java/11 : java.base/java/util/Base64.java

Base64
https://openjdk.java.net/
GPLv2 + Classpath Exception
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package java.util;

import java.io.FilterOutputStream;
import java.io.InputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import jdk.internal.HotSpotIntrinsicCandidate;

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
RFC 4648 and
RFC 2045.

Basic
 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.
URL and Filename safe
 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.
MIME
 Uses "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 '\r' followed immediately by a linefeed '\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.

 Unless otherwise noted, passing a null argument to a method of this class will cause a 
NullPointerException to be thrown. 
Author:  Xueming Shen
Since:   1.8/**
 * 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 id="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 id="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 id="mime"><b>MIME</b></a>
 * <p> Uses "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 Encoder that encodes using the Basic type base64 encoding scheme.
Returns:  A Base64 encoder./**
     * 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 Encoder that encodes using the URL and Filename safe type base64
encoding scheme.
Returns:  A Base64 encoder./**
     * 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 Encoder that encodes using the MIME type base64 encoding scheme.
Returns:  A Base64 encoder./**
     * 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 Encoder that encodes using the MIME type base64 encoding scheme
with specified line length and line separators.
Params: lineLength – 
         the length of each output line (rounded down to nearest multiple
         of 4). If the rounded down line length is not a positive value,
         the output will not be separated in lines
lineSeparator – 
         the line separator for each output line
Throws: IllegalArgumentException – if lineSeparator includes any character of "The Base64 Alphabet" as specified in Table 1 of RFC 2045.
Returns:  A Base64 encoder./**
     * 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 the rounded down line length is not a positive value,
     *          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));
         }
         // round down to nearest multiple of 4
         lineLength &= ~0b11;
         if (lineLength <= 0) {
             return Encoder.RFC4648;
         }
         return new Encoder(false, lineSeparator, lineLength, true);
    }

    Returns a Decoder that decodes using the Basic type base64 encoding scheme.
Returns:  A Base64 decoder./**
     * 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 Decoder that decodes using the URL and Filename safe type base64
encoding scheme.
Returns:  A Base64 decoder./**
     * 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 Decoder that decodes using the MIME type base64 decoding scheme.
Returns:  A Base64 decoder./**
     * 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.
 Instances of Encoder class are safe for use by multiple concurrent threads. 
 Unless otherwise noted, passing a null argument to a method of this class will cause a NullPointerException to be thrown. 
See Also: Decoder
Since:   1.8/**
     * 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).
/**
         * 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.
/**
         * 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 Base64 encoding scheme. The returned byte array is of the length of the resulting bytes. 
Params: src – 
         the byte array to encode
Returns:  A newly-allocated byte array containing the resulting
         encoded bytes./**
         * 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 Base64 encoding scheme, writing the resulting bytes to the given output byte array, starting at offset 0.  It is the responsibility of the invoker of this method to make sure the output byte array 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. 
Params: src – 
         the byte array to encode
dst – 
         the output byte array
Throws: IllegalArgumentException – if dst does not have enough space for encoding all input bytes.
Returns:  The number of bytes written to the output byte array/**
         * 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 Base64 encoding scheme.  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 
ISO-8859-1 charset. 
 In other words, an invocation of this method has exactly the same effect as invoking new String(encode(src), StandardCharsets.ISO_8859_1). 
Params: src – 
         the byte array to encode
Returns:  A String containing the resulting Base64 encoded characters/**
         * 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 Base64 encoding scheme. 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. 
Params: buffer – 
         the source ByteBuffer to encode
Returns:  A newly-allocated byte buffer containing the encoded bytes./**
         * Encodes all remaining bytes from the specified byte buffer into
         * a newly-allocated ByteBuffer using the {@link Base64} encoding
         * scheme.
         *
         * 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 Base64 encoding scheme.  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.
Params: os – 
         the output stream.
Returns:  the output stream for encoding the byte data into the
         specified Base64 encoded format/**
         * 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.
 The encoding scheme of this encoder instance is unaffected by
this invocation. The returned encoder instance should be used for
non-padding encoding operation.
Returns: an equivalent encoder that encodes without adding any
        padding character at the end/**
         * 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);
        }

        @HotSpotIntrinsicCandidate
        private void encodeBlock(byte[] src, int sp, int sl, byte[] dst, int dp, boolean isURL) {
            char[] base64 = isURL ? toBase64URL : toBase64;
            for (int sp0 = sp, dp0 = dp ; sp0 < sl; ) {
                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];
            }
        }

        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);
                encodeBlock(src, sp, sl0, dst, dp, isURL);
                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.
 The Base64 padding character '=' 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 IllegalArgumentException ( IOException when reading from a Base64 stream) is thrown during decoding. 
 Instances of Decoder class are safe for use by multiple concurrent threads. 
 Unless otherwise noted, passing a null argument to a method of this class will cause a NullPointerException to be thrown. 
See Also: Encoder
Since:   1.8/**
     * 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.
/**
         * 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.
/**
         * 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 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. 
Params: src – 
         the byte array to decode
Throws: IllegalArgumentException –  if src is not in valid Base64 scheme
Returns:  A newly-allocated byte array containing the decoded bytes./**
         * 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 Base64 encoding scheme.  An invocation of this method has exactly the same effect as invoking decode(src.getBytes(StandardCharsets.ISO_8859_1)) 
Params: src – 
         the string to decode
Throws: IllegalArgumentException –  if src is not in valid Base64 scheme
Returns:  A newly-allocated byte array containing the decoded bytes./**
         * 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 Base64 encoding scheme, writing the results into the given output byte array, starting at offset 0.  It is the responsibility of the invoker of this method to make sure the output byte array dst has enough space for decoding 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. 
 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.
Params: src – 
         the byte array to decode
dst – 
         the output byte array
Throws: IllegalArgumentException –  if src is not in valid Base64 scheme, or dst does not have enough space for decoding all input bytes.
Returns:  The number of bytes written to the output byte array/**
         * 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 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 Base64 encoding scheme, writing the results into a newly-allocated ByteBuffer.  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
 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. 
Params: buffer – 
         the ByteBuffer to decode
Throws: IllegalArgumentException –  if src is not in valid Base64 scheme.
Returns:  A newly-allocated byte buffer containing the decoded bytes/**
         * 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 Base64 encoded byte stream.  The read methods of the returned InputStream will throw IOException when reading bytes that cannot be decoded. 
 Closing the returned input stream will close the underlying
input stream.
Params: is – 
         the input stream
Returns:  the input stream for decoding the specified Base64 encoded
         byte stream/**
         * 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) {
                if (shiftto == 18 && sp + 4 < sl) {       // fast path
                    int sl0 = sp + ((sl - sp) & ~0b11);
                    while (sp < sl0) {
                        int b1 = base64[src[sp++] & 0xff];
                        int b2 = base64[src[sp++] & 0xff];
                        int b3 = base64[src[sp++] & 0xff];
                        int b4 = base64[src[sp++] & 0xff];
                        if ((b1 | b2 | b3 | b4) < 0) {    // non base64 byte
                            sp -= 4;
                            break;
                        }
                        int bits0 = b1 << 18 | b2 << 12 | b3 << 6 | b4;
                        dst[dp++] = (byte)(bits0 >> 16);
                        dst[dp++] = (byte)(bits0 >>  8);
                        dst[dp++] = (byte)(bits0);
                    }
                    if (sp >= sl)
                        break;
                }
                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++] & 0xff] < 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;
        private byte[] buf;

        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;
            this.buf = new byte[linemax <= 0 ? 8124 : linemax];
        }

        @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;
            }
        }

        private void writeb4(char b1, char b2, char b3, char b4) throws IOException {
            buf[0] = (byte)b1;
            buf[1] = (byte)b2;
            buf[2] = (byte)b3;
            buf[3] = (byte)b4;
            out.write(buf, 0, 4);
        }

        @Override
        public void write(byte[] b, int off, int len) throws IOException {
            if (closed)
                throw new IOException("Stream is closed");
            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();
                writeb4(base64[b0 >> 2],
                        base64[(b0 << 4) & 0x3f | (b1 >> 4)],
                        base64[(b1 << 2) & 0x3f | (b2 >> 6)],
                        base64[b2 & 0x3f]);
                linepos += 4;
            }
            int nBits24 = len / 3;
            leftover = len - (nBits24 * 3);

            while (nBits24 > 0) {
                checkNewline();
                int dl = linemax <= 0 ? buf.length : buf.length - linepos;
                int sl = off + Math.min(nBits24, dl / 4) * 3;
                int dp = 0;
                for (int sp = off; sp < sl; ) {
                    int bits = (b[sp++] & 0xff) << 16 |
                               (b[sp++] & 0xff) <<  8 |
                               (b[sp++] & 0xff);
                    buf[dp++] = (byte)base64[(bits >>> 18) & 0x3f];
                    buf[dp++] = (byte)base64[(bits >>> 12) & 0x3f];
                    buf[dp++] = (byte)base64[(bits >>> 6)  & 0x3f];
                    buf[dp++] = (byte)base64[bits & 0x3f];
                }
                out.write(buf, 0, dp);
                off = sl;
                linepos += dp;
                nBits24 -= dp / 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;
        }

        private int eof(byte[] b, int off, int len, int oldOff)
            throws IOException
        {
            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));
                if (nextin == 0) {           // only one padding byte
                    if (len == 1) {          // no enough output space
                        bits >>= 8;          // shift to lowest byte
                        nextout = 0;
                    } else {
                        b[off++] = (byte) (bits >>  8);
                    }
                }
            }
            return off == oldOff ? -1 : off - oldOff;
        }

        private int padding(byte[] b, int off, int len, int oldOff)
            throws IOException
        {
            // =     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));
            if (nextin == 0) {           // only one padding byte
                if (len == 1) {          // no enough output space
                    bits >>= 8;          // shift to lowest byte
                    nextout = 0;
                } else {
                    b[off++] = (byte) (bits >>  8);
                }
            }
            eof = true;
            return off - oldOff;
        }

        @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;
            while (nextout >= 0) {       // leftover output byte(s) in bits buf
                if (len == 0)
                    return off - oldOff;
                b[off++] = (byte)(bits >> nextout);
                len--;
                nextout -= 8;
            }
            bits = 0;
            while (len > 0) {
                int v = is.read();
                if (v == -1) {
                    return eof(b, off, len, oldOff);
                }
                if ((v = base64[v]) < 0) {
                    if (v == -2) {       // padding byte(s)
                        return padding(b, off, len, oldOff);
                    }
                    if (v == -1) {
                        if (!isMIME)
                            throw new IOException("Illegal base64 character " +
                                Integer.toString(v, 16));
                        continue;        // skip if for rfc2045
                    }
                    // neve be here
                }
                bits |= (v << nextin);
                if (nextin == 0) {
                    nextin = 18;         // clear for next in
                    b[off++] = (byte)(bits >> 16);
                    if (len == 1) {
                        nextout = 8;    // 2 bytes left in bits
                        break;
                    }
                    b[off++] = (byte)(bits >> 8);
                    if (len == 2) {
                        nextout = 0;    // 1 byte left in bits
                        break;
                    }
                    b[off++] = (byte)bits;
                    len -= 3;
                    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();
            }
        }
    }
}
Params:	lineLength – the length of each output line (rounded down to nearest multiple of 4). If the rounded down line length is not a positive value, the output will not be separated in lines lineSeparator – the line separator for each output line
Throws:	IllegalArgumentException – if `lineSeparator` includes any character of "The Base64 Alphabet" as specified in Table 1 of RFC 2045.
Returns:	A Base64 encoder.
Params:	src – the byte array to encode
Returns:	A newly-allocated byte array containing the resulting encoded bytes.
Params:	src – the byte array to encode dst – the output byte array
Throws:	IllegalArgumentException – if `dst` does not have enough space for encoding all input bytes.
Returns:	The number of bytes written to the output byte array
Params:	buffer – the source ByteBuffer to encode
Returns:	A newly-allocated byte buffer containing the encoded bytes.
Params:	os – the output stream.
Returns:	the output stream for encoding the byte data into the specified Base64 encoded format
Params:	src – the byte array to decode
Throws:	IllegalArgumentException – if `src` is not in valid Base64 scheme
Returns:	A newly-allocated byte array containing the decoded bytes.
Params:	src – the string to decode
Throws:	IllegalArgumentException – if `src` is not in valid Base64 scheme
Returns:	A newly-allocated byte array containing the decoded bytes.
Params:	src – the byte array to decode dst – the output byte array
Throws:	IllegalArgumentException – if `src` is not in valid Base64 scheme, or `dst` does not have enough space for decoding all input bytes.
Returns:	The number of bytes written to the output byte array
Params:	buffer – the ByteBuffer to decode
Throws:	IllegalArgumentException – if `src` is not in valid Base64 scheme.
Returns:	A newly-allocated byte buffer containing the decoded bytes
Params:	is – the input stream
Returns:	the input stream for decoding the specified Base64 encoded byte stream
/

java/ 11/ java.base/java/util/Base64.java
