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1   /*
2    * Copyright (c) 1995, 1997, 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  package sun.misc;
26  
27  import java.io.OutputStream;
28  import java.io.InputStream;
29  import java.io.PrintStream;
30  import java.io.IOException;
31  
32  /**
33   * This class implements a BASE64 Character encoder as specified in RFC1521.
34   * This RFC is part of the MIME specification as published by the Internet
35   * Engineering Task Force (IETF). Unlike some other encoding schemes there
36   * is nothing in this encoding that indicates
37   * where a buffer starts or ends.
38   *
39   * This means that the encoded text will simply start with the first line
40   * of encoded text and end with the last line of encoded text.
41   *
42   * @author      Chuck McManis
43   * @see         CharacterEncoder
44   * @see         BASE64Decoder
45   */
46  
47  public class BASE64Encoder extends CharacterEncoder {
48  
49      /** this class encodes three bytes per atom. */
50      protected int bytesPerAtom() {
51          return (3);
52      }
53  
54      /**
55       * this class encodes 57 bytes per line. This results in a maximum
56       * of 57/3 * 4 or 76 characters per output line. Not counting the
57       * line termination.
58       */
59      protected int bytesPerLine() {
60          return (57);
61      }
62  
63      /** This array maps the characters to their 6 bit values */
64      private final static char pem_array[] = {
65          //       0   1   2   3   4   5   6   7
66                  'A','B','C','D','E','F','G','H', // 0
67                  'I','J','K','L','M','N','O','P', // 1
68                  'Q','R','S','T','U','V','W','X', // 2
69                  'Y','Z','a','b','c','d','e','f', // 3
70                  'g','h','i','j','k','l','m','n', // 4
71                  'o','p','q','r','s','t','u','v', // 5
72                  'w','x','y','z','0','1','2','3', // 6
73                  '4','5','6','7','8','9','+','/'  // 7
74          };
75  
76      /**
77       * encodeAtom - Take three bytes of input and encode it as 4
78       * printable characters. Note that if the length in len is less
79       * than three is encodes either one or two '=' signs to indicate
80       * padding characters.
81       */
82      protected void encodeAtom(OutputStream outStream, byte data[], int offset, int len)
83          throws IOException {
84          byte a, b, c;
85  
86          if (len == 1) {
87              a = data[offset];
88              b = 0;
89              c = 0;
90              outStream.write(pem_array[(a >>> 2) & 0x3F]);
91              outStream.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
92              outStream.write('=');
93              outStream.write('=');
94          } else if (len == 2) {
95              a = data[offset];
96              b = data[offset+1];
97              c = 0;
98              outStream.write(pem_array[(a >>> 2) & 0x3F]);
99              outStream.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
100             outStream.write(pem_array[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)]);
101             outStream.write('=');
102         } else {
103             a = data[offset];
104             b = data[offset+1];
105             c = data[offset+2];
106             outStream.write(pem_array[(a >>> 2) & 0x3F]);
107             outStream.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
108             outStream.write(pem_array[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)]);
109             outStream.write(pem_array[c & 0x3F]);
110         }
111     }
112 }