feat(inputs.knx_listener): Add support for string data type

[martinvonwittich]

Summary

KNX has string data types like DPT 16.000 (ASCII text) which can transfer up to 14 bytes of ASCII text. knx_listener didn't support these yet and therefore couldn't log telegrams of this type; this PR adds the required support.

Please review this carefully; I've never written Go before.

Checklist

• No AI generated code was used in this PR

Related issues

resolves #15158

[telegraf-tiger]

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[powersj]

@martinvonwittich,

Thanks for taking the time to put this up! I think the only thing missing would be a test. In knx_listener_test.go, there is a test called TestRegularReceives_DPT. It has a long table of tests, could you add one that ensures the string it parsed like the following:

    {"16/1/1", "16.000", false, "foobar", "foobar"},

@srebhan is that the right address and DPT to use?

[martinvonwittich]

@martinvonwittich,

Thanks for taking the time to put this up! I think the only thing missing would be a test.

The PR should contain a test...? It displays for me:

{"16/0/0", "16.000", false, "hello world", "hello world"},

[powersj]

The PR should contain a test...? It displays for me:

🤦 how did I miss that in a 5 line diff

[martinvonwittich]

Also a side note about the test that I forgot to mention: when creating the PR, I used git stash to temporarily stash the feature implementation and implemented the test first, to ensure that the test fails when the feature isn't implemented. This didn't work quite as expected - without the feature implementation, the test just hangs forever. Running it with go test -v shows that it throws the expected error, but then never terminates:

[...]
2024/04/16 20:30:27 D! [knx_listener] Matched GA "14/0/3" to measurement "test" with value 92.69 s⁻¹
2024/04/16 20:30:27 D! [knx_listener] Matched GA "14/0/4" to measurement "test" with value 1.01 mol
2024/04/16 20:30:27 D! [knx_listener] Matched GA "14/1/0" to measurement "test" with value 5963.78 m²
2024/04/16 20:30:27 D! [knx_listener] Matched GA "14/1/1" to measurement "test" with value 150.95 F
2024/04/16 20:30:27 D! [knx_listener] Matched GA "16/0/0" to measurement "test" with value hello world
2024/04/16 20:30:27 E! [knx_listener] Type conversion string failed for address "16/0/0"

When the feature is implemented, the test works as expected:

[...]
2024/04/16 20:31:36 D! [knx_listener] Matched GA "14/1/0" to measurement "test" with value 5963.78 m²
2024/04/16 20:31:36 D! [knx_listener] Matched GA "14/1/1" to measurement "test" with value 150.95 F
2024/04/16 20:31:36 D! [knx_listener] Matched GA "16/0/0" to measurement "test" with value hello world
--- PASS: TestRegularReceives_DPT (0.00s)
=== RUN   TestRegularReceives_MultipleMessages
2024/04/16 20:31:36 D! [knx_listener] Group-address mapping for measurement "temperature":
2024/04/16 20:31:36 D! [knx_listener]   1/1/1 --> 1.001
2024/04/16 20:31:36 I! [knx_listener] Trying to connect to "dummy" at ""
2024/04/16 20:31:36 I! [knx_listener] Connected!
2024/04/16 20:31:36 D! [knx_listener] Matched GA "1/1/1" to measurement "temperature" with value On
2024/04/16 20:31:36 D! [knx_listener] Matched GA "1/1/1" to measurement "temperature" with value Off
2024/04/16 20:31:36 I! [knx_listener] Ignoring message {Command:Write Source:0.0.0 Destination:1/1/2 Data:[0]} for unknown GA "1/1/2"
--- PASS: TestRegularReceives_MultipleMessages (0.00s)
=== RUN   TestReconnect
2024/04/16 20:31:36 D! [knx_listener] Group-address mapping for measurement "temperature":
2024/04/16 20:31:36 D! [knx_listener]   1/1/1 --> 1.001
2024/04/16 20:31:36 I! [knx_listener] Trying to connect to "dummy" at ""
2024/04/16 20:31:36 I! [knx_listener] Connected!
2024/04/16 20:31:36 D! [knx_listener] Matched GA "1/1/1" to measurement "temperature" with value On
2024/04/16 20:31:36 D! [knx_listener] Matched GA "1/1/1" to measurement "temperature" with value Off
2024/04/16 20:31:36 I! [knx_listener] Ignoring message {Command:Write Source:0.0.0 Destination:1/1/2 Data:[0]} for unknown GA "1/1/2"
2024/04/16 20:31:36 I! [knx_listener] Trying to connect to "dummy" at ""
2024/04/16 20:31:36 I! [knx_listener] Connected!
2024/04/16 20:31:36 D! [knx_listener] Matched GA "1/1/1" to measurement "temperature" with value On
2024/04/16 20:31:36 D! [knx_listener] Matched GA "1/1/1" to measurement "temperature" with value Off
--- PASS: TestReconnect (0.40s)
PASS
ok      github.com/influxdata/telegraf/plugins/inputs/knx_listener      0.455s

I assume that the strange failing behavior is an existing issue in the test code.

[srebhan]

Thanks for your contribution @martinvonwittich!