// Copyright (C) 1999-2002 by Jason Hunter <jhunter_AT_acm_DOT_org>.
// All rights reserved. Use of this class is limited.
// Please see the LICENSE for more information.
package com.knowgate.misc;
import java.io.*;
/**
* <p>A class to decode Base64 streams and strings.</p>
* <p>See RFC 1521 section 5.2 for details of the Base64 algorithm.</p>
* <p>
* This class can be used for decoding strings:
* <blockquote><pre>
* String encoded = "d2VibWFzdGVyOnRyeTJndWVTUw";
* String decoded = Base64Decoder.decode(encoded);
* </pre></blockquote>
* or for decoding streams:
* <blockquote><pre>
* InputStream in = new Base64Decoder(System.in);
* </pre></blockquote>
*
* @author <b>Jason Hunter</b>, Copyright © 2000
* @version 1.1, 2002/11/01, added decodeToBytes() to better handle binary
* data (thanks to Sean Graham)
* @version 1.0, 2000/06/11
*/
public class Base64Decoder extends FilterInputStream {
private static final char[] chars = {
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd',
'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x',
'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7',
'8', '9', '+', '/'
};
// A mapping between char values and six-bit integers
private static final int[] ints = new int[128];
static {
for (int i = 0; i < 64; i++) {
ints[chars[i]] = i;
}
}
private int charCount;
private int carryOver;
/**
* Constructs a new Base64 decoder that reads input from the given
* InputStream.
*
* @param in the input stream
*/
public Base64Decoder(InputStream in) {
super(in);
}
/**
* Returns the next decoded character from the stream, or -1 if
* end of stream was reached.
*
* @return the decoded character, or -1 if the end of the
* input stream is reached
* @exception IOException if an I/O error occurs
*/
public int read() throws IOException {
// Read the next non-whitespace character
int x;
do {
x = in.read();
if (x == -1) {
return -1;
}
} while (Character.isWhitespace((char)x));
charCount++;
// The '=' sign is just padding
if (x == '=') {
return -1; // effective end of stream
}
// Convert from raw form to 6-bit form
x = ints[x];
// Calculate which character we're decoding now
int mode = (charCount - 1) % 4;
// First char save all six bits, go for another
if (mode == 0) {
carryOver = x & 63;
return read();
}
// Second char use previous six bits and first two new bits,
// save last four bits
else if (mode == 1) {
int decoded = ((carryOver << 2) + (x >> 4)) & 255;
carryOver = x & 15;
return decoded;
}
// Third char use previous four bits and first four new bits,
// save last two bits
else if (mode == 2) {
int decoded = ((carryOver << 4) + (x >> 2)) & 255;
carryOver = x & 3;
return decoded;
}
// Fourth char use previous two bits and all six new bits
else if (mode == 3) {
int decoded = ((carryOver << 6) + x) & 255;
return decoded;
}
return -1; // can't actually reach this line
}
/**
* Reads decoded data into an array of bytes and returns the actual
* number of bytes read, or -1 if end of stream was reached.
*
* @param buf the buffer into which the data is read
* @param off the start offset of the data
* @param len the maximum number of bytes to read
* @return the actual number of bytes read, or -1 if the end of the
* input stream is reached
* @exception IOException if an I/O error occurs
*/
public int read(byte[] buf, int off, int len) throws IOException {
if (buf.length < (len + off - 1)) {
throw new IOException("The input buffer is too small: " + len +
" bytes requested starting at offset " + off + " while the buffer " +
" is only " + buf.length + " bytes long.");
}
// This could of course be optimized
int i;
for (i = 0; i < len; i++) {
int x = read();
if (x == -1 && i == 0) { // an immediate -1 returns -1
return -1;
}
else if (x == -1) { // a later -1 returns the chars read so far
break;
}
buf[off + i] = (byte) x;
}
return i;
}
/**
* Returns the decoded form of the given encoded string, as a String.
* Note that not all binary data can be represented as a String, so this
* method should only be used for encoded String data. Use decodeToBytes()
* otherwise.
*
* @param encoded the string to decode
* @return the decoded form of the encoded string
*/
public static String decode(String encoded) {
return new String(decodeToBytes(encoded));
}
/**
* Returns the decoded form of the given encoded string, as bytes.
*
* @param encoded the string to decode
* @return the decoded form of the encoded string
*/
public static byte[] decodeToBytes(String encoded) {
byte[] bytes = null;
try {
bytes = encoded.getBytes("8859_1");
}
catch (UnsupportedEncodingException ignored) { }
Base64Decoder in = new Base64Decoder(
new ByteArrayInputStream(bytes));
ByteArrayOutputStream out =
new ByteArrayOutputStream((int) (bytes.length * 0.67));
try {
byte[] buf = new byte[4 * 1024]; // 4K buffer
int bytesRead;
while ((bytesRead = in.read(buf)) != -1) {
out.write(buf, 0, bytesRead);
}
out.close();
return out.toByteArray();
}
catch (IOException ignored) { return null; }
}
public static void main(String[] args) throws Exception {
if (args.length != 1) {
System.err.println("Usage: java Base64Decoder fileToDecode");
return;
}
Base64Decoder decoder = null;
try {
decoder = new Base64Decoder(
new BufferedInputStream(
new FileInputStream(args[0])));
byte[] buf = new byte[4 * 1024]; // 4K buffer
int bytesRead;
while ((bytesRead = decoder.read(buf)) != -1) {
System.out.write(buf, 0, bytesRead);
}
}
finally {
if (decoder != null) decoder.close();
}
}
}