A class to decode Base64 streams and strings. : Base64 « Development Class « Java

1. Java
2. Development Class
3. Base64

A class to decode Base64 streams and strings.

     
/*
This file is part of Socks via HTTP.

This package is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

Socks via HTTP is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with Socks via HTTP; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

// Title :        Base64Decoder.java
// Version :      1.2
// Copyright :    Copyright (c) 2001-2002
// Author :       Florent CUETO  & Sebastien LEBRETON <socksviahttp@cqs.dyndns.org>
// Description :  Base 64 Decoder

//package socksviahttp.core.util;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;

/**
 * A class to decode Base64 streams and strings. See RFC 1521 section 5.2 for
 * details of the Base64 algorithm.
 * <p>
 * This class can be used for decoding strings: <blockquote>
 * 
 * <pre>
 * String encoded = &quot;d2VibWFzdGVyOnRyeTJndWVTUw&quot;;
 * String decoded = Base64Decoder.decode(encoded);
 * </pre>
 * 
 * </blockquote> or for decoding streams: <blockquote>
 * 
 * <pre>
 * InputStream in = new Base64Decoder(System.in);
 * </pre>
 * 
 * </blockquote>
 */

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[] b, int off, int len) throws IOException {
    // 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;
      }
      b[off + i] = (byte) x;
    }
    return i;
  }

  /**
   * Returns the decoded form of the given encoded string.
   * 
   * @param encoded
   *            the string to decode
   * @return the decoded form of the encoded string
   */
  public static String decode(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.toString("8859_1");
    } catch (IOException ignored) {
      return null;
    }
  }
}

   
    
    
    
    
  

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