1/*
2 * Copyright (C) 2007 Esmertec AG.
3 * Copyright (C) 2007 The Android Open Source Project
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * 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
18package com.google.android.mms.pdu;
19
20public class Base64 {
21    /**
22     * Used to get the number of Quadruples.
23     */
24    static final int FOURBYTE = 4;
25
26    /**
27     * Byte used to pad output.
28     */
29    static final byte PAD = (byte) '=';
30
31    /**
32     * The base length.
33     */
34    static final int BASELENGTH = 255;
35
36    // Create arrays to hold the base64 characters
37    private static byte[] base64Alphabet = new byte[BASELENGTH];
38
39    // Populating the character arrays
40    static {
41        for (int i = 0; i < BASELENGTH; i++) {
42            base64Alphabet[i] = (byte) -1;
43        }
44        for (int i = 'Z'; i >= 'A'; i--) {
45            base64Alphabet[i] = (byte) (i - 'A');
46        }
47        for (int i = 'z'; i >= 'a'; i--) {
48            base64Alphabet[i] = (byte) (i - 'a' + 26);
49        }
50        for (int i = '9'; i >= '0'; i--) {
51            base64Alphabet[i] = (byte) (i - '0' + 52);
52        }
53
54        base64Alphabet['+'] = 62;
55        base64Alphabet['/'] = 63;
56    }
57
58    /**
59     * Decodes Base64 data into octects
60     *
61     * @param base64Data Byte array containing Base64 data
62     * @return Array containing decoded data.
63     */
64    public static byte[] decodeBase64(byte[] base64Data) {
65        // RFC 2045 requires that we discard ALL non-Base64 characters
66        base64Data = discardNonBase64(base64Data);
67
68        // handle the edge case, so we don't have to worry about it later
69        if (base64Data.length == 0) {
70            return new byte[0];
71        }
72
73        int numberQuadruple = base64Data.length / FOURBYTE;
74        byte decodedData[] = null;
75        byte b1 = 0, b2 = 0, b3 = 0, b4 = 0, marker0 = 0, marker1 = 0;
76
77        // Throw away anything not in base64Data
78
79        int encodedIndex = 0;
80        int dataIndex = 0;
81        {
82            // this sizes the output array properly - rlw
83            int lastData = base64Data.length;
84            // ignore the '=' padding
85            while (base64Data[lastData - 1] == PAD) {
86                if (--lastData == 0) {
87                    return new byte[0];
88                }
89            }
90            decodedData = new byte[lastData - numberQuadruple];
91        }
92
93        for (int i = 0; i < numberQuadruple; i++) {
94            dataIndex = i * 4;
95            marker0 = base64Data[dataIndex + 2];
96            marker1 = base64Data[dataIndex + 3];
97
98            b1 = base64Alphabet[base64Data[dataIndex]];
99            b2 = base64Alphabet[base64Data[dataIndex + 1]];
100
101            if (marker0 != PAD && marker1 != PAD) {
102                //No PAD e.g 3cQl
103                b3 = base64Alphabet[marker0];
104                b4 = base64Alphabet[marker1];
105
106                decodedData[encodedIndex] = (byte) (b1 << 2 | b2 >> 4);
107                decodedData[encodedIndex + 1] =
108                    (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));
109                decodedData[encodedIndex + 2] = (byte) (b3 << 6 | b4);
110            } else if (marker0 == PAD) {
111                //Two PAD e.g. 3c[Pad][Pad]
112                decodedData[encodedIndex] = (byte) (b1 << 2 | b2 >> 4);
113            } else if (marker1 == PAD) {
114                //One PAD e.g. 3cQ[Pad]
115                b3 = base64Alphabet[marker0];
116
117                decodedData[encodedIndex] = (byte) (b1 << 2 | b2 >> 4);
118                decodedData[encodedIndex + 1] =
119                    (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));
120            }
121            encodedIndex += 3;
122        }
123        return decodedData;
124    }
125
126    /**
127     * Check octect wheter it is a base64 encoding.
128     *
129     * @param octect to be checked byte
130     * @return ture if it is base64 encoding, false otherwise.
131     */
132    private static boolean isBase64(byte octect) {
133        if (octect == PAD) {
134            return true;
135        } else if (base64Alphabet[octect] == -1) {
136            return false;
137        } else {
138            return true;
139        }
140    }
141
142    /**
143     * Discards any characters outside of the base64 alphabet, per
144     * the requirements on page 25 of RFC 2045 - "Any characters
145     * outside of the base64 alphabet are to be ignored in base64
146     * encoded data."
147     *
148     * @param data The base-64 encoded data to groom
149     * @return The data, less non-base64 characters (see RFC 2045).
150     */
151    static byte[] discardNonBase64(byte[] data) {
152        byte groomedData[] = new byte[data.length];
153        int bytesCopied = 0;
154
155        for (int i = 0; i < data.length; i++) {
156            if (isBase64(data[i])) {
157                groomedData[bytesCopied++] = data[i];
158            }
159        }
160
161        byte packedData[] = new byte[bytesCopied];
162
163        System.arraycopy(groomedData, 0, packedData, 0, bytesCopied);
164
165        return packedData;
166    }
167}
168