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 
18 package com.example.android.mmslib.pdu;
19 
20 public 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      */
decodeBase64(byte[] base64Data)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      */
isBase64(byte octect)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      */
discardNonBase64(byte[] data)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