1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.fileupload.util.mime;
18
19 import java.io.IOException;
20 import java.io.OutputStream;
21
22 /**
23 * @since 1.3
24 */
25 final class Base64Decoder {
26
27 /**
28 * Decoding table value for invalid bytes.
29 */
30 private static final int INVALID_BYTE = -1; // must be outside range 0-63
31
32 /**
33 * Decoding table value for padding bytes, so can detect PAD afer conversion.
34 */
35 private static final int PAD_BYTE = -2; // must be outside range 0-63
36
37 /**
38 * Mask to treat byte as unsigned integer.
39 */
40 private static final int MASK_BYTE_UNSIGNED = 0xFF;
41
42 /**
43 * Number of bytes per encoded chunk - 4 6bit bytes produce 3 8bit bytes on output.
44 */
45 private static final int INPUT_BYTES_PER_CHUNK = 4;
46
47 /**
48 * Set up the encoding table.
49 */
50 private static final byte[] ENCODING_TABLE = {
51 (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F', (byte) 'G',
52 (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K', (byte) 'L', (byte) 'M', (byte) 'N',
53 (byte) 'O', (byte) 'P', (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U',
54 (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z',
55 (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f', (byte) 'g',
56 (byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n',
57 (byte) 'o', (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't', (byte) 'u',
58 (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y', (byte) 'z',
59 (byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6',
60 (byte) '7', (byte) '8', (byte) '9',
61 (byte) '+', (byte) '/'
62 };
63
64 /**
65 * The padding byte.
66 */
67 private static final byte PADDING = (byte) '=';
68
69 /**
70 * Set up the decoding table; this is indexed by a byte converted to an unsigned int,
71 * so must be at least as large as the number of different byte values,
72 * positive and negative and zero.
73 */
74 private static final byte[] DECODING_TABLE = new byte[Byte.MAX_VALUE - Byte.MIN_VALUE + 1];
75
76 static {
77 // Initialise as all invalid characters
78 for (int i = 0; i < DECODING_TABLE.length; i++) {
79 DECODING_TABLE[i] = INVALID_BYTE;
80 }
81 // set up valid characters
82 for (int i = 0; i < ENCODING_TABLE.length; i++) {
83 DECODING_TABLE[ENCODING_TABLE[i]] = (byte) i;
84 }
85 // Allow pad byte to be easily detected after conversion
86 DECODING_TABLE[PADDING] = PAD_BYTE;
87 }
88
89 /**
90 * Hidden constructor, this class must not be instantiated.
91 */
92 private Base64Decoder() {
93 // do nothing
94 }
95
96 /**
97 * Decode the base 64 encoded byte data writing it to the given output stream,
98 * whitespace characters will be ignored.
99 *
100 * @param data the buffer containing the Base64-encoded data
101 * @param out the output stream to hold the decoded bytes
102 *
103 * @return the number of bytes produced.
104 * @throws IOException thrown when the padding is incorrect or the input is truncated.
105 */
106 public static int decode(byte[] data, OutputStream out) throws IOException {
107 int outLen = 0;
108 byte [] cache = new byte[INPUT_BYTES_PER_CHUNK];
109 int cachedBytes = 0;
110
111 for (byte b : data) {
112 final byte d = DECODING_TABLE[MASK_BYTE_UNSIGNED & b];
113 if (d == INVALID_BYTE) {
114 continue; // Ignore invalid bytes
115 }
116 cache[cachedBytes++] = d;
117 if (cachedBytes == INPUT_BYTES_PER_CHUNK) {
118 // CHECKSTYLE IGNORE MagicNumber FOR NEXT 4 LINES
119 final byte b1 = cache[0];
120 final byte b2 = cache[1];
121 final byte b3 = cache[2];
122 final byte b4 = cache[3];
123 if (b1 == PAD_BYTE || b2 == PAD_BYTE) {
124 throw new IOException("Invalid Base64 input: incorrect padding, first two bytes cannot be padding");
125 }
126 // Convert 4 6-bit bytes to 3 8-bit bytes
127 // CHECKSTYLE IGNORE MagicNumber FOR NEXT 1 LINE
128 out.write((b1 << 2) | (b2 >> 4)); // 6 bits of b1 plus 2 bits of b2
129 outLen++;
130 if (b3 != PAD_BYTE) {
131 // CHECKSTYLE IGNORE MagicNumber FOR NEXT 1 LINE
132 out.write((b2 << 4) | (b3 >> 2)); // 4 bits of b2 plus 4 bits of b3
133 outLen++;
134 if (b4 != PAD_BYTE) {
135 // CHECKSTYLE IGNORE MagicNumber FOR NEXT 1 LINE
136 out.write((b3 << 6) | b4); // 2 bits of b3 plus 6 bits of b4
137 outLen++;
138 }
139 } else if (b4 != PAD_BYTE) { // if byte 3 is pad, byte 4 must be pad too
140 throw new // line wrap to avoid 120 char limit
141 IOException("Invalid Base64 input: incorrect padding, 4th byte must be padding if 3rd byte is");
142 }
143 cachedBytes = 0;
144 }
145 }
146 // Check for anything left over
147 if (cachedBytes != 0) {
148 throw new IOException("Invalid Base64 input: truncated");
149 }
150 return outLen;
151 }
152 }