Android Open Source - ubihelper Base64

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License

The source code is released under:

GNU General Public License

Java Source Code

/**
 * Copyright (c) 2012 The University of Nottingham
 * //from   w  w  w  .jav  a  2 s .  co m
 * This file is part of ubihelper
 *
 *  ubihelper is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Affero General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  ubihelper 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 Affero General Public License for more details.
 *
 *  You should have received a copy of the GNU Affero General Public License
 *  along with ubihelper. If not, see <http://www.gnu.org/licenses/>.
 *  
 *  @author Chris Greenhalgh (cmg@cs.nott.ac.uk), The University of Nottingham
 */

package uk.ac.horizon.ubihelper.j2se;

/**
 * @author cmg
 *
 */
public class Base64 {
  static char chars[] = new char[] {
    'A','B','C','D','E','F','G','H',//8
    'I','J','K','L','M','N','O','P',//16
    'Q','R','S','T','U','V','W','X',//24
    'Y','Z','a','b','c','d','e','f',//32
    'g','h','i','j','k','l','m','n',//40
    'o','p','q','r','s','t','u','v',//48
    'w','x','y','z','0','1','2','3',//56
    '4','5','6','7','8','9','+','/' //64
  };
  static int bytes[] = new int[128];
  static {
    for (int i=0; i<chars.length; i++)
      bytes[(int)chars[i]] = i;
    bytes[(int)'='] = 0;
  }
  public static String encode(byte data[]) {
    StringBuilder sb = new StringBuilder();
    int pos = 0;
    while(pos+2<data.length) {
      int bs = ((data[pos++] & 0xff) << 16) |
          ((data[pos++] & 0xff) << 8) |
          ((data[pos++] & 0xff));
      sb.append(chars[(bs >> 18) & 0x3f]);
      sb.append(chars[(bs >> 12) & 0x3f]);
      sb.append(chars[(bs >> 6) & 0x3f]);
      sb.append(chars[(bs) & 0x3f]);      
    }
    if (pos<data.length) {
      if (pos+1<data.length) {
        // 2 bytes
        int bs = ((data[pos++] & 0xff) << 16) |
            ((data[pos++] & 0xff) << 8);
        sb.append(chars[(bs >> 18) & 0x3f]);
        sb.append(chars[(bs >> 12) & 0x3f]);
        sb.append(chars[(bs >> 6) & 0x3f]);
        sb.append("=");
      } else {
        // 1 byte
        int bs = ((data[pos++] & 0xff) << 16);
        sb.append(chars[(bs >> 18) & 0x3f]);
        sb.append(chars[(bs >> 12) & 0x3f]);
        sb.append("=");
        sb.append("=");
      }
    }
    return sb.toString();
  }
  /** NB no errors are raised for badly formatted base64.
   * E.g. = included in body will cause early termination.
   * @param s
   * @return
   */
  public static byte[] decode(String s) {
    // size?
    int spos = 0;
    int size = 0;
    while (spos<s.length()) {
      char c = s.charAt(spos++);
      if (Character.isWhitespace(c))
        continue;
      if (c=='=')
        break;
      size++;
    }
    int bsize = (size*3)/4;
    byte data[] = new byte[bsize];
    int bpos = 0;
    spos = 0;
    char cs[] = new char[4];
    int cpos = 0;
    while (spos<s.length()) {
      char c = s.charAt(spos++);
      if (Character.isWhitespace(c))
        continue;
      cs[cpos++] = c;
      if (cpos==4) {
        int bs = (bytes[cs[0] & 0x7f] << 18) |
            (bytes[cs[1] & 0x7f] << 12) |
            (bytes[cs[2] & 0x7f] << 6) |
            (bytes[cs[3] & 0x7f]);
        data[bpos++] = (byte)((bs >> 16) & 0xff);
        if (cs[2]=='=') 
          break;
        data[bpos++] = (byte)((bs >> 8) & 0xff);
        if (cs[3]=='=')
          break;
        data[bpos++] = (byte)((bs) & 0xff);          
        cpos = 0;
      }
    }
    return data;
  }
  
  public static void main(String args[]) {
    byte bs1[] = new byte[8];
    test(bs1);
    byte bs2[] = new byte[9];
    test(bs2);
    byte bs3[] = new byte[10];
    test(bs3);
  }
  private static void test(byte[] bs) {
    for (int i=0; i<bs.length; i++)
      bs[i] = (byte)(i+1);
    String enc = encode(bs);
    System.out.println("Test "+bs.length+" bytes -> "+enc);
    byte rs[] = decode(enc);
    if (rs.length!=bs.length) {
      System.err.println("Error: encoded "+bs.length+" bytes -> "+rs.length+" bytes");
      return;
    }
    else {
      for (int i=0; i<bs.length; i++) {
        if (bs[i]!=rs[i]) {
          System.err.println("Error: byte "+i+" wrong ("+bs[i]+" vs "+rs[i]+")");
          return;
        }
      }
    }
    System.out.println("OK");
  }
}

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