1 files changed, 49 insertions, 0 deletions
diff --git a/lib/cache.php b/lib/cache.php
index ea0ff769d..dc667654a 100644
--- a/lib/cache.php
+++ b/lib/cache.php
@@ -87,6 +87,55 @@ class Cache
     }
 
     /**
+     * Create a cache key for data dependent on code
+     *
+     * For cache elements that are dependent on changes in code, this creates
+     * a more-or-less fingerprint of the current running code and adds it to
+     * the cache key. In the case of an upgrade of core, or addition or
+     * removal of plugins, a new unique fingerprint is generated and used.
+     * 
+     * There can still be problems with a) differences in versions of the 
+     * plugins and b) people running code between official versions. This is
+     * usually a problem only for experienced users like developers, who know
+     * how to clear their cache.
+     *
+     * For sites that run code between versions (like the status.net cloud),
+     * there's an additional build number configuration setting.
+     * 
+     * @param string $extra the real part of the key
+     *
+     * @return string full key
+     */
+    
+    static function codeKey($extra)
+    {
+        static $prefix = null;
+	
+        if (empty($prefix)) {
+	    
+            $plugins     = StatusNet::getActivePlugins();
+            $names       = array();
+	    
+            foreach ($plugins as $plugin) {
+                $names[] = $plugin[0];
+            }
+	    
+            $names = array_unique($names);
+            asort($names);
+	    
+            // Unique enough.
+	
+            $uniq = crc32(implode(',', $names));
+
+            $build = common_config('site', 'build');
+
+            $prefix = STATUSNET_VERSION.':'.$build.':'.$uniq;
+        }
+	
+        return Cache::key($prefix.':'.$extra);
+    }
+    
+    /**
      * Make a string suitable for use as a key
      *
      * Useful for turning primary keys of tables into cache keys.