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Status

Current state: Under Discussion

Discussion thread: here

JIRA: here

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Though there does exist a converter in the connect-json library called "JsonConverter", there are limitations as to the domain of JSON payloads this converter is compatible with on the Sink Connector side when serializing them into Kafka Connect datatypes; When reading byte arrays from Kafka, the JsonConverter expects its inputs to be a JSON envelope that contains the fields "schema" and "payload", otherwise it'll throw a DataException reporting:

...

 private Schema inferSchema(JsonNode jsonValue) {
        switch (jsonValue.getNodeType()) {
            case NULL:
                return Schema.OPTIONAL_STRING_SCHEMA;
            case BOOLEAN:
                return Schema.BOOLEAN_SCHEMA;
            case NUMBER:
                if (jsonValue.isIntegralNumber()) {
                    return Schema.INT64_SCHEMA;
                }
                else {
                    return Schema.FLOAT64_SCHEMA;
                }
            case ARRAY:
                SchemaBuilder arrayBuilder = SchemaBuilder.array(inferSchema(jsonValue.elements().next()));
                return arrayBuilder.build();
            case OBJECT:
                SchemaBuilder structBuilder = SchemaBuilder.struct();
                Iterator<Map.Entry<String, JsonNode>> it = jsonValue.fields();
                while (it.hasNext()) {
                    Map.Entry<String, JsonNode> entry = it.next();
                    structBuilder.field(entry.getKey(), inferSchema(entry.getValue()));
                }
                return structBuilder.build();
            case STRING:
                return Schema.STRING_SCHEMA;
            default:
                return null;
        }
    }

Compatibility, Deprecation, and Migration Plan

• What impact (if any) will there be on existing users?
• If we are changing behavior how will we phase out the older behavior?
• If we need special migration tools, describe them here.
• When will we remove the existing behavior?

Rejected Alternatives

Since the default value for schemas.infer.enable is false, existing instances of JsonConverters will remain unaffected. In order to migrate to using these new capabilities for existing converters, users will have to send a PUT request to the /connectors/{connector name}/config endpoint and include this property:

value.converter.schemas.infer.enable: "true"

Rejected Alternatives

N/AIf there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.