content: /*
   * 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.kafka.trogdor.workload;
  
  import org.apache.kafka.common.utils.Time;
  
  import com.fasterxml.jackson.annotation.JsonCreator;
  import com.fasterxml.jackson.annotation.JsonProperty;
  
  import java.nio.ByteBuffer;
  import java.nio.ByteOrder;
  import java.util.Random;
  
  /**
   * This class behaves identically to TimestampConstantPayloadGenerator, except the message size follows a gaussian
   * distribution.
   *
   * This should be used in conjunction with TimestampRecordProcessor in the Consumer to measure true end-to-end latency
   * of a system.
   *
   * `messageSizeAverage` - The average size in bytes of each message.
   * `messageSizeDeviation` - The standard deviation to use when calculating message size.
   * `messagesUntilSizeChange` - The number of messages to keep at the same size.
   *
   * Here is an example spec:
   *
   * {
   *    "type": "gaussianTimestampConstant",
   *    "messageSizeAverage": 512,
   *    "messageSizeDeviation": 100,
   *    "messagesUntilSizeChange": 100
   * }
   *
   * This will generate messages on a gaussian distribution with an average size each 512-bytes. The message sizes will
   * have a standard deviation of 100 bytes, and the size will only change every 100 messages.  The distribution of
   * messages will be as follows:
   *
   *    The average size of the messages are 512 bytes.
   *    ~68% of the messages are between 412 and 612 bytes
   *    ~95% of the messages are between 312 and 712 bytes
   *    ~99% of the messages are between 212 and 812 bytes
   */
  
  public class GaussianTimestampConstantPayloadGenerator implements PayloadGenerator {
      private final int messageSizeAverage;
      private final double messageSizeDeviation;
      private final int messagesUntilSizeChange;
      private final long seed;
  
      private final Random random = new Random();
      private final ByteBuffer buffer;
  
      private int messageTracker = 0;
      private int messageSize = 0;
  
      @JsonCreator
      public GaussianTimestampConstantPayloadGenerator(@JsonProperty("messageSizeAverage") int messageSizeAverage,
                                                       @JsonProperty("messageSizeDeviation") double messageSizeDeviation,
                                                       @JsonProperty("messagesUntilSizeChange") int messagesUntilSizeChange,
                                                       @JsonProperty("seed") long seed) {
          this.messageSizeAverage = messageSizeAverage;
          this.messageSizeDeviation = messageSizeDeviation;
          this.seed = seed;
          this.messagesUntilSizeChange = messagesUntilSizeChange;
          buffer = ByteBuffer.allocate(Long.BYTES);
          buffer.order(ByteOrder.LITTLE_ENDIAN);
      }
  
      @JsonProperty
      public int messageSizeAverage() {
          return messageSizeAverage;
      }
  
      @JsonProperty
      public double messageSizeDeviation() {
          return messageSizeDeviation;
      }
  
      @JsonProperty
      public int messagesUntilSizeChange() {
          return messagesUntilSizeChange;
      }
  
      @JsonProperty
      public long seed() {
          return seed;
      }
  
      @Override
      public synchronized byte[] generate(long position) {
          // Make the random number generator deterministic for unit tests.
          random.setSeed(seed + position);
  
          // Calculate the next message size based on a gaussian distribution.
          if ((messageSize == 0) || (messageTracker >= messagesUntilSizeChange)) {
              messageTracker = 0;
              messageSize = Math.max((int) (random.nextGaussian() * messageSizeDeviation) + messageSizeAverage, Long.BYTES);
          }
          messageTracker += 1;
  
          // Generate the byte array before the timestamp generation.
          byte[] result = new byte[messageSize];
  
          // Do the timestamp generation as the very last task.
          buffer.clear();
          buffer.putLong(Time.SYSTEM.milliseconds());
          buffer.rewind();
          System.arraycopy(buffer.array(), 0, result, 0, Long.BYTES);
          return result;
      }
  }
  