fix(cdc): avoid serde the schema field in the Debzium connector

java/connector-node/risingwave-connector-service/src/main/java/com/risingwave/connector/source/core/DbzCdcEventConsumer.java

@@ -50,11 +50,14 @@ public class DbzCdcEventConsumer
         this.outputChannel = store;
         this.heartbeatTopicPrefix = heartbeatTopicPrefix;
 
-        var jsonConverter = new JsonConverter();
+        // The default JSON converter will output the schema field in the JSON which is unnecessary
+        // to source parser, we use a customized JSON converter to avoid outputting the `schema`
+        // field.
+        var jsonConverter = new DbzJsonConverter();
         final HashMap<String, Object> configs = new HashMap<>(2);
         // only serialize the value part
         configs.put(ConverterConfig.TYPE_CONFIG, ConverterType.VALUE.getName());
-        // include record schema
+        // include record schema to output JSON in { "schema": { ... }, "payload": { ... } } format
         configs.put(JsonConverterConfig.SCHEMAS_ENABLE_CONFIG, true);
         jsonConverter.configure(configs);
         this.converter = jsonConverter;

java/connector-node/risingwave-connector-service/src/main/java/com/risingwave/connector/source/core/DbzJsonConverter.java

@@ -0,0 +1,39 @@
+// Copyright 2023 RisingWave Labs
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.risingwave.connector.source.core;
+
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import org.apache.kafka.connect.data.Schema;
+import org.apache.kafka.connect.json.JsonConverter;
+
+/**
+ * Customize the JSON converter to avoid outputting the `schema` field but retian `payload` field in
+ * the JSON output. e.g.
+ *
+ * <pre>
+ * {
+ *     "schema": null,
+ *     "payload": {
+ *     	...
+ *     }
+ * }
+ * </pre>
+ */
+public class DbzJsonConverter extends JsonConverter {
+    @Override
+    public ObjectNode asJsonSchema(Schema schema) {
+        return null;
+    }
+}