1 /*
   2  * Copyright (c) 1996, 2013, 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.security;
  27 
  28 import java.io.IOException;
  29 import java.io.EOFException;
  30 import java.io.InputStream;
  31 import java.io.FilterInputStream;
  32 import java.io.PrintStream;
  33 import java.io.ByteArrayInputStream;
  34 
  35 /**
  36  * A transparent stream that updates the associated message digest using
  37  * the bits going through the stream.
  38  *
  39  * <p>To complete the message digest computation, call one of the
  40  * {@code digest} methods on the associated message
  41  * digest after your calls to one of this digest input stream's
  42  * {@link #read() read} methods.
  43  *
  44  * <p>It is possible to turn this stream on or off (see
  45  * {@link #on(boolean) on}). When it is on, a call to one of the
  46  * {@code read} methods
  47  * results in an update on the message digest.  But when it is off,
  48  * the message digest is not updated. The default is for the stream
  49  * to be on.
  50  *
  51  * <p>Note that digest objects can compute only one digest (see
  52  * {@link MessageDigest}),
  53  * so that in order to compute intermediate digests, a caller should
  54  * retain a handle onto the digest object, and clone it for each
  55  * digest to be computed, leaving the original digest untouched.
  56  *
  57  * @see MessageDigest
  58  *
  59  * @see DigestOutputStream
  60  *
  61  * @author Benjamin Renaud
  62  * @since 1.2
  63  */
  64 
  65 public class DigestInputStream extends FilterInputStream {
  66 
  67     /* NOTE: This should be made a generic UpdaterInputStream */
  68 
  69     /* Are we on or off? */
  70     private boolean on = true;
  71 
  72     /**
  73      * The message digest associated with this stream.
  74      */
  75     protected MessageDigest digest;
  76 
  77     /**
  78      * Creates a digest input stream, using the specified input stream
  79      * and message digest.
  80      *
  81      * @param stream the input stream.
  82      *
  83      * @param digest the message digest to associate with this stream.
  84      */
  85     public DigestInputStream(InputStream stream, MessageDigest digest) {
  86         super(stream);
  87         setMessageDigest(digest);
  88     }
  89 
  90     /**
  91      * Returns the message digest associated with this stream.
  92      *
  93      * @return the message digest associated with this stream.
  94      * @see #setMessageDigest(java.security.MessageDigest)
  95      */
  96     public MessageDigest getMessageDigest() {
  97         return digest;
  98     }
  99 
 100     /**
 101      * Associates the specified message digest with this stream.
 102      *
 103      * @param digest the message digest to be associated with this stream.
 104      * @see #getMessageDigest()
 105      */
 106     public void setMessageDigest(MessageDigest digest) {
 107         this.digest = digest;
 108     }
 109 
 110     /**
 111      * Reads a byte, and updates the message digest (if the digest
 112      * function is on).  That is, this method reads a byte from the
 113      * input stream, blocking until the byte is actually read. If the
 114      * digest function is on (see {@link #on(boolean) on}), this method
 115      * will then call {@code update} on the message digest associated
 116      * with this stream, passing it the byte read.
 117      *
 118      * @return the byte read.
 119      *
 120      * @exception IOException if an I/O error occurs.
 121      *
 122      * @see MessageDigest#update(byte)
 123      */
 124     public int read() throws IOException {
 125         int ch = in.read();
 126         if (on && ch != -1) {
 127             digest.update((byte)ch);
 128         }
 129         return ch;
 130     }
 131 
 132     /**
 133      * Reads into a byte array, and updates the message digest (if the
 134      * digest function is on).  That is, this method reads up to
 135      * {@code len} bytes from the input stream into the array
 136      * {@code b}, starting at offset {@code off}. This method
 137      * blocks until the data is actually
 138      * read. If the digest function is on (see
 139      * {@link #on(boolean) on}), this method will then call {@code update}
 140      * on the message digest associated with this stream, passing it
 141      * the data.
 142      *
 143      * @param b the array into which the data is read.
 144      *
 145      * @param off the starting offset into {@code b} of where the
 146      * data should be placed.
 147      *
 148      * @param len the maximum number of bytes to be read from the input
 149      * stream into b, starting at offset {@code off}.
 150      *
 151      * @return  the actual number of bytes read. This is less than
 152      * {@code len} if the end of the stream is reached prior to
 153      * reading {@code len} bytes. -1 is returned if no bytes were
 154      * read because the end of the stream had already been reached when
 155      * the call was made.
 156      *
 157      * @exception IOException if an I/O error occurs.
 158      *
 159      * @see MessageDigest#update(byte[], int, int)
 160      */
 161     public int read(byte[] b, int off, int len) throws IOException {
 162         int result = in.read(b, off, len);
 163         if (on && result != -1) {
 164             digest.update(b, off, result);
 165         }
 166         return result;
 167     }
 168 
 169     /**
 170      * Turns the digest function on or off. The default is on.  When
 171      * it is on, a call to one of the {@code read} methods results in an
 172      * update on the message digest.  But when it is off, the message
 173      * digest is not updated.
 174      *
 175      * @param on true to turn the digest function on, false to turn
 176      * it off.
 177      */
 178     public void on(boolean on) {
 179         this.on = on;
 180     }
 181 
 182     /**
 183      * Prints a string representation of this digest input stream and
 184      * its associated message digest object.
 185      */
 186      public String toString() {
 187          return "[Digest Input Stream] " + digest.toString();
 188      }
 189 }