1 /*
   2  * Copyright (c) 1996, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.util.zip;
  27 
  28 import java.io.FilterInputStream;
  29 import java.io.InputStream;
  30 import java.io.IOException;
  31 
  32 /**
  33  * An input stream that also maintains a checksum of the data being read.
  34  * The checksum can then be used to verify the integrity of the input data.
  35  *
  36  * @see         Checksum
  37  * @author      David Connelly
  38  * @since 1.1
  39  */
  40 public
  41 class CheckedInputStream extends FilterInputStream {
  42     private Checksum cksum;
  43 
  44     /**
  45      * Creates an input stream using the specified Checksum.
  46      * @param in the input stream
  47      * @param cksum the Checksum
  48      */
  49     public CheckedInputStream(InputStream in, Checksum cksum) {
  50         super(in);
  51         this.cksum = cksum;
  52     }
  53 
  54     /**
  55      * Reads a byte. Will block if no input is available.
  56      * @return the byte read, or -1 if the end of the stream is reached.
  57      * @throws    IOException if an I/O error has occurred
  58      */
  59     public int read() throws IOException {
  60         int b = in.read();
  61         if (b != -1) {
  62             cksum.update(b);
  63         }
  64         return b;
  65     }
  66 
  67     /**
  68      * Reads into an array of bytes. If <code>len</code> is not zero, the method
  69      * blocks until some input is available; otherwise, no
  70      * bytes are read and <code>0</code> is returned.
  71      * @param buf the buffer into which the data is read
  72      * @param off the start offset in the destination array <code>b</code>
  73      * @param len the maximum number of bytes read
  74      * @return    the actual number of bytes read, or -1 if the end
  75      *            of the stream is reached.
  76      * @throws     NullPointerException If <code>buf</code> is <code>null</code>.
  77      * @throws     IndexOutOfBoundsException If <code>off</code> is negative,
  78      * <code>len</code> is negative, or <code>len</code> is greater than
  79      * <code>buf.length - off</code>
  80      * @throws    IOException if an I/O error has occurred
  81      */
  82     public int read(byte[] buf, int off, int len) throws IOException {
  83         len = in.read(buf, off, len);
  84         if (len != -1) {
  85             cksum.update(buf, off, len);
  86         }
  87         return len;
  88     }
  89 
  90     /**
  91      * Skips specified number of bytes of input.
  92      * @param n the number of bytes to skip
  93      * @return the actual number of bytes skipped
  94      * @throws    IOException if an I/O error has occurred
  95      */
  96     public long skip(long n) throws IOException {
  97         byte[] buf = new byte[512];
  98         long total = 0;
  99         while (total < n) {
 100             long len = n - total;
 101             len = read(buf, 0, len < buf.length ? (int)len : buf.length);
 102             if (len == -1) {
 103                 return total;
 104             }
 105             total += len;
 106         }
 107         return total;
 108     }
 109 
 110     /**
 111      * Returns the Checksum for this input stream.
 112      * @return the Checksum value
 113      */
 114     public Checksum getChecksum() {
 115         return cksum;
 116     }
 117 }