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'rapiddweller Common' is an open source Java library forked from Databene Commons by Volker Bergmann. It provides extensions to the Java core library by utility classes, abstract concepts and concrete implementations.
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/*
 * Copyright (C) 2004-2015 Volker Bergmann ([email protected]).
 * All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.rapiddweller.common;

import java.util.Arrays;

/**
 * Codes/Decodes Base64 strings.
 *
 * @author Volker Bergmann
 * @since 0.2.04
 */
public class Base64Codec {

  private static final char[] DIGITS = createDigits();
  private static final byte[] INDICES = createIndices();

  private Base64Codec() {
  }

  // interface ----------------------------------------------------------------------------------------

  /**
   * Encode string.
   *
   * @param source the source
   * @return the string
   */
  public static String encode(byte[] source) {
    int srcLength = source.length;
    int srcCursor = 0;
    int unpaddedLength = (srcLength * 4 + 2) / 3;
    int paddedLength = ((srcLength + 2) / 3) * 4;
    char[] buffer = new char[paddedLength];
    int bufferCursor = 0;
    while (srcCursor < srcLength) {
      int d0 = source[srcCursor++] & 0xff;
      int d1 = srcCursor < srcLength ? source[srcCursor++] & 0xff : 0;
      int d2 = srcCursor < srcLength ? source[srcCursor++] & 0xff : 0;
      buffer[bufferCursor++] = DIGITS[d0 >>> 2];
      buffer[bufferCursor++] = DIGITS[((d0 & 0x3) << 4) | (d1 >>> 4)];
      buffer[bufferCursor] = bufferCursor++ < unpaddedLength ? DIGITS[((d1 & 0xf) << 2) | (d2 >>> 6)] : '=';
      buffer[bufferCursor] = bufferCursor++ < unpaddedLength ? DIGITS[d2 & 0x3F] : '=';
    }
    return new String(buffer);
  }

  /**
   * Decode byte [ ].
   *
   * @param code the code
   * @return the byte [ ]
   */
  public static byte[] decode(String code) {
    if (code == null) {
      throw new IllegalArgumentException("code is null");
    }
    char[] codeBuffer = code.toCharArray();
    int codeLength = codeBuffer.length;
    if (codeLength % 4 != 0) {
      throw new IllegalArgumentException("Length of Base64 encoded input string is not a multiple of 4.");
    }
    while (codeLength > 0 && codeBuffer[codeLength - 1] == '=') {
      codeLength--;
    }
    for (int i = 0; i < codeLength; i++) {
      if (!isBase64Char(codeBuffer[i])) {
        throw new IllegalArgumentException("Not a base64 code: " + code);
      }
    }
    int resultLength = (codeLength * 3) / 4;
    byte[] result = new byte[resultLength];
    int codeCursor = 0;
    int resultCursor = 0;
    while (codeCursor < codeLength) {
      int b0 = INDICES[codeBuffer[codeCursor++]];
      int b1 = INDICES[codeBuffer[codeCursor++]];
      int b2 = (codeCursor < codeLength ? INDICES[codeBuffer[codeCursor++]] : 0);
      int b3 = (codeCursor < codeLength ? INDICES[codeBuffer[codeCursor++]] : 0);
      result[resultCursor++] = (byte) ((b0 << 2) | (b1 >>> 4));
      if (resultCursor < resultLength) {
        result[resultCursor++] = (byte) (((b1 & 0xf) << 4) | (b2 >>> 2));
      }
      if (resultCursor < resultLength) {
        result[resultCursor++] = (byte) (((b2 & 3) << 6) | b3);
      }
    }
    return result;
  }

  // private helpers -------------------------------------------------------------------------------------

  /**
   * Is base 64 char boolean.
   *
   * @param c the c
   * @return the boolean
   */
  public static boolean isBase64Char(char c) {
    return ('A' <= c && c <= 'Z') || ('a' <= c && c <= 'z') || ('0' <= c && c <= '9') || c == '+' || c == '/';
  }

  private static char[] createDigits() {
    char[] digits = new char[64];
    int i = 0;
    for (char c = 'A'; c <= 'Z'; c++) {
      digits[i++] = c;
    }
    for (char c = 'a'; c <= 'z'; c++) {
      digits[i++] = c;
    }
    for (char c = '0'; c <= '9'; c++) {
      digits[i++] = c;
    }
    digits[i++] = '+';
    digits[i++] = '/';
    return digits;
  }

  private static byte[] createIndices() {
    byte[] indices = new byte[128];
    Arrays.fill(indices, 0, indices.length, (byte) -1);
    for (int i = 0; i < 64; i++) {
      indices[DIGITS[i]] = (byte) i;
    }
    return indices;
  }
}