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
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:
Uncaught SecurityError : Failed to execute ‘getImageData‘ on ‘CanvasRenderingContext2D‘ : The canvas has been tainted by cross-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,
//color: "#a9a9a7",
image2:"imgdata.php?url=http://js.xxx.com/static/activity/sq/guagua315/images/card_inner.jpg",
scratchMove:function() {
}
});
或:
xi= new XMLHttpRequest ();
xi.open( "GET" , "imgdata.php?url=" +yourImageURL, true );
xi.send();
xi.onreadystatechange= function () {
if (xi.readyState== 4 && xi.status== 200 ) {
img= new Image ;
img.onload= function (){
ctx.drawImage(img, 0 , 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: Header Value‘); 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:
# # A CORS (Cross-Origin Resouce Sharing) config for nginx # # == Purpose # # This nginx configuration enables CORS requests in the following way: # - enables CORS just for origins on a whitelist specified by a regular expression # - CORS preflight request (OPTIONS) are responded immediately # - Access-Control-Allow-Credentials=true for GET and POST requests # - Access-Control-Max-Age=20days, to minimize repetitive OPTIONS requests # - various superluous settings to accommodate nonconformant browsers # # == Comment on echoing Access-Control-Allow-Origin # # How do you allow CORS requests only from certain domains? The last # published W3C candidate recommendation states that the # Access-Control-Allow-Origin header can include a list of origins. # (See: http://www.w3.org/TR/2013/CR-cors-20130129/#access-control-allow-origin-response-header ) # However, browsers do not support this well and it likely will be # dropped from the spec (see, http://www.rfc-editor.org/errata_search.php?rfc=6454&eid=3249 ). # # The usual workaround is for the server to keep a whitelist of # acceptable origins (as a regular expression), match the request‘s # Origin header against the list, and echo back the matched value. # # (Yes you can use ‘*‘ to accept all origins but this is too open and # prevents using ‘Access-Control-Allow-Credentials: true‘, which is # needed for HTTP Basic Access authentication.) # # == Comment on spec # # Comments below are all based on my reading of the CORS spec as of # 2013-Jan-29 ( http://www.w3.org/TR/2013/CR-cors-20130129/ ), the # XMLHttpRequest spec ( # http://www.w3.org/TR/2012/WD-XMLHttpRequest-20121206/ ), and # experimentation with latest versions of Firefox, Chrome, Safari at # that point in time. # # == Changelog # # shared at: https://gist.github.com/algal/5480916 # based on: https://gist.github.com/alexjs/4165271 # location / { # if the request included an Origin: header with an origin on the whitelist, # then it is some kind of CORS request. # specifically, this example allow CORS requests from # scheme : http or https # authority : any authority ending in ".mckinsey.com" # port : nothing, or : if ($http_origin ~* (https?://[^/]*\.mckinsey\.com(:[0-9]+)?)$) { set $cors "true"; } # Nginx doesn‘t support nested If statements, so we use string # concatenation to create a flag for compound conditions # OPTIONS indicates a CORS pre-flight request if ($request_method = ‘OPTIONS‘) { set $cors "${cors}options"; } # non-OPTIONS indicates a normal CORS request if ($request_method = ‘GET‘) { set $cors "${cors}get"; } if ($request_method = ‘POST‘) { set $cors "${cors}post"; } # if it‘s a GET or POST, set the standard CORS responses header if ($cors = "trueget") { # Tells the browser this origin may make cross-origin requests # (Here, we echo the requesting origin, which matched the whitelist.) add_header ‘Access-Control-Allow-Origin‘ "$http_origin"; # Tells the browser it may show the response, when XmlHttpRequest.withCredentials=true. add_header ‘Access-Control-Allow-Credentials‘ ‘true‘; # # Tell the browser which response headers the JS can see, besides the "simple response headers" # add_header ‘Access-Control-Expose-Headers‘ ‘myresponseheader‘; } if ($cors = "truepost") { # Tells the browser this origin may make cross-origin requests # (Here, we echo the requesting origin, which matched the whitelist.) add_header ‘Access-Control-Allow-Origin‘ "$http_origin"; # Tells the browser it may show the response, when XmlHttpRequest.withCredentials=true. add_header ‘Access-Control-Allow-Credentials‘ ‘true‘; # # Tell the browser which response headers the JS can see, besides the "simple response headers" # add_header ‘Access-Control-Expose-Headers‘ ‘myresponseheader‘; } # if it‘s OPTIONS, then it‘s a CORS preflight request so respond immediately with no response body if ($cors = "trueoptions") { # Tells the browser this origin may make cross-origin requests # (Here, we echo the requesting origin, which matched the whitelist.) add_header ‘Access-Control-Allow-Origin‘ "$http_origin"; # in a preflight response, tells browser the subsequent actual request can include user credentials (e.g., cookies) add_header ‘Access-Control-Allow-Credentials‘ ‘true‘; # # Return special preflight info # # Tell browser to cache this pre-flight info for 20 days add_header ‘Access-Control-Max-Age‘ 1728000; # Tell browser we respond to GET,POST,OPTIONS in normal CORS requests. # # Not officially needed but still included to help non-conforming browsers. # # OPTIONS should not be needed here, since the field is used # to indicate methods allowed for "actual request" not the # preflight request. # # GET,POST also should not be needed, since the "simple # methods" GET,POST,HEAD are included by default. # # We should only need this header for non-simple requests # methods (e.g., DELETE), or custom request methods (e.g., XMODIFY) add_header ‘Access-Control-Allow-Methods‘ ‘GET, POST, OPTIONS‘; # Tell browser we accept these headers in the actual request # # A dynamic, wide-open config would just echo back all the headers # listed in the preflight request‘s # Access-Control-Request-Headers. # # A dynamic, restrictive config, would just echo back the # subset of Access-Control-Request-Headers headers which are # allowed for this resource. # # This static, fairly open config just returns a hardcoded set of # headers that covers many cases, including some headers that # are officially unnecessary but actually needed to support # non-conforming browsers # # Comment on some particular headers below: # # Authorization -- practically and officially needed to support # requests using HTTP Basic Access authentication. Browser JS # can use HTTP BA authentication with an XmlHttpRequest object # req by calling # # req.withCredentials=true, and # req.setRequestHeader(‘Authorization‘,‘Basic ‘ + window.btoa(theusername + ‘:‘ + thepassword)) # # Counterintuitively, the username and password fields on # XmlHttpRequest#open cannot be used to set the authorization # field automatically for CORS requests. # # Content-Type -- this is a "simple header" only when it‘s # value is either application/x-www-form-urlencoded, # multipart/form-data, or text/plain; and in that case it does # not officially need to be included. But, if your browser # code sets the content type as application/json, for example, # then that makes the header non-simple, and then your server # must declare that it allows the Content-Type header. # # Accept,Accept-Language,Content-Language -- these are the # "simple headers" and they are officially never # required. Practically, possibly required. # # Origin -- logically, should not need to be explicitly # required, since it‘s implicitly required by all of # CORS. officially, it is unclear if it is required or # forbidden! practically, probably required by existing # browsers (Gecko does not request it but WebKit does, so # WebKit might choke if it‘s not returned back). # # User-Agent,DNT -- officially, should not be required, as # they cannot be set as "author request headers". practically, # may be required. # # My Comment: # # The specs are contradictory, or else just confusing to me, # in how they describe certain headers as required by CORS but # forbidden by XmlHttpRequest. The CORS spec says the browser # is supposed to set Access-Control-Request-Headers to include # only "author request headers" (section 7.1.5). And then the # server is supposed to use Access-Control-Allow-Headers to # echo back the subset of those which is allowed, telling the # browser that it should not continue and perform the actual # request if it includes additional headers (section 7.1.5, # step 8). So this implies the browser client code must take # care to include all necessary headers as author request # headers. # # However, the spec for XmlHttpRequest#setRequestHeader # (section 4.6.2) provides a long list of headers which the # the browser client code is forbidden to set, including for # instance Origin, DNT (do not track), User-Agent, etc.. This # is understandable: these are all headers that we want the # browser itself to control, so that malicious browser client # code cannot spoof them and for instance pretend to be from a # different origin, etc.. # # But if XmlHttpRequest forbids the browser client code from # setting these (as per the XmlHttpRequest spec), then they # are not author request headers. And if they are not author # request headers, then the browser should not include them in # the preflight request‘s Access-Control-Request-Headers. And # if they are not included in Access-Control-Request-Headers, # then they should not be echoed by # Access-Control-Allow-Headers. And if they are not echoed by # Access-Control-Allow-Headers, then the browser should not # continue and execute actual request. So this seems to imply # that the CORS and XmlHttpRequest specs forbid certain # widely-used fields in CORS requests, including the Origin # field, which they also require for CORS requests. # # The bottom line: it seems there are headers needed for the # web and CORS to work, which at the moment you should # hard-code into Access-Control-Allow-Headers, although # official specs imply this should not be necessary. # add_header ‘Access-Control-Allow-Headers‘ ‘Authorization,Content-Type,Accept,Origin,User-Agent,DNT,Cache-Control,X-Mx-ReqToken,Keep-Alive,X-Requested-With,If-Modified-Since‘; # build entire response to the preflight request # no body in this response add_header ‘Content-Length‘ 0; # (should not be necessary, but included for non-conforming browsers) add_header ‘Content-Type‘ ‘text/plain charset=UTF-8‘; # indicate successful return with no content return 204; } # --PUT YOUR REGULAR NGINX CODE HERE-- }
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_header Access-Control-Allow-Origin *; }
若服务器为Apache,则可以按照如下配置:
<IfModule mod_setenvif.c> <IfModule mod_headers.c> <FilesMatch "\.(cur|gif|ico|jpe?g|png|svgz?|webp)$"> SetEnvIf Origin ":" IS_CORS Header set Access-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" ;
var img = new Image, canvas = document.createElement("canvas"), ctx = canvas.getContext("2d"), src = "http://example.com/image"; // insert image url here img.crossOrigin = "Anonymous"; img.onload = function() { canvas.width = img.width; canvas.height = img.height; ctx.drawImage( img, 0, 0 ); localStorage.setItem( "savedImageData", canvas.toDataURL("image/png") ); } img.src = src; // make sure the load event fires for cached images too if ( img.complete || img.complete === undefined ) { img.src = "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw=="; img.src = src; }
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
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