[jira] [Commented] (KAFKA-4852) ByteBufferSerializer not compatible with offsets

["LinShunkang (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-4852?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17609089#comment-17609089 ] 

LinShunkang commented on KAFKA-4852:
------------------------------------

Agree! I also found this bug:
{code:java}
@Test
public void testByteBufferSerializer() {
    final byte[] bytes = "Hello".getBytes(UTF_8);
    final ByteBuffer buffer = ByteBuffer.allocate(7);
    buffer.put(bytes);

    try (final ByteBufferSerializer serializer = new ByteBufferSerializer()) {
        assertArrayEquals(bytes, serializer.serialize(topic, buffer));
    }
} {code}
Executing the above test case will throw the following exception:
{code:java}
array lengths differ, expected: <5> but was: <7>
Expected :5
Actual   :7
<Click to see difference>org.opentest4j.AssertionFailedError: array lengths differ, expected: <5> but was: <7>
...
    at org.apache.kafka.common.serialization.SerializationTest.testByteBufferSerializer(SerializationTest.java:397)
...
at java.util.ArrayList.forEach(ArrayList.java:1259)
...
at java.util.ArrayList.forEach(ArrayList.java:1259)
...
at worker.org.gradle.process.internal.worker.GradleWorkerMain.run(GradleWorkerMain.java:69)
    at worker.org.gradle.process.internal.worker.GradleWorkerMain.main(GradleWorkerMain.java:74){code}

> ByteBufferSerializer not compatible with offsets
> ------------------------------------------------
>
>                 Key: KAFKA-4852
>                 URL: https://issues.apache.org/jira/browse/KAFKA-4852
>             Project: Kafka
>          Issue Type: Bug
>          Components: clients
>    Affects Versions: 0.10.1.1
>         Environment: all
>            Reporter: Werner Daehn
>            Priority: Minor
>
> Quick intro: A ByteBuffer.rewind() resets the position to zero. What if the ByteBuffer was created with an offset? new ByteBuffer(data, 3, 10)? The ByteBufferSerializer will send from pos=0 and not from pos=3 onwards.
> Solution: No rewind() but flip() for reading a ByteBuffer. That's what the flip is meant for.
> Story:
> Imagine the incoming data comes from a byte[], e.g. a network stream containing topicname, partition, key, value, ... and you want to create a new ProducerRecord for that. As the constructor of ProducerRecord requires (topic, partition, key, value) you have to copy from above byte[] the key and value. That means there is a memcopy taking place. Since the payload can be potentially large, that introduces a lot of overhead. Twice the memory.
> A nice solution to this problem is to simply wrap the network byte[] into new ByteBuffers:
> ByteBuffer key = ByteBuffer.wrap(data, keystart, keylength);
> ByteBuffer value = ByteBuffer.wrap(data, valuestart, valuelength);
> and then use the ByteBufferSerializer instead of the ByteArraySerializer.
> But that does not work as the ByteBufferSerializer does a rewind(), hence both, key and value, will start at position=0 of the data[].
> public class ByteBufferSerializer implements Serializer<ByteBuffer> {
>     public byte[] serialize(String topic, ByteBuffer data) {
>          data.rewind();



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