[sr-dev] [kamailio/kamailio] Kamailio crashing when applying s.prefixes transformation on empty string (#2467)

[cmcom-gb]

### Description
Applying a simple `{s.prefixes}` transformation on a variable with an empty value crashes Kamailio. It is not specific to a particular SIP message being processed. 

### Troubleshooting

#### Reproduction

```
request_route {
        $var(empty) = "";
        $var(result) = $(var(empty){s.prefixes});
        drop;
}
```

#### Debugging Data

```
(paste your debugging data here)
```

#### Log Messages

```
kernel: [27707776.714159] kamailio[13060]: segfault at 562232762ff0 ip 00007f82a1e76391 sp 00007ffc3bc7fcd8 error 4 in libc-2.24.so[7f82a1d4d000+195000]
```

#### SIP Traffic

Any SIP traffic will do, as long as this particular scenario is hit, for whatever reason. Could be buggy business logic.

### Possible Solutions

The only thing I could think of is to place the transformation inside an `if` statement which checks for an empty value of the variable the `{s.prefixes]` transformation is being applied to.

### Additional Information

I've tested this with Kamailio 5.1 and 5.4, and both have this issue. 

  * **Kamailio Version** - output of `kamailio -v`

```
version: kamailio 5.4.0 (x86_64/linux)
version: kamailio 5.1.10 (x86_64/linux)
```

* **Operating System**:

```
Kamailio 5.1.10 -> Debian GNU/Linux 9.13 (stretch)
Kamailio 5.4.0 -> Debian GNU/Linux 9.8 (stretch)
```


-- 
You are receiving this because you are subscribed to this thread.
Reply to this email directly or view it on GitHub:
https://github.com/kamailio/kamailio/issues/2467
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.kamailio.org/pipermail/sr-dev/attachments/20200902/8d359b84/attachment.htm>