View Javadoc
1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  package com.jsql.util.bruter;
19  
20  import org.apache.commons.codec.BinaryDecoder;
21  import org.apache.commons.codec.BinaryEncoder;
22  import org.apache.commons.codec.DecoderException;
23  import org.apache.commons.codec.EncoderException;
24  import org.apache.commons.codec.binary.StringUtils;
25  
26  import java.util.Arrays;
27  import java.util.Objects;
28  
29  /**
30   * Abstract superclass for Base-N encoders and decoders.
31   *
32   * <p>
33   * This class is thread-safe.
34   * </p>
35   *
36   * You can set the decoding behavior when the input bytes contain leftover trailing bits that cannot be created by a valid
37   * encoding. These can be bits that are unused from the final character or entire characters. The default mode is
38   * lenient decoding.
39   * <ul>
40   * <li>Lenient: Any trailing bits are composed into 8-bit bytes where possible. The remainder are discarded.
41   * <li>Strict: The decoding will raise an {@link IllegalArgumentException} if trailing bits are not part of a valid
42   * encoding. Any unused bits from the final character must be zero. Impossible counts of entire final characters are not
43   * allowed.
44   * </ul>
45   * <p>
46   * When strict decoding is enabled it is expected that the decoded bytes will be re-encoded to a byte array that matches
47   * the original, i.e. no changes occur on the final character. This requires that the input bytes use the same padding
48   * and alphabet as the encoder.
49   * </p>
50   */
51  public abstract class BaseNCodec implements BinaryEncoder, BinaryDecoder {
52  
53      /**
54       * EOF
55       *
56       * @since 1.7
57       */
58      private static final int EOF = -1;
59  
60      /**
61       *  MIME chunk size per RFC 2045 section 6.8.
62       *
63       * <p>
64       * The {@value} character limit does not count the trailing CRLF, but counts all other characters, including any
65       * equal signs.
66       * </p>
67       *
68       * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045 section 6.8</a>
69       */
70      public static final int MIME_CHUNK_SIZE = 76;
71  
72      /**
73       * PEM chunk size per RFC 1421 section 4.3.2.4.
74       *
75       * <p>
76       * The {@value} character limit does not count the trailing CRLF, but counts all other characters, including any
77       * equal signs.
78       * </p>
79       *
80       * @see <a href="http://tools.ietf.org/html/rfc1421">RFC 1421 section 4.3.2.4</a>
81       */
82      public static final int PEM_CHUNK_SIZE = 64;
83  
84      private static final int DEFAULT_BUFFER_RESIZE_FACTOR = 2;
85  
86      /**
87       * Defines the default buffer size - currently {@value}
88       * - must be large enough for at least one encoded block+separator
89       */
90      private static final int DEFAULT_BUFFER_SIZE = 8192;
91  
92      /**
93       * The maximum size buffer to allocate.
94       *
95       * <p>This is set to the same size used in the JDK {@code java.util.ArrayList}:</p>
96       * <blockquote>
97       * Some VMs reserve some header words in an array.
98       * Attempts to allocate larger arrays may result in
99       * OutOfMemoryError: Requested array size exceeds VM limit.
100      * </blockquote>
101      */
102     private static final int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;
103 
104     /** Mask used to extract 8 bits, used in decoding bytes */
105     protected static final int MASK_8BITS = 0xff;
106 
107     /**
108      * Byte used to pad output.
109      */
110     protected static final byte PAD_DEFAULT = '='; // Allow static access to default
111 
112     /**
113      * The default decoding policy.
114      * @since 1.15
115      */
116     protected static final CodecPolicy DECODING_POLICY_DEFAULT = CodecPolicy.LENIENT;
117 
118     /**
119      * Chunk separator per RFC 2045 section 2.1.
120      *
121      * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045 section 2.1</a>
122      */
123     private static final byte[] CHUNK_SEPARATOR = {'\r', '\n'};
124 
125     protected final byte pad; // instance variable just in case it needs to vary later
126 
127     /** Number of bytes in each full block of unencoded data, e.g. 4 for Base64 and 5 for Base32 */
128     private final int unencodedBlockSize;
129 
130     /** Number of bytes in each full block of encoded data, e.g. 3 for Base64 and 8 for Base32 */
131     private final int encodedBlockSize;
132 
133     /**
134      * Chunksize for encoding. Not used when decoding.
135      * A value of zero or less implies no chunking of the encoded data.
136      * Rounded down to nearest multiple of encodedBlockSize.
137      */
138     protected final int lineLength;
139 
140     /**
141      * Size of chunk separator. Not used unless {@link #lineLength} &gt; 0.
142      */
143     private final int chunkSeparatorLength;
144 
145     /**
146      * Defines the decoding behavior when the input bytes contain leftover trailing bits that
147      * cannot be created by a valid encoding. These can be bits that are unused from the final
148      * character or entire characters. The default mode is lenient decoding. Set this to
149      * {@code true} to enable strict decoding.
150      * <ul>
151      * <li>Lenient: Any trailing bits are composed into 8-bit bytes where possible.
152      *     The remainder are discarded.
153      * <li>Strict: The decoding will raise an {@link IllegalArgumentException} if trailing bits
154      *     are not part of a valid encoding. Any unused bits from the final character must
155      *     be zero. Impossible counts of entire final characters are not allowed.
156      * </ul>
157      *
158      * <p>When strict decoding is enabled it is expected that the decoded bytes will be re-encoded
159      * to a byte array that matches the original, i.e. no changes occur on the final
160      * character. This requires that the input bytes use the same padding and alphabet
161      * as the encoder.
162      */
163     private final CodecPolicy decodingPolicy;
164 
165     /**
166      * Note {@code lineLength} is rounded down to the nearest multiple of the encoded block size.
167      * If {@code chunkSeparatorLength} is zero, then chunking is disabled.
168      * @param unencodedBlockSize the size of an unencoded block (e.g. Base64 = 3)
169      * @param encodedBlockSize the size of an encoded block (e.g. Base64 = 4)
170      * @param lineLength if &gt; 0, use chunking with a length {@code lineLength}
171      * @param chunkSeparatorLength the chunk separator length, if relevant
172      */
173     protected BaseNCodec(
174         final int unencodedBlockSize,
175         final int encodedBlockSize,
176         final int lineLength,
177         final int chunkSeparatorLength
178     ) {
179         this(unencodedBlockSize, encodedBlockSize, lineLength, chunkSeparatorLength, BaseNCodec.PAD_DEFAULT);
180     }
181 
182     /**
183      * Note {@code lineLength} is rounded down to the nearest multiple of the encoded block size.
184      * If {@code chunkSeparatorLength} is zero, then chunking is disabled.
185      * @param unencodedBlockSize the size of an unencoded block (e.g. Base64 = 3)
186      * @param encodedBlockSize the size of an encoded block (e.g. Base64 = 4)
187      * @param lineLength if &gt; 0, use chunking with a length {@code lineLength}
188      * @param chunkSeparatorLength the chunk separator length, if relevant
189      * @param pad byte used as padding byte.
190      */
191     protected BaseNCodec(
192         final int unencodedBlockSize,
193         final int encodedBlockSize,
194         final int lineLength,
195         final int chunkSeparatorLength,
196         final byte pad
197     ) {
198         this(unencodedBlockSize, encodedBlockSize, lineLength, chunkSeparatorLength, pad, BaseNCodec.DECODING_POLICY_DEFAULT);
199     }
200 
201     /**
202      * Note {@code lineLength} is rounded down to the nearest multiple of the encoded block size.
203      * If {@code chunkSeparatorLength} is zero, then chunking is disabled.
204      * @param unencodedBlockSize the size of an unencoded block (e.g. Base64 = 3)
205      * @param encodedBlockSize the size of an encoded block (e.g. Base64 = 4)
206      * @param lineLength if &gt; 0, use chunking with a length {@code lineLength}
207      * @param chunkSeparatorLength the chunk separator length, if relevant
208      * @param pad byte used as padding byte.
209      * @param decodingPolicy Decoding policy.
210      * @since 1.15
211      */
212     protected BaseNCodec(
213         final int unencodedBlockSize,
214         final int encodedBlockSize,
215         final int lineLength,
216         final int chunkSeparatorLength,
217         final byte pad,
218         final CodecPolicy decodingPolicy
219     ) {
220         this.unencodedBlockSize = unencodedBlockSize;
221         this.encodedBlockSize = encodedBlockSize;
222         final boolean useChunking = lineLength > 0 && chunkSeparatorLength > 0;
223         this.lineLength = useChunking ? (lineLength / encodedBlockSize) * encodedBlockSize : 0;
224         this.chunkSeparatorLength = chunkSeparatorLength;
225         this.pad = pad;
226         this.decodingPolicy = Objects.requireNonNull(decodingPolicy, "codecPolicy");
227     }
228 
229     /**
230      * Compares two {@code int} values numerically treating the values
231      * as unsigned. Taken from JDK 1.8.
232      *
233      * @param  x the first {@code int} to compare
234      * @param  y the second {@code int} to compare
235      * @return the value {@code 0} if {@code x == y}; a value less
236      *         than {@code 0} if {@code x < y} as unsigned values; and
237      *         a value greater than {@code 0} if {@code x > y} as
238      *         unsigned values
239      */
240     private static int compareUnsigned(final int x, final int y) {
241         return Integer.compare(x + Integer.MIN_VALUE, y + Integer.MIN_VALUE);
242     }
243 
244     /**
245      * Create a positive capacity at least as large the minimum required capacity.
246      * If the minimum capacity is negative then this throws an OutOfMemoryError as no array
247      * can be allocated.
248      *
249      * @param minCapacity the minimum capacity
250      * @return the capacity
251      * @throws OutOfMemoryError if the {@code minCapacity} is negative
252      */
253     private static int createPositiveCapacity(final int minCapacity) {
254         if (minCapacity < 0) {
255             // overflow
256             throw new OutOfMemoryError("Unable to allocate array size: " + (minCapacity & 0xffffffffL));
257         }
258         // This is called when we require buffer expansion to a very big array.
259         // Use the conservative maximum buffer size if possible, otherwise the biggest required.
260         //
261         // Note: In this situation JDK 1.8 java.util.ArrayList returns Integer.MAX_VALUE.
262         // This excludes some VMs that can exceed MAX_BUFFER_SIZE but not allocate a full
263         // Integer.MAX_VALUE length array.
264         // The result is that we may have to allocate an array of this size more than once if
265         // the capacity must be expanded again.
266         return Math.max(minCapacity, BaseNCodec.MAX_BUFFER_SIZE);
267     }
268 
269     /**
270      * Gets a copy of the chunk separator per RFC 2045 section 2.1.
271      *
272      * @return the chunk separator
273      * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045 section 2.1</a>
274      * @since 1.15
275      */
276     public static byte[] getChunkSeparator() {
277         return BaseNCodec.CHUNK_SEPARATOR.clone();
278     }
279 
280     /**
281      * Checks if a byte value is whitespace or not.
282      * Whitespace is taken to mean: space, tab, CR, LF
283      * @param byteToCheck
284      *            the byte to check
285      * @return true if byte is whitespace, false otherwise
286      */
287     protected static boolean isWhiteSpace(final byte byteToCheck) {
288         switch (byteToCheck) {
289             case ' ' :
290             case '\n' :
291             case '\r' :
292             case '\t' :
293                 return true;
294             default :
295                 return false;
296         }
297     }
298 
299     /**
300      * Increases our buffer by the {@link #DEFAULT_BUFFER_RESIZE_FACTOR}.
301      * @param context the context to be used
302      * @param minCapacity the minimum required capacity
303      * @return the resized byte[] buffer
304      * @throws OutOfMemoryError if the {@code minCapacity} is negative
305      */
306     private static byte[] resizeBuffer(final Context context, final int minCapacity) {
307         // Overflow-conscious code treats the min and new capacity as unsigned.
308         final int oldCapacity = context.buffer.length;
309         int newCapacity = oldCapacity * BaseNCodec.DEFAULT_BUFFER_RESIZE_FACTOR;
310         if (BaseNCodec.compareUnsigned(newCapacity, minCapacity) < 0) {
311             newCapacity = minCapacity;
312         }
313         if (BaseNCodec.compareUnsigned(newCapacity, BaseNCodec.MAX_BUFFER_SIZE) > 0) {
314             newCapacity = BaseNCodec.createPositiveCapacity(minCapacity);
315         }
316         final var b = new byte[newCapacity];
317         System.arraycopy(context.buffer, 0, b, 0, context.buffer.length);
318         context.buffer = b;
319         return b;
320     }
321 
322     /**
323      * Returns the amount of buffered data available for reading.
324      *
325      * @param context the context to be used
326      * @return The amount of buffered data available for reading.
327      */
328     private int available(final Context context) {  // package protected for access from I/O streams
329         return context.buffer != null ? context.pos - context.readPos : 0;
330     }
331 
332     /**
333      * Tests a given byte array to see if it contains any characters within the alphabet or PAD.
334      *
335      * Intended for use in checking line-ending arrays
336      *
337      * @param arrayOctet
338      *            byte array to test
339      * @return {@code true} if any byte is a valid character in the alphabet or PAD; {@code false} otherwise
340      */
341     protected boolean containsAlphabetOrPad(final byte[] arrayOctet) {
342         if (arrayOctet == null) {
343             return false;
344         }
345         for (final byte element : arrayOctet) {
346             if (this.pad == element || this.isInAlphabet(element)) {
347                 return true;
348             }
349         }
350         return false;
351     }
352 
353     /**
354      * Decodes a byte[] containing characters in the Base-N alphabet.
355      *
356      * @param pArray
357      *            A byte array containing Base-N character data
358      * @return a byte array containing binary data
359      */
360     @Override
361     public byte[] decode(final byte[] pArray) {
362         if (pArray == null || pArray.length == 0) {
363             return pArray;
364         }
365         final var context = new Context();
366         this.decode(pArray, 0, pArray.length, context);
367         this.decode(pArray, 0, BaseNCodec.EOF, context); // Notify decoder of EOF.
368         final var result = new byte[context.pos];
369         this.readResults(result, 0, result.length, context);
370         return result;
371     }
372 
373     // package protected for access from I/O streams
374     public abstract void decode(byte[] pArray, int i, int length, Context context);
375 
376     /**
377      * Decodes an Object using the Base-N algorithm. This method is provided in order to satisfy the requirements of
378      * the Decoder interface, and will throw a DecoderException if the supplied object is not of type byte[] or String.
379      *
380      * @param obj
381      *            Object to decode
382      * @return An object (of type byte[]) containing the binary data which corresponds to the byte[] or String
383      *         supplied.
384      * @throws DecoderException
385      *             if the parameter supplied is not of type byte[]
386      */
387     @Override
388     public Object decode(final Object obj) throws DecoderException {
389         if (obj instanceof byte[]) {
390             return this.decode((byte[]) obj);
391         } else if (obj instanceof String) {
392             return this.decode((String) obj);
393         } else {
394             throw new DecoderException("Parameter supplied to Base-N decode is not a byte[] or a String");
395         }
396     }
397 
398     /**
399      * Decodes a String containing characters in the Base-N alphabet.
400      *
401      * @param pArray
402      *            A String containing Base-N character data
403      * @return a byte array containing binary data
404      */
405     public byte[] decode(final String pArray) {
406         return this.decode(StringUtils.getBytesUtf8(pArray));
407     }
408 
409     /**
410      * Encodes a byte[] containing binary data, into a byte[] containing characters in the alphabet.
411      *
412      * @param pArray
413      *            a byte array containing binary data
414      * @return A byte array containing only the base N alphabetic character data
415      */
416     @Override
417     public byte[] encode(final byte[] pArray) {
418         if (pArray == null || pArray.length == 0) {
419             return pArray;
420         }
421         return this.encode(pArray, 0, pArray.length);
422     }
423 
424     /**
425      * Encodes a byte[] containing binary data, into a byte[] containing
426      * characters in the alphabet.
427      *
428      * @param pArray
429      *            a byte array containing binary data
430      * @param offset
431      *            initial offset of the subarray.
432      * @param length
433      *            length of the subarray.
434      * @return A byte array containing only the base N alphabetic character data
435      * @since 1.11
436      */
437     public byte[] encode(final byte[] pArray, final int offset, final int length) {
438         if (pArray == null || pArray.length == 0) {
439             return pArray;
440         }
441         final var context = new Context();
442         this.encode(pArray, offset, length, context);
443         this.encode(pArray, offset, BaseNCodec.EOF, context); // Notify encoder of EOF.
444         final var buf = new byte[context.pos - context.readPos];
445         this.readResults(buf, 0, buf.length, context);
446         return buf;
447     }
448 
449     // package protected for access from I/O streams
450     public abstract void encode(byte[] pArray, int i, int length, Context context);
451 
452     /**
453      * Encodes an Object using the Base-N algorithm. This method is provided in order to satisfy the requirements of
454      * the Encoder interface, and will throw an EncoderException if the supplied object is not of type byte[].
455      *
456      * @param obj
457      *            Object to encode
458      * @return An object (of type byte[]) containing the Base-N encoded data which corresponds to the byte[] supplied.
459      * @throws EncoderException
460      *             if the parameter supplied is not of type byte[]
461      */
462     @Override
463     public Object encode(final Object obj) throws EncoderException {
464         if (!(obj instanceof byte[])) {
465             throw new EncoderException("Parameter supplied to Base-N encode is not a byte[]");
466         }
467         return this.encode((byte[]) obj);
468     }
469 
470     /**
471      * Encodes a byte[] containing binary data, into a String containing characters in the appropriate alphabet.
472      * Uses UTF8 encoding.
473      *
474      * @param pArray a byte array containing binary data
475      * @return String containing only character data in the appropriate alphabet.
476      * @since 1.5
477      * This is a duplicate of {@link #encodeToString(byte[])}; it was merged during refactoring.
478     */
479     public String encodeAsString(final byte[] pArray){
480         return StringUtils.newStringUtf8(this.encode(pArray));
481     }
482 
483     /**
484      * Encodes a byte[] containing binary data, into a String containing characters in the Base-N alphabet.
485      * Uses UTF8 encoding.
486      *
487      * @param pArray
488      *            a byte array containing binary data
489      * @return A String containing only Base-N character data
490      */
491     public String encodeToString(final byte[] pArray) {
492         return StringUtils.newStringUtf8(this.encode(pArray));
493     }
494 
495     /**
496      * Ensure that the buffer has room for {@code size} bytes
497      *
498      * @param size minimum spare space required
499      * @param context the context to be used
500      * @return the buffer
501      */
502     protected byte[] ensureBufferSize(final int size, final Context context) {
503         if (context.buffer == null) {
504             context.buffer = new byte[Math.max(size, this.getDefaultBufferSize())];
505             context.pos = 0;
506             context.readPos = 0;
507             // Overflow-conscious:
508             // x + y > z  ==  x + y - z > 0
509         } else if (context.pos + size - context.buffer.length > 0) {
510             return BaseNCodec.resizeBuffer(context, context.pos + size);
511         }
512         return context.buffer;
513     }
514 
515     /**
516      * Returns the decoding behavior policy.
517      * 
518      * <p>
519      * The default is lenient. If the decoding policy is strict, then decoding will raise an
520      * {@link IllegalArgumentException} if trailing bits are not part of a valid encoding. Decoding will compose
521      * trailing bits into 8-bit bytes and discard the remainder.
522      * </p>
523      *
524      * @since 1.15
525      */
526     public CodecPolicy getCodecPolicy() {
527         return this.decodingPolicy;
528     }
529 
530     /**
531      * Get the default buffer size. Can be overridden.
532      *
533      * @return the default buffer size.
534      */
535     protected int getDefaultBufferSize() {
536         return BaseNCodec.DEFAULT_BUFFER_SIZE;
537     }
538 
539     /**
540      * Calculates the amount of space needed to encode the supplied array.
541      *
542      * @param pArray byte[] array which will later be encoded
543      *
544      * @return amount of space needed to encode the supplied array.
545      * Returns a long since a max-len array will require &gt; Integer.MAX_VALUE
546      */
547     public long getEncodedLength(final byte[] pArray) {
548         // Calculate non-chunked size - rounded up to allow for padding
549         // cast to long is needed to avoid possibility of overflow
550         long len = ((pArray.length + this.unencodedBlockSize-1)  / this.unencodedBlockSize) * (long) this.encodedBlockSize;
551         if (this.lineLength > 0) { // We're using chunking
552             // Round up to nearest multiple
553             len += ((len + this.lineLength-1) / this.lineLength) * this.chunkSeparatorLength;
554         }
555         return len;
556     }
557 
558     /**
559      * Returns true if this object has buffered data for reading.
560      *
561      * @param context the context to be used
562      * @return true if there is data still available for reading.
563      */
564     public boolean hasData(final Context context) {  // package protected for access from I/O streams
565         return context.buffer != null;
566     }
567 
568     /**
569      * Returns whether the {@code octet} is in the current alphabet.
570      * Does not allow whitespace or pad.
571      *
572      * @param value The value to test
573      *
574      * @return {@code true} if the value is defined in the current alphabet, {@code false} otherwise.
575      */
576     protected abstract boolean isInAlphabet(byte value);
577 
578     /**
579      * Tests a given byte array to see if it contains only valid characters within the alphabet.
580      * The method optionally treats whitespace and pad as valid.
581      *
582      * @param arrayOctet byte array to test
583      * @param allowWSPad if {@code true}, then whitespace and PAD are also allowed
584      *
585      * @return {@code true} if all bytes are valid characters in the alphabet or if the byte array is empty;
586      *         {@code false}, otherwise
587      */
588     public boolean isInAlphabet(final byte[] arrayOctet, final boolean allowWSPad) {
589         for (final byte octet : arrayOctet) {
590             if (
591                 !this.isInAlphabet(octet)
592                 && (!allowWSPad || (octet != this.pad)
593                 && !BaseNCodec.isWhiteSpace(octet))
594             ) {
595                 return false;
596             }
597         }
598         return true;
599     }
600 
601     /**
602      * Tests a given String to see if it contains only valid characters within the alphabet.
603      * The method treats whitespace and PAD as valid.
604      *
605      * @param basen String to test
606      * @return {@code true} if all characters in the String are valid characters in the alphabet or if
607      *         the String is empty; {@code false}, otherwise
608      * @see #isInAlphabet(byte[], boolean)
609      */
610     public boolean isInAlphabet(final String basen) {
611         return this.isInAlphabet(StringUtils.getBytesUtf8(basen), true);
612     }
613 
614     /**
615      * Returns true if decoding behavior is strict. Decoding will raise an {@link IllegalArgumentException} if trailing
616      * bits are not part of a valid encoding.
617      *
618      * <p>
619      * The default is false for lenient decoding. Decoding will compose trailing bits into 8-bit bytes and discard the
620      * remainder.
621      * </p>
622      *
623      * @return true if using strict decoding
624      * @since 1.15
625      */
626     public boolean isStrictDecoding() {
627         return this.decodingPolicy == CodecPolicy.STRICT;
628     }
629 
630     /**
631      * Extracts buffered data into the provided byte[] array, starting at position bPos, up to a maximum of bAvail
632      * bytes. Returns how many bytes were actually extracted.
633      * <p>
634      * Package protected for access from I/O streams.
635      *
636      * @param b       byte[] array to extract the buffered data into.
637      * @param bPos    position in byte[] array to start extraction at.
638      * @param bAvail  amount of bytes we're allowed to extract. We may extract fewer (if fewer are available).
639      * @param context the context to be used
640      */
641     private void readResults(final byte[] b, final int bPos, final int bAvail, final Context context) {
642         if (context.buffer != null) {
643             final int len = Math.min(this.available(context), bAvail);
644             System.arraycopy(context.buffer, context.readPos, b, bPos, len);
645             context.readPos += len;
646             if (context.readPos >= context.pos) {
647                 context.buffer = null; // so hasData() will return false, and this method can return -1
648             }
649         }
650     }
651 
652     /**
653      * Holds thread context so classes can be thread-safe.
654      *
655      * This class is not itself thread-safe; each thread must allocate its own copy.
656      *
657      * @since 1.7
658      */
659     protected static class Context {
660 
661         /**
662          * Placeholder for the bytes we're dealing with for our based logic.
663          * Bitwise operations store and extract the encoding or decoding from this variable.
664          */
665         protected int ibitWorkArea;
666 
667         /**
668          * Placeholder for the bytes we're dealing with for our based logic.
669          * Bitwise operations store and extract the encoding or decoding from this variable.
670          */
671         protected long lbitWorkArea;
672 
673         /**
674          * Buffer for streaming.
675          */
676         protected byte[] buffer;
677 
678         /**
679          * Position where next character should be written in the buffer.
680          */
681         protected int pos;
682 
683         /**
684          * Position where next character should be read from the buffer.
685          */
686         protected int readPos;
687 
688         /**
689          * Boolean flag to indicate the EOF has been reached. Once EOF has been reached, this object becomes useless,
690          * and must be thrown away.
691          */
692         protected boolean eof;
693 
694         /**
695          * Variable tracks how many characters have been written to the current line. Only used when encoding. We use
696          * it to make sure each encoded line never goes beyond lineLength (if lineLength &gt; 0).
697          */
698         protected int currentLinePos;
699 
700         /**
701          * Writes to the buffer only occur after every 3/5 reads when encoding, and every 4/8 reads when decoding. This
702          * variable helps track that.
703          */
704         protected int modulus;
705 
706         /**
707          * Returns a String useful for debugging (especially within a debugger.)
708          *
709          * @return a String useful for debugging.
710          */
711         @SuppressWarnings("boxing") // OK to ignore boxing here
712         @Override
713         public String toString() {
714             return String.format(
715                 "%s[buffer=%s, currentLinePos=%s, eof=%s, ibitWorkArea=%s, lbitWorkArea=%s, modulus=%s, pos=%s, readPos=%s]",
716                 this.getClass().getSimpleName(),
717                 Arrays.toString(this.buffer),
718                 this.currentLinePos,
719                 this.eof,
720                 this.ibitWorkArea,
721                 this.lbitWorkArea,
722                 this.modulus,
723                 this.pos,
724                 this.readPos
725             );
726         }
727     }
728 }
729