1、问题引发点:
前不久发现一个问题: 前端并没有设置请求头信息里面的Accept-Encoding:gzip...但是在请求头中可以明显的看到Accept-Encoding:gzip, deflate, sdch,并且我尝试修改这个请求头，发现 不 生 效；
2、XMLHttpRequest对象提供了一个设置请求头的方法:setRequestHeader，对应的jQuery可以再beforeSend回调里面设置请求头：
$.ajax({
type: "GET",
url: "test.php",
success: function(data) {
console.log(data);
},
beforeSend: function(xhr) {
xhr.setRequestHeader("User-Agent", "headertest");
}
});
3、后来看W3C标准文档发现，这个请求头不是什么都可以设置的，标准里面明确规定了以下请求头信息是浏览器控制，开发者不允许设置这些请求头
Terminate these steps if header is a case-insensitive match for one of the following headers:
Accept-CharsetAccept-EncodingAccess-Control-Request-HeadersAccess-Control-Request-MethodConnectionContent-LengthCookieCookie2DateDNTExpectHostKeep-AliveOriginRefererTETrailerTransfer-EncodingUpgradeUser-AgentVia
… or if the start of header is a case-insensitive match for Proxy- or Sec- (including when header is just Proxy- or Sec-).
The above headers are controlled by the user agent to let it control those aspects of transport. This guarantees data integrity to some extent. Header names starting with Sec- are not allowed to be set to allow new headers to be minted that are guaranteed not to come fromXMLHttpRequest.
4、例子:
testAE.html
<!DOCTYPE html>
<html>
<head>
<title>test</title>
</head>
<script type="text/javascript" src="./jquery.1.8.1.min.js"></script>
<body>
<script type="text/javascript">
$.ajax({
type: "GET",
url: "./testAE.php",
success: function(data) {
$("body").append(data);
},
beforeSend: function(xhr) {
xhr.setRequestHeader("Accept-Encoding", "testAE");
}
});
</script>
</body>
</html>
testAE.php
<?php /*回传ACCEPT_ENCODING*/ echo $_SERVER['HTTP_ACCEPT_ENCODING']; ?>
chrome:
ie:
控制台:
可以看到jQuery也会提示你这样设置是不安全的。
在mozila官方论坛里面也有相应的讨论：Ajax setRequestHeader;