #arenotauthorrequestheaders.Andiftheyarenotauthor
 #requestheaders,thenthebrowsershouldnotincludethemin
 #thepreflightrequest'sAccess-Control-Request-Headers.And
 #iftheyarenotincludedinAccess-Control-Request-Headers,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important"> #thentheyshouldnotbeechoedby
 #Access-Control-Allow-Headers.Andiftheyarenotechoedby
 #Access-Control-Allow-Headers,thenthebrowsershouldnot
 #continueandexecuteactualrequest.Sothisseemstoimply
 #thattheCORSandXmlHttpRequestspecsforbidcertain
 #widely-usedfieldsinCORSrequests,includingtheOrigin
 #field,whichtheyalsorequireforCORSrequests.
 #Thebottomline:itseemsthereareheadersneededforthe
 #webandCORStowork,whichatthemomentyoushould
 #hard-codeintoAccess-Control-Allow-Headers,although
 #officialspecsimplythisshouldnotbenecessary.
 add_header'Access-Control-Allow-Headers''Authorization,Content-Type,Accept,Origin,DNT,Cache-Control,X-Mx-ReqToken,Keep-Alive,X-Requested-With,If-Modified-Since';
 #buildentireresponsetothepreflightrequest
 #nobodyinthisresponse
 add_header'Content-Length'0;
 #(shouldnotbenecessary,butincludedfornon-conformingbrowsers)
 add_header'Content-Type''text/plaincharset=UTF-8';
 #indicatesuccessfulreturnwithnocontent
 return204;
 #--PUTYOURREGULARNGINXCODEHERE--
 

服务器解析流程如下：

a.首先查看http头部有无origin字段；

b.如果没有，或者不允许，直接当成普通请求处理，结束；

c.如果有并且是允许的，那么再看是否是preflight(method=OPTIONS)；

d.如果是preflight，就返回Allow-Headers、Allow-Methods等，内容为空；

e.如果不是preflight，就返回Allow-Origin、Allow-Credentials等，并返回正常内容。

若服务器为nginx，可以在 nginx 的 conf 文件中加入以下内容：

location/{

add_headerAccess-Control-Allow-Origin*;
}

若服务器为Apache，则可以按照如下配置：

<IfModulemod_setenvif.c>

<IfModulemod_headers.c>
<FilesMatch".(cur|gif|ico|jpe?g|png|svgz?|webp)$">
SetEnvIfOrigin":"IS_CORS
HeadersetAccess-Control-Allow-Origin"*"env=IS_CORS
</FilesMatch>
</IfModule>
</IfModule>

为安全起见，Access-Control-Allow-Origin也可设为特定域名的方式。

在HTML5中，有些HTML元素为CORS提供了支持，如img、video新增了crossOrigin属性，属性值可以为anonymous或use-credentials。比如，canvas绘图要用到跨域图片，在JavaScript中要设置img.crossOrigin="Anonymous";

[javascript] 
   

varimg=newImage,

canvas=document.createElement("canvas"),
ctx=canvas.getContext("2d"),248)"> src="http://example.com/image";//insertimageurlhere
img.crossOrigin="Anonymous";
img.onload=function(){
canvas.width=img.width;
canvas.height=img.height;
ctx.drawImage(img,0);
localStorage.setItem("savedImageData",canvas.toDataURL("image/png"));
img.src=src;
//makesuretheloadeventfiresforcachedimagestoo
if(img.complete||img.complete===undefined){
img.src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==";
上述配置完成后，重启服务器，CORS启用。

然后我们再刷新页面，查询请求头的参数，可以发现多出一个：Access-Control-Allow-Origin:*

，到此证明服务器配置已经生效。同时我们的canvas绘图也可以正常使用了。

刷新页面返回请求响应结果后，HTTP Request Headers的内容：

Remote Address:222.132.18.xx:80

Request URL:http://js.xx.com/static/activity/sq/guagua315/images/card_inner.jpg

Request Method:GET

Status Code:200 OK

Request Headersview source

Accept:image/webp,*/*;q=0.8

Accept-Encoding:gzip,deflate,sdch

Accept-Language:zh-CN,zh;q=0.8

Cache-Control:no-cache

Connection:keep-alive

Host:js.xx.com

Origin:http://act.xx.com

Pragma:no-cache

RA-Sid:7CCAD53E-20140704-054839-03c57a-85faf2

RA-Ver:2.8.8

Referer:http://act.xx.com/sq/guagua315?uuid=46124642&fid=2&sign=xxx

User-Agent:Mozilla/5.0 (Windows NT 6.1;WOW64) AppleWebKit/537.36 (KHTML,like Gecko) Chrome/40.0.2214.115Safari/537.36

Response Headersview source

Accept-Ranges:bytes

Access-Control-Allow-Origin:*

Connection:close

Content-Length:4010

Content-Type:image/jpeg

Date:Thu,12 Mar 2015 02:29:43 GMT

ETag:"54f7d1b4-faa"

Last-Modified:Thu,05 Mar 2015 03:47:00 GMT

Powered-By-ChinaCache:MISS fromCNC-WF-3-3X6

Powered-By-ChinaCache:MISS fromCNC-WF-3-3X5

Server:Tengine
Switch:FSCS
附图：

参考文章：

CORS enabled image https://developer.mozilla.org/en-US/docs/Web/HTML/CORS_enabled_image

CORS on Nginx http://enable-cors.org/server_nginx.html

Nginx CORS实现JS跨域 http://www.52php.cn/article/p-xhzdhafc-bbp.html

转载请注明出处，文章来自于freshlover的CSDN空间《Ajax跨域、Json跨域、Socket跨域和Canvas跨域等同源策略限制的解决方法》

http://www.52php.cn/article/p-dsqvmmtq-yn.html

（编辑：李大同）

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