In-App purchasing demo

 /* Copyright (c) 2012 Google Inc.
  * Copyright (c) 2015 The Qt Company 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 org.qtproject.qt.android.purchasing;

 // This code was converted from code at http://iharder.sourceforge.net/base64/
 // Lots of extraneous features were removed.
 /* The original code said:
  * <p>
  * I am placing this code in the Public Domain. Do with it as you will.
  * This software comes with no guarantees or warranties but with
  * plenty of well-wishing instead!
  * Please visit
  * <a href="http://iharder.net/xmlizable">http://iharder.net/xmlizable</a>
  * periodically to check for updates or to contribute improvements.
  * </p>
  *
  * @author Robert Harder
  * @author rharder@usa.net
  * @version 1.3
  */

 /**
  * Base64 converter class. This code is not a complete MIME encoder;
  * it simply converts binary data to base64 data and back.
  *
  * <p>Note {@link CharBase64} is a GWT-compatible implementation of this
  * class.
  */
 public class Base64 {
     /** Specify encoding (value is {@code true}). */
     public final static boolean ENCODE = true;

     /** Specify decoding (value is {@code false}). */
     public final static boolean DECODE = false;

     /** The equals sign (=) as a byte. */
     private final static byte EQUALS_SIGN = (byte) '=';

     /** The new line character (\n) as a byte. */
     private final static byte NEW_LINE = (byte) '\n';

     /**
      * The 64 valid Base64 values.
      */
     private final static byte[] ALPHABET =
         {(byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F',
         (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K',
         (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P',
         (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U',
         (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z',
         (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e',
         (byte) 'f', (byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j',
         (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o',
         (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't',
         (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y',
         (byte) 'z', (byte) '0', (byte) '1', (byte) '2', (byte) '3',
         (byte) '4', (byte) '5', (byte) '6', (byte) '7', (byte) '8',
         (byte) '9', (byte) '+', (byte) '/'};

     /**
      * The 64 valid web safe Base64 values.
      */
     private final static byte[] WEBSAFE_ALPHABET =
         {(byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F',
         (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K',
         (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P',
         (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U',
         (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z',
         (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e',
         (byte) 'f', (byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j',
         (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o',
         (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't',
         (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y',
         (byte) 'z', (byte) '0', (byte) '1', (byte) '2', (byte) '3',
         (byte) '4', (byte) '5', (byte) '6', (byte) '7', (byte) '8',
         (byte) '9', (byte) '-', (byte) '_'};

     /**
      * Translates a Base64 value to either its 6-bit reconstruction value
      * or a negative number indicating some other meaning.
      **/
     private final static byte[] DECODABET = {-9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal  0 -  8
         -5, -5, // Whitespace: Tab and Linefeed
         -9, -9, // Decimal 11 - 12
         -5, // Whitespace: Carriage Return
         -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 14 - 26
         -9, -9, -9, -9, -9, // Decimal 27 - 31
         -5, // Whitespace: Space
         -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 33 - 42
         62, // Plus sign at decimal 43
         -9, -9, -9, // Decimal 44 - 46
         63, // Slash at decimal 47
         52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // Numbers zero through nine
         -9, -9, -9, // Decimal 58 - 60
         -1, // Equals sign at decimal 61
         -9, -9, -9, // Decimal 62 - 64
         0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, // Letters 'A' through 'N'
         14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // Letters 'O' through 'Z'
         -9, -9, -9, -9, -9, -9, // Decimal 91 - 96
         26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // Letters 'a' through 'm'
         39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // Letters 'n' through 'z'
         -9, -9, -9, -9, -9 // Decimal 123 - 127
         /*  ,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 128 - 139
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 140 - 152
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 153 - 165
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 166 - 178
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 179 - 191
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 192 - 204
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 205 - 217
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 218 - 230
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 231 - 243
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9         // Decimal 244 - 255 */
     };

     /** The web safe decodabet */
     private final static byte[] WEBSAFE_DECODABET =
         {-9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal  0 -  8
         -5, -5, // Whitespace: Tab and Linefeed
         -9, -9, // Decimal 11 - 12
         -5, // Whitespace: Carriage Return
         -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 14 - 26
         -9, -9, -9, -9, -9, // Decimal 27 - 31
         -5, // Whitespace: Space
         -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 33 - 44
         62, // Dash '-' sign at decimal 45
         -9, -9, // Decimal 46-47
         52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // Numbers zero through nine
         -9, -9, -9, // Decimal 58 - 60
         -1, // Equals sign at decimal 61
         -9, -9, -9, // Decimal 62 - 64
         0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, // Letters 'A' through 'N'
         14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // Letters 'O' through 'Z'
         -9, -9, -9, -9, // Decimal 91-94
         63, // Underscore '_' at decimal 95
         -9, // Decimal 96
         26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // Letters 'a' through 'm'
         39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // Letters 'n' through 'z'
         -9, -9, -9, -9, -9 // Decimal 123 - 127
         /*  ,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 128 - 139
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 140 - 152
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 153 - 165
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 166 - 178
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 179 - 191
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 192 - 204
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 205 - 217
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 218 - 230
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 231 - 243
         -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9         // Decimal 244 - 255 */
         };

     // Indicates white space in encoding
     private final static byte WHITE_SPACE_ENC = -5;
     // Indicates equals sign in encoding
     private final static byte EQUALS_SIGN_ENC = -1;

     /** Defeats instantiation. */
     private Base64() {
     }

     /* ********  E N C O D I N G   M E T H O D S  ******** */

     /**
      * Encodes up to three bytes of the array <var>source</var>
      * and writes the resulting four Base64 bytes to <var>destination</var>.
      * The source and destination arrays can be manipulated
      * anywhere along their length by specifying
      * <var>srcOffset</var> and <var>destOffset</var>.
      * This method does not check to make sure your arrays
      * are large enough to accommodate <var>srcOffset</var> + 3 for
      * the <var>source</var> array or <var>destOffset</var> + 4 for
      * the <var>destination</var> array.
      * The actual number of significant bytes in your array is
      * given by <var>numSigBytes</var>.
      *
      * @param source the array to convert
      * @param srcOffset the index where conversion begins
      * @param numSigBytes the number of significant bytes in your array
      * @param destination the array to hold the conversion
      * @param destOffset the index where output will be put
      * @param alphabet is the encoding alphabet
      * @return the <var>destination</var> array
      * @since 1.3
      */
     private static byte[] encode3to4(byte[] source, int srcOffset,
             int numSigBytes, byte[] destination, int destOffset, byte[] alphabet) {
         //           1         2         3
         // 01234567890123456789012345678901 Bit position
         // --------000000001111111122222222 Array position from threeBytes
         // --------|    ||    ||    ||    | Six bit groups to index alphabet
         //          >>18  >>12  >> 6  >> 0  Right shift necessary
         //                0x3f  0x3f  0x3f  Additional AND

         // Create buffer with zero-padding if there are only one or two
         // significant bytes passed in the array.
         // We have to shift left 24 in order to flush out the 1's that appear
         // when Java treats a value as negative that is cast from a byte to an int.
         int inBuff =
                 (numSigBytes > 0 ? ((source[srcOffset] << 24) >>> 8) : 0)
                 | (numSigBytes > 1 ? ((source[srcOffset + 1] << 24) >>> 16) : 0)
                 | (numSigBytes > 2 ? ((source[srcOffset + 2] << 24) >>> 24) : 0);

         switch (numSigBytes) {
             case 3:
                 destination[destOffset] = alphabet[(inBuff >>> 18)];
                 destination[destOffset + 1] = alphabet[(inBuff >>> 12) & 0x3f];
                 destination[destOffset + 2] = alphabet[(inBuff >>> 6) & 0x3f];
                 destination[destOffset + 3] = alphabet[(inBuff) & 0x3f];
                 return destination;
             case 2:
                 destination[destOffset] = alphabet[(inBuff >>> 18)];
                 destination[destOffset + 1] = alphabet[(inBuff >>> 12) & 0x3f];
                 destination[destOffset + 2] = alphabet[(inBuff >>> 6) & 0x3f];
                 destination[destOffset + 3] = EQUALS_SIGN;
                 return destination;
             case 1:
                 destination[destOffset] = alphabet[(inBuff >>> 18)];
                 destination[destOffset + 1] = alphabet[(inBuff >>> 12) & 0x3f];
                 destination[destOffset + 2] = EQUALS_SIGN;
                 destination[destOffset + 3] = EQUALS_SIGN;
                 return destination;
             default:
                 return destination;
         } // end switch
     } // end encode3to4

     /**
      * Encodes a byte array into Base64 notation.
      * Equivalent to calling
      * {@code encodeBytes(source, 0, source.length)}
      *
      * @param source The data to convert
      * @since 1.4
      */
     public static String encode(byte[] source) {
         return encode(source, 0, source.length, ALPHABET, true);
     }

     /**
      * Encodes a byte array into web safe Base64 notation.
      *
      * @param source The data to convert
      * @param doPadding is {@code true} to pad result with '=' chars
      *        if it does not fall on 3 byte boundaries
      */
     public static String encodeWebSafe(byte[] source, boolean doPadding) {
         return encode(source, 0, source.length, WEBSAFE_ALPHABET, doPadding);
     }

     /**
      * Encodes a byte array into Base64 notation.
      *
      * @param source the data to convert
      * @param off offset in array where conversion should begin
      * @param len length of data to convert
      * @param alphabet the encoding alphabet
      * @param doPadding is {@code true} to pad result with '=' chars
      * if it does not fall on 3 byte boundaries
      * @since 1.4
      */
     public static String encode(byte[] source, int off, int len, byte[] alphabet,
             boolean doPadding) {
         byte[] outBuff = encode(source, off, len, alphabet, Integer.MAX_VALUE);
         int outLen = outBuff.length;

         // If doPadding is false, set length to truncate '='
         // padding characters
         while (doPadding == false && outLen > 0) {
             if (outBuff[outLen - 1] != '=') {
                 break;
             }
             outLen -= 1;
         }

         return new String(outBuff, 0, outLen);
     }

     /**
      * Encodes a byte array into Base64 notation.
      *
      * @param source the data to convert
      * @param off offset in array where conversion should begin
      * @param len length of data to convert
      * @param alphabet is the encoding alphabet
      * @param maxLineLength maximum length of one line.
      * @return the BASE64-encoded byte array
      */
     public static byte[] encode(byte[] source, int off, int len, byte[] alphabet,
             int maxLineLength) {
         int lenDiv3 = (len + 2) / 3; // ceil(len / 3)
         int len43 = lenDiv3 * 4;
         byte[] outBuff = new byte[len43 // Main 4:3
                                   + (len43 / maxLineLength)]; // New lines

         int d = 0;
         int e = 0;
         int len2 = len - 2;
         int lineLength = 0;
         for (; d < len2; d += 3, e += 4) {

             // The following block of code is the same as
             // encode3to4( source, d + off, 3, outBuff, e, alphabet );
             // but inlined for faster encoding (~20% improvement)
             int inBuff =
                     ((source[d + off] << 24) >>> 8)
                     | ((source[d + 1 + off] << 24) >>> 16)
                     | ((source[d + 2 + off] << 24) >>> 24);
             outBuff[e] = alphabet[(inBuff >>> 18)];
             outBuff[e + 1] = alphabet[(inBuff >>> 12) & 0x3f];
             outBuff[e + 2] = alphabet[(inBuff >>> 6) & 0x3f];
             outBuff[e + 3] = alphabet[(inBuff) & 0x3f];

             lineLength += 4;
             if (lineLength == maxLineLength) {
                 outBuff[e + 4] = NEW_LINE;
                 e++;
                 lineLength = 0;
             } // end if: end of line
         } // end for: each piece of array

         if (d < len) {
             encode3to4(source, d + off, len - d, outBuff, e, alphabet);

             lineLength += 4;
             if (lineLength == maxLineLength) {
                 // Add a last newline
                 outBuff[e + 4] = NEW_LINE;
                 e++;
             }
             e += 4;
         }

         assert (e == outBuff.length);
         return outBuff;
     }

     /* ********  D E C O D I N G   M E T H O D S  ******** */

     /**
      * Decodes four bytes from array <var>source</var>
      * and writes the resulting bytes (up to three of them)
      * to <var>destination</var>.
      * The source and destination arrays can be manipulated
      * anywhere along their length by specifying
      * <var>srcOffset</var> and <var>destOffset</var>.
      * This method does not check to make sure your arrays
      * are large enough to accommodate <var>srcOffset</var> + 4 for
      * the <var>source</var> array or <var>destOffset</var> + 3 for
      * the <var>destination</var> array.
      * This method returns the actual number of bytes that
      * were converted from the Base64 encoding.
      *
      *
      * @param source the array to convert
      * @param srcOffset the index where conversion begins
      * @param destination the array to hold the conversion
      * @param destOffset the index where output will be put
      * @param decodabet the decodabet for decoding Base64 content
      * @return the number of decoded bytes converted
      * @since 1.3
      */
     private static int decode4to3(byte[] source, int srcOffset,
             byte[] destination, int destOffset, byte[] decodabet) {
         // Example: Dk==
         if (source[srcOffset + 2] == EQUALS_SIGN) {
             int outBuff =
                     ((decodabet[source[srcOffset]] << 24) >>> 6)
                     | ((decodabet[source[srcOffset + 1]] << 24) >>> 12);

             destination[destOffset] = (byte) (outBuff >>> 16);
             return 1;
         } else if (source[srcOffset + 3] == EQUALS_SIGN) {
             // Example: DkL=
             int outBuff =
                     ((decodabet[source[srcOffset]] << 24) >>> 6)
                     | ((decodabet[source[srcOffset + 1]] << 24) >>> 12)
                     | ((decodabet[source[srcOffset + 2]] << 24) >>> 18);

             destination[destOffset] = (byte) (outBuff >>> 16);
             destination[destOffset + 1] = (byte) (outBuff >>> 8);
             return 2;
         } else {
             // Example: DkLE
             int outBuff =
                     ((decodabet[source[srcOffset]] << 24) >>> 6)
                     | ((decodabet[source[srcOffset + 1]] << 24) >>> 12)
                     | ((decodabet[source[srcOffset + 2]] << 24) >>> 18)
                     | ((decodabet[source[srcOffset + 3]] << 24) >>> 24);

             destination[destOffset] = (byte) (outBuff >> 16);
             destination[destOffset + 1] = (byte) (outBuff >> 8);
             destination[destOffset + 2] = (byte) (outBuff);
             return 3;
         }
     } // end decodeToBytes

     /**
      * Decodes data from Base64 notation.
      *
      * @param s the string to decode (decoded in default encoding)
      * @return the decoded data
      * @since 1.4
      */
     public static byte[] decode(String s) throws Base64DecoderException {
         byte[] bytes = s.getBytes();
         return decode(bytes, 0, bytes.length);
     }

     /**
      * Decodes data from web safe Base64 notation.
      * Web safe encoding uses '-' instead of '+', '_' instead of '/'
      *
      * @param s the string to decode (decoded in default encoding)
      * @return the decoded data
      */
     public static byte[] decodeWebSafe(String s) throws Base64DecoderException {
         byte[] bytes = s.getBytes();
         return decodeWebSafe(bytes, 0, bytes.length);
     }

     /**
      * Decodes Base64 content in byte array format and returns
      * the decoded byte array.
      *
      * @param source The Base64 encoded data
      * @return decoded data
      * @since 1.3
      * @throws Base64DecoderException
      */
     public static byte[] decode(byte[] source) throws Base64DecoderException {
         return decode(source, 0, source.length);
     }

     /**
      * Decodes web safe Base64 content in byte array format and returns
      * the decoded data.
      * Web safe encoding uses '-' instead of '+', '_' instead of '/'
      *
      * @param source the string to decode (decoded in default encoding)
      * @return the decoded data
      */
     public static byte[] decodeWebSafe(byte[] source)
             throws Base64DecoderException {
         return decodeWebSafe(source, 0, source.length);
     }

     /**
      * Decodes Base64 content in byte array format and returns
      * the decoded byte array.
      *
      * @param source the Base64 encoded data
      * @param off    the offset of where to begin decoding
      * @param len    the length of characters to decode
      * @return decoded data
      * @since 1.3
      * @throws Base64DecoderException
      */
     public static byte[] decode(byte[] source, int off, int len)
             throws Base64DecoderException {
         return decode(source, off, len, DECODABET);
     }

     /**
      * Decodes web safe Base64 content in byte array format and returns
      * the decoded byte array.
      * Web safe encoding uses '-' instead of '+', '_' instead of '/'
      *
      * @param source the Base64 encoded data
      * @param off    the offset of where to begin decoding
      * @param len    the length of characters to decode
      * @return decoded data
      */
     public static byte[] decodeWebSafe(byte[] source, int off, int len)
             throws Base64DecoderException {
         return decode(source, off, len, WEBSAFE_DECODABET);
     }

     /**
      * Decodes Base64 content using the supplied decodabet and returns
      * the decoded byte array.
      *
      * @param source the Base64 encoded data
      * @param off the offset of where to begin decoding
      * @param len the length of characters to decode
      * @param decodabet the decodabet for decoding Base64 content
      * @return decoded data
      */
     public static byte[] decode(byte[] source, int off, int len, byte[] decodabet)
             throws Base64DecoderException {
         int len34 = len * 3 / 4;
         byte[] outBuff = new byte[2 + len34]; // Upper limit on size of output
         int outBuffPosn = 0;

         byte[] b4 = new byte[4];
         int b4Posn = 0;
         int i = 0;
         byte sbiCrop = 0;
         byte sbiDecode = 0;
         for (i = 0; i < len; i++) {
             sbiCrop = (byte) (source[i + off] & 0x7f); // Only the low seven bits
             sbiDecode = decodabet[sbiCrop];

             if (sbiDecode >= WHITE_SPACE_ENC) { // White space Equals sign or better
                 if (sbiDecode >= EQUALS_SIGN_ENC) {
                     // An equals sign (for padding) must not occur at position 0 or 1
                     // and must be the last byte[s] in the encoded value
                     if (sbiCrop == EQUALS_SIGN) {
                         int bytesLeft = len - i;
                         byte lastByte = (byte) (source[len - 1 + off] & 0x7f);
                         if (b4Posn == 0 || b4Posn == 1) {
                             throw new Base64DecoderException(
                                     "invalid padding byte '=' at byte offset " + i);
                         } else if ((b4Posn == 3 && bytesLeft > 2)
                                 || (b4Posn == 4 && bytesLeft > 1)) {
                             throw new Base64DecoderException(
                                     "padding byte '=' falsely signals end of encoded value "
                                             + "at offset " + i);
                         } else if (lastByte != EQUALS_SIGN && lastByte != NEW_LINE) {
                             throw new Base64DecoderException(
                                     "encoded value has invalid trailing byte");
                         }
                         break;
                     }

                     b4[b4Posn++] = sbiCrop;
                     if (b4Posn == 4) {
                         outBuffPosn += decode4to3(b4, 0, outBuff, outBuffPosn, decodabet);
                         b4Posn = 0;
                     }
                 }
             } else {
                 throw new Base64DecoderException("Bad Base64 input character at " + i
                         + ": " + source[i + off] + "(decimal)");
             }
         }

         // Because web safe encoding allows non padding base64 encodes, we
         // need to pad the rest of the b4 buffer with equal signs when
         // b4Posn != 0.  There can be at most 2 equal signs at the end of
         // four characters, so the b4 buffer must have two or three
         // characters.  This also catches the case where the input is
         // padded with EQUALS_SIGN
         if (b4Posn != 0) {
             if (b4Posn == 1) {
                 throw new Base64DecoderException("single trailing character at offset "
                         + (len - 1));
             }
             b4[b4Posn++] = EQUALS_SIGN;
             outBuffPosn += decode4to3(b4, 0, outBuff, outBuffPosn, decodabet);
         }

         byte[] out = new byte[outBuffPosn];
         System.arraycopy(outBuff, 0, out, 0, outBuffPosn);
         return out;
     }
 }