ijuma commented on a change in pull request #9758:
URL: https://github.com/apache/kafka/pull/9758#discussion_r585656791



##########
File path: 
clients/src/test/java/org/apache/kafka/common/requests/RequestResponseTest.java
##########
@@ -791,15 +791,17 @@ public void produceRequestGetErrorResponseTest() {
 
     @Test
     public void fetchResponseVersionTest() {
-        LinkedHashMap<TopicPartition, 
FetchResponse.PartitionData<MemoryRecords>> responseData = new 
LinkedHashMap<>();
+        LinkedHashMap<TopicPartition, FetchResponseData.PartitionData> 
responseData = new LinkedHashMap<>();
 
         MemoryRecords records = 
MemoryRecords.readableRecords(ByteBuffer.allocate(10));
-        responseData.put(new TopicPartition("test", 0), new 
FetchResponse.PartitionData<>(
-                Errors.NONE, 1000000, FetchResponse.INVALID_LAST_STABLE_OFFSET,
-                0L, Optional.empty(), Collections.emptyList(), records));
-
-        FetchResponse<MemoryRecords> v0Response = new 
FetchResponse<>(Errors.NONE, responseData, 0, INVALID_SESSION_ID);
-        FetchResponse<MemoryRecords> v1Response = new 
FetchResponse<>(Errors.NONE, responseData, 10, INVALID_SESSION_ID);
+        responseData.put(new TopicPartition("test", 0),
+                new FetchResponseData.PartitionData()

Review comment:
       Set partition id.

##########
File path: 
clients/src/test/java/org/apache/kafka/common/requests/RequestResponseTest.java
##########
@@ -1146,38 +1160,45 @@ private FetchRequest createFetchRequest(int version) {
         return FetchRequest.Builder.forConsumer(100, 100000, 
fetchData).setMaxBytes(1000).build((short) version);
     }
 
-    private FetchResponse<MemoryRecords> createFetchResponse(Errors error, int 
sessionId) {
-        return new FetchResponse<>(error, new LinkedHashMap<>(), 25, 
sessionId);
+    private FetchResponse createFetchResponse(Errors error, int sessionId) {
+        return FetchResponse.of(error, 25, sessionId, new LinkedHashMap<>());
     }
 
-    private FetchResponse<MemoryRecords> createFetchResponse(int sessionId) {
-        LinkedHashMap<TopicPartition, 
FetchResponse.PartitionData<MemoryRecords>> responseData = new 
LinkedHashMap<>();
+    private FetchResponse createFetchResponse(int sessionId) {
+        LinkedHashMap<TopicPartition, FetchResponseData.PartitionData> 
responseData = new LinkedHashMap<>();
         MemoryRecords records = 
MemoryRecords.withRecords(CompressionType.NONE, new 
SimpleRecord("blah".getBytes()));
-        responseData.put(new TopicPartition("test", 0), new 
FetchResponse.PartitionData<>(Errors.NONE,
-            1000000, FetchResponse.INVALID_LAST_STABLE_OFFSET, 0L, 
Optional.empty(), Collections.emptyList(), records));
-        List<FetchResponse.AbortedTransaction> abortedTransactions = 
Collections.singletonList(
-            new FetchResponse.AbortedTransaction(234L, 999L));
-        responseData.put(new TopicPartition("test", 1), new 
FetchResponse.PartitionData<>(Errors.NONE,
-            1000000, FetchResponse.INVALID_LAST_STABLE_OFFSET, 0L, 
Optional.empty(), abortedTransactions, MemoryRecords.EMPTY));
-        return new FetchResponse<>(Errors.NONE, responseData, 25, sessionId);
-    }
-
-    private FetchResponse<MemoryRecords> createFetchResponse(boolean 
includeAborted) {
-        LinkedHashMap<TopicPartition, 
FetchResponse.PartitionData<MemoryRecords>> responseData = new 
LinkedHashMap<>();
+        responseData.put(new TopicPartition("test", 0), new 
FetchResponseData.PartitionData()
+                        .setHighWatermark(1000000)

Review comment:
       Set partition id.

##########
File path: core/src/main/scala/kafka/server/KafkaApis.scala
##########
@@ -761,79 +754,85 @@ class KafkaApis(val requestChannel: RequestChannel,
             // For fetch requests from clients, check if down-conversion is 
disabled for the particular partition
             if (!fetchRequest.isFromFollower && 
!logConfig.forall(_.messageDownConversionEnable)) {
               trace(s"Conversion to message format ${downConvertMagic.get} is 
disabled for partition $tp. Sending unsupported version response to $clientId.")
-              errorResponse(Errors.UNSUPPORTED_VERSION)
+              FetchResponse.partitionResponse(tp.partition, 
Errors.UNSUPPORTED_VERSION)
             } else {
               try {
                 trace(s"Down converting records from partition $tp to message 
format version $magic for fetch request from $clientId")
                 // Because down-conversion is extremely memory intensive, we 
want to try and delay the down-conversion as much
                 // as possible. With KIP-283, we have the ability to lazily 
down-convert in a chunked manner. The lazy, chunked
                 // down-conversion always guarantees that at least one batch 
of messages is down-converted and sent out to the
                 // client.
-                val error = maybeDownConvertStorageError(partitionData.error)
-                new FetchResponse.PartitionData[BaseRecords](error, 
partitionData.highWatermark,
-                  partitionData.lastStableOffset, partitionData.logStartOffset,
-                  partitionData.preferredReadReplica, 
partitionData.abortedTransactions,
-                  new LazyDownConversionRecords(tp, unconvertedRecords, magic, 
fetchContext.getFetchOffset(tp).get, time))
+                new FetchResponseData.PartitionData()
+                  .setPartitionIndex(tp.partition)
+                  
.setErrorCode(maybeDownConvertStorageError(Errors.forCode(partitionData.errorCode)).code)
+                  .setHighWatermark(partitionData.highWatermark)
+                  .setLastStableOffset(partitionData.lastStableOffset)
+                  .setLogStartOffset(partitionData.logStartOffset)
+                  .setAbortedTransactions(partitionData.abortedTransactions)
+                  .setRecords(new LazyDownConversionRecords(tp, 
unconvertedRecords, magic, fetchContext.getFetchOffset(tp).get, time))
+                  
.setPreferredReadReplica(partitionData.preferredReadReplica())
               } catch {
                 case e: UnsupportedCompressionTypeException =>
                   trace("Received unsupported compression type error during 
down-conversion", e)
-                  errorResponse(Errors.UNSUPPORTED_COMPRESSION_TYPE)
+                  FetchResponse.partitionResponse(tp.partition, 
Errors.UNSUPPORTED_COMPRESSION_TYPE)
               }
             }
           case None =>
-            val error = maybeDownConvertStorageError(partitionData.error)
-            new FetchResponse.PartitionData[BaseRecords](error,
-              partitionData.highWatermark,
-              partitionData.lastStableOffset,
-              partitionData.logStartOffset,
-              partitionData.preferredReadReplica,
-              partitionData.abortedTransactions,
-              partitionData.divergingEpoch,
-              unconvertedRecords)
+            new FetchResponseData.PartitionData()
+              .setPartitionIndex(tp.partition)
+              
.setErrorCode(maybeDownConvertStorageError(Errors.forCode(partitionData.errorCode)).code)
+              .setHighWatermark(partitionData.highWatermark)
+              .setLastStableOffset(partitionData.lastStableOffset)
+              .setLogStartOffset(partitionData.logStartOffset)
+              .setAbortedTransactions(partitionData.abortedTransactions)
+              .setRecords(unconvertedRecords)
+              .setPreferredReadReplica(partitionData.preferredReadReplica)
+              .setDivergingEpoch(partitionData.divergingEpoch)
         }
       }
     }
 
     // the callback for process a fetch response, invoked before throttling
     def processResponseCallback(responsePartitionData: Seq[(TopicPartition, 
FetchPartitionData)]): Unit = {
-      val partitions = new util.LinkedHashMap[TopicPartition, 
FetchResponse.PartitionData[Records]]
+      val partitions = new util.LinkedHashMap[TopicPartition, 
FetchResponseData.PartitionData]
       val reassigningPartitions = mutable.Set[TopicPartition]()
       responsePartitionData.foreach { case (tp, data) =>
         val abortedTransactions = data.abortedTransactions.map(_.asJava).orNull
         val lastStableOffset = 
data.lastStableOffset.getOrElse(FetchResponse.INVALID_LAST_STABLE_OFFSET)
-        if (data.isReassignmentFetch)
-          reassigningPartitions.add(tp)
-        val error = maybeDownConvertStorageError(data.error)
-        partitions.put(tp, new FetchResponse.PartitionData(
-          error,
-          data.highWatermark,
-          lastStableOffset,
-          data.logStartOffset,
-          data.preferredReadReplica.map(int2Integer).asJava,
-          abortedTransactions,
-          data.divergingEpoch.asJava,
-          data.records))
+        if (data.isReassignmentFetch) reassigningPartitions.add(tp)
+        val partitionData = new FetchResponseData.PartitionData()
+          .setPartitionIndex(tp.partition)
+          .setErrorCode(maybeDownConvertStorageError(data.error).code)
+          .setHighWatermark(data.highWatermark)
+          .setLastStableOffset(lastStableOffset)
+          .setLogStartOffset(data.logStartOffset)
+          .setAbortedTransactions(abortedTransactions)
+          .setRecords(data.records)
+          
.setPreferredReadReplica(data.preferredReadReplica.getOrElse(FetchResponse.INVALID_PREFERRED_REPLICA_ID))
+        data.divergingEpoch.foreach(partitionData.setDivergingEpoch)
+        partitions.put(tp, partitionData)
       }
       erroneous.foreach { case (tp, data) => partitions.put(tp, data) }
 
-      var unconvertedFetchResponse: FetchResponse[Records] = null
+      var unconvertedFetchResponse: FetchResponse = null
 
-      def createResponse(throttleTimeMs: Int): FetchResponse[BaseRecords] = {
+      def createResponse(throttleTimeMs: Int): FetchResponse = {
         // Down-convert messages for each partition if required
-        val convertedData = new util.LinkedHashMap[TopicPartition, 
FetchResponse.PartitionData[BaseRecords]]
+        val convertedData = new util.LinkedHashMap[TopicPartition, 
FetchResponseData.PartitionData]
         unconvertedFetchResponse.responseData.forEach { (tp, 
unconvertedPartitionData) =>
-          if (unconvertedPartitionData.error != Errors.NONE)
+          val error = Errors.forCode(unconvertedPartitionData.errorCode)
+          if (error != Errors.NONE)
             debug(s"Fetch request with correlation id 
${request.header.correlationId} from client $clientId " +
-              s"on partition $tp failed due to 
${unconvertedPartitionData.error.exceptionName}")
+              s"on partition $tp failed due to ${error.exceptionName}")
           convertedData.put(tp, maybeConvertFetchedData(tp, 
unconvertedPartitionData))
         }
 
         // Prepare fetch response from converted data
-        val response = new FetchResponse(unconvertedFetchResponse.error, 
convertedData, throttleTimeMs,
-          unconvertedFetchResponse.sessionId)
+        val response = FetchResponse.of(unconvertedFetchResponse.error, 
throttleTimeMs, unconvertedFetchResponse.sessionId, convertedData)
         // record the bytes out metrics only when the response is being sent
         response.responseData.forEach { (tp, data) =>
-          brokerTopicStats.updateBytesOut(tp.topic, 
fetchRequest.isFromFollower, reassigningPartitions.contains(tp), 
data.records.sizeInBytes)
+          brokerTopicStats.updateBytesOut(tp.topic, 
fetchRequest.isFromFollower,
+            reassigningPartitions.contains(tp), if (data.records  == null) 0 
else data.records.sizeInBytes)

Review comment:
       We can use the utility method you added to avoid the null check.

##########
File path: 
clients/src/test/java/org/apache/kafka/common/requests/RequestResponseTest.java
##########
@@ -1146,38 +1160,45 @@ private FetchRequest createFetchRequest(int version) {
         return FetchRequest.Builder.forConsumer(100, 100000, 
fetchData).setMaxBytes(1000).build((short) version);
     }
 
-    private FetchResponse<MemoryRecords> createFetchResponse(Errors error, int 
sessionId) {
-        return new FetchResponse<>(error, new LinkedHashMap<>(), 25, 
sessionId);
+    private FetchResponse createFetchResponse(Errors error, int sessionId) {
+        return FetchResponse.of(error, 25, sessionId, new LinkedHashMap<>());
     }
 
-    private FetchResponse<MemoryRecords> createFetchResponse(int sessionId) {
-        LinkedHashMap<TopicPartition, 
FetchResponse.PartitionData<MemoryRecords>> responseData = new 
LinkedHashMap<>();
+    private FetchResponse createFetchResponse(int sessionId) {
+        LinkedHashMap<TopicPartition, FetchResponseData.PartitionData> 
responseData = new LinkedHashMap<>();
         MemoryRecords records = 
MemoryRecords.withRecords(CompressionType.NONE, new 
SimpleRecord("blah".getBytes()));
-        responseData.put(new TopicPartition("test", 0), new 
FetchResponse.PartitionData<>(Errors.NONE,
-            1000000, FetchResponse.INVALID_LAST_STABLE_OFFSET, 0L, 
Optional.empty(), Collections.emptyList(), records));
-        List<FetchResponse.AbortedTransaction> abortedTransactions = 
Collections.singletonList(
-            new FetchResponse.AbortedTransaction(234L, 999L));
-        responseData.put(new TopicPartition("test", 1), new 
FetchResponse.PartitionData<>(Errors.NONE,
-            1000000, FetchResponse.INVALID_LAST_STABLE_OFFSET, 0L, 
Optional.empty(), abortedTransactions, MemoryRecords.EMPTY));
-        return new FetchResponse<>(Errors.NONE, responseData, 25, sessionId);
-    }
-
-    private FetchResponse<MemoryRecords> createFetchResponse(boolean 
includeAborted) {
-        LinkedHashMap<TopicPartition, 
FetchResponse.PartitionData<MemoryRecords>> responseData = new 
LinkedHashMap<>();
+        responseData.put(new TopicPartition("test", 0), new 
FetchResponseData.PartitionData()
+                        .setHighWatermark(1000000)
+                        .setLogStartOffset(0)
+                        .setRecords(records));
+        List<FetchResponseData.AbortedTransaction> abortedTransactions = 
Collections.singletonList(
+            new 
FetchResponseData.AbortedTransaction().setProducerId(234L).setFirstOffset(999L));
+        responseData.put(new TopicPartition("test", 1), new 
FetchResponseData.PartitionData()
+                        .setHighWatermark(1000000)
+                        .setLogStartOffset(0)
+                        .setAbortedTransactions(abortedTransactions));
+        return FetchResponse.of(Errors.NONE, 25, sessionId, responseData);
+    }
+
+    private FetchResponse createFetchResponse(boolean includeAborted) {
+        LinkedHashMap<TopicPartition, FetchResponseData.PartitionData> 
responseData = new LinkedHashMap<>();
         MemoryRecords records = 
MemoryRecords.withRecords(CompressionType.NONE, new 
SimpleRecord("blah".getBytes()));
+        responseData.put(new TopicPartition("test", 0), new 
FetchResponseData.PartitionData()
+                        .setHighWatermark(1000000)

Review comment:
       Set partition id.

##########
File path: 
clients/src/main/java/org/apache/kafka/common/requests/FetchResponse.java
##########
@@ -365,17 +126,98 @@ public int sessionId() {
      * @param partIterator  The partition iterator.
      * @return              The response size in bytes.
      */
-    public static <T extends BaseRecords> int sizeOf(short version,
-                                                     
Iterator<Map.Entry<TopicPartition, PartitionData<T>>> partIterator) {
+    public static int sizeOf(short version,
+                             Iterator<Map.Entry<TopicPartition, 
FetchResponseData.PartitionData>> partIterator) {
         // Since the throttleTimeMs and metadata field sizes are constant and 
fixed, we can
         // use arbitrary values here without affecting the result.
-        FetchResponseData data = toMessage(0, Errors.NONE, partIterator, 
INVALID_SESSION_ID);
+        LinkedHashMap<TopicPartition, FetchResponseData.PartitionData> data = 
new LinkedHashMap<>();
+        partIterator.forEachRemaining(entry -> data.put(entry.getKey(), 
entry.getValue()));
         ObjectSerializationCache cache = new ObjectSerializationCache();
-        return 4 + data.size(cache, version);
+        return 4 + FetchResponse.of(Errors.NONE, 0, INVALID_SESSION_ID, 
data).data.size(cache, version);
     }
 
     @Override
     public boolean shouldClientThrottle(short version) {
         return version >= 8;
     }
-}
+
+    public static Optional<FetchResponseData.EpochEndOffset> 
divergingEpoch(FetchResponseData.PartitionData partitionResponse) {
+        return partitionResponse.divergingEpoch().epoch() < 0 ? 
Optional.empty()
+                : Optional.of(partitionResponse.divergingEpoch());
+    }
+
+    public static boolean isDivergingEpoch(FetchResponseData.PartitionData 
partitionResponse) {
+        return partitionResponse.divergingEpoch().epoch() >= 0;
+    }
+
+    public static Optional<Integer> 
preferredReadReplica(FetchResponseData.PartitionData partitionResponse) {
+        return partitionResponse.preferredReadReplica() == 
INVALID_PREFERRED_REPLICA_ID ? Optional.empty()
+                : Optional.of(partitionResponse.preferredReadReplica());
+    }
+
+    public static boolean isPreferredReplica(FetchResponseData.PartitionData 
partitionResponse) {
+        return partitionResponse.preferredReadReplica() != 
INVALID_PREFERRED_REPLICA_ID;
+    }
+
+    public static FetchResponseData.PartitionData partitionResponse(int 
partition, Errors error) {
+        return new FetchResponseData.PartitionData()
+            .setPartitionIndex(partition)
+            .setErrorCode(error.code())
+            .setHighWatermark(FetchResponse.INVALID_HIGH_WATERMARK);
+    }
+
+    /**
+     * Returns `partition.records` as `Records` (instead of `BaseRecords`). If 
`records` is `null`, returns `MemoryRecords.EMPTY`.
+     *
+     * If this response was deserialized after a fetch, this method should 
never fail. An example where this would
+     * fail is a down-converted response (e.g. LazyDownConversionRecords) on 
the broker (before it's serialized and
+     * sent on the wire).
+     *
+     * @param partition partition data
+     * @return Records or empty record if the records in PartitionData is null.
+     */
+    public static Records records(FetchResponseData.PartitionData partition) {
+        if (partition.records() == null) return MemoryRecords.EMPTY;
+        else if (partition.records() instanceof Records) return (Records) 
partition.records();
+        else throw new IllegalStateException("the record type is " + 
partition.records().getClass().getSimpleName() +

Review comment:
       No `else` needed since we used `return` for both other cases. For the 
exception, I think we can just throw `ClassCastException` since 
`IllegalStateException` doesn't fit very well for this case. I would also make 
the message a bit more generic to avoid it going stale when we add more 
`Records` subtypes. For example:
   
   ```java
   "The record type is " + partition.records().getClass().getSimpleName() + ", 
which is not a subtype of " +
   Records.class.getSimpleName() + ". This method is only safe to call if the 
`FetchResponse` was
   deserialized from bytes."

##########
File path: 
clients/src/test/java/org/apache/kafka/common/requests/RequestResponseTest.java
##########
@@ -1146,38 +1160,45 @@ private FetchRequest createFetchRequest(int version) {
         return FetchRequest.Builder.forConsumer(100, 100000, 
fetchData).setMaxBytes(1000).build((short) version);
     }
 
-    private FetchResponse<MemoryRecords> createFetchResponse(Errors error, int 
sessionId) {
-        return new FetchResponse<>(error, new LinkedHashMap<>(), 25, 
sessionId);
+    private FetchResponse createFetchResponse(Errors error, int sessionId) {
+        return FetchResponse.of(error, 25, sessionId, new LinkedHashMap<>());
     }
 
-    private FetchResponse<MemoryRecords> createFetchResponse(int sessionId) {
-        LinkedHashMap<TopicPartition, 
FetchResponse.PartitionData<MemoryRecords>> responseData = new 
LinkedHashMap<>();
+    private FetchResponse createFetchResponse(int sessionId) {
+        LinkedHashMap<TopicPartition, FetchResponseData.PartitionData> 
responseData = new LinkedHashMap<>();
         MemoryRecords records = 
MemoryRecords.withRecords(CompressionType.NONE, new 
SimpleRecord("blah".getBytes()));
-        responseData.put(new TopicPartition("test", 0), new 
FetchResponse.PartitionData<>(Errors.NONE,
-            1000000, FetchResponse.INVALID_LAST_STABLE_OFFSET, 0L, 
Optional.empty(), Collections.emptyList(), records));
-        List<FetchResponse.AbortedTransaction> abortedTransactions = 
Collections.singletonList(
-            new FetchResponse.AbortedTransaction(234L, 999L));
-        responseData.put(new TopicPartition("test", 1), new 
FetchResponse.PartitionData<>(Errors.NONE,
-            1000000, FetchResponse.INVALID_LAST_STABLE_OFFSET, 0L, 
Optional.empty(), abortedTransactions, MemoryRecords.EMPTY));
-        return new FetchResponse<>(Errors.NONE, responseData, 25, sessionId);
-    }
-
-    private FetchResponse<MemoryRecords> createFetchResponse(boolean 
includeAborted) {
-        LinkedHashMap<TopicPartition, 
FetchResponse.PartitionData<MemoryRecords>> responseData = new 
LinkedHashMap<>();
+        responseData.put(new TopicPartition("test", 0), new 
FetchResponseData.PartitionData()
+                        .setHighWatermark(1000000)
+                        .setLogStartOffset(0)
+                        .setRecords(records));
+        List<FetchResponseData.AbortedTransaction> abortedTransactions = 
Collections.singletonList(
+            new 
FetchResponseData.AbortedTransaction().setProducerId(234L).setFirstOffset(999L));
+        responseData.put(new TopicPartition("test", 1), new 
FetchResponseData.PartitionData()
+                        .setHighWatermark(1000000)

Review comment:
       Set partition id.

##########
File path: 
clients/src/test/java/org/apache/kafka/common/requests/RequestResponseTest.java
##########
@@ -1146,38 +1160,45 @@ private FetchRequest createFetchRequest(int version) {
         return FetchRequest.Builder.forConsumer(100, 100000, 
fetchData).setMaxBytes(1000).build((short) version);
     }
 
-    private FetchResponse<MemoryRecords> createFetchResponse(Errors error, int 
sessionId) {
-        return new FetchResponse<>(error, new LinkedHashMap<>(), 25, 
sessionId);
+    private FetchResponse createFetchResponse(Errors error, int sessionId) {
+        return FetchResponse.of(error, 25, sessionId, new LinkedHashMap<>());
     }
 
-    private FetchResponse<MemoryRecords> createFetchResponse(int sessionId) {
-        LinkedHashMap<TopicPartition, 
FetchResponse.PartitionData<MemoryRecords>> responseData = new 
LinkedHashMap<>();
+    private FetchResponse createFetchResponse(int sessionId) {
+        LinkedHashMap<TopicPartition, FetchResponseData.PartitionData> 
responseData = new LinkedHashMap<>();
         MemoryRecords records = 
MemoryRecords.withRecords(CompressionType.NONE, new 
SimpleRecord("blah".getBytes()));
-        responseData.put(new TopicPartition("test", 0), new 
FetchResponse.PartitionData<>(Errors.NONE,
-            1000000, FetchResponse.INVALID_LAST_STABLE_OFFSET, 0L, 
Optional.empty(), Collections.emptyList(), records));
-        List<FetchResponse.AbortedTransaction> abortedTransactions = 
Collections.singletonList(
-            new FetchResponse.AbortedTransaction(234L, 999L));
-        responseData.put(new TopicPartition("test", 1), new 
FetchResponse.PartitionData<>(Errors.NONE,
-            1000000, FetchResponse.INVALID_LAST_STABLE_OFFSET, 0L, 
Optional.empty(), abortedTransactions, MemoryRecords.EMPTY));
-        return new FetchResponse<>(Errors.NONE, responseData, 25, sessionId);
-    }
-
-    private FetchResponse<MemoryRecords> createFetchResponse(boolean 
includeAborted) {
-        LinkedHashMap<TopicPartition, 
FetchResponse.PartitionData<MemoryRecords>> responseData = new 
LinkedHashMap<>();
+        responseData.put(new TopicPartition("test", 0), new 
FetchResponseData.PartitionData()
+                        .setHighWatermark(1000000)
+                        .setLogStartOffset(0)
+                        .setRecords(records));
+        List<FetchResponseData.AbortedTransaction> abortedTransactions = 
Collections.singletonList(
+            new 
FetchResponseData.AbortedTransaction().setProducerId(234L).setFirstOffset(999L));
+        responseData.put(new TopicPartition("test", 1), new 
FetchResponseData.PartitionData()
+                        .setHighWatermark(1000000)
+                        .setLogStartOffset(0)
+                        .setAbortedTransactions(abortedTransactions));
+        return FetchResponse.of(Errors.NONE, 25, sessionId, responseData);
+    }
+
+    private FetchResponse createFetchResponse(boolean includeAborted) {
+        LinkedHashMap<TopicPartition, FetchResponseData.PartitionData> 
responseData = new LinkedHashMap<>();
         MemoryRecords records = 
MemoryRecords.withRecords(CompressionType.NONE, new 
SimpleRecord("blah".getBytes()));
+        responseData.put(new TopicPartition("test", 0), new 
FetchResponseData.PartitionData()
+                        .setHighWatermark(1000000)
+                        .setLogStartOffset(0)
+                        .setRecords(records));
 
-        responseData.put(new TopicPartition("test", 0), new 
FetchResponse.PartitionData<>(Errors.NONE,
-                1000000, FetchResponse.INVALID_LAST_STABLE_OFFSET, 0L, 
Optional.empty(), Collections.emptyList(), records));
-
-        List<FetchResponse.AbortedTransaction> abortedTransactions = 
Collections.emptyList();
+        List<FetchResponseData.AbortedTransaction> abortedTransactions = 
Collections.emptyList();
         if (includeAborted) {
             abortedTransactions = Collections.singletonList(
-                    new FetchResponse.AbortedTransaction(234L, 999L));
+                    new 
FetchResponseData.AbortedTransaction().setProducerId(234L).setFirstOffset(999L));
         }
-        responseData.put(new TopicPartition("test", 1), new 
FetchResponse.PartitionData<>(Errors.NONE,
-                1000000, FetchResponse.INVALID_LAST_STABLE_OFFSET, 0L, 
Optional.empty(), abortedTransactions, MemoryRecords.EMPTY));
+        responseData.put(new TopicPartition("test", 1), new 
FetchResponseData.PartitionData()
+                        .setHighWatermark(1000000)

Review comment:
       Set partition id.




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