DigestedInputStream


1   /*******************************************************************************
2    * Copyright (c) 2006, 2007 IBM Corporation and others.
3    * All rights reserved. This program and the accompanying materials
4    * are made available under the terms of the Eclipse Public License v1.0
5    * which accompanies this distribution, and is available at
6    * http://www.eclipse.org/legal/epl-v10.html
7    * 
8    * Contributors:
9    *     IBM Corporation - initial API and implementation
10   *******************************************************************************/
11  
12  package org.eclipse.osgi.internal.verifier;
13  
14  import java.io.*;
15  import java.security.MessageDigest  ;
16  
17  /**
18   * This InputStream will calculate the digest of bytes as they are read. At the
19   * end of the InputStream, it will calculate the digests and throw an exception
20   * if the calculated digest do not match the expected digests.
21   */
22  class DigestedInputStream extends FilterInputStream {
23      MessageDigest   digest;
24      byte result[];
25      long remaining;
26  
27      /**
28       * Constructs an InputStream that uses another InputStream as a source and
29       * calculates the digest. At the end of the stream an exception will be
30       * thrown if the calculated digest doesn't match the passed digest.
31       * 
32       * @param in the stream to use as an input source.
33       * @param digestAlgorithm the MessageDigest algorithm to use.
34       * @param result the expected digest.
35       */
36      DigestedInputStream(InputStream in, String   digestAlgorithm, byte result[], long size) {
37          super(in);
38          this.remaining = size;
39          this.digest = SignedBundleFile.getMessageDigest(digestAlgorithm);
40          this.result = result;
41      }
42  
43      /**
44       * Not supported.
45       */
46      public synchronized void mark(int readlimit) {
47          // Noop, we don't want to support this
48      }
49  
50      /**
51       * Always returns false.
52       */
53      public boolean markSupported() {
54          return false;
55      }
56  
57      /**
58       * Read a byte from the InputStream. Digests are calculated on reads. At the
59       * end of the stream the calculated digests must match the expected digests.
60       * 
61       * @return the character read or -1 at end of stream.
62       * @throws IOException if there was an problem reading the byte or at the
63       *         end of the stream the calculated digests do not match the
64       *         expected digests.
65       * @see java.io.InputStream#read()
66       */
67      public int read() throws IOException {
68          if (remaining <= 0)
69              return -1;
70          int c = super.read();
71          if (c != -1) {
72              digest.update((byte) c);
73              remaining--;
74          } else {
75              // We hit eof so set remaining to zero
76              remaining = 0;
77          }
78          if (remaining == 0)
79              verifyDigests();
80          return c;
81      }
82  
83      private void verifyDigests() throws IOException {
84          // Check the digest at end of file
85          byte rc[] = digest.digest();
86          if (!MessageDigest.isEqual(result, rc))
87              throw new IOException("Corrupted file: the digest is valid for " + digest.getAlgorithm()); //$NON-NLS-1$
88      }
89  
90      /**
91       * Read bytes from the InputStream. Digests are calculated on reads. At the
92       * end of the stream the calculated digests must match the expected digests.
93       * 
94       * @return the number of characters read or -1 at end of stream.
95       * @throws IOException if there was an problem reading or at the
96       *         end of the stream the calculated digests do not match the
97       *         expected digests.
98       * @see java.io.InputStream#read()
99       */
100     public int read(byte[] b, int off, int len) throws IOException {
101         if (remaining <= 0)
102             return -1;
103         int rc = super.read(b, off, len);
104         if (rc != -1) {
105             digest.update(b, off, rc);
106             remaining -= rc;
107         } else {
108             // We hit eof so set remaining to zero
109             remaining = 0;
110         }
111         if (remaining <= 0)
112             verifyDigests();
113         return rc;
114     }
115 
116     /**
117      * Not supported.
118      * 
119      * @throws IOException always thrown if this method is called since mark/reset is not supported.
120      * @see java.io.InputStream#reset()
121      */
122     public synchronized void reset() throws IOException {
123         // Throw IOException, we don't want to support this
124         throw new IOException("Reset not supported"); //$NON-NLS-1$
125     }
126 
127     /**
128      * This method is implemented as a read into a bitbucket.
129      */
130     public long skip(long n) throws IOException {
131         byte buffer[] = new byte[4096];
132         long count = 0;
133         while (n - count > 0) {
134             int rc = (n - count) > buffer.length ? buffer.length : (int) (n - count);
135             rc = read(buffer, 0, rc);
136             if (rc == -1)
137                 break;
138             count += rc;
139             n -= rc;
140         }
141         return count;
142     }
143 }
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