je-ik commented on code in PR #39051: URL: https://github.com/apache/beam/pull/39051#discussion_r3450627463
########## runners/kafka-streams/src/main/java/org/apache/beam/runners/kafka/streams/translation/KStreamsPayloadSerde.java: ########## @@ -0,0 +1,121 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you 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 org.apache.beam.runners.kafka.streams.translation; + +import java.io.ByteArrayInputStream; +import java.io.ByteArrayOutputStream; +import java.io.DataInputStream; +import java.io.DataOutputStream; +import java.io.IOException; +import org.apache.beam.sdk.coders.Coder; +import org.apache.beam.sdk.values.WindowedValue; +import org.apache.kafka.common.errors.SerializationException; +import org.apache.kafka.common.serialization.Deserializer; +import org.apache.kafka.common.serialization.Serde; +import org.apache.kafka.common.serialization.Serializer; + +/** + * Kafka {@link Serde} for {@link KStreamsPayload}, enabling the envelope to cross topic boundaries + * (e.g. the repartition topic a {@code GroupByKey} introduces). Until now {@link KStreamsPayload} + * only flowed in-JVM via {@code ProcessorContext#forward}, so no serialization was needed. + * + * <p>The wire format is a one-byte discriminator followed by the variant body: + * + * <ul> + * <li><b>data</b>: {@code [0x00][windowedValueCoder-encoded WindowedValue]} — the data element is + * encoded with the {@link Coder} supplied for the topic's PCollection. + * <li><b>watermark</b>: {@code [0x01][long watermarkMillis][int sourcePartition][int + * totalSourcePartitions]} — the in-band watermark report, coder-independent. + * </ul> + * + * <p>A {@link KStreamsPayloadSerde} is parameterized by the {@link Coder} for the data variant + * because different topics carry different element types; the watermark variant needs no coder. + * + * <p>The serde assumes non-null payloads: the topics it is used on (repartition and watermark + * fan-out) are not log-compacted, so no tombstone (null-valued) records occur. + * + * @param <T> the data element type carried by data payloads on this topic + */ +public final class KStreamsPayloadSerde<T> implements Serde<KStreamsPayload<T>> { + + private static final byte DATA_TAG = 0; + private static final byte WATERMARK_TAG = 1; + + private final Coder<WindowedValue<T>> dataCoder; + + public KStreamsPayloadSerde(Coder<WindowedValue<T>> dataCoder) { + this.dataCoder = dataCoder; + } + + @Override + public Serializer<KStreamsPayload<T>> serializer() { + return new PayloadSerializer(); + } + + @Override + public Deserializer<KStreamsPayload<T>> deserializer() { + return new PayloadDeserializer(); + } + + private final class PayloadSerializer implements Serializer<KStreamsPayload<T>> { + @Override + public byte[] serialize(String topic, KStreamsPayload<T> payload) { + ByteArrayOutputStream out = new ByteArrayOutputStream(); + try { + if (payload.isData()) { + out.write(DATA_TAG); + dataCoder.encode(payload.getData(), out); + } else { + WatermarkPayload watermark = payload.asWatermark(); + DataOutputStream dataOut = new DataOutputStream(out); + dataOut.writeByte(WATERMARK_TAG); + dataOut.writeLong(watermark.getWatermarkMillis()); + dataOut.writeInt(watermark.getSourcePartition()); Review Comment: It would be probably better to use protocol buffers for the serialization. It naturally supports schema evolution in a compatible way and also optimized payload sizes through varint/varlong encoders. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
