Plain `["null","int"]` union field cannot be serialized — bare value and wrapped `{"int": N}` both fail (v2.1.0, also v1.3.0)

[sagarkancharla19]

Environment

• k6 v1.7.1 (go1.26.4, windows/amd64) — prebuilt binary from the releases page
• Extensions:
  • github.com/mostafa/xk6-kafka/v2 v2.1.0, k6/x/kafka [js]
  • github.com/oleiade/xk6-kv v1.3.0 (unrelated)
• Confluent Schema Registry with basic auth; schema fetched via schemaRegistry.getSchema() and serialized with SCHEMA_TYPE_AVRO

Schema fragment

The failing field sits inside an array of records (billOfMaterial.lines[]):

{"name": "lineNumber", "type": ["null", "int"], "default": null}

Reproduction

Case 1 — bare value (as documented in the README: "you can usually provide union values directly without wrapping them"):

"lineNumber": 1

fails with:

ERRO[0002] GoError: Failed to encode data into binary, OriginalError: billOfMaterial: lines: []interface {}: []interface {}: lineNumber: avro: unknown union type double
  at github.com/mostafa/xk6-kafka/v2/pkg/kafka.(*Kafka).schemaRegistryClientClass.func4 (native)

Case 2 — wrapped primitive (per the v1.3.0 release notes / schema-registry docs):

"lineNumber": {"int": 1}

fails with:

ERRO[0002] GoError: Failed to encode data into binary, OriginalError: billOfMaterial: lines: []interface {}: []interface {}: lineNumber: avro: float64 is unsupported for Avro int
  at github.com/mostafa/xk6-kafka/v2/pkg/kafka.(*Kafka).schemaRegistryClientClass.func4 (native)

Expected behavior

Either representation should serialize, given the documented "automatic conversion of JavaScript float64 to Avro int32/int64" and the wrapped-primitive union support added in v1.3.0.

Actual behavior

Both representations fail, so there is currently no working input representation for a plain ["null","int"] union field. It looks like the float64 normalization applied to logical-type unions (e.g. int.date) does not run for plain int/long union branches — JS numbers arrive as float64 and are never converted before hamba/avro resolves or encodes the branch.

Additional observations

• Reproduces identically on the v1.3.0 prebuilt binary (same two errors, github.com/mostafa/xk6-kafka.(*Kafka).schemaRegistryClientClass.func4), so it affects the hamba-based serde in both the v1 and v2 lines.
• Works on v1.1.0 (last goavro-based release) using the wrapped form {"int": 1} — currently my workaround, but I'd like to move back to v2.x for the confluent-kafka-go performance.

Happy to provide a full minimal script or test against a patch. Thanks for the great extension!

[sagarkancharla19]

@mostafa
fix suggested by AI in pkg/kafka/avro.go
// Arrays and maps are unnamed composite types: recurse into their
// elements so nested int/long fields get converted, and return the
// value unwrapped (hamba/avro resolves the branch by Go type).
if actualType.Type() == avro.Array || actualType.Type() == avro.Map {
if !isValueCompatibleWithSchema(fieldValue, actualType) {
continue
}
converted, err := convertFloat64ToIntForIntegerFields(fieldValue, actualType)
if err != nil {
continue
}
return converted, nil
}
check if this makes sense.

[mostafa]

@sagarkancharla19 Please raise a PR.

[sagarkancharla19]

@mostafa PR raised
#410

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.

[mostafa]

Released in v2.2.0.