Nginx CORS实现JS跨域

时间:2023-06-29 13:38:31

1. 什么是跨域

简单地理解就是因为JavaScript同源策略的限制,a.com 域名下的js无法操作b.com或是c.a.com域名下的对象。

同源是指相同的协议、域名、端口。特别注意两点:

  • 如果是协议和端口造成的跨域问题“前台”是无能为力的,
  • 在跨域问题上,域仅仅是通过“协议+域名+端口”来识别,两个不同的域名即便指向同一个ip地址,也是跨域的。

2. 跨域解决方案

跨域解决方案有多种,大多是利用JS Hack:

3. CORS

CORS: 跨域资源共享(Cross-Origin Resource Sharing)http://www.w3.org/TR/cors/

当前几乎所有的浏览器(Internet Explorer 8+, Firefox 3.5+, Safari 4+和 Chrome 3+)都可通过名为跨域资源共享(Cross-Origin Resource Sharing)的协议支持ajax跨域调用。(see: http://caniuse.com/#search=cors)

Chrome, Firefox, Opera and Safari 都使用的是 XMLHttpRequest2 对象, IE使用XDomainRequest。XMLHttpRequest2的Request属性:open()、setRequestHeader()、timeout、withCredentials、upload、send()、send()、abort()。

XMLHttpRequest2的Response属性:status、statusText、getResponseHeader()、getAllResponseHeaders()、entity、overrideMimeType()、responseType、response、responseText、responseXML。

启用 CORS 请求

假设您的应用已经在 example.com 上了,而您想要从 www.example2.com 提取数据。一般情况下,如果您尝试进行这种类型的 AJAX 调用,请求将会失败,而浏览器将会出现“源不匹配”的错误。利用 CORS,www.example2.com 服务端只需添加一个HTTP Response头,就可以允许来自 example.com 的请求:

Access-Control-Allow-Origin: http://example.com
Access-Control-Allow-Credentials: true(可选)

可将 Access-Control-Allow-Origin 添加到某网站下或整个域中的单个资源。要允许任何域向您提交请求,请设置如下:

Access-Control-Allow-Origin: *
Access-Control-Allow-Credentials: true(可选)

其实,该网站 (html5rocks.com) 已在其所有网页上均启用了 CORS。启用开发人员工具后,您就会在我们的响应中看到 Access-Control-Allow-Origin 了。

提交跨域请求

如果服务器端已启用了 CORS,那么提交跨域请求就和普通的 XMLHttpRequest 请求没什么区别。例如,现在 example.com 可以向 www.example2.com 提交请求了:

var xhr = new XMLHttpRequest();
// xhr.withCredentials = true; //如果需要Cookie等
xhr.open('GET', 'http://www.example2.com/hello.json');
xhr.onload = function(e) {
var data = JSON.parse(this.response);
...
}
xhr.send();

4. 服务端Nginx配置

要实现CORS跨域,服务端需要这个一个流程:http://www.html5rocks.com/static/images/cors_server_flowchart.png

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

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。

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

流程如下:

  1. 首先查看http头部有无origin字段;
  2. 如果没有,或者不允许,直接当成普通请求处理,结束;
  3. 如果有并且是允许的,那么再看是否是preflight(method=OPTIONS);
  4. 如果是preflight,就返回Allow-Headers、Allow-Methods等,内容为空;
  5. 如果不是preflight,就返回Allow-Origin、Allow-Credentials等,并返回正常内容。

用伪代码表示:

location /pub/(.+) {
if ($http_origin ~ <允许的域(正则匹配)>) {
add_header 'Access-Control-Allow-Origin' "$http_origin";
add_header 'Access-Control-Allow-Credentials' "true";
if ($request_method = "OPTIONS") {
add_header 'Access-Control-Max-Age' 86400;
add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS, DELETE';
add_header 'Access-Control-Allow-Headers' 'reqid, nid, host, x-real-ip, x-forwarded-ip, event-type, event-id, accept, content-type';
add_header 'Content-Length' 0;
add_header 'Content-Type' 'text/plain, charset=utf-8';
return 204;
}
}
# 正常nginx配置
......
}

但是由于Nginx 的 if 是邪恶的,所以配置就相当地让人不爽(是我的配置不够简洁吗?)。下面nginx-spdy-push里/pub接口启用CORS的配置:

# push publish
# broadcast channel name must start with '_'
# (i.e., normal channel must not start with '_') # GET /pub/channel_id -> get statistics about a channel
# POST /pub/channel_id -> publish a message to the channel
# DELETE /pub_admin?id=channel_id -> delete the channel #rewrite_log on; # server_name test.gw.com.cn
# listen 2443 ssl spdy location ~ ^/pub/([-_.A-Za-z0-9]+)$ { set $cors "local"; # configure CORS based on https://gist.github.com/alexjs/4165271
# (See: http://www.w3.org/TR/2013/CR-cors-20130129/#access-control-allow-origin-response-header ) if ( $http_origin ~* "https://.+\.gw\.com\.cn(?=:[0-9]+)?" ) {
set $cors "allow";
}
if ($request_method = "OPTIONS") {
set $cors "${cors}options";
} # if CORS request is not a simple method
if ($cors = "allowoptions") {
# Tells the browser this origin may make cross-origin requests
add_header 'Access-Control-Allow-Origin' "$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 1 day
add_header 'Access-Control-Max-Age' 86400; # 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, DELETE'; # Tell browser we accept these headers in the actual request
add_header 'Access-Control-Allow-Headers' 'reqid, nid, host, x-real-ip, x-forwarded-ip, event-type, event-id, accept, content-type'; # === response for OPTIONS method === # 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;
} if ($cors = "allow") {
rewrite /pub/(.*) /pub_cors/$1 last;
} if ($cors = "local") {
rewrite /pub/(.*) /pub_int/$1 last;
}
} location ~ /pub_cors/(.*) {
internal;
# Tells the browser this origin may make cross-origin requests
add_header 'Access-Control-Allow-Origin' "$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"; push_stream_publisher admin; # enable delete channel
set $push_stream_channel_id $1; push_stream_store_messages on; # enable /sub/ch.b3
push_stream_channel_info_on_publish on;
} location ~ /pub_int/(.*) {
# internal;
push_stream_publisher admin; # enable delete channel
set $push_stream_channel_id $1; push_stream_store_messages on; # enable /sub/ch.b3
push_stream_channel_info_on_publish on;
}

5. 客户端javascript代码

下面是https://spdy.gw.com.cn/sse.html里的代码

var xhr = new XMLHttpRequest();
//xhr.withCredentials = true;
xhr.open("POST", "https://test.gw.com.cn:2443/pub/ch1", true);
// xhr.setRequestHeader("accept", "application/json"); xhr.onload = function() {
$('back').innerHTML = xhr.responseText;
$('ch1').value = + $('ch1').value + 1;
}
xhr.onerror = function() {
alert('Woops, there was an error making the request.');
}; xhr.send($('ch1').value);

页面的域是https://spdy.gw.com.cn, XMLHttpRequest的域是https://test.gw.com.cn:2443,不同的域,并且Post方式。

用Chrome测试,可以发现有一次OPTIONS应答。如过没有OPTIONS应答,可能是之前已经应答过,被浏览器缓存了'Access-Control-Max-Age' 86400;,清除缓存,再试验。

6. 相关链接