[PATCH log-tracker] handle smtp filter message: prevent panicking with non-standard output

[Dominik Csapak <d.csapak@proxmox.com>]

Currently a custom checkscript can print it's output into the syslog
under the guise of the pmg-smtp-filter unit, so it will picked up
by the log tracker. In case there is a line with a delimiter and nothing
after it, every thing before is detected as a qid but the remaining
message only contains the delimiter.

Prevent the panicking here by checking its length beforehand.

While the real fix is either to prevent custom check scripts to output
to syslog, or to prefix it with something we can filter away here,
protecting against malformed output still makes sense.

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
---
 src/main.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/main.rs b/src/main.rs
index efdfd30..4787a36 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -115,6 +115,11 @@ fn handle_pmg_smtp_filter_message(msg: &[u8], parser: &mut Parser, complete_line
         Some((q, m)) => (q, m),
         None => return,
     };
+    if data.len() < 2 {
+        // after the QID there is no separator and space, so it can't be a proper smtp-filter
+        // message. It's possibly output from a custom check script or a malformed log line.
+        return;
+    }
     // skip ': ' following the QID
     let data = &data[2..];
 
-- 
2.47.3