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8  * particular file as subject to the "Classpath" exception as provided
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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).
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24  */
25 package sun.misc;
26 
27 import java.io.OutputStream;
28 import java.io.PushbackInputStream;
29 import java.io.PrintStream;
30 
31 /**
32  * This class implements a BASE64 Character decoder as specified in RFC1521.
33  *
34  * This RFC is part of the MIME specification which is published by the
35  * Internet Engineering Task Force (IETF). Unlike some other encoding
36  * schemes there is nothing in this encoding that tells the decoder
37  * where a buffer starts or stops, so to use it you will need to isolate
38  * your encoded data into a single chunk and then feed them this decoder.
39  * The simplest way to do that is to read all of the encoded data into a
40  * string and then use:
41  * <pre>
42  *      byte    mydata[];
43  *      BASE64Decoder base64 = new BASE64Decoder();
44  *
45  *      mydata = base64.decodeBuffer(bufferString);
46  * </pre>
47  * This will decode the String in <i>bufferString</i> and give you an array
48  * of bytes in the array <i>myData</i>.
49  *
50  * On errors, this class throws a CEFormatException with the following detail
51  * strings:
52  * <pre>
53  *    "BASE64Decoder: Not enough bytes for an atom."
54  * </pre>
55  *
56  * @author      Chuck McManis
57  * @see         CharacterEncoder
58  * @see         BASE64Decoder
59  */
60 
61 public class BASE64Decoder extends CharacterDecoder {
62 
63     /** This class has 4 bytes per atom */
bytesPerAtom()64     protected int bytesPerAtom() {
65         return (4);
66     }
67 
68     /** Any multiple of 4 will do, 72 might be common */
bytesPerLine()69     protected int bytesPerLine() {
70         return (72);
71     }
72 
73     /**
74      * This character array provides the character to value map
75      * based on RFC1521.
76      */
77     private final static char pem_array[] = {
78         //       0   1   2   3   4   5   6   7
79                 'A','B','C','D','E','F','G','H', // 0
80                 'I','J','K','L','M','N','O','P', // 1
81                 'Q','R','S','T','U','V','W','X', // 2
82                 'Y','Z','a','b','c','d','e','f', // 3
83                 'g','h','i','j','k','l','m','n', // 4
84                 'o','p','q','r','s','t','u','v', // 5
85                 'w','x','y','z','0','1','2','3', // 6
86                 '4','5','6','7','8','9','+','/'  // 7
87         };
88 
89     private final static byte pem_convert_array[] = new byte[256];
90 
91     static {
92         for (int i = 0; i < 255; i++) {
93             pem_convert_array[i] = -1;
94         }
95         for (int i = 0; i < pem_array.length; i++) {
96             pem_convert_array[pem_array[i]] = (byte) i;
97         }
98     }
99 
100     byte decode_buffer[] = new byte[4];
101 
102     /**
103      * Decode one BASE64 atom into 1, 2, or 3 bytes of data.
104      */
decodeAtom(PushbackInputStream inStream, OutputStream outStream, int rem)105     protected void decodeAtom(PushbackInputStream inStream, OutputStream outStream, int rem)
106         throws java.io.IOException
107     {
108         int     i;
109         byte    a = -1, b = -1, c = -1, d = -1;
110 
111         if (rem < 2) {
112             throw new CEFormatException("BASE64Decoder: Not enough bytes for an atom.");
113         }
114         do {
115             i = inStream.read();
116             if (i == -1) {
117                 throw new CEStreamExhausted();
118             }
119         } while (i == '\n' || i == '\r');
120         decode_buffer[0] = (byte) i;
121 
122         i = readFully(inStream, decode_buffer, 1, rem-1);
123         if (i == -1) {
124             throw new CEStreamExhausted();
125         }
126 
127         if (rem > 3 && decode_buffer[3] == '=') {
128             rem = 3;
129         }
130         if (rem > 2 && decode_buffer[2] == '=') {
131             rem = 2;
132         }
133         switch (rem) {
134         case 4:
135             d = pem_convert_array[decode_buffer[3] & 0xff];
136             // NOBREAK
137         case 3:
138             c = pem_convert_array[decode_buffer[2] & 0xff];
139             // NOBREAK
140         case 2:
141             b = pem_convert_array[decode_buffer[1] & 0xff];
142             a = pem_convert_array[decode_buffer[0] & 0xff];
143             break;
144         }
145 
146         switch (rem) {
147         case 2:
148             outStream.write( (byte)(((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
149             break;
150         case 3:
151             outStream.write( (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
152             outStream.write( (byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf)) );
153             break;
154         case 4:
155             outStream.write( (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
156             outStream.write( (byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf)) );
157             outStream.write( (byte) (((c << 6) & 0xc0) | (d  & 0x3f)) );
158             break;
159         }
160         return;
161     }
162 }
163