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.utils;
  
  import java.nio.ByteBuffer;
  import java.nio.charset.StandardCharsets;
  import java.security.MessageDigest;
  import java.util.Arrays;
  
  /**
   * The result of the computation of an MD5 digest.
   *
   * A MD5 is really just a byte[] but arrays are a no go as map keys. We could
   * wrap it in a ByteBuffer but:
   *   1. MD5Digest is a more explicit name than ByteBuffer to represent a md5.
   *   2. Using our own class allows to use our FastByteComparison for equals.
   */
  public class MD5Digest
  {
      /**
       * In the interest not breaking things, we're consciously keeping this single remaining instance
       * of MessageDigest around for usage by GuidGenerator (which is only ever used by RandomPartitioner)
       * and some client native transport methods, where we're tied to the usage of MD5 in the protocol.
       * As RandomPartitioner will always be MD5 and cannot be changed, we can switch over all our
       * other digest usage to Guava's Hasher to make switching the hashing function used during message
       * digests etc possible, but not regress on performance or bugs in RandomPartitioner's usage of
       * MD5 and MessageDigest.
       */
      private static final ThreadLocal<MessageDigest> localMD5Digest = new ThreadLocal<MessageDigest>()
      {
          @Override
          protected MessageDigest initialValue()
          {
              return FBUtilities.newMessageDigest("MD5");
          }
  
          @Override
          public MessageDigest get()
          {
              MessageDigest digest = super.get();
              digest.reset();
              return digest;
          }
      };
  
      public final byte[] bytes;
      private final int hashCode;
  
      private MD5Digest(byte[] bytes)
      {
          this.bytes = bytes;
          hashCode = Arrays.hashCode(bytes);
      }
  
      public static MD5Digest wrap(byte[] digest)
      {
          return new MD5Digest(digest);
      }
  
      public static MD5Digest compute(byte[] toHash)
      {
          return new MD5Digest(localMD5Digest.get().digest(toHash));
      }
  
      public static MD5Digest compute(String toHash)
      {
          return compute(toHash.getBytes(StandardCharsets.UTF_8));
      }
  
      public ByteBuffer byteBuffer()
      {
          return ByteBuffer.wrap(bytes);
      }
  
      @Override
      public final int hashCode()
      {
          return hashCode;
      }
  
      @Override
      public final boolean equals(Object o)
      {
          if(!(o instanceof MD5Digest))
              return false;
          MD5Digest that = (MD5Digest)o;
          // handles nulls properly
          return FBUtilities.compareUnsigned(this.bytes, that.bytes, 0, 0, this.bytes.length, that.bytes.length) == 0;
      }
  
      @Override
      public String toString()
      {
          return Hex.bytesToHex(bytes);
      }
  
      public static MessageDigest threadLocalMD5Digest()
      {
          return localMD5Digest.get();
      }
  
      public int size()
      {
          return bytes.length + //bytes
                  4; // int hashCode
      }
  }
  