Disabled connection_timeout because it's unsafe to use

The current implementation of the session timeout functionality is not safe to
use. Added a warning to the documentation and disabled the code. If the user
tries to use it, a warning is logged.

Documentation/Getting-Started/Configuration-Guide.md

@@ -467,6 +467,8 @@ MaxScale normally suppresses warning messages about failed authentication. Enabl
 
 #### `connection_timeout`
 
+**NOTE**: This parameter is not safe to use in version 1.3.0. Please do not use it.
+
 The connection_timeout parameter is used to disconnect sessions to MaxScale that have been idle for too long. The session timeouts are disabled by default. To enable them, define the timeout in seconds in the service's configuration section.
 
 Example:

Documentation/Release-Notes/MaxScale-1.3.0-Release-Notes.md

@@ -236,6 +236,8 @@ details, please read the [Monitor Common](../Monitors/Monitor-Common.md) documen
 There are a number bugs and known limitations within this version of MaxScale,
 the most serious of this are listed below.
 
+* The `connection_timeout` service parameter is not safe to use in version 1.3.0.
+
 * MaxScale can not manage authentication that uses wildcard matching in hostnames in the mysql.user table of the backend database. The only wildcards that can be used are in IP address entries.
 
 * When users have different passwords based on the host from which they connect MaxScale is unable to determine which password it should use to connect to the backend database. This results in failed connections and unusable usernames in MaxScale.

server/core/service.c

@@ -66,6 +66,7 @@
 #include <gw.h>
 #include <gwdirs.h>
 #include <math.h>
+#include <version.h>
 
 static RSA *rsa_512 = NULL;
 static RSA *rsa_1024 = NULL;
@@ -1103,8 +1104,12 @@ serviceSetTimeout(SERVICE *service, int val)
     {
         return 0;
     }
+#ifdef UNSAFE_CODE
     service->conn_timeout = val;
-
+#else
+    MXS_WARNING("The `connection_timeout` parameter is not safe for use. "
+        "The functionality is disabled for MaxScale "MAXSCALE_VERSION".");
+#endif
     return 1;
 }