在开发调试支付宝接口时，突然发现支付宝接口的URL很长，远远大于之前自己印象中的255个字符。赶紧搜索查证了一番，理解如下：
URL不能大于255bytes的说法确实存在，在RFC2616中提到：
代码如下:
hey serve,and SHOULD be able to handle URIs of unbounded length if they provide GET-based forms that Could generate such URIs. A server SHOULD return 414 (Request-URI Too Long) status if a URI is longer than the server can handle (see section 10.4.15).
Note: Servers ought to be cautIoUs about depending on URI lengths above
255
bytes,because some older client or proxy implementations might not properly support these lengths.从上一点也可以看出，255bytes的说法也是为了兼容性考虑。实际上现代浏览器的限制如下：
代码如下:
Microsoft Internet Explorer (browser)
Microsoft states that the maximum length of a URL in Internet Explorer is 2,083 characters,with no more than 2,048 characters in the path portion of the URL. In my tests,attempts to use URLs longer than this produced a clear error message in Internet Explorer.
Firefox (browser)
After 65,536 characters,the location bar no longer displays the URL in Windows Firefox 1.5.x. However,longer URLs will work. I stopped testing after 100,000 characters.Safari (browser)
At least 80,000 characters will work. I stopped testing after 80,000 characters.Opera (browser)
At least 190,000 characters will work. I stopped testing after 190,000 characters. Opera 9 for Windows continued to display a fully editable,copyable and pasteable URL in the location bar even at 190,000 characters.Apache (Server)
My early attempts to measure the maximum URL length in web browsers bumped into a server URL length limit of approximately 4,000 characters,after which Apache produces a “413 Entity Too Large” error. I used the current up to date Apache build found in Red Hat Enterprise Linux 4. The official Apache documentation only mentions an 8,192-byte limit on an individual field in a request.Microsoft Internet information Server
The default limit is 16,384 characters (yes,Microsoft's web server accepts longer URLs than Microsoft's web browser). This is configurable.Perl HTTP::Daemon (Server)
Up to 8,000 bytes will work. Those constructing web application servers with Perl's HTTP::Daemon module will encounter a 16,384 byte limit on the combined size of all HTTP request headers. This does not include POST-method form data,file uploads,etc.,but it does include the URL. In practice this resulted in a 413 error when a URL was significantly longer than 8,000 characters. This limitation can be easily removed. Look for all occurrences of 16×1024 in Daemon.pm and replace them with a larger value. Of course,this does increase your exposure to denial of service attacks.另外值得注意的是，有文章提到作为的href属性时，URL不能超过1024bytes，这点没有详细查证
综上，URL还是不适合太长，不是不得已，尽量不要通过GET方式提交大量参数，可以考虑用POST方式（大约在2M左右，应该是和服务器及设定有关）。另外这么长的URL在访问和收藏（有文章提到有些浏览器在收藏超长地址时也是会出现问题）时也是相当不友好的。当然，之前数据库字段设置时还是作为255bytes处理，现在可能要考虑扩充一下了。
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