Quelle Base64.java Sprache: JAVA

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* 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
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* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
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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 sun.nio.cs.ISO_8859_1;
import jdk.internal.util.Preconditions;
import jdk.internal.vm.annotation.IntrinsicCandidate;

/**
* 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">Basic</a>
* 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.</li>
*
* <li><a id="url">URL and Filename safe</a>
* 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.</li>
*
* <li><a id="mime">MIME</a>
* 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.</li>
* </ul>
*
* 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 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 {@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.
 *
 * Instances of {@link Encoder} class are safe for use by
 * multiple concurrent threads.
 *
 * 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.
 * If the encoded byte output of the needed size can not
 * be allocated, the encode methods of this class will
 * cause an {@link java.lang.OutOfMemoryError OutOfMemoryError}
 * 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);

 /**
 * Calculates the length of the encoded output bytes.
 *
 * @param srclen length of the bytes to encode
 * @param throwOOME if true, throws OutOfMemoryError if the length of
 * the encoded bytes overflows; else returns the
 * length
 * @return length of the encoded bytes, or -1 if the length overflows
 *
 */
 private final int encodedOutLength(int srclen, boolean throwOOME) {
 int len = 0;
 try {
 if (doPadding) {
 len = Math.multiplyExact(4, (Math.addExact(srclen, 2) / 3));
 } else {
 int n = srclen % 3;
 len = Math.addExact(Math.multiplyExact(4, (srclen / 3)), (n == 0 ? 0 : n + 1));
 }
 if (linemax > 0) { // line separators
 len = Math.addExact(len, (len - 1) / linemax * newline.length);
 }
 } catch (ArithmeticException ex) {
 if (throwOOME) {
 throw new OutOfMemoryError("Encoded size is too large");
 } else {
 // let the caller know that encoded bytes length
 // is too large
 len = -1;
 }
 }
 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 = encodedOutLength(src.length, true); // 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.
 *
 * 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 = encodedOutLength(src.length, false); // dst array size
 if (dst.length < len || len == -1)
 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.
 *
 * 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.
 *
 * 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.
 *
 * 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 = encodedOutLength(buffer.remaining(), true);
 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.
 *
 * 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.
 *
 * @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);
 }

 @IntrinsicCandidate
 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 {@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.
 *
 * Instances of {@link Decoder} class are safe for use by
 * multiple concurrent threads.
 *
 * 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.
 * If the decoded byte output of the needed size can not
 * be allocated, the decode methods of this class will
 * cause an {@link java.lang.OutOfMemoryError OutOfMemoryError}
 * 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[decodedOutLength(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.
 *
 * 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(ISO_8859_1.INSTANCE));
 }

 /**
 * 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.
 *
 * 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.
 *
 * 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 = decodedOutLength(src, 0, src.length);
 if (dst.length < len || len == -1)
 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.
 *
 * 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
 *
 * {@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 buffer} 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[decodedOutLength(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.
 *
 * The {@code read} methods of the returned {@code InputStream} will
 * throw {@code IOException} when reading bytes that cannot be decoded.
 *
 * 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);
 }

 /**
 * Calculates the length of the decoded output bytes.
 *
 * @param src the byte array to decode
 * @param sp the source position
 * @param sl the source limit
 *
 * @return length of the decoded bytes
 *
 */
 private int decodedOutLength(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);

 // If len is near to Integer.MAX_VALUE, (len + 3)
 // can possibly overflow, perform this operation as
 // long and cast it back to integer when the value comes under
 // integer limit. The final value will always be in integer
 // limits
 return 3 * (int) ((len + 3L) / 4) - paddings;
 }

 /**
 * Decodes base64 characters, and returns the number of data bytes
 * written into the destination array.
 *
 * It is the fast path for full 4-byte to 3-byte decoding w/o errors.
 *
 * decodeBlock() can be overridden by an arch-specific intrinsic.
 * decodeBlock can choose to decode all, none, or a variable-sized
 * prefix of the src bytes. This allows the intrinsic to decode in
 * chunks of the src that are of a favorable size for the specific
 * processor it's running on.
 *
 * If any illegal base64 bytes are encountered in src by the
 * intrinsic, the intrinsic must return the actual number of valid
 * data bytes already written to dst. Note that the '=' pad
 * character is treated as an illegal Base64 character by
 * decodeBlock, so it will not process a block of 4 bytes
 * containing pad characters. However, MIME decoding ignores
 * illegal characters, so any intrinsic overriding decodeBlock
 * can choose how to handle illegal characters based on the isMIME
 * parameter.
 *
 * Given the parameters, no length check is possible on dst, so dst
 * is assumed to be large enough to store the decoded bytes.
 *
 * @param src
 * the source byte array of Base64 encoded bytes
 * @param sp
 * the offset into src array to begin reading
 * @param sl
 * the offset (exclusive) past the last byte to be converted.
 * @param dst
 * the destination byte array of decoded data bytes
 * @param dp
 * the offset into dst array to begin writing
 * @param isURL
 * boolean, when true decode RFC4648 URL-safe base64 characters
 * @param isMIME
 * boolean, when true decode according to RFC2045 (ignore illegal chars)
 * @return the number of destination data bytes produced
 */
 @IntrinsicCandidate
 private int decodeBlock(byte[] src, int sp, int sl, byte[] dst, int dp, boolean isURL, boolean isMIME) {
 int[] base64 = isURL ? fromBase64URL : fromBase64;
 int sl0 = sp + ((sl - sp) & ~0b11);
 int new_dp = dp;
 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
 return new_dp - dp;
 }
 int bits0 = b1 << 18 | b2 << 12 | b3 << 6 | b4;
 dst[new_dp++] = (byte)(bits0 >> 16);
 dst[new_dp++] = (byte)(bits0 >> 8);
 dst[new_dp++] = (byte)(bits0);
 }
 return new_dp - dp;
 }

 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 < sl - 4) { // fast path
 int dl = decodeBlock(src, sp, sl, dst, dp, isURL, isMIME);
 /*
 * Calculate how many characters were processed by how many
 * bytes of data were returned.
 */
 int chars_decoded = ((dl + 2) / 3) * 4;

 sp += chars_decoded;
 dp += dl;
 }
 if (sp >= sl) {
 // we're done
 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");
 Preconditions.checkFromIndexSize(len, off, b.length, Preconditions.AIOOBE_FORMATTER);
 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

 /* writing bit pos inside bits; one of 24 (left, msb), 18, 12, 6, 0 */
 private int wpos = 0;

 /* reading bit pos inside bits: one of 24 (left, msb), 16, 8, 0 */
 private int rpos = 0;

 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 leftovers(byte[] b, int off, int pos, int limit) {
 eof = true;

 /*
 * We use a loop here, as this method is executed only a few times.
 * Unrolling the loop would probably not contribute much here.
 */
 while (rpos - 8 >= wpos && pos != limit) {
 rpos -= 8;
 b[pos++] = (byte) (bits >> rpos);
 }
 return pos - off != 0 || rpos - 8 >= wpos ? pos - off : -1;
 }

 private int eof(byte[] b, int off, int pos, int limit) throws IOException {
 /*
 * pos != limit
 *
 * wpos == 18: x dangling single x, invalid unit
 * accept ending xx or xxx without padding characters
 */
 if (wpos == 18) {
 throw new IOException("Base64 stream has one un-decoded dangling byte.");
 }
 rpos = 24;
 return leftovers(b, off, pos, limit);
 }

 private int padding(byte[] b, int off, int pos, int limit) throws IOException {
 /*
 * pos != limit
 *
 * wpos == 24: = (unnecessary padding)
 * wpos == 18: x= (dangling single x, invalid unit)
 * wpos == 12 and missing last '=': xx= (invalid padding)
 * wpos == 12 and last is not '=': xx=x (invalid padding)
 */
 if (wpos >= 18 || wpos == 12 && is.read() != '=') {
 throw new IOException("Illegal base64 ending sequence:" + wpos);
 }
 rpos = 24;
 return leftovers(b, off, pos, limit);
 }

 @Override
 public int read(byte[] b, int off, int len) throws IOException {
 if (closed) {
 throw new IOException("Stream is closed");
 }
 Objects.checkFromIndexSize(off, len, b.length);
 if (len == 0) {
 return 0;
 }

 /*
 * Rather than keeping 2 running vars (e.g., off and len),
 * we only keep one (pos), while definitely fixing the boundaries
 * of the range [off, limit).
 * More specifically, each use of pos as an index in b meets
 * pos - off >= 0 & limit - pos > 0
 *
 * Note that limit can overflow to Integer.MIN_VALUE. However,
 * as long as comparisons with pos are as coded, there's no harm.
 */
 int pos = off;
 final int limit = off + len;
 if (eof) {
 return leftovers(b, off, pos, limit);
 }

 /*
 * Leftovers from previous invocation; here, wpos = 0.
 * There can be at most 2 leftover bytes (rpos <= 16).
 * Further, b has at least one free place.
 *
 * The logic could be coded as a loop, (as in method leftovers())
 * but the explicit "unrolling" makes it possible to generate
 * better byte extraction code.
 */
 if (rpos == 16) {
 b[pos++] = (byte) (bits >> 8);
 rpos = 8;
 if (pos == limit) {
 return len;
 }
 }
 if (rpos == 8) {
 b[pos++] = (byte) bits;
 rpos = 0;
 if (pos == limit) {
 return len;
 }
 }

 bits = 0;
 wpos = 24;
 for (;;) {
 /* pos != limit & rpos == 0 */
 final int i = is.read();
 if (i < 0) {
 return eof(b, off, pos, limit);
 }
 final int v = base64[i];
 if (v < 0) {
 /*
 * i not in alphabet, thus
 * v == -2: i is '=', the padding
 * v == -1: i is something else, typically CR or LF
 */
 if (v == -1) {
 if (isMIME) {
 continue;
 }
 throw new IOException("Illegal base64 character 0x" +
 Integer.toHexString(i));
 }
 return padding(b, off, pos, limit);
 }
 wpos -= 6;
 bits |= v << wpos;
 if (wpos != 0) {
 continue;
 }
 if (limit - pos >= 3) {
 /* frequently taken fast path, no need to track rpos */
 b[pos++] = (byte) (bits >> 16);
 b[pos++] = (byte) (bits >> 8);
 b[pos++] = (byte) bits;
 bits = 0;
 wpos = 24;
 if (pos == limit) {
 return len;
 }
 continue;
 }

 /* b has either 1 or 2 free places */
 b[pos++] = (byte) (bits >> 16);
 if (pos == limit) {
 rpos = 16;
 return len;
 }
 b[pos++] = (byte) (bits >> 8);
 /* pos == limit, no need for an if */
 rpos = 8;
 return len;
 }
 }

 @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();
 }
 }
 }
}

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