/*
* @(#)Base64.java 1.8 02/07/24 @(#)
*
* Copyright (c) 1995-2001 Sun Microsystems, Inc. All rights reserved.
* PROPRIETARY/CONFIDENTIAL
* Use is subject to license terms.
*/
package com.sun.midp.io;
import java.io.IOException;
/**
* This class contains a Base64 encoder and decoder. It cannot be
* instantiated. The encoder and decoder are based on RFC 1521, except that
* encoder do not break up lines and the decoder will treat a line break as
* as invalid characters. This done since MIDP JAD's can not have line breaks
* with in an attribute. Also different RFC's use different lengths for
* base64 strings such as; 76 for 1521, 64 for 1421, and no breaks for 2228.
* <p>
* For example to decode:
* <pre>
* String encodedData;
* byte binaryData[];
*
* binaryData = Base64.decode(encodedData);
* </pre>
* This will decode the String in <i>encodedData</i> and give you an array
* of bytes in the array <i>binaryData</i>.
*
* On errors, this class throws an IOException with the following detail
* strings:
* <pre>
* "Base64 string not a mulitple of 4"
* "Invalid character in Base64 string"
* </pre>
*/
public class Base64 {
/** prevents anyone from instantiating this class */
private Base64() {
}
/**
* This character array provides the alphabet map from RFC1521.
*/
private final static char ALPHABET[] = {
// 0 1 2 3 4 5 6 7
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', // 0
'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', // 1
'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', // 2
'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', // 3
'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', // 4
'o', 'p', 'q', 'r', 's', 't', 'u', 'v', // 5
'w', 'x', 'y', 'z', '0', '1', '2', '3', // 6
'4', '5', '6', '7', '8', '9', '+', '/' // 7
};
/**
* Decodes a 7 bit Base64 character into its binary value.
*/
private static int valueDecoding[] = new int[128];
/**
* initializes the value decoding array from the
* character map
*/
static {
for (int i = 0; i < valueDecoding.length; i++) {
valueDecoding[i] = -1;
}
for (int i = 0; i < ALPHABET.length; i++) {
valueDecoding[ALPHABET[i]] = i;
}
}
/**
* Converts a byte array into a Base64 encoded string.
* @param data bytes to encode
* @param offset which byte to start at
* @param length how many bytes to encode; padding will be added if needed
* @return base64 encoding of data; 4 chars for every 3 bytes
*/
public static String encode(byte[] data, int offset, int length) {
int i;
int encodedLen;
char[] encoded;
// 4 chars for 3 bytes, run input up to a multiple of 3
encodedLen = (length + 2) / 3 * 4;
encoded = new char [encodedLen];
for (i = 0, encodedLen = 0; encodedLen < encoded.length;
i += 3, encodedLen += 4) {
encodeQuantum(data, offset + i, length - i, encoded, encodedLen);
}
return new String(encoded);
}
/**
* Encodes 1, 2, or 3 bytes of data as 4 Base64 chars.
*
* @param in buffer of bytes to encode
* @param inOffset where the first byte to encode is
* @param len how many bytes to encode
* @param out buffer to put the output in
* @param outOffset where in the output buffer to put the chars
*/
private static void encodeQuantum(byte in[], int inOffset, int len,
char out[], int outOffset) {
byte a = 0, b = 0, c = 0;
a = in[inOffset];
out[outOffset] = ALPHABET[(a >>> 2) & 0x3F];
if (len > 2) {
b = in[inOffset + 1];
c = in[inOffset + 2];
out[outOffset + 1] = ALPHABET[((a << 4) & 0x30) +
((b >>> 4) & 0xf)];
out[outOffset + 2] = ALPHABET[((b << 2) & 0x3c) +
((c >>> 6) & 0x3)];
out[outOffset + 3] = ALPHABET[c & 0x3F];
} else if (len > 1) {
b = in[inOffset + 1];
out[outOffset + 1] = ALPHABET[((a << 4) & 0x30) +
((b >>> 4) & 0xf)];
out[outOffset + 2] = ALPHABET[((b << 2) & 0x3c) +
((c >>> 6) & 0x3)];
out[outOffset + 3] = '=';
} else {
out[outOffset + 1] = ALPHABET[((a << 4) & 0x30) +
((b >>> 4) & 0xf)];
out[outOffset + 2] = '=';
out[outOffset + 3] = '=';
}
}
/**
* Converts a Base64 encoded string to a byte array.
* @param encoded Base64 encoded data
* @return decode binary data; 3 bytes for every 4 chars - minus padding
* @exception IOException is thrown, if an I/O error occurs reading the data
*/
public static byte[] decode(String encoded)
throws IOException {
return decode(encoded, 0, encoded.length());
}
/**
* Converts an embedded Base64 encoded string to a byte array.
* @param encoded a String with Base64 data embedded in it
* @param offset which char of the String to start at
* @param length how many chars to decode; must be a multiple of 4
* @return decode binary data; 3 bytes for every 4 chars - minus padding
* @exception IOException is thrown, if an I/O error occurs reading the data
*/
public static byte[] decode(String encoded, int offset, int length)
throws IOException {
int i;
int decodedLen;
byte[] decoded;
// the input must be a multiple of 4
if (length % 4 != 0) {
throw new IOException(
"Base64 string length is not multiple of 4");
}
// 4 chars for 3 bytes, but there may have been pad bytes
decodedLen = length / 4 * 3;
if (encoded.charAt(offset + length - 1) == '=') {
decodedLen--;
if (encoded.charAt(offset + length - 2) == '=') {
decodedLen--;
}
}
decoded = new byte [decodedLen];
for (i = 0, decodedLen = 0; i < length; i += 4, decodedLen += 3) {
decodeQuantum(encoded.charAt(offset + i),
encoded.charAt(offset + i + 1),
encoded.charAt(offset + i + 2),
encoded.charAt(offset + i + 3),
decoded, decodedLen);
}
return decoded;
}
/**
* Decode 4 Base64 chars as 1, 2, or 3 bytes of data.
*
* @param in1 first char of quantum to decode
* @param in2 second char of quantum to decode
* @param in3 third char of quantum to decode
* @param in4 forth char of quantum to decode
* @param out buffer to put the output in
* @param outOffset where in the output buffer to put the bytes
*/
private static void decodeQuantum(char in1, char in2, char in3, char in4,
byte[] out, int outOffset)
throws IOException {
int a = 0, b = 0, c = 0, d = 0;
int pad = 0;
a = valueDecoding[in1 & 127];
b = valueDecoding[in2 & 127];
if (in4 == '=') {
pad++;
if (in3 == '=') {
pad++;
} else {
c = valueDecoding[in3 & 127];
}
} else {
c = valueDecoding[in3 & 127];
d = valueDecoding[in4 & 127];
}
if (a < 0 || b < 0 || c < 0 || d < 0) {
throw new IOException("Invalid character in Base64 string");
}
// the first byte is the 6 bits of a and 2 bits of b
out[outOffset] = (byte)(((a << 2) & 0xfc) | ((b >>> 4) & 3));
if (pad < 2) {
// the second byte is 4 bits of b and 4 bits of c
out[outOffset + 1] = (byte)(((b << 4) & 0xf0) | ((c >>> 2) & 0xf));
if (pad < 1) {
// the third byte is 2 bits of c and 4 bits of d
out[outOffset + 2] =
(byte)(((c << 6) & 0xc0) | (d & 0x3f));
}
}
}
}
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