content: /*
   * Copyright (c) 2012, 2016, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code 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 General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  package com.aaron.yespdf.common.utils;
  
  import java.io.FilterOutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.nio.ByteBuffer;
  import java.nio.charset.StandardCharsets;
  import java.util.Arrays;
  import java.util.Objects;
  
  /**
   * This class consists exclusively of static methods for obtaining
   * encoders and decoders for the Base64 encoding scheme. The
   * implementation of this class supports the following types of Base64
   * as specified in
   * <a href="http://www.ietf.org/rfc/rfc4648.txt">RFC 4648</a> and
   * <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>.
   *
   * <ul>
   * <li><a name="basic"><b>Basic</b></a>
   * <p> Uses "The Base64 Alphabet" as specified in Table 1 of
   *     RFC 4648 and RFC 2045 for encoding and decoding operation.
   *     The encoder does not add any line feed (line separator)
   *     character. The decoder rejects data that contains characters
   *     outside the base64 alphabet.</p></li>
   *
   * <li><a name="url"><b>URL and Filename safe</b></a>
   * <p> Uses the "URL and Filename safe Base64 Alphabet" as specified
   *     in Table 2 of RFC 4648 for encoding and decoding. The
   *     encoder does not add any line feed (line separator) character.
   *     The decoder rejects data that contains characters outside the
   *     base64 alphabet.</p></li>
   *
   * <li><a name="mime"><b>MIME</b></a>
   * <p> Uses the "The Base64 Alphabet" as specified in Table 1 of
   *     RFC 2045 for encoding and decoding operation. The encoded output
   *     must be represented in lines of no more than 76 characters each
   *     and uses a carriage return {@code '\r'} followed immediately by
   *     a linefeed {@code '\n'} as the line separator. No line separator
   *     is added to the end of the encoded output. All line separators
   *     or other characters not found in the base64 alphabet table are
   *     ignored in decoding operation.</p></li>
   * </ul>
   *
   * <p> Unless otherwise noted, passing a {@code null} argument to a
   * method of this class will cause a {@link java.lang.NullPointerException
   * NullPointerException} to be thrown.
   *
   * @author Xueming Shen
   * @since 1.8
   */
  
  public class Base64 {
  
      private Base64() {
      }
  
      /**
       * Returns a {@link Encoder} that encodes using the
       * <a href="#basic">Basic</a> type base64 encoding scheme.
       *
       * @return A Base64 encoder.
       */
      public static Encoder getEncoder() {
          return Encoder.RFC4648;
      }
  
      /**
       * Returns a {@link Encoder} that encodes using the
       * <a href="#url">URL and Filename safe</a> type base64
       * encoding scheme.
       *
       * @return A Base64 encoder.
       */
      public static Encoder getUrlEncoder() {
          return Encoder.RFC4648_URLSAFE;
      }
  
      /**
       * Returns a {@link Encoder} that encodes using the
       * <a href="#mime">MIME</a> type base64 encoding scheme.
       *
       * @return A Base64 encoder.
       */
      public static Encoder getMimeEncoder() {
          return Encoder.RFC2045;
      }
  
      /**
       * Returns a {@link Encoder} that encodes using the
       * <a href="#mime">MIME</a> type base64 encoding scheme
       * with specified line length and line separators.
       *
       * @param lineLength    the length of each output line (rounded down to nearest multiple
       *                      of 4). If {@code lineLength <= 0} the output will not be separated
       *                      in lines
       * @param lineSeparator the line separator for each output line
       * @return A Base64 encoder.
       * @throws IllegalArgumentException if {@code lineSeparator} includes any
       *                                  character of "The Base64 Alphabet" as specified in Table 1 of
       *                                  RFC 2045.
       */
      public static Encoder getMimeEncoder(int lineLength, byte[] lineSeparator) {
          Objects.requireNonNull(lineSeparator);
          int[] base64 = Decoder.fromBase64;
          for (byte b : lineSeparator) {
              if (base64[b & 0xff] != -1)
                  throw new IllegalArgumentException(
                          "Illegal base64 line separator character 0x" + Integer.toString(b, 16));
          }
          if (lineLength <= 0) {
              return Encoder.RFC4648;
          }
          return new Encoder(false, lineSeparator, lineLength >> 2 << 2, true);
      }
  
      /**
       * Returns a {@link Decoder} that decodes using the
       * <a href="#basic">Basic</a> type base64 encoding scheme.
       *
       * @return A Base64 decoder.
       */
      public static Decoder getDecoder() {
          return Decoder.RFC4648;
      }
  
      /**
       * Returns a {@link Decoder} that decodes using the
       * <a href="#url">URL and Filename safe</a> type base64
       * encoding scheme.
       *
       * @return A Base64 decoder.
       */
      public static Decoder getUrlDecoder() {
          return Decoder.RFC4648_URLSAFE;
      }
  
      /**
       * Returns a {@link Decoder} that decodes using the
       * <a href="#mime">MIME</a> type base64 decoding scheme.
       *
       * @return A Base64 decoder.
       */
      public static Decoder getMimeDecoder() {
          return Decoder.RFC2045;
      }
  
      /**
       * This class implements an encoder for encoding byte data using
       * the Base64 encoding scheme as specified in RFC 4648 and RFC 2045.
       *
       * <p> Instances of {@link Encoder} class are safe for use by
       * multiple concurrent threads.
       *
       * <p> Unless otherwise noted, passing a {@code null} argument to
       * a method of this class will cause a
       * {@link java.lang.NullPointerException NullPointerException} to
       * be thrown.
       *
       * @see Decoder
       * @since 1.8
       */
      public static class Encoder {
  
          private final byte[] newline;
          private final int linemax;
          private final boolean isURL;
          private final boolean doPadding;
  
          private Encoder(boolean isURL, byte[] newline, int linemax, boolean doPadding) {
              this.isURL = isURL;
              this.newline = newline;
              this.linemax = linemax;
              this.doPadding = doPadding;
          }
  
          /**
           * This array is a lookup table that translates 6-bit positive integer
           * index values into their "Base64 Alphabet" equivalents as specified
           * in "Table 1: The Base64 Alphabet" of RFC 2045 (and RFC 4648).
           */
          private static final char[] toBase64 = {
                  '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', '+', '/'
          };
  
          /**
           * It's the lookup table for "URL and Filename safe Base64" as specified
           * in Table 2 of the RFC 4648, with the '+' and '/' changed to '-' and
           * '_'. This table is used when BASE64_URL is specified.
           */
          private static final char[] toBase64URL = {
                  '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', '-', '_'
          };
  
          private static final int MIMELINEMAX = 76;
          private static final byte[] CRLF = new byte[]{'\r', '\n'};
  
          static final Encoder RFC4648 = new Encoder(false, null, -1, true);
          static final Encoder RFC4648_URLSAFE = new Encoder(true, null, -1, true);
          static final Encoder RFC2045 = new Encoder(false, CRLF, MIMELINEMAX, true);
  
          private final int outLength(int srclen) {
              int len = 0;
              if (doPadding) {
                  len = 4 * ((srclen + 2) / 3);
              } else {
                  int n = srclen % 3;
                  len = 4 * (srclen / 3) + (n == 0 ? 0 : n + 1);
              }
              if (linemax > 0)                                  // line separators
                  len += (len - 1) / linemax * newline.length;
              return len;
          }
  
          /**
           * Encodes all bytes from the specified byte array into a newly-allocated
           * byte array using the {@link Base64} encoding scheme. The returned byte
           * array is of the length of the resulting bytes.
           *
           * @param src the byte array to encode
           * @return A newly-allocated byte array containing the resulting
           * encoded bytes.
           */
          public byte[] encode(byte[] src) {
              int len = outLength(src.length);          // dst array size
              byte[] dst = new byte[len];
              int ret = encode0(src, 0, src.length, dst);
              if (ret != dst.length)
                  return Arrays.copyOf(dst, ret);
              return dst;
          }
  
          /**
           * Encodes all bytes from the specified byte array using the
           * {@link Base64} encoding scheme, writing the resulting bytes to the
           * given output byte array, starting at offset 0.
           *
           * <p> It is the responsibility of the invoker of this method to make
           * sure the output byte array {@code dst} has enough space for encoding
           * all bytes from the input byte array. No bytes will be written to the
           * output byte array if the output byte array is not big enough.
           *
           * @param src the byte array to encode
           * @param dst the output byte array
           * @return The number of bytes written to the output byte array
           * @throws IllegalArgumentException if {@code dst} does not have enough
           *                                  space for encoding all input bytes.
           */
          public int encode(byte[] src, byte[] dst) {
              int len = outLength(src.length);         // dst array size
              if (dst.length < len)
                  throw new IllegalArgumentException(
                          "Output byte array is too small for encoding all input bytes");
              return encode0(src, 0, src.length, dst);
          }
  
          /**
           * Encodes the specified byte array into a String using the {@link Base64}
           * encoding scheme.
           *
           * <p> This method first encodes all input bytes into a base64 encoded
           * byte array and then constructs a new String by using the encoded byte
           * array and the {@link java.nio.charset.StandardCharsets#ISO_8859_1
           * ISO-8859-1} charset.
           *
           * <p> In other words, an invocation of this method has exactly the same
           * effect as invoking
           * {@code new String(encode(src), StandardCharsets.ISO_8859_1)}.
           *
           * @param src the byte array to encode
           * @return A String containing the resulting Base64 encoded characters
           */
          @SuppressWarnings("deprecation")
          public String encodeToString(byte[] src) {
              byte[] encoded = encode(src);
              return new String(encoded, 0, 0, encoded.length);
          }
  
          /**
           * Encodes all remaining bytes from the specified byte buffer into
           * a newly-allocated ByteBuffer using the {@link Base64} encoding
           * scheme.
           * <p>
           * Upon return, the source buffer's position will be updated to
           * its limit; its limit will not have been changed. The returned
           * output buffer's position will be zero and its limit will be the
           * number of resulting encoded bytes.
           *
           * @param buffer the source ByteBuffer to encode
           * @return A newly-allocated byte buffer containing the encoded bytes.
           */
          public ByteBuffer encode(ByteBuffer buffer) {
              int len = outLength(buffer.remaining());
              byte[] dst = new byte[len];
              int ret = 0;
              if (buffer.hasArray()) {
                  ret = encode0(buffer.array(),
                          buffer.arrayOffset() + buffer.position(),
                          buffer.arrayOffset() + buffer.limit(),
                          dst);
                  buffer.position(buffer.limit());
              } else {
                  byte[] src = new byte[buffer.remaining()];
                  buffer.get(src);
                  ret = encode0(src, 0, src.length, dst);
              }
              if (ret != dst.length)
                  dst = Arrays.copyOf(dst, ret);
              return ByteBuffer.wrap(dst);
          }
  
          /**
           * Wraps an output stream for encoding byte data using the {@link Base64}
           * encoding scheme.
           *
           * <p> It is recommended to promptly close the returned output stream after
           * use, during which it will flush all possible leftover bytes to the underlying
           * output stream. Closing the returned output stream will close the underlying
           * output stream.
           *
           * @param os the output stream.
           * @return the output stream for encoding the byte data into the
           * specified Base64 encoded format
           */
          public OutputStream wrap(OutputStream os) {
              Objects.requireNonNull(os);
              return new EncOutputStream(os, isURL ? toBase64URL : toBase64,
                      newline, linemax, doPadding);
          }
  
          /**
           * Returns an encoder instance that encodes equivalently to this one,
           * but without adding any padding character at the end of the encoded
           * byte data.
           *
           * <p> The encoding scheme of this encoder instance is unaffected by
           * this invocation. The returned encoder instance should be used for
           * non-padding encoding operation.
           *
           * @return an equivalent encoder that encodes without adding any
           * padding character at the end
           */
          public Encoder withoutPadding() {
              if (!doPadding)
                  return this;
              return new Encoder(isURL, newline, linemax, false);
          }
  
          private int encode0(byte[] src, int off, int end, byte[] dst) {
              char[] base64 = isURL ? toBase64URL : toBase64;
              int sp = off;
              int slen = (end - off) / 3 * 3;
              int sl = off + slen;
              if (linemax > 0 && slen > linemax / 4 * 3)
                  slen = linemax / 4 * 3;
              int dp = 0;
              while (sp < sl) {
                  int sl0 = Math.min(sp + slen, sl);
                  for (int sp0 = sp, dp0 = dp; sp0 < sl0; ) {
                      int bits = (src[sp0++] & 0xff) << 16 |
                              (src[sp0++] & 0xff) << 8 |
                              (src[sp0++] & 0xff);
                      dst[dp0++] = (byte) base64[(bits >>> 18) & 0x3f];
                      dst[dp0++] = (byte) base64[(bits >>> 12) & 0x3f];
                      dst[dp0++] = (byte) base64[(bits >>> 6) & 0x3f];
                      dst[dp0++] = (byte) base64[bits & 0x3f];
                  }
                  int dlen = (sl0 - sp) / 3 * 4;
                  dp += dlen;
                  sp = sl0;
                  if (dlen == linemax && sp < end) {
                      for (byte b : newline) {
                          dst[dp++] = b;
                      }
                  }
              }
              if (sp < end) {               // 1 or 2 leftover bytes
                  int b0 = src[sp++] & 0xff;
                  dst[dp++] = (byte) base64[b0 >> 2];
                  if (sp == end) {
                      dst[dp++] = (byte) base64[(b0 << 4) & 0x3f];
                      if (doPadding) {
                          dst[dp++] = '=';
                          dst[dp++] = '=';
                      }
                  } else {
                      int b1 = src[sp++] & 0xff;
                      dst[dp++] = (byte) base64[(b0 << 4) & 0x3f | (b1 >> 4)];
                      dst[dp++] = (byte) base64[(b1 << 2) & 0x3f];
                      if (doPadding) {
                          dst[dp++] = '=';
                      }
                  }
              }
              return dp;
          }
      }
  
      /**
       * This class implements a decoder for decoding byte data using the
       * Base64 encoding scheme as specified in RFC 4648 and RFC 2045.
       *
       * <p> The Base64 padding character {@code '='} is accepted and
       * interpreted as the end of the encoded byte data, but is not
       * required. So if the final unit of the encoded byte data only has
       * two or three Base64 characters (without the corresponding padding
       * character(s) padded), they are decoded as if followed by padding
       * character(s). If there is a padding character present in the
       * final unit, the correct number of padding character(s) must be
       * present, otherwise {@code IllegalArgumentException} (
       * {@code IOException} when reading from a Base64 stream) is thrown
       * during decoding.
       *
       * <p> Instances of {@link Decoder} class are safe for use by
       * multiple concurrent threads.
       *
       * <p> Unless otherwise noted, passing a {@code null} argument to
       * a method of this class will cause a
       * {@link java.lang.NullPointerException NullPointerException} to
       * be thrown.
       *
       * @see Encoder
       * @since 1.8
       */
      public static class Decoder {
  
          private final boolean isURL;
          private final boolean isMIME;
  
          private Decoder(boolean isURL, boolean isMIME) {
              this.isURL = isURL;
              this.isMIME = isMIME;
          }
  
          /**
           * Lookup table for decoding 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 encoded to -1.
           */
          private static final int[] fromBase64 = new int[256];
  
          static {
              Arrays.fill(fromBase64, -1);
              for (int i = 0; i < Encoder.toBase64.length; i++)
                  fromBase64[Encoder.toBase64[i]] = i;
              fromBase64['='] = -2;
          }
  
          /**
           * Lookup table for decoding "URL and Filename safe Base64 Alphabet"
           * as specified in Table2 of the RFC 4648.
           */
          private static final int[] fromBase64URL = new int[256];
  
          static {
              Arrays.fill(fromBase64URL, -1);
              for (int i = 0; i < Encoder.toBase64URL.length; i++)
                  fromBase64URL[Encoder.toBase64URL[i]] = i;
              fromBase64URL['='] = -2;
          }
  
          static final Decoder RFC4648 = new Decoder(false, false);
          static final Decoder RFC4648_URLSAFE = new Decoder(true, false);
          static final Decoder RFC2045 = new Decoder(false, true);
  
          /**
           * Decodes all bytes from the input byte array using the {@link Base64}
           * encoding scheme, writing the results into a newly-allocated output
           * byte array. The returned byte array is of the length of the resulting
           * bytes.
           *
           * @param src the byte array to decode
           * @return A newly-allocated byte array containing the decoded bytes.
           * @throws IllegalArgumentException if {@code src} is not in valid Base64 scheme
           */
          public byte[] decode(byte[] src) {
              byte[] dst = new byte[outLength(src, 0, src.length)];
              int ret = decode0(src, 0, src.length, dst);
              if (ret != dst.length) {
                  dst = Arrays.copyOf(dst, ret);
              }
              return dst;
          }
  
          /**
           * Decodes a Base64 encoded String into a newly-allocated byte array
           * using the {@link Base64} encoding scheme.
           *
           * <p> An invocation of this method has exactly the same effect as invoking
           * {@code decode(src.getBytes(StandardCharsets.ISO_8859_1))}
           *
           * @param src the string to decode
           * @return A newly-allocated byte array containing the decoded bytes.
           * @throws IllegalArgumentException if {@code src} is not in valid Base64 scheme
           */
          public byte[] decode(String src) {
              return decode(src.getBytes(StandardCharsets.ISO_8859_1));
          }
  
          /**
           * Decodes all bytes from the input byte array using the {@link Base64}
           * encoding scheme, writing the results into the given output byte array,
           * starting at offset 0.
           *
           * <p> It is the responsibility of the invoker of this method to make
           * sure the output byte array {@code dst} has enough space for decoding
           * all bytes from the input byte array. No bytes will be be written to
           * the output byte array if the output byte array is not big enough.
           *
           * <p> If the input byte array is not in valid Base64 encoding scheme
           * then some bytes may have been written to the output byte array before
           * IllegalargumentException is thrown.
           *
           * @param src the byte array to decode
           * @param dst the output byte array
           * @return The number of bytes written to the output byte array
           * @throws IllegalArgumentException if {@code src} is not in valid Base64 scheme, or {@code dst}
           *                                  does not have enough space for decoding all input bytes.
           */
          public int decode(byte[] src, byte[] dst) {
              int len = outLength(src, 0, src.length);
              if (dst.length < len)
                  throw new IllegalArgumentException(
                          "Output byte array is too small for decoding all input bytes");
              return decode0(src, 0, src.length, dst);
          }
  
          /**
           * Decodes all bytes from the input byte buffer using the {@link Base64}
           * encoding scheme, writing the results into a newly-allocated ByteBuffer.
           *
           * <p> Upon return, the source buffer's position will be updated to
           * its limit; its limit will not have been changed. The returned
           * output buffer's position will be zero and its limit will be the
           * number of resulting decoded bytes
           *
           * <p> {@code IllegalArgumentException} is thrown if the input buffer
           * is not in valid Base64 encoding scheme. The position of the input
           * buffer will not be advanced in this case.
           *
           * @param buffer the ByteBuffer to decode
           * @return A newly-allocated byte buffer containing the decoded bytes
           * @throws IllegalArgumentException if {@code src} is not in valid Base64 scheme.
           */
          public ByteBuffer decode(ByteBuffer buffer) {
              int pos0 = buffer.position();
              try {
                  byte[] src;
                  int sp, sl;
                  if (buffer.hasArray()) {
                      src = buffer.array();
                      sp = buffer.arrayOffset() + buffer.position();
                      sl = buffer.arrayOffset() + buffer.limit();
                      buffer.position(buffer.limit());
                  } else {
                      src = new byte[buffer.remaining()];
                      buffer.get(src);
                      sp = 0;
                      sl = src.length;
                  }
                  byte[] dst = new byte[outLength(src, sp, sl)];
                  return ByteBuffer.wrap(dst, 0, decode0(src, sp, sl, dst));
              } catch (IllegalArgumentException iae) {
                  buffer.position(pos0);
                  throw iae;
              }
          }
  
          /**
           * Returns an input stream for decoding {@link Base64} encoded byte stream.
           *
           * <p> The {@code read}  methods of the returned {@code InputStream} will
           * throw {@code IOException} when reading bytes that cannot be decoded.
           *
           * <p> Closing the returned input stream will close the underlying
           * input stream.
           *
           * @param is the input stream
           * @return the input stream for decoding the specified Base64 encoded
           * byte stream
           */
          public InputStream wrap(InputStream is) {
              Objects.requireNonNull(is);
              return new DecInputStream(is, isURL ? fromBase64URL : fromBase64, isMIME);
          }
  
          private int outLength(byte[] src, int sp, int sl) {
              int[] base64 = isURL ? fromBase64URL : fromBase64;
              int paddings = 0;
              int len = sl - sp;
              if (len == 0)
                  return 0;
              if (len < 2) {
                  if (isMIME && base64[0] == -1)
                      return 0;
                  throw new IllegalArgumentException(
                          "Input byte[] should at least have 2 bytes for base64 bytes");
              }
              if (isMIME) {
                  // scan all bytes to fill out all non-alphabet. a performance
                  // trade-off of pre-scan or Arrays.copyOf
                  int n = 0;
                  while (sp < sl) {
                      int b = src[sp++] & 0xff;
                      if (b == '=') {
                          len -= (sl - sp + 1);
                          break;
                      }
                      if ((b = base64[b]) == -1)
                          n++;
                  }
                  len -= n;
              } else {
                  if (src[sl - 1] == '=') {
                      paddings++;
                      if (src[sl - 2] == '=')
                          paddings++;
                  }
              }
              if (paddings == 0 && (len & 0x3) != 0)
                  paddings = 4 - (len & 0x3);
              return 3 * ((len + 3) / 4) - paddings;
          }
  
          private int decode0(byte[] src, int sp, int sl, byte[] dst) {
              int[] base64 = isURL ? fromBase64URL : fromBase64;
              int dp = 0;
              int bits = 0;
              int shiftto = 18;       // pos of first byte of 4-byte atom
              while (sp < sl) {
                  int b = src[sp++] & 0xff;
                  if ((b = base64[b]) < 0) {
                      if (b == -2) {         // padding byte '='
                          // =     shiftto==18 unnecessary padding
                          // x=    shiftto==12 a dangling single x
                          // x     to be handled together with non-padding case
                          // xx=   shiftto==6&&sp==sl missing last =
                          // xx=y  shiftto==6 last is not =
                          if (shiftto == 6 && (sp == sl || src[sp++] != '=') ||
                                  shiftto == 18) {
                              throw new IllegalArgumentException(
                                      "Input byte array has wrong 4-byte ending unit");
                          }
                          break;
                      }
                      if (isMIME)    // skip if for rfc2045
                          continue;
                      else
                          throw new IllegalArgumentException(
                                  "Illegal base64 character " +
                                          Integer.toString(src[sp - 1], 16));
                  }
                  bits |= (b << shiftto);
                  shiftto -= 6;
                  if (shiftto < 0) {
                      dst[dp++] = (byte) (bits >> 16);
                      dst[dp++] = (byte) (bits >> 8);
                      dst[dp++] = (byte) (bits);
                      shiftto = 18;
                      bits = 0;
                  }
              }
              // reached end of byte array or hit padding '=' characters.
              if (shiftto == 6) {
                  dst[dp++] = (byte) (bits >> 16);
              } else if (shiftto == 0) {
                  dst[dp++] = (byte) (bits >> 16);
                  dst[dp++] = (byte) (bits >> 8);
              } else if (shiftto == 12) {
                  // dangling single "x", incorrectly encoded.
                  throw new IllegalArgumentException(
                          "Last unit does not have enough valid bits");
              }
              // anything left is invalid, if is not MIME.
              // if MIME, ignore all non-base64 character
              while (sp < sl) {
                  if (isMIME && base64[src[sp++]] < 0)
                      continue;
                  throw new IllegalArgumentException(
                          "Input byte array has incorrect ending byte at " + sp);
              }
              return dp;
          }
      }
  
      /*
       * An output stream for encoding bytes into the Base64.
       */
      private static class EncOutputStream extends FilterOutputStream {
  
          private int leftover = 0;
          private int b0, b1, b2;
          private boolean closed = false;
  
          private final char[] base64;    // byte->base64 mapping
          private final byte[] newline;   // line separator, if needed
          private final int linemax;
          private final boolean doPadding;// whether or not to pad
          private int linepos = 0;
  
          EncOutputStream(OutputStream os, char[] base64,
                          byte[] newline, int linemax, boolean doPadding) {
              super(os);
              this.base64 = base64;
              this.newline = newline;
              this.linemax = linemax;
              this.doPadding = doPadding;
          }
  
          @Override
          public void write(int b) throws IOException {
              byte[] buf = new byte[1];
              buf[0] = (byte) (b & 0xff);
              write(buf, 0, 1);
          }
  
          private void checkNewline() throws IOException {
              if (linepos == linemax) {
                  out.write(newline);
                  linepos = 0;
              }
          }
  
          @Override
          public void write(byte[] b, int off, int len) throws IOException {
              if (closed)
                  throw new IOException("Stream is closed");
              // Android-changed: Upstream fix to avoid overflow.
              // This upstream fix is from beyond OpenJDK8u121-b13. http://b/62368386
              // if (off < 0 || len < 0 || off + len > b.length)
              if (off < 0 || len < 0 || len > b.length - off)
                  throw new ArrayIndexOutOfBoundsException();
              if (len == 0)
                  return;
              if (leftover != 0) {
                  if (leftover == 1) {
                      b1 = b[off++] & 0xff;
                      len--;
                      if (len == 0) {
                          leftover++;
                          return;
                      }
                  }
                  b2 = b[off++] & 0xff;
                  len--;
                  checkNewline();
                  out.write(base64[b0 >> 2]);
                  out.write(base64[(b0 << 4) & 0x3f | (b1 >> 4)]);
                  out.write(base64[(b1 << 2) & 0x3f | (b2 >> 6)]);
                  out.write(base64[b2 & 0x3f]);
                  linepos += 4;
              }
              int nBits24 = len / 3;
              leftover = len - (nBits24 * 3);
              while (nBits24-- > 0) {
                  checkNewline();
                  int bits = (b[off++] & 0xff) << 16 |
                          (b[off++] & 0xff) << 8 |
                          (b[off++] & 0xff);
                  out.write(base64[(bits >>> 18) & 0x3f]);
                  out.write(base64[(bits >>> 12) & 0x3f]);
                  out.write(base64[(bits >>> 6) & 0x3f]);
                  out.write(base64[bits & 0x3f]);
                  linepos += 4;
              }
              if (leftover == 1) {
                  b0 = b[off++] & 0xff;
              } else if (leftover == 2) {
                  b0 = b[off++] & 0xff;
                  b1 = b[off++] & 0xff;
              }
          }
  
          @Override
          public void close() throws IOException {
              if (!closed) {
                  closed = true;
                  if (leftover == 1) {
                      checkNewline();
                      out.write(base64[b0 >> 2]);
                      out.write(base64[(b0 << 4) & 0x3f]);
                      if (doPadding) {
                          out.write('=');
                          out.write('=');
                      }
                  } else if (leftover == 2) {
                      checkNewline();
                      out.write(base64[b0 >> 2]);
                      out.write(base64[(b0 << 4) & 0x3f | (b1 >> 4)]);
                      out.write(base64[(b1 << 2) & 0x3f]);
                      if (doPadding) {
                          out.write('=');
                      }
                  }
                  leftover = 0;
                  out.close();
              }
          }
      }
  
      /*
       * An input stream for decoding Base64 bytes
       */
      private static class DecInputStream extends InputStream {
  
          private final InputStream is;
          private final boolean isMIME;
          private final int[] base64;      // base64 -> byte mapping
          private int bits = 0;            // 24-bit buffer for decoding
          private int nextin = 18;         // next available "off" in "bits" for input;
          // -> 18, 12, 6, 0
          private int nextout = -8;        // next available "off" in "bits" for output;
          // -> 8, 0, -8 (no byte for output)
          private boolean eof = false;
          private boolean closed = false;
  
          DecInputStream(InputStream is, int[] base64, boolean isMIME) {
              this.is = is;
              this.base64 = base64;
              this.isMIME = isMIME;
          }
  
          private byte[] sbBuf = new byte[1];
  
          @Override
          public int read() throws IOException {
              return read(sbBuf, 0, 1) == -1 ? -1 : sbBuf[0] & 0xff;
          }
  
          @Override
          public int read(byte[] b, int off, int len) throws IOException {
              if (closed)
                  throw new IOException("Stream is closed");
              if (eof && nextout < 0)    // eof and no leftover
                  return -1;
              if (off < 0 || len < 0 || len > b.length - off)
                  throw new IndexOutOfBoundsException();
              int oldOff = off;
              if (nextout >= 0) {       // leftover output byte(s) in bits buf
                  do {
                      if (len == 0)
                          return off - oldOff;
                      b[off++] = (byte) (bits >> nextout);
                      len--;
                      nextout -= 8;
                  } while (nextout >= 0);
                  bits = 0;
              }
              while (len > 0) {
                  int v = is.read();
                  if (v == -1) {
                      eof = true;
                      if (nextin != 18) {
                          if (nextin == 12)
                              throw new IOException("Base64 stream has one un-decoded dangling byte.");
                          // treat ending xx/xxx without padding character legal.
                          // same logic as v == '=' below
                          b[off++] = (byte) (bits >> (16));
                          len--;
                          if (nextin == 0) {           // only one padding byte
                              if (len == 0) {          // no enough output space
                                  bits >>= 8;          // shift to lowest byte
                                  nextout = 0;
                              } else {
                                  b[off++] = (byte) (bits >> 8);
                              }
                          }
                      }
                      if (off == oldOff)
                          return -1;
                      else
                          return off - oldOff;
                  }
                  if (v == '=') {                  // padding byte(s)
                      // =     shiftto==18 unnecessary padding
                      // x=    shiftto==12 dangling x, invalid unit
                      // xx=   shiftto==6 && missing last '='
                      // xx=y  or last is not '='
                      if (nextin == 18 || nextin == 12 ||
                              nextin == 6 && is.read() != '=') {
                          throw new IOException("Illegal base64 ending sequence:" + nextin);
                      }
                      b[off++] = (byte) (bits >> (16));
                      len--;
                      if (nextin == 0) {           // only one padding byte
                          if (len == 0) {          // no enough output space
                              bits >>= 8;          // shift to lowest byte
                              nextout = 0;
                          } else {
                              b[off++] = (byte) (bits >> 8);
                          }
                      }
                      eof = true;
                      break;
                  }
                  if ((v = base64[v]) == -1) {
                      if (isMIME)                 // skip if for rfc2045
                          continue;
                      else
                          throw new IOException("Illegal base64 character " +
                                  Integer.toString(v, 16));
                  }
                  bits |= (v << nextin);
                  if (nextin == 0) {
                      nextin = 18;    // clear for next
                      nextout = 16;
                      while (nextout >= 0) {
                          b[off++] = (byte) (bits >> nextout);
                          len--;
                          nextout -= 8;
                          if (len == 0 && nextout >= 0) {  // don't clean "bits"
                              return off - oldOff;
                          }
                      }
                      bits = 0;
                  } else {
                      nextin -= 6;
                  }
              }
              return off - oldOff;
          }
  
          @Override
          public int available() throws IOException {
              if (closed)
                  throw new IOException("Stream is closed");
              return is.available();   // TBD:
          }
  
          @Override
          public void close() throws IOException {
              if (!closed) {
                  closed = true;
                  is.close();
              }
          }
      }
  }
  