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 QuotedPrintableDecoder {
26
27 /**
28 * Carriage return character '{@value}'.
29 */
30 private static final char CR = '\r';
31
32 /**
33 * Equal character '{@value}'.
34 */
35 private static final char EQUAL = '=';
36
37 /**
38 * Line feed character '{@value}'.
39 */
40 private static final char LF = '\n';
41
42 /**
43 * Space character '{@value}'.
44 */
45 private static final char SP = ' ';
46
47 /**
48 * Underscore character '{@value}'.
49 */
50 private static final char UNDERSCORE = '_';
51
52 /**
53 * The shift value required to create the upper nibble
54 * from the first of 2 byte values converted from ASCII hex.
55 */
56 private static final int UPPER_NIBBLE_SHIFT = Byte.SIZE / 2;
57
58 /**
59 * Decode the encoded byte data writing it to the given output stream.
60 *
61 * @param data The array of byte data to decode.
62 * @param out The output stream used to return the decoded data.
63 * @return the number of bytes produced.
64 * @throws IOException if an IO error occurs
65 */
66 public static int decode(final byte[] data, final OutputStream out) throws IOException {
67 int off = 0;
68 final int length = data.length;
69 final int endOffset = off + length;
70 int bytesWritten = 0;
71
72 while (off < endOffset) {
73 final byte ch = data[off++];
74
75 // space characters were translated to '_' on encode, so we need to translate them back.
76 if (ch == UNDERSCORE) {
77 out.write(SP);
78 } else if (ch == EQUAL) {
79 // we found an encoded character. Reduce the 3 char sequence to one.
80 // but first, make sure we have two characters to work with.
81 if (off + 1 >= endOffset) {
82 throw new IOException("Invalid quoted printable encoding; truncated escape sequence");
83 }
84
85 final byte b1 = data[off++];
86 final byte b2 = data[off++];
87
88 // we've found an encoded carriage return. The next char needs to be a newline
89 if (b1 == CR) {
90 if (b2 != LF) {
91 throw new IOException("Invalid quoted printable encoding; CR must be followed by LF");
92 }
93 // this was a soft linebreak inserted by the encoding. We just toss this away
94 // on decode.
95 } else {
96 // this is a hex pair we need to convert back to a single byte.
97 final int c1 = hexToBinary(b1);
98 final int c2 = hexToBinary(b2);
99 out.write(c1 << UPPER_NIBBLE_SHIFT | c2);
100 // 3 bytes in, one byte out
101 bytesWritten++;
102 }
103 } else {
104 // simple character, just write it out.
105 out.write(ch);
106 bytesWritten++;
107 }
108 }
109
110 return bytesWritten;
111 }
112
113 /**
114 * Convert a hex digit to the binary value it represents.
115 *
116 * @param b the ASCII hex byte to convert (0-0, A-F, a-f)
117 * @return the int value of the hex byte, 0-15
118 * @throws IOException if the byte is not a valid hex digit.
119 */
120 private static int hexToBinary(final byte b) throws IOException {
121 // CHECKSTYLE IGNORE MagicNumber FOR NEXT 1 LINE
122 final int i = Character.digit((char) b, 16);
123 if (i == -1) {
124 throw new IOException("Invalid quoted printable encoding: not a valid hex digit: " + b);
125 }
126 return i;
127 }
128
129 /**
130 * Hidden constructor, this class must not be instantiated.
131 */
132 private QuotedPrintableDecoder() {
133 // do nothing
134 }
135
136 }