Improve Cache Query String behaviour

Typically, in most cases, we do not need to cache all the Query String variables. That's why I suggest to improve `Cache Include Query String` behaviour — allow the developer to independently specify which variables should be cached.

For example, consider a query to the following URL address:
http://site.com/search?q=query&page=2&session=abcd&utm_source=web

In this case we don't need to build md5 hash for entire query string, because `session` or `utm_source` can be different for all users. The only variables which should be used for md5 hash should be `q` and `page`. Thus, in `config.php` we can use `$config['cache_query_string'] = array('page', 'q');`.

So:
`$config['cache_query_string'] = FALSE;` → Cache Include Query String is disabled
`$config['cache_query_string'] = TRUE;` → Cache Include Query String is enabled for all
`$config['cache_query_string'] = array('page', 'q');` → enabled only for specified variables

1 files changed, 27 insertions, 6 deletions

diff --git a/system/core/Output.php b/system/core/Output.php
index f1859ccf6..4aed62a86 100644
--- a/system/core/Output.php
+++ b/system/core/Output.php
@@ -556,9 +556,16 @@ class CI_Output {
 			.$CI->config->item('index_page')
 			.$CI->uri->uri_string();
 
-		if ($CI->config->item('cache_query_string') && ! empty($_SERVER['QUERY_STRING']))
+		if (($cache_query_string = $CI->config->item('cache_query_string')) && !empty($_SERVER['QUERY_STRING']))
 		{
-			$uri .= '?'.$_SERVER['QUERY_STRING'];
+			if (is_array($cache_query_string))
+			{
+				$uri .= '?'.http_build_query(array_intersect_key($_GET, array_flip($cache_query_string)));
+			}
+			else
+			{
+				$uri .= '?'.$_SERVER['QUERY_STRING'];
+			}
 		}
 
 		$cache_path .= md5($uri);
@@ -646,9 +653,16 @@ class CI_Output {
 		// Build the file path. The file name is an MD5 hash of the full URI
 		$uri = $CFG->item('base_url').$CFG->item('index_page').$URI->uri_string;
 
-		if ($CFG->item('cache_query_string') && ! empty($_SERVER['QUERY_STRING']))
+		if (($cache_query_string = $CFG->item('cache_query_string')) && !empty($_SERVER['QUERY_STRING']))
 		{
-			$uri .= '?'.$_SERVER['QUERY_STRING'];
+			if (is_array($cache_query_string))
+			{
+				$uri .= '?'.http_build_query(array_intersect_key($_GET, array_flip($cache_query_string)));
+			}
+			else
+			{
+				$uri .= '?'.$_SERVER['QUERY_STRING'];
+			}
 		}
 
 		$filepath = $cache_path.md5($uri);
@@ -729,9 +743,16 @@ class CI_Output {
 		{
 			$uri = $CI->uri->uri_string();
 
-			if ($CI->config->item('cache_query_string') && ! empty($_SERVER['QUERY_STRING']))
+			if (($cache_query_string = $CI->config->item('cache_query_string')) && !empty($_SERVER['QUERY_STRING']))
 			{
-				$uri .= '?'.$_SERVER['QUERY_STRING'];
+				if (is_array($cache_query_string))
+				{
+					$uri .= '?'.http_build_query(array_intersect_key($_GET, array_flip($cache_query_string)));
+				}
+				else
+				{
+					$uri .= '?'.$_SERVER['QUERY_STRING'];
+				}
 			}
 		}