feat(app): implement Google Play App Licensing

Signed-off-by: YuutaW <17158086+Trumeet@users.noreply.github.com>

1 files changed, 556 insertions, 0 deletions

diff --git a/app/src/main/java/moe/yuuta/gplicense/util/Base64.java b/app/src/main/java/moe/yuuta/gplicense/util/Base64.java
new file mode 100644
index 0000000..0e87d17
--- /dev/null
+++ b/app/src/main/java/moe/yuuta/gplicense/util/Base64.java
@@ -0,0 +1,556 @@
+package moe.yuuta.gplicense.util;
+
+// 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 full-blown 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 is 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;
+    }
+}
\ No newline at end of file