浏览器可以自动修改URL？
今天，一个同事访问http://www.ibm.com.cn网站时，觉得很奇怪，明明键入的是http://www.ibm.com.cn，怎么IE自动把它变成了http://www.ibm.com/cn/，而且已访问结果也是正确的。他觉得很费解，IE难道有这么智能？
只要了解HTTP协议，以上转换的原理很简单，其过程大致如下：
1.为了从www.ibm.com.cn上取得网页，浏览器做了类似下面的事情。
telnet www.ibm.com.cn 80
GET / HTTP/1.1
Host: www.ibm.com.cn
Accept-Languge: zh_CN
这时WEB服务器上返回如下内容：
HTTP/1.1 301 Moved Permanently
Date: Thu, 16 Feb 2006 12:14:13 GMT
Server: IBM_HTTP_Server
Location: http://www.ibm.com/link/redirect.www.ibm.com/www.ibm.com.cn/
Content-Length: 268
Content-Type: text/html
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html>
<head><title>301 Moved Permanently</title></head><body>
h1>Moved Permanently</h1>
<p>The document has moved
<a href="http://www.ibm.com/link/redirect.www.ibm.com/www.ibm.com.cn/">here</a>.
</p>
</body>
</html>
根据HTTP协议里的规定，3开头的错误码表示重定向，并告诉浏览器从指定的URL重新获取文件。
2.于是，浏览器又做了类似下面的事情。
telnet www.ibm.com 80
GET /link/redirect.www.ibm.com/www.ibm.com.cn/
Host: www.ibm.com.cn
Accept-Languge: zh_CN
这时WEB服务器上返回如下内容：
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head><title>302 Found</title></head><body>
<h1>Found</h1>
<p>The document has moved
<a href="http://www.ibm.com/cn/">here</a>.</p>
</body></html>
还是重定向。
3.于是，浏览器又做了类似下面的事情。
telnet www.ibm.com 80
GET /cn/ HTTP/1.1
Host: www.ibm.com.cn
Accept-Languge: zh_CN
这回终于得到了网面真正的内容。
参考：RFC 2616中的错误码：
Status-Code =
"100" ; Section 10.1.1: Continue
| "101" ; Section 10.1.2: Switching Protocols
| "200" ; Section 10.2.1: OK
| "201" ; Section 10.2.2: Created
| "202" ; Section 10.2.3: Accepted
| "203" ; Section 10.2.4: Non-Authoritative Information
| "204" ; Section 10.2.5: No Content
| "205" ; Section 10.2.6: Reset Content
| "206" ; Section 10.2.7: Partial Content
| "300" ; Section 10.3.1: Multiple Choices
| "301" ; Section 10.3.2: Moved Permanently
| "302" ; Section 10.3.3: Found
| "303" ; Section 10.3.4: See Other
| "304" ; Section 10.3.5: Not Modified
| "305" ; Section 10.3.6: Use Proxy
| "307" ; Section 10.3.8: Temporary Redirect
| "400" ; Section 10.4.1: Bad Request
| "401" ; Section 10.4.2: Unauthorized
| "402" ; Section 10.4.3: Payment Required
| "403" ; Section 10.4.4: Forbidden
| "404" ; Section 10.4.5: Not Found
| "405" ; Section 10.4.6: Method Not Allowed
| "406" ; Section 10.4.7: Not Acceptable
| "407" ; Section 10.4.8: Proxy Authentication Required
| "408" ; Section 10.4.9: Request Time-out
| "409" ; Section 10.4.10: Conflict
| "410" ; Section 10.4.11: Gone
| "411" ; Section 10.4.12: Length Required
| "412" ; Section 10.4.13: Precondition Failed
| "413" ; Section 10.4.14: Request Entity Too Large
| "414" ; Section 10.4.15: Request-URI Too Large
| "415" ; Section 10.4.16: Unsupported Media Type
| "416" ; Section 10.4.17: Requested range not satisfiable
| "417" ; Section 10.4.18: Expectation Failed
| "500" ; Section 10.5.1: Internal Server Error
| "501" ; Section 10.5.2: Not Implemented
| "502" ; Section 10.5.3: Bad Gateway
| "503" ; Section 10.5.4: Service Unavailable
| "504" ; Section 10.5.5: Gateway Time-out
| "505" ; Section 10.5.6: HTTP Version not supported
| extension-code