Allow plugin columns to pre-validate user input

core/classes/MantisFilter.class.php

@@ -49,6 +49,17 @@ abstract class MantisFilter {
 	 */
 	public $size = null;
 
+	/**
+	 * Validate the filter input, returning true if input is
+	 * valid, or returning false if invalid.  Invalid inputs will
+	 * be replaced with the filter's default value.
+	 * @param multi Filter field input
+	 * @return boolean Input valid (true) or invalid (false)
+	 */
+	public function validate( $p_filter_input ) {
+		return true;
+	}
+
 	/**
 	 * Build the SQL query elements 'join', 'where', and 'params'
 	 * as used by core/filter_api.php to create the primary filter

core/filter_api.php

@@ -570,6 +570,10 @@ function filter_ensure_valid_filter( $p_filter_arr ) {
 					$p_filter_arr[ $t_field_name ] = META_FILTER_ANY;
 			}
 		}
+
+		if ( ! $t_filter_object->validate( $p_filter_arr[ $t_field_name ] ) ) {
+			$p_filter_arr[ $t_field_name ] = $t_filter_object->default;
+		}
 	}
 
 	$t_custom_fields = custom_field_get_ids();