URL重定向的实现

URL重定向的实现

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URL重定向也称为URL转发，域名重定向或者域名转发，是一项W3C联盟用来让一个web页面使用其他链接仍能打开的技术。

主要功能包括
1.目的：
1.1 相似的域名；
1.2 更改一个网站使用新的域名；
1.3 积累外部链接；
1.4 给一个较长的动态链接地址定义一个更短的、更有意义的固定链接；
1.5 操纵搜索引擎；
1.6 讽刺或者评论；
1.7 操纵访问者访问的页面。
2.技巧：
2.1 手工重定向；
2.2 http 3xx状态码
2.2.1 利用服务脚本实现重定向；
2.2.2 使用.htaccess文件重定向；
2.3 刷新Meta标签以及http header；
2.4 JavaScript脚本重定向；
2.5 Frame框架重定向；
2.6 闭合重定向（重定向循环）；
3.服务：
3.1 URL重定向服务；
3.2 URL隐藏服务；
4.也看看这些：
5.参考
6.外部链接

Contents
1 Purposes
1.1 Similar domain names
1.2 Moving a site to a new domain
1.3 Logging outgoing links
1.4 Short, meaningful, persistent aliases for long or changing URLs
1.5 Manipulating search engines
1.6 Satire and criticism
1.7 Manipulating visitors
2 Techniques
2.1 Manual redirect
2.2 HTTP status codes 3xx
2.2.1 Using server-side scripting for Redirection
2.2.2 Using .htaccess for Redirection
2.3 Refresh Meta tag and HTTP refresh header
2.4 JavaScript redirects
2.5 Frame redirects
2.6 Redirect loops
3 Services
3.1 URL redirection services
3.2 URL obfuscation services
4 See also
5 References
6 External links

目的
有很多原因使站长们使用重定向There are several reasons for a webmaster to use redirection:

相似的域名Similar domain names

一个网站浏览者可能很容易将"google.com"和"googel.com"这种相似的域名搞混了，一些机构和组织经常要把这些容易拼错的域名重定向到整群的地址。又例如，域名example.com和wxample.net可能会被重定向到一个相同的域甚甚至是网页例如example.org。这种技术同样被用于域名的保护，或者将".edu"、".net"等重定向到诸如".com"这样的更容易被接受的域名。

A web browser user might mis-type a URL -- for example, "gooogle.com" and "googel.com". Organizations often register these "mis-spelled" domains and re-direct them to the "correct" location: google.com. For example: the addresses example.com and example.net could both redirect to a single domain, or web page, such as example.org. This technique is often used to "reserve" other TLDs with the same name, or make it easier for a true ".edu" or ".net" to redirect to a more recognizable ".com" domain.

将网站搬迁至一个新的域名
Moving a site to a new domain
为什么不使用重定向页面的方法呢？
Why redirect a web page?

一个网站或者需要更换域名，一个作者也有可能需要将他的页面转移到新的域名，两个网站合二为一也并非不可能。使用URL重定向，当外链链入地址已经失效的时候可以将其转发到正确的地址。这些链接的更改可能在其他网站并没有意识到的情况下已经在他们浏览器的书签/收藏中保存。对搜索引擎亦有同样的效应，这些搜索引擎在他们的数据库中保存着大量的旧域名以及旧域名上面的大量页面并将使用者带向这些链接。如果使用了重定向的技术，搜索引擎的使用者可以仍然到达正确的页面。当然，在下一个搜索路径，搜索引擎将提供新的页面索引地址。
A web site might need to change its domain name.
An author might move his or her pages to a new domain.
Two web sites might merge.
With URL redirects, incoming links to an outdated URL can be sent to the correct location. These links might be from other sites that have not realized that there is a change or from bookmarks/favorites that users have saved in their browsers.

The same applies to search engines. They often have the older/outdated domain names and links in their database and will send search users to these old URLs. By using a "moved permanently" redirect to the new URL, visitors will still end at the correct page. Also, in the next search engine pass, the search engine should detect and use the newer URL.

记录外部点击
网站的日志文件记录着网站浏览者的来源以及他们怎样浏览网站的详细信息。但是这些日志并不能留住浏览者或者记录这些浏览者的去向，，以为当这些浏览者点击外部链接的时候他们的浏览器并不需要跟网站的原始提供者沟通。但是这种信息可以通过很多种方式被抓去，例如通过URL重定向将访问重定向到原始网站的域名而非直接转发到相应的页面。这个请求的痕迹将被完全的保留在日志上以显示访问者的去向。这种技术也被某些社团或者公司用于在网站放置一个"警告"页面以声明对某种并不一定附属于其的技术或言论负责。这种技术消极地降低的网站页面的访问效率。对于网站希望去显示一个"警告"对话会框，这个行为确实对用户时间的一种附加浪费。
Logging outgoing links
The access logs of most web servers keep detailed information from where visitors came and how they browsed the hosted site. They do not, however, log which links visitors left by. This is because the visitor's browser has no need to communicate with the original server when the visitor clicks on an out-going link.

This information can be captured in several ways. One way involves URL redirection. Instead of sending the visitor straight to the other site, links on the site can direct to a URL on the original website's domain that automatically redirects to the real target. This added request will leave a trace in the server logs saying exactly which link was followed. This technique is also used by some corporate websites to have a "warning" page that the content is off-site and not necessarily affiliated with the corporation. This technique does bear the downside in the delay of an additional request to the original website's server. For websites that wish to display a "warning" page before automatically forwarding, the length of time the warning is displayed is an additional delay.

将过长的动态链接改为短一些的固定链接
web工程师一般都倾向于通过在链接地址中增加描述性的属性或者更多的层次分布来控制站点的结构，访问结构（具体页面的访问路径）。这样就会产生一大堆又长又难记的链接地址。有时候页面的内容改变了，链接地址却没有改变。而URL重定向可以帮助我们将这些又长又难记的域名变得更短一些。
Short, meaningful, persistent aliases for long or changing URLs
Currently, web engineers tend to pass descriptive attributes in the URL to represent data hierarchies, command structures, transaction paths and session information. This results in a URL that is aesthetically unpleasant and difficult to remember. Sometimes the URL of a page changes even though the content stays the same.

操纵搜索引擎
若干年前，重定向技术甚至用于愚弄搜索引擎。比如一个对搜索引擎友好的页面把浏览者重定向重定向到一个完全不同的页面；还有一种方法使用重定向将一个页面的PR劫持而用于另一个完全不同的页面，这通常使用的是302 http状态码的重定向。
搜索引擎提供者后来意识到了问题的存在，并采取了适当的措施，惩罚了那些采用这类措施操纵搜索引擎的站点，或者降低他们的权重，甚至将其从搜索结果中删除。
现在，采用重定向作弊的网站往往获得的曝光率远远低于没使用的。
Manipulating search engines
Some years ago, redirect techniques were used to fool search engines. For example, one page could show popular search terms to search engines but redirect the visitors to a different target page. There are also cases where redirects have been used to "steal" the page rank of one popular page and use it for a different page, usually involving the 302 HTTP status code of "moved temporarily."

Search engine providers noticed the problem and took appropriate actions. Usually, sites that employ such techniques to manipulate search engines are punished automatically by reducing their ranking or by excluding them from the search index.

As a result, today, such manipulations usually result in less rather than more site exposure.

讽刺和评论
同时，Google bomb可以用于讽刺性的评论以及政治评论，一个域名的某种特殊含义可以被不怀好意的重定向到任意一个域名。
Satire and criticism
In the same way that a Google bomb can be used for satire and political criticism, a domain name that conveys one meaning can be redirected to any other web page, sometimes with malicious intent.

操纵浏览者
URL重定向有时候也被部分用于网络钓鱼，以困惑浏览者他们究竟浏览的是那个网站。
Manipulating visitors
URL redirection is sometimes used as a part of phishing attacks that confuse visitors about which web site they are visiting.

技巧
Techniques

实现URL重定向有好几种办法，很多案例使用meta标签是最简单的方法之一。无论如何，对于使用URL重定向的这几个方法有以下的看法。
There are several techniques to implement a redirect. In many cases, Refresh meta tag is the simplest one. However, there exist several strong opinions discouraging this method.

手动重定向
最简单的办法是询问浏览者是否愿意访问新的页面地址，这种办法通常使用在html停泊页面。
Manual redirect
The simplest technique is to ask the visitor to follow a link to the new page, usually using an HTML anchor as such:

代码：
 

这种方法通常被用于自动跳转的，如果浏览者的浏览器不支持自动重定向的方法，那么浏览者同样会通过链接到达新的链接。
This method is often used as a fall-back for automatic methods - if the visitor's browser does not support the automatic redirect method, the visitor can still reach the target document by following the link.

http 3xx状态码
在W3C制定的相关标准中，重定向是一种以3开头的状态码的页面跳转到另一个窗口的响应。http标准定义了以下状态码给重定向：
300 多样化选择（例如不同的语言）；
301 永久的转移；
302 建立（例如临时性的重定向）
303 其他可见（例如cgi脚本的结果）
307 临时性的重定向
所有以上这些状态码都需要将重定向的目标地址给出在相应的位置：http响应的头部。300多样选择可能会在信息的主体部分列出所有的选项，并在头部展示不同的选择。

除了这些3xx状态码之外，还有一些状态码是十分不同的重定向（不做讨论）
304 不做修订
305 使用代理
306 未使用的
这里有一段简单的产生301状态码的重定向代码：

HTTP status codes 3xx
In the HTTP computer protocol used by the World Wide Web, a redirect is a response with a status code beginning with 3 that induces a browser to go to another location.

The HTTP standard defines several status codes for redirection:

300 multiple choices (e.g. offer different languages)
301 moved permanently
302 found (e.g. temporary redirect)
303 see other (e.g. for results of cgi-scripts)
307 temporary redirect
All of these status codes require that the URL of the redirect target is given in the Location: header of the HTTP response. The 300 multiple choices will usually list all choices in the body of the message and show the default choice in the Location: header.

Within the 3xx range, there are also some status codes that are quite different from the above redirects (they are not discussed here with their details):

304 not modified
305 use proxy
306 not used
This is a sample of a HTTP response that uses the 301 "moved permanently" redirect:

使用脚本实现重定向
通常，网站的作者没有足够的权限去制造这些http状态码：这些http url始于程序自动生成而非从链接中读取。甚至是CGI脚本，web伺服者通常自动生成这些状态码并将其添加到headers脚本中。要使用CGI脚本生成http状态码，必须要提供相应的规则。
有时候，同一个普通的CGI脚本提供URL的转发header是足够实现的，很多网站设计者选择其中一种跳转来定义这种跳转。
http草案规定，所有的重定向必须是自发的并不附加任何网页资料。这导致web程序员们必须保证重定向的跳转必须是网页的第一步相应或者是所有响应的一部分。在ASP脚本中，重定向跳转同样可以被响应方法实现：response.buffer=true and response.redirect "http://www.example.com".在php可以使用header("loction:http://example.com");.
根据http标准，location header 必须包含一个绝对的链接。当在不同的站点页面之间进行重定向的时候，使用相对链接肯定会铸成大错。同样浏览器的差异也将导致相对链接的可用性受到质疑。
Using server-side scripting for Redirection
Often, web authors don't have sufficient permissions to produce these status codes: The HTTP header is generated by the web server program and not read from the file for that URL. Even for CGI scripts, the web server usually generates the status code automatically and allows custom headers to be added by the script. To produce HTTP status codes with cgi-scripts, one needs to enable non-parsed-headers.

Sometimes, it is sufficient to print the "Location: 'url'" header line from a normal CGI script. Many web servers choose one of the 3xx status codes for such replies.

The HTTP protocol requires that the redirect be sent all by itself, without any web page data. As a result, the web programmer who is using a scripting language to redirect the user's browser to another page must ensure that the redirect is the first or only part of the response. In the ASP scripting language, this can also be accomplished using the methods response.buffer=true and response.redirect "http://www.example.com". Using PHP, one can use header("Location: http://www.example.com");.

According to the HTTP standard, the Location header must contain an absolute URI. When redirecting from one page to another within the same site, it is a common mistake to use a relative URI. As a result most browsers tolerate relative URIs in the Location header, but some browsers display a warning to the end user.

使用.htaccess实现重定向
当你使用Apache web服务器的时候，.htaccess文件（）将十分有用，例如重定向一个简单的页面：

Redirect 301 /oldpage.html http://www.example.com/newpage.html

更改域名：

使用.htaccess文件实现重定向，几乎不需要多余的权限。

Using .htaccess for Redirection
When using the Apache web server, directory-specific .htaccess files (as well as apache's main configuration files) can be used. For example, to redirect a single page:

To change domain names:

Use of .htaccess for this purpose usually does not require administrative permissions, though it can be disabled.

使用Meta标签实现重定向跳转
Netscape公司介绍了对现实页面进行刷新之后的某几个特定的操作的反应。这种方法通常称为"meta refresh跳转"，这完全可以实现在一定时间间隔之后用新的页面替换原有的页面：html <meta>标签
一个可探测的动态文档，所有权的外延，超时0秒自动跳转，这里有一个使用此技术的例子：

这种方法可以应用于任何网站，可以被任何网页作者使用，因为meta 标签本身就包含在html文档中；
meta标签必须被放置在html文件的头部；
标记出正文当中的陌生句法；
这个例子中的数字"0"可以被更换成其他有实际意义的数字，以实现数秒的延迟；
如果没有任何理由的跳转，很多浏览者将视其不友好；
这项技术是Netscape公司的一项专利，大部分浏览器均支持此跳转；
这里有一个可以实现相同效果的例子：

Please follow <a href="http://www.example.com/">link</a>!

这段代码更容易通过CGI实现，因为它并不需要更改不同的状态码。这里有一段简单的CGI代码实现相同的功能。

注释：通常，http服务将状态码自动加入。

这种方法是少数被W3C认可的实现重定向的方法之一，直到有一天，新旧页面之间不再发生任何实质性的信息传递给彼此。W3C的指导方针是使所有创作者无法操纵任何浏览器的跳转规则。包括W3C等电子刊物上已经刊登一些电子版本的指导方针：让浏览者控制跳转的规则，不破坏向后键的使用。

Refresh Meta tag and HTTP refresh header
Netscape introduced a feature to refresh the displayed page after a certain amount of time. This method is often called meta refresh. It is possible to specify the URL of the new page, thus replacing one page after some time by another page:

HTML <meta> tag
An exploration of dynamic documents
Proprietary extensions
A timeout of 0 seconds means an immediate redirect.

This is an example of a simple HTML document that uses this technique:

<html><head>
<meta http-equiv="Refresh" content="0; url=http://www.example.com/">
</head><body>
<p>Please follow <a href="http://www.example.com/">link</a>!</p>
</body></html>
This technique is usable by all web authors because the meta tag is contained inside the document itself.
The meta tag must be placed in the "head" section of the HTML file.
Note the strange syntax of the content field.
The number "0" in this example may be replaced by another number to achieve a delay of as many seconds.
Many users regard a delay of this kind as annoying unless there is a reason for it.
This is a proprietary/non-standard extension by Netscape. It is supported by most web browsers.
This is an example of achieving the same effect by issuing a HTTP refresh header:

This response is easier to generate by CGI programs because one does not need to change the default status code. Here is a simple CGI program that effects this redirect:

Note: Usually, the HTTP server adds the status line and the Content-length header automatically.

This method is considered by the W3C to be a poor method of redirection, since it does not communicate any information about either the original or new resource, to the browser (or search engine). The W3C's Web Content Accessibility Guidelines (7.4) discourage the creation of auto-refreshing pages, since most web browsers do not allow the user to disable or control the refresh rate. Some articles that they have written on the issue include W3C Web Content Accessibility Guidelines (1.0): Ensure user control of time-sensitive content changes and Use standard redirects: don't break the back button!

通过JavaScript实现重定向跳转
JavaScript提供在浏览器显示不同页面的好几种方法，经常地，被用作重定向。无论如何，我们有一大堆的理由更喜欢使用meta标签or http header，而不是用JavaScript来进行重定向。
有几个原因可以导致JavaScript失效：
安全因素；
浏览器支持；
爬虫不支持；
没有一个标准的方法实现：搜索"你正在重定向"将会找出几乎所有JavaScript的使用方法。这导致web程序员几乎无法仅仅通过JavaScript实现所需功能的重定向跳转。
JavaScript redirects
JavaScript offers several ways to display a different page in the current browser window. Quite frequently, they are used for a redirect. However, there are several reasons to prefer HTTP header or the refresh meta tag (whenever it is possible) over JavaScript redirects:

There are several reasons for some users to disable JavaScript:
Security considerations
Some browsers don't support JavaScript
many crawlers (e.g. from search engines) don't execute JavaScript.
There is no "standard" way of doing it: A search for "you are being redirected" will find that virtually each JavaScript redirect employs different methods. This makes it difficult for Web client programmers to honor your redirect request without implementing all of JavaScript.

框架实现重定向
一些细微的差别将影响fram包含的目标页面的重定向的创造性的应用。

以上两个重定向方法的一个主要的不同就是框架的重定向，浏览器地址栏显示的是框架的URL地址，而非框架页面的目标地址。
这种欺诈性的操作方式叫做嵌套。当读者找到一篇值得珍藏的文章或内容，他收藏的并不是自己需要的那部分，而是具有欺诈性的框架页面。
Frame redirects
A slightly different effect can be achieved by creating a single HTML frame that contains the target page:

<frameset rows="100%">
<frame src="http://www.example.com/">
</frameset>
<noframes>
<body>Please follow <a href="http://www.example.com/">link</a>!</body>
</noframes>
One main difference to the above redirect methods is that for a frame redirect, the browser displays the URL of the frame document and not the URL of the target page in the URL bar.

This technique is commonly called cloaking. This may be used so that the reader sees a more memorable URL or, with fraudulent intentions, to conceal a phishing site as part of website spoofing.

重定向循环：
一个重定向引向另一个重定向是同样可能存在的情况，例如链接http://www.wikipedia.com/wiki/URL_redirection（注意域名的不同）首先被重定向到http://www.wikipedia.org/wiki/URL_redirection，然后又被重定向到http://en.wikipedia.org/wiki/URL_redirection。这是合适的：第一次重定向改正了错误的域名，而第二次重定向选择正确的语言、章节。最终，浏览器中显示的是正确的页面。
有时候，一个小小的错误将导致重定向返回到第一个页面，一起一个无限的循环的重定向，浏览器通常会在几步之后中断循环的重定向，显示错误信息。
http标准声明：
客户端应当可以检测并发现永久循环的重定向，直到为每一个重定向操作完毕。
在执行最多不超过5种被推荐的重定向规则之前，一些委托方可能会有这样类似的固定限制。
Redirect loops
It is quite possible that one redirect leads to another redirect. For example, the URL http://www.wikipedia.com/wiki/URL_redirection (note the differences in the domain name) is first redirected to http://www.wikipedia.org/wiki/URL_redirection and again redirected to the correct URL: http://en.wikipedia.org/wiki/URL_redirection. This is appropriate: the first redirection corrects the wrong domain name. The second redirection selects the correct language section. Finally, the browser displays the correct page.

Sometimes, however, a mistake can cause the redirection to point back to the first page, leading to an infinite loop of redirects. Browsers usually break that loop after a few steps and display an error message instead.

The HTTP standard states:

A client SHOULD detect infinite redirection loops, since such loops generate network traffic for each redirection.

Previous versions of this specification recommended a maximum of five redirections; some clients may exist that implement such a fixed limitation.

URL重定向服务
可以通过URL重定向服务将网页的链接弄得更短。
一些web发行者对于网页的浏览者吹毛求疵，要求采用抹去某些文件信息的更短的URL代替即长又复杂的链接地址，例如其中一个链接指向黑名单中的网站。
超链接包含一些URL转发服务平凡的应用于群发信息到一些博客和百科上面。因此，为了防止恶意群发，一些百科平台禁止编辑或包含含有位置网站链接的重定向服务。拥有者仍将拥有编辑、注释但是屏蔽恶意SPAM规则。
最近，ERL转发由于使用AJAX技术而变得拥有更多的效率，使用更友好的方法创造更短的链接。

URL redirection services
URL redirection services exist to shorten long URLs.

Some web publishers have criticized the use of these services, arguing that replacing a URL with an encoded shortcut effectively erases information from a document. For instance, a redirected URL may link to a blacklisted site.

Hyperlinks involving URL redirection services are frequently used in spam messages directed at blogs and wikis. Thus, one way to reduce spam is to reject all edits and comments containing hyperlinks to known URL redirection services; however, this will also remove legitimate edits and comments and may not be an effective method to reduce spam.

Recently, URL redirection services have taken to using AJAX as an efficient, user friendly method for creating shortened URLs.

URL迷惑服务
存在一种通过meta标签隐藏重定向地址的服务已隐藏文件真正的目录。
使用php可以通过一些如下的简单语句实现：

这段代码可以作为例子使用，

http://example.org/redirect.php?url=http://www.google.com

如果输入的内容不遵从安全要求（使用html特殊的字段）一些人可以通过执行一些代码达到挟持网站的险恶目的。

URL obfuscation services
There exist redirection services for hiding the referrer using META refresh.

This is very easy to do with PHP, such as in this example.

Technorati : 301, META, SEO, 搜索引擎优化