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.cassandra.io.sstable;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.nio.ByteBuffer;
  
  /**
   * Reads keys from an SSTable.
   * <p/>
   * It is specific to SSTable format how the keys are read but in general the assumption is that it will read all the
   * keys in the order as they are placed in data file.
   * <p/>
   * After creating it, it should be at the first key. Unless the SSTable is empty, {@link #key()},
   * {@link #keyPositionForSecondaryIndex()} and {@link #dataPosition()} should return approriate values. If there is
   * no data, {@link #isExhausted()} returns {@code true}. In order to move to the next key, {@link #advance()} should be
   * called. It returns {@code true} if the reader moved to the next key; otherwise, there is no more data to read and
   * the reader is exhausted. When the reader is exhausted, return values of {@link #key()},
   * {@link #keyPositionForSecondaryIndex()} and {@link #dataPosition()} are undefined.
   */
  public interface KeyReader extends Closeable
  {
      /**
       * Current key
       */
      ByteBuffer key();
  
      /**
       * Position in the component preferred for reading keys. This is specific to SSTable implementation
       */
      long keyPositionForSecondaryIndex();
  
      /**
       * Position in the data file where the associated content resides
       */
      long dataPosition();
  
      /**
       * Moves the iterator forward. Returns false if we reach EOF and there nothing more to read
       */
      boolean advance() throws IOException;
  
      /**
       * Returns true if we reach EOF
       */
      boolean isExhausted();
  
      /**
       * Resets the iterator to the initial position
       */
      void reset() throws IOException;
  
      /**
       * Closes the iterator quietly
       */
      @Override
      void close();
  }