content: package org.apache.lucene.util;
  
  /**
   * 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.
   */
  
  
  import java.io.IOException;
  
  import org.apache.lucene.index.CorruptIndexException;
  import org.apache.lucene.index.IndexFormatTooNewException;
  import org.apache.lucene.index.IndexFormatTooOldException;
  import org.apache.lucene.store.DataInput;
  import org.apache.lucene.store.DataOutput;
  
  /**
   * @lucene.experimental
   */
  
  public final class CodecUtil {
    private CodecUtil() {} // no instance
  
    private final static int CODEC_MAGIC = 0x3fd76c17;
  
    public static DataOutput writeHeader(DataOutput out, String codec, int version)
      throws IOException {
      BytesRef bytes = new BytesRef(codec);
      if (bytes.length != codec.length() || bytes.length >= 128) {
        throw new IllegalArgumentException("codec must be simple ASCII, less than 128 characters in length [got " + codec + "]");
      }
      out.writeInt(CODEC_MAGIC);
      out.writeString(codec);
      out.writeInt(version);
  
      return out;
    }
  
    public static int headerLength(String codec) {
      return 9+codec.length();
    }
  
    public static int checkHeader(DataInput in, String codec, int minVersion, int maxVersion)
      throws IOException {
  
      // Safety to guard against reading a bogus string:
      final int actualHeader = in.readInt();
      if (actualHeader != CODEC_MAGIC) {
        throw new CorruptIndexException("codec header mismatch: actual header=" + actualHeader + " vs expected header=" + CODEC_MAGIC + " (resource: " + in + ")");
      }
  
      final String actualCodec = in.readString();
      if (!actualCodec.equals(codec)) {
        throw new CorruptIndexException("codec mismatch: actual codec=" + actualCodec + " vs expected codec=" + codec + " (resource: " + in + ")");
      }
  
      final int actualVersion = in.readInt();
      if (actualVersion < minVersion) {
        throw new IndexFormatTooOldException(in, actualVersion, minVersion, maxVersion);
      }
      if (actualVersion > maxVersion) {
        throw new IndexFormatTooNewException(in, actualVersion, minVersion, maxVersion);
      }
  
      return actualVersion;
    }
  }
  