Page History

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1. Add a new headers length and value (byte[]) to the core message format.
2. Create a Header Interface and implementing class

   1. Interface

      Code Block
      public interface Header { String key(); byte[] value(); }

   2. Implementation Detail

      1. Add a String key field to Header implementing class

      2. Add a byte[] value field to Header implementing class

3. Create a Headers Interface and implementing class 

   1. Interface

      Code Block
      public interface Headers extends Iterable<Header> { Headers add(String key, byte[] valueHeader header); Collection<byte[]>Collection<Header> get(String key); Set<String> keys(); }

   2. Implementation Detail

      1. Add a headers Header[] field to Headers implementation class

      2. Add accessor methods on the Headers class - Headers add(String key, byte[] valueHeader) and a Collection<byte[]> Collection<Header> get(String)
      3. implement Iterable<Header>
      4. interceptors are expected to add headers during the produce intercept stage.
4. Add a headers field to ProducerRecord and ConsumerRecord. 
5. Add constructor(s) of Producer/ConsumerRecord to allow passing in of Iterable<Header> 
   1. use case is MirrorMakers able to copy headers.
6. Add accessor methods on the Producer/ConsumerRecord Headers headers()
   

   1. Code Block
      public class ProducerRecord<K, V> {   ... public Headers headers(); ... }

      Code Block
      public class ConsumerRecord<K, V> { ... public Headers headers(); ... }

7. Add ProduceRequest/ProduceResponse V4 which uses the new message format.
8. Add FetchRequest/FetchResponse V4 which uses the new message format.
9. The serialisation of the [String, byte[]] header array will on the wire using a strict format
10. Each headers value will be custom serialisable by the interceptors/plugins that use the header.

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Wire protocol change - add array of headers to end of the message format

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