關於get方式傳遞字串的最大長度問題

以前一直以為1024位元組(即包括查詢字串在內的url總長度)，今天聽到有人說256位元組...

自己測試了下，發現都不是
firefox，chrome，IE9下，允許的最大長度都為8193位元組...

疑問：
這個值到底是依據什麼而定的呢？根據我的測試結果，三種瀏覽器允許的最大長度都一致，這說明應該不是瀏覽器的問題，那是伺服器的配置問題嗎？如果是的話，是什麼配置項起的作用呢？

下面是測試用的代碼：
urllenchk.php

$url = 'http://localhost/lab/urllen.php?query=';    $queryString = str_repeat('a', 8192-strlen($url)+1);    $curl = curl_init();    curl_setopt($curl, CURLOPT_URL, $url.$queryString);    curl_setopt($curl, CURLOPT_TIMEOUT, 10);    curl_exec($curl);

urllen.php

echo strlen('http://'.$_SERVER['SERVER_NAME'].$_SERVER['SCRIPT_NAME'].'?'.$_SERVER['QUERY_STRING'])."
";echo strlen($_GET['query']);

回複內容：

以前一直以為1024位元組(即包括查詢字串在內的url總長度)，今天聽到有人說256位元組...

自己測試了下，發現都不是
firefox，chrome，IE9下，允許的最大長度都為8193位元組...

疑問：
這個值到底是依據什麼而定的呢？根據我的測試結果，三種瀏覽器允許的最大長度都一致，這說明應該不是瀏覽器的問題，那是伺服器的配置問題嗎？如果是的話，是什麼配置項起的作用呢？

下面是測試用的代碼：
urllenchk.php

$url = 'http://localhost/lab/urllen.php?query=';    $queryString = str_repeat('a', 8192-strlen($url)+1);    $curl = curl_init();    curl_setopt($curl, CURLOPT_URL, $url.$queryString);    curl_setopt($curl, CURLOPT_TIMEOUT, 10);    curl_exec($curl);

urllen.php

echo strlen('http://'.$_SERVER['SERVER_NAME'].$_SERVER['SCRIPT_NAME'].'?'.$_SERVER['QUERY_STRING'])."
";echo strlen($_GET['query']);

RFC文檔 Form submission method

get: With the HTTP "get" method, the form data set is appended to the URI specified by the action attribute (with a question-mark ("?") as separator) and this new URI is sent to the processing agent.

post: With the HTTP "post" method, the form data set is included in the body of the form and sent to the processing agent.

這裡面並沒有規定get和post的長度，大家所看到的長度限制是由瀏覽器廠商實現所自己規定的。MSIE是2k，Opera 4K, Firefox 8K. 超出以後會返回414錯誤.

關於get和post更詳細的討論參見文章http://stackoverflow.com/a/2659995/13...

The limit is dependent on both the server and the client used (and if applicable, also the proxy the server or the client is using).

Most webservers have a limit of 8192 bytes (8KB), which is usually configureable somewhere in the server configuration. As to the client side matter, the HTTP 1.1 specification even warns about this, here's an extract of chapter 3.2.1:

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.

The limit is in MSIE and Safari about 2KB, in Opera about 4KB and in Firefox about 8KB. We may thus assume that 8KB is the maximum possible length and that 2KB is a more affordable length to rely on at the server side and that 255 bytes is the safest length to assume that the entire URL will come in.

If the limit is exceeded in either the browser or the server, most will just truncate the characters outside the limit without any warning. Some servers however may send a HTTP 414 error. If you need to send large data, then better use POST instead of GET. Its limit is much higher, but more dependent on the server used than the client. Usually up to around 2GB is allowed by the average webserver. This is also configureable somewhere in the server settings. The average server will display a server-specific error/exception when the POST limit is exceeded, usually as HTTP 500 error.

RFC 2616 (Hypertext Transfer Protocol HTTP/1.1) section 3.2.1有以下描述：

The HTTP protocol does not place any a priori limit on the length of
a URI. Servers MUST be able to handle the URI of any resource they 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.

也就是說協議本身並沒有限制url最大長度，server可以按照自身能力儘可能處理最大長度，否則返回414錯誤。
另外在apache配置url最大長度的方法如下：
LimitRequestLine 4094

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