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  /*
   * Copyright 2010-2015 Amazon.com, Inc. or its affiliates. All Rights Reserved.
   *
   * Licensed under the Apache License, Version 2.0 (the "License").
   * You may not use this file except in compliance with the License.
   * A copy of the License is located at
   * 
   *  http://aws.amazon.com/apache2.0
   * 
  * or in the "license" file accompanying this file. This file 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 com.amazonaws.services.s3.internal;
 
 
Simple InputStream wrapper that examines the wrapped stream's contents as they are read and calculates and MD5 digest.
 
 public class MD5DigestCalculatingInputStream extends SdkFilterInputStream {
    
The MD5 message digest being calculated by this input stream
 
     private MessageDigest digest;
    
The MD5 message digest as at the time when the last mark(int) operation was called; always null if mark is not supported.
 
     private MessageDigest digestLastMarked;
 
         super(in);
          = newMD5();
     }
 
     private MessageDigest newMD5() {
         try {
             return MessageDigest.getInstance("MD5");
         } catch (NoSuchAlgorithmException e) { // should never occur
             throw new IllegalStateException("unexpected"e);
         }
     }
     
     private MessageDigest cloneFrom(MessageDigest from) {
         try {
             return (MessageDigest)from.clone();
         } catch (CloneNotSupportedException e) { // should never occur
             throw new IllegalStateException("unexpected"e);
         }
     }
 
     public byte[] getMd5Digest() {
         return .digest();
     }
 
     @Override
     public void mark(int readlimit) {
         if (markSupported()) {
             super.mark(readlimit);
              = cloneFrom();
         }
     }

    
Resets the wrapped input stream and the in progress message digest.
 
     @Override
     public void reset() throws IOException {
         if (markSupported()) {
             super.reset();
              = ( == null)
                    // This is necessary so that should there be a reset without a
                    // preceding mark, the MD5 would still be computed correctly.
                    ? newMD5()
                    : cloneFrom();
         } else {
             throw new IOException("mark/reset not supported");
         }
     }
 
     @Override
     public int read() throws IOException {
         int ch = super.read();
         if (ch != -1) {
             .update((byte)ch);
         }
         return ch;
     }
 
     @Override
     public int read(byte[] bint offint lenthrows IOException {
         int result = super.read(bofflen);
         if (result != -1) {
            .update(boffresult);
        }
        return result;
    }
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