content: /*
   * Copyright 1999-2018 Alibaba Group Holding Ltd.
   *
   * 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.alibaba.druid.util;
  
  /**
   * Static methods for translating Base64 encoded strings to byte arrays and vice-versa.
   *
   * @author Josh Bloch
   * @version %I%, %G%
   * @since 1.4
   */
  public class Base64 {
      /**
       * Translates the specified byte array into a Base64 string as per Preferences.put(byte[]).
       */
      public static String byteArrayToBase64(byte[] a) {
          return byteArrayToBase64(a, false);
      }
  
      /**
       * Translates the specified byte array into an "alternate representation" Base64 string. This non-standard variant
       * uses an alphabet that does not contain the uppercase alphabetic characters, which makes it suitable for use in
       * situations where case-folding occurs.
       */
      public static String byteArrayToAltBase64(byte[] a) {
          return byteArrayToBase64(a, true);
      }
  
      private static String byteArrayToBase64(byte[] a, boolean alternate) {
          int aLen = a.length;
          int numFullGroups = aLen / 3;
          int numBytesInPartialGroup = aLen - 3 * numFullGroups;
          int resultLen = 4 * ((aLen + 2) / 3);
          StringBuilder result = new StringBuilder(resultLen);
          char[] intToAlpha = (alternate ? intToAltBase64 : intToBase64);
  
          // Translate all full groups from byte array elements to Base64
          int inCursor = 0;
          for (int i = 0; i < numFullGroups; i++) {
              int byte0 = a[inCursor++] & 0xff;
              int byte1 = a[inCursor++] & 0xff;
              int byte2 = a[inCursor++] & 0xff;
              result.append(intToAlpha[byte0 >> 2]);
              result.append(intToAlpha[(byte0 << 4) & 0x3f | (byte1 >> 4)]);
              result.append(intToAlpha[(byte1 << 2) & 0x3f | (byte2 >> 6)]);
              result.append(intToAlpha[byte2 & 0x3f]);
          }
  
          // Translate partial group if present
          if (numBytesInPartialGroup != 0) {
              int byte0 = a[inCursor++] & 0xff;
              result.append(intToAlpha[byte0 >> 2]);
              if (numBytesInPartialGroup == 1) {
                  result.append(intToAlpha[(byte0 << 4) & 0x3f]);
                  result.append("==");
              } else {
                  // assert numBytesInPartialGroup == 2;
                  int byte1 = a[inCursor++] & 0xff;
                  result.append(intToAlpha[(byte0 << 4) & 0x3f | (byte1 >> 4)]);
                  result.append(intToAlpha[(byte1 << 2) & 0x3f]);
                  result.append('=');
              }
          }
          // assert inCursor == a.length;
          // assert result.length() == resultLen;
          return result.toString();
      }
  
      /**
       * This array is a lookup table that translates 6-bit positive integer index values into their "Base64 Alphabet"
       * equivalents as specified in Table 1 of RFC 2045.
       */
      private static final char[] intToBase64 = {'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', '+', '/'};
  
      /**
       * This array is a lookup table that translates 6-bit positive integer index values into their
       * "Alternate Base64 Alphabet" equivalents. This is NOT the real Base64 Alphabet as per in Table 1 of RFC 2045. This
       * alternate alphabet does not use the capital letters. It is designed for use in environments where "case folding"
       * occurs.
       */
      private static final char[] intToAltBase64 = {'!', '"', '#', '$', '%', '&', '\'', '(', ')', ',', '-', '.', ':',
              ';', '<', '>', '@', '[', ']', '^', '`', '_', '{', '|', '}', '~', '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', '+', '?'};
  
      /**
       * Translates the specified Base64 string (as per Preferences.get(byte[])) into a byte array.
       */
      public static byte[] base64ToByteArray(String s) {
          return base64ToByteArray(s, false);
      }
  
      /**
       * Translates the specified "alternate representation" Base64 string into a byte array.
       */
      public static byte[] altBase64ToByteArray(String s) {
          return base64ToByteArray(s, true);
      }
  
      private static byte[] base64ToByteArray(String s, boolean alternate) {
          byte[] alphaToInt = (alternate ? altBase64ToInt : base64ToInt);
          int sLen = s.length();
          int numGroups = sLen / 4;
          if (4 * numGroups != sLen) {
              throw new IllegalArgumentException("String length must be a multiple of four.");
          }
          int missingBytesInLastGroup = 0;
          int numFullGroups = numGroups;
          if (sLen != 0) {
              if (s.charAt(sLen - 1) == '=') {
                  missingBytesInLastGroup++;
                  numFullGroups--;
              }
              if (s.charAt(sLen - 2) == '=') {
                  missingBytesInLastGroup++;
              }
          }
          byte[] result = new byte[3 * numGroups - missingBytesInLastGroup];
  
          // Translate all full groups from base64 to byte array elements
          int inCursor = 0, outCursor = 0;
          for (int i = 0; i < numFullGroups; i++) {
              int ch0 = base64toInt(s.charAt(inCursor++), alphaToInt);
              int ch1 = base64toInt(s.charAt(inCursor++), alphaToInt);
              int ch2 = base64toInt(s.charAt(inCursor++), alphaToInt);
              int ch3 = base64toInt(s.charAt(inCursor++), alphaToInt);
              result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4));
              result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2));
              result[outCursor++] = (byte) ((ch2 << 6) | ch3);
          }
  
          // Translate partial group, if present
          if (missingBytesInLastGroup != 0) {
              int ch0 = base64toInt(s.charAt(inCursor++), alphaToInt);
              int ch1 = base64toInt(s.charAt(inCursor++), alphaToInt);
              result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4));
  
              if (missingBytesInLastGroup == 1) {
                  int ch2 = base64toInt(s.charAt(inCursor++), alphaToInt);
                  result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2));
              }
          }
          // assert inCursor == s.length()-missingBytesInLastGroup;
          // assert outCursor == result.length;
          return result;
      }
  
      /**
       * Translates the specified character, which is assumed to be in the "Base 64 Alphabet" into its equivalent 6-bit
       * positive integer.
       *
       * @throw IllegalArgumentException or ArrayOutOfBoundsException if c is not in the Base64 Alphabet.
       */
      private static int base64toInt(char c, byte[] alphaToInt) {
          int result = alphaToInt[c];
          if (result < 0) {
              throw new IllegalArgumentException("Illegal character " + c);
          }
          return result;
      }
  
      /**
       * This array is a lookup table that translates unicode characters drawn from the "Base64 Alphabet" (as specified in
       * Table 1 of RFC 2045) into their 6-bit positive integer equivalents. Characters that are not in the Base64
       * alphabet but fall within the bounds of the array are translated to -1.
       */
      private static final byte[] base64ToInt = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
              -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62,
              -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7,
              8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28,
              29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51};
  
      /**
       * This array is the analogue of base64ToInt, but for the nonstandard variant that avoids the use of uppercase
       * alphabetic characters.
       */
      private static final byte[] altBase64ToInt = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
              -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, -1, 62, 9, 10,
              11, -1, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 12, 13, 14, -1, 15, 63, 16, -1, -1, -1, -1, -1, -1, -1, -1,
              -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 17, -1, 18, 19, 21, 20, 26, 27, 28,
              29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 22, 23, 24, 25};
  
  }
  