inputs.knx_listener: add support for String data type

[martinvonwittich]

Use Case

I'm using the knx_listener input to monitor a KNX bus. On the bus there's an MDT Glass Push-button that can receive a 14 byte Message telegram of type DPT 16.000 (ASCII text). I want to log and all other telegrams to a database.

Expected behavior

knx_listener should convert DPT 16.000 (ASCII text) to string.

Actual behavior

knx_listener fails to convert DPT 16.000 (ASCII text) to string:

Apr 15 11:46:16 hostname telegraf[1058269]: 2024-04-15T09:46:16Z D! [inputs.knx_listener] Matched GA "5/3/5" to measurement "<name of GA>" with value <ASCII contents of the message>
Apr 15 11:46:16 hostname telegraf[1058269]: 2024-04-15T09:46:16Z E! [inputs.knx_listener] Type conversion string failed for address "5/3/5"

This prevents the DPT 16.000 (ASCII text) telegrams from being logged.

Additional info

I'm not really familiar with Go, but this seems to be a simple fix - just add String to the existing conversion table:

hostname ~/telegraf # git diff plugins/inputs/knx_listener/knx_listener.go
diff --git a/plugins/inputs/knx_listener/knx_listener.go b/plugins/inputs/knx_listener/knx_listener.go
index f013fe638..f81dc9e1a 100644
--- a/plugins/inputs/knx_listener/knx_listener.go
+++ b/plugins/inputs/knx_listener/knx_listener.go
@@ -187,6 +187,8 @@ func (kl *KNXListener) listen(acc telegraf.Accumulator) {
                                value = vi.Uint()
                        case reflect.Float32, reflect.Float64:
                                value = vi.Float()
+                       case reflect.String:
+                               value = vi.String()
                        default:
                                kl.Log.Errorf("Type conversion %v failed for address %q", vi.Kind(), ga)
                                continue

This seems to be working for me, knx_listener now successfully produces strings for the message telegrams.

[srebhan]

@martinvonwittich your change looks reasonable. Could you please submit a PR!?

[martinvonwittich]

@martinvonwittich your change looks reasonable. Could you please submit a PR!?

Done!