Quarkus adapter startup fails with Kafka config property having empty string value

[calohmn]

Trying to deploy a Quarkus-based protocol adapter built using current master, startup fails with this exception:

ERROR: Failed to start application (with profile prod)
java.util.NoSuchElementException: SRCFG00040: The config property hono.kafka.commonClientConfig."ssl.endpoint.identification.algorithm" is defined as the empty String ("") which the following Converter considered to be null: io.smallrye.config.Converters$BuiltInConverter
at io.smallrye.config.SmallRyeConfig.convertValue(SmallRyeConfig.java:284)
at io.smallrye.config.SmallRyeConfig.getValue(SmallRyeConfig.java:239)
at io.smallrye.config.ConfigMappingProvider.lambda$processLazyMap$0(ConfigMappingProvider.java:540)
at io.smallrye.config.ConfigMappingProvider.mapConfiguration(ConfigMappingProvider.java:844)

The issue can be reproduced with the QuarkusPropertyBindingTest unit test (in the adapter-base-quarkus module) by adding a property with an empty string value in adapter-base-quarkus/src/test/resources/application.yaml.

[calohmn]

I thought, using Map<String, Optional<String>> as return values in the KafkaClientOptions methods would help here, but that causes a ClassCastException. I also had no luck with a custom converter. @sophokles73 Any idea here?

[sophokles73]

I do not really understand what you are trying to achieve and what problem you are experiencing. Can you be a little more elaborate?

[calohmn]

When using the IoT Packages Hono helm chart with Kafka parameters, the Kafka config contains this by default:

      kafka:
        commonClientConfig:
          ssl.endpoint.identification.algorithm: ""

When installing the Helm chart, using Kafka and using the Hono quarkus images from current master, the adapter startup fails with the above exception.
The same kind of error comes when running QuarkusPropertyBindingTest in the adapter-base-quarkus module, having added a field with an empty string value in adapter-base-quarkus/src/test/resources/application.yaml, like this:

[...]
  kafka:
    commonClientConfig:
      empty: ""
[...]

So, the question is how to make it possible that the Maps returned by the KafkaClientOptions class can contain empty-string values.

[sophokles73]

Well, we could also simply prevent the empty string being used as the property value, couldn't we? Have you checked if it works if you simply omit the ""?

[calohmn]

When omitting the "", there won't be the NoSuchElementException, but then the map entry value will be null.
And this has different semantics and will also cause the adapter startup to fail.
The intention is here to explicitly set the "ssl.endpoint.identification.algorithm" property value to the empty string in order to override the default value (https). It looks like a null value would let the default value be used.

There are long discussions on the handling of empty string values in SmallRye/Eclipse MicroProfile Config - see microprofile/microprofile-config#671. Unfortunately, there currently doesn't seem to be a straightforward way to differentiate between a String with a null value and an empty String.

I've created #2944 now to apply the solution mentioned in microprofile/microprofile-config#671 - using the ConfigValue API.