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1   
2   /*
3    * Licensed to the Apache Software Foundation (ASF) under one or more
4    * contributor license agreements.  See the NOTICE file distributed with
5    * this work for additional information regarding copyright ownership.
6    * The ASF licenses this file to You under the Apache License, Version 2.0
7    * (the "License"); you may not use this file except in compliance with
8    * the License.  You may obtain a copy of the License at
9    *
10   *      http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  
19  package com.jsql.util.bruter;
20  
21  import org.apache.commons.codec.BinaryDecoder;
22  import org.apache.commons.codec.BinaryEncoder;
23  import org.apache.commons.codec.DecoderException;
24  import org.apache.commons.codec.EncoderException;
25  import org.apache.commons.codec.binary.StringUtils;
26  
27  import java.util.Arrays;
28  import java.util.Objects;
29  
30  /**
31   * Abstract superclass for Base-N encoders and decoders.
32   *
33   * <p>
34   * This class is thread-safe.
35   * </p>
36   *
37   * You can set the decoding behavior when the input bytes contain leftover trailing bits that cannot be created by a valid
38   * encoding. These can be bits that are unused from the final character or entire characters. The default mode is
39   * lenient decoding.
40   * <ul>
41   * <li>Lenient: Any trailing bits are composed into 8-bit bytes where possible. The remainder are discarded.
42   * <li>Strict: The decoding will raise an {@link IllegalArgumentException} if trailing bits are not part of a valid
43   * encoding. Any unused bits from the final character must be zero. Impossible counts of entire final characters are not
44   * allowed.
45   * </ul>
46   * <p>
47   * When strict decoding is enabled it is expected that the decoded bytes will be re-encoded to a byte array that matches
48   * the original, i.e. no changes occur on the final character. This requires that the input bytes use the same padding
49   * and alphabet as the encoder.
50   * </p>
51   */
52  public abstract class BaseNCodec implements BinaryEncoder, BinaryDecoder {
53  
54      /**
55       * EOF
56       *
57       * @since 1.7
58       */
59      private static final int EOF = -1;
60  
61      /**
62       *  MIME chunk size per RFC 2045 section 6.8.
63       *
64       * <p>
65       * The {@value} character limit does not count the trailing CRLF, but counts all other characters, including any
66       * equal signs.
67       * </p>
68       *
69       * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045 section 6.8</a>
70       */
71      public static final int MIME_CHUNK_SIZE = 76;
72  
73      /**
74       * PEM chunk size per RFC 1421 section 4.3.2.4.
75       *
76       * <p>
77       * The {@value} character limit does not count the trailing CRLF, but counts all other characters, including any
78       * equal signs.
79       * </p>
80       *
81       * @see <a href="http://tools.ietf.org/html/rfc1421">RFC 1421 section 4.3.2.4</a>
82       */
83      public static final int PEM_CHUNK_SIZE = 64;
84  
85      private static final int DEFAULT_BUFFER_RESIZE_FACTOR = 2;
86  
87      /**
88       * Defines the default buffer size - currently {@value}
89       * - must be large enough for at least one encoded block+separator
90       */
91      private static final int DEFAULT_BUFFER_SIZE = 8192;
92  
93      /**
94       * The maximum size buffer to allocate.
95       *
96       * <p>This is set to the same size used in the JDK {@code java.util.ArrayList}:</p>
97       * <blockquote>
98       * Some VMs reserve some header words in an array.
99       * Attempts to allocate larger arrays may result in
100      * OutOfMemoryError: Requested array size exceeds VM limit.
101      * </blockquote>
102      */
103     private static final int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;
104 
105     /** Mask used to extract 8 bits, used in decoding bytes */
106     protected static final int MASK_8BITS = 0xff;
107 
108     /**
109      * Byte used to pad output.
110      */
111     protected static final byte PAD_DEFAULT = '='; // Allow static access to default
112 
113     /**
114      * The default decoding policy.
115      * @since 1.15
116      */
117     protected static final CodecPolicy DECODING_POLICY_DEFAULT = CodecPolicy.LENIENT;
118 
119     /**
120      * Chunk separator per RFC 2045 section 2.1.
121      *
122      * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045 section 2.1</a>
123      */
124     private static final byte[] CHUNK_SEPARATOR = {'\r', '\n'};
125 
126     protected final byte pad; // instance variable just in case it needs to vary later
127 
128     /** Number of bytes in each full block of unencoded data, e.g. 4 for Base64 and 5 for Base32 */
129     private final int unencodedBlockSize;
130 
131     /** Number of bytes in each full block of encoded data, e.g. 3 for Base64 and 8 for Base32 */
132     private final int encodedBlockSize;
133 
134     /**
135      * Chunksize for encoding. Not used when decoding.
136      * A value of zero or less implies no chunking of the encoded data.
137      * Rounded down to nearest multiple of encodedBlockSize.
138      */
139     protected final int lineLength;
140 
141     /**
142      * Size of chunk separator. Not used unless {@link #lineLength} &gt; 0.
143      */
144     private final int chunkSeparatorLength;
145 
146     /**
147      * Defines the decoding behavior when the input bytes contain leftover trailing bits that
148      * cannot be created by a valid encoding. These can be bits that are unused from the final
149      * character or entire characters. The default mode is lenient decoding. Set this to
150      * {@code true} to enable strict decoding.
151      * <ul>
152      * <li>Lenient: Any trailing bits are composed into 8-bit bytes where possible.
153      *     The remainder are discarded.
154      * <li>Strict: The decoding will raise an {@link IllegalArgumentException} if trailing bits
155      *     are not part of a valid encoding. Any unused bits from the final character must
156      *     be zero. Impossible counts of entire final characters are not allowed.
157      * </ul>
158      *
159      * <p>When strict decoding is enabled it is expected that the decoded bytes will be re-encoded
160      * to a byte array that matches the original, i.e. no changes occur on the final
161      * character. This requires that the input bytes use the same padding and alphabet
162      * as the encoder.
163      */
164     private final CodecPolicy decodingPolicy;
165 
166     /**
167      * Note {@code lineLength} is rounded down to the nearest multiple of the encoded block size.
168      * If {@code chunkSeparatorLength} is zero, then chunking is disabled.
169      * @param unencodedBlockSize the size of an unencoded block (e.g. Base64 = 3)
170      * @param encodedBlockSize the size of an encoded block (e.g. Base64 = 4)
171      * @param lineLength if &gt; 0, use chunking with a length {@code lineLength}
172      * @param chunkSeparatorLength the chunk separator length, if relevant
173      */
174     protected BaseNCodec(
175         final int unencodedBlockSize,
176         final int encodedBlockSize,
177         final int lineLength,
178         final int chunkSeparatorLength
179     ) {
180         this(unencodedBlockSize, encodedBlockSize, lineLength, chunkSeparatorLength, PAD_DEFAULT);
181     }
182 
183     /**
184      * Note {@code lineLength} is rounded down to the nearest multiple of the encoded block size.
185      * If {@code chunkSeparatorLength} is zero, then chunking is disabled.
186      * @param unencodedBlockSize the size of an unencoded block (e.g. Base64 = 3)
187      * @param encodedBlockSize the size of an encoded block (e.g. Base64 = 4)
188      * @param lineLength if &gt; 0, use chunking with a length {@code lineLength}
189      * @param chunkSeparatorLength the chunk separator length, if relevant
190      * @param pad byte used as padding byte.
191      */
192     protected BaseNCodec(
193         final int unencodedBlockSize,
194         final int encodedBlockSize,
195         final int lineLength,
196         final int chunkSeparatorLength,
197         final byte pad
198     ) {
199         this(unencodedBlockSize, encodedBlockSize, lineLength, chunkSeparatorLength, pad, DECODING_POLICY_DEFAULT);
200     }
201 
202     /**
203      * Note {@code lineLength} is rounded down to the nearest multiple of the encoded block size.
204      * If {@code chunkSeparatorLength} is zero, then chunking is disabled.
205      * @param unencodedBlockSize the size of an unencoded block (e.g. Base64 = 3)
206      * @param encodedBlockSize the size of an encoded block (e.g. Base64 = 4)
207      * @param lineLength if &gt; 0, use chunking with a length {@code lineLength}
208      * @param chunkSeparatorLength the chunk separator length, if relevant
209      * @param pad byte used as padding byte.
210      * @param decodingPolicy Decoding policy.
211      * @since 1.15
212      */
213     protected BaseNCodec(
214         final int unencodedBlockSize,
215         final int encodedBlockSize,
216         final int lineLength,
217         final int chunkSeparatorLength,
218         final byte pad,
219         final CodecPolicy decodingPolicy
220     ) {
221         
222         this.unencodedBlockSize = unencodedBlockSize;
223         this.encodedBlockSize = encodedBlockSize;
224         final boolean useChunking = lineLength > 0 && chunkSeparatorLength > 0;
225         this.lineLength = useChunking ? (lineLength / encodedBlockSize) * encodedBlockSize : 0;
226         this.chunkSeparatorLength = chunkSeparatorLength;
227         this.pad = pad;
228         this.decodingPolicy = Objects.requireNonNull(decodingPolicy, "codecPolicy");
229     }
230 
231     /**
232      * Compares two {@code int} values numerically treating the values
233      * as unsigned. Taken from JDK 1.8.
234      *
235      * @param  x the first {@code int} to compare
236      * @param  y the second {@code int} to compare
237      * @return the value {@code 0} if {@code x == y}; a value less
238      *         than {@code 0} if {@code x < y} as unsigned values; and
239      *         a value greater than {@code 0} if {@code x > y} as
240      *         unsigned values
241      */
242     private static int compareUnsigned(final int x, final int y) {
243         return Integer.compare(x + Integer.MIN_VALUE, y + Integer.MIN_VALUE);
244     }
245 
246     /**
247      * Create a positive capacity at least as large the minimum required capacity.
248      * If the minimum capacity is negative then this throws an OutOfMemoryError as no array
249      * can be allocated.
250      *
251      * @param minCapacity the minimum capacity
252      * @return the capacity
253      * @throws OutOfMemoryError if the {@code minCapacity} is negative
254      */
255     private static int createPositiveCapacity(final int minCapacity) {
256         
257         if (minCapacity < 0) {
258             // overflow
259             throw new OutOfMemoryError("Unable to allocate array size: " + (minCapacity & 0xffffffffL));
260         }
261         
262         // This is called when we require buffer expansion to a very big array.
263         // Use the conservative maximum buffer size if possible, otherwise the biggest required.
264         //
265         // Note: In this situation JDK 1.8 java.util.ArrayList returns Integer.MAX_VALUE.
266         // This excludes some VMs that can exceed MAX_BUFFER_SIZE but not allocate a full
267         // Integer.MAX_VALUE length array.
268         // The result is that we may have to allocate an array of this size more than once if
269         // the capacity must be expanded again.
270         return Math.max(minCapacity, MAX_BUFFER_SIZE);
271     }
272 
273     /**
274      * Gets a copy of the chunk separator per RFC 2045 section 2.1.
275      *
276      * @return the chunk separator
277      * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045 section 2.1</a>
278      * @since 1.15
279      */
280     public static byte[] getChunkSeparator() {
281         return CHUNK_SEPARATOR.clone();
282     }
283 
284     /**
285      * Checks if a byte value is whitespace or not.
286      * Whitespace is taken to mean: space, tab, CR, LF
287      * @param byteToCheck
288      *            the byte to check
289      * @return true if byte is whitespace, false otherwise
290      */
291     protected static boolean isWhiteSpace(final byte byteToCheck) {
292         
293         switch (byteToCheck) {
294             case ' ' :
295             case '\n' :
296             case '\r' :
297             case '\t' :
298                 return true;
299             default :
300                 return false;
301         }
302     }
303 
304     /**
305      * Increases our buffer by the {@link #DEFAULT_BUFFER_RESIZE_FACTOR}.
306      * @param context the context to be used
307      * @param minCapacity the minimum required capacity
308      * @return the resized byte[] buffer
309      * @throws OutOfMemoryError if the {@code minCapacity} is negative
310      */
311     private static byte[] resizeBuffer(final Context context, final int minCapacity) {
312         
313         // Overflow-conscious code treats the min and new capacity as unsigned.
314         final int oldCapacity = context.buffer.length;
315         int newCapacity = oldCapacity * DEFAULT_BUFFER_RESIZE_FACTOR;
316         
317         if (compareUnsigned(newCapacity, minCapacity) < 0) {
318             newCapacity = minCapacity;
319         }
320         
321         if (compareUnsigned(newCapacity, MAX_BUFFER_SIZE) > 0) {
322             newCapacity = createPositiveCapacity(minCapacity);
323         }
324 
325         final var b = new byte[newCapacity];
326         System.arraycopy(context.buffer, 0, b, 0, context.buffer.length);
327         context.buffer = b;
328         
329         return b;
330     }
331 
332     /**
333      * Returns the amount of buffered data available for reading.
334      *
335      * @param context the context to be used
336      * @return The amount of buffered data available for reading.
337      */
338     private int available(final Context context) {  // package protected for access from I/O streams
339         return context.buffer != null ? context.pos - context.readPos : 0;
340     }
341 
342     /**
343      * Tests a given byte array to see if it contains any characters within the alphabet or PAD.
344      *
345      * Intended for use in checking line-ending arrays
346      *
347      * @param arrayOctet
348      *            byte array to test
349      * @return {@code true} if any byte is a valid character in the alphabet or PAD; {@code false} otherwise
350      */
351     protected boolean containsAlphabetOrPad(final byte[] arrayOctet) {
352         
353         if (arrayOctet == null) {
354             return false;
355         }
356         
357         for (final byte element : arrayOctet) {
358             if (this.pad == element || this.isInAlphabet(element)) {
359                 return true;
360             }
361         }
362         
363         return false;
364     }
365 
366     /**
367      * Decodes a byte[] containing characters in the Base-N alphabet.
368      *
369      * @param pArray
370      *            A byte array containing Base-N character data
371      * @return a byte array containing binary data
372      */
373     @Override
374     public byte[] decode(final byte[] pArray) {
375         
376         if (pArray == null || pArray.length == 0) {
377             return pArray;
378         }
379         
380         final var context = new Context();
381         this.decode(pArray, 0, pArray.length, context);
382         this.decode(pArray, 0, EOF, context); // Notify decoder of EOF.
383         final var result = new byte[context.pos];
384         this.readResults(result, 0, result.length, context);
385         
386         return result;
387     }
388 
389     // package protected for access from I/O streams
390     public abstract void decode(byte[] pArray, int i, int length, Context context);
391 
392     /**
393      * Decodes an Object using the Base-N algorithm. This method is provided in order to satisfy the requirements of
394      * the Decoder interface, and will throw a DecoderException if the supplied object is not of type byte[] or String.
395      *
396      * @param obj
397      *            Object to decode
398      * @return An object (of type byte[]) containing the binary data which corresponds to the byte[] or String
399      *         supplied.
400      * @throws DecoderException
401      *             if the parameter supplied is not of type byte[]
402      */
403     @Override
404     public Object decode(final Object obj) throws DecoderException {
405         if (obj instanceof byte[]) {
406             return this.decode((byte[]) obj);
407         } else if (obj instanceof String) {
408             return this.decode((String) obj);
409         } else {
410             throw new DecoderException("Parameter supplied to Base-N decode is not a byte[] or a String");
411         }
412     }
413 
414     /**
415      * Decodes a String containing characters in the Base-N alphabet.
416      *
417      * @param pArray
418      *            A String containing Base-N character data
419      * @return a byte array containing binary data
420      */
421     public byte[] decode(final String pArray) {
422         return this.decode(StringUtils.getBytesUtf8(pArray));
423     }
424 
425     /**
426      * Encodes a byte[] containing binary data, into a byte[] containing characters in the alphabet.
427      *
428      * @param pArray
429      *            a byte array containing binary data
430      * @return A byte array containing only the base N alphabetic character data
431      */
432     @Override
433     public byte[] encode(final byte[] pArray) {
434         
435         if (pArray == null || pArray.length == 0) {
436             return pArray;
437         }
438         
439         return this.encode(pArray, 0, pArray.length);
440     }
441 
442     /**
443      * Encodes a byte[] containing binary data, into a byte[] containing
444      * characters in the alphabet.
445      *
446      * @param pArray
447      *            a byte array containing binary data
448      * @param offset
449      *            initial offset of the subarray.
450      * @param length
451      *            length of the subarray.
452      * @return A byte array containing only the base N alphabetic character data
453      * @since 1.11
454      */
455     public byte[] encode(final byte[] pArray, final int offset, final int length) {
456         
457         if (pArray == null || pArray.length == 0) {
458             return pArray;
459         }
460         
461         final var context = new Context();
462         this.encode(pArray, offset, length, context);
463         this.encode(pArray, offset, EOF, context); // Notify encoder of EOF.
464         final var buf = new byte[context.pos - context.readPos];
465         this.readResults(buf, 0, buf.length, context);
466         
467         return buf;
468     }
469 
470     // package protected for access from I/O streams
471     public abstract void encode(byte[] pArray, int i, int length, Context context);
472 
473     /**
474      * Encodes an Object using the Base-N algorithm. This method is provided in order to satisfy the requirements of
475      * the Encoder interface, and will throw an EncoderException if the supplied object is not of type byte[].
476      *
477      * @param obj
478      *            Object to encode
479      * @return An object (of type byte[]) containing the Base-N encoded data which corresponds to the byte[] supplied.
480      * @throws EncoderException
481      *             if the parameter supplied is not of type byte[]
482      */
483     @Override
484     public Object encode(final Object obj) throws EncoderException {
485         
486         if (!(obj instanceof byte[])) {
487             throw new EncoderException("Parameter supplied to Base-N encode is not a byte[]");
488         }
489         
490         return this.encode((byte[]) obj);
491     }
492 
493     /**
494      * Encodes a byte[] containing binary data, into a String containing characters in the appropriate alphabet.
495      * Uses UTF8 encoding.
496      *
497      * @param pArray a byte array containing binary data
498      * @return String containing only character data in the appropriate alphabet.
499      * @since 1.5
500      * This is a duplicate of {@link #encodeToString(byte[])}; it was merged during refactoring.
501     */
502     public String encodeAsString(final byte[] pArray){
503         return StringUtils.newStringUtf8(this.encode(pArray));
504     }
505 
506     /**
507      * Encodes a byte[] containing binary data, into a String containing characters in the Base-N alphabet.
508      * Uses UTF8 encoding.
509      *
510      * @param pArray
511      *            a byte array containing binary data
512      * @return A String containing only Base-N character data
513      */
514     public String encodeToString(final byte[] pArray) {
515         return StringUtils.newStringUtf8(this.encode(pArray));
516     }
517 
518     /**
519      * Ensure that the buffer has room for {@code size} bytes
520      *
521      * @param size minimum spare space required
522      * @param context the context to be used
523      * @return the buffer
524      */
525     protected byte[] ensureBufferSize(final int size, final Context context) {
526         
527         if (context.buffer == null) {
528             
529             context.buffer = new byte[Math.max(size, this.getDefaultBufferSize())];
530             context.pos = 0;
531             context.readPos = 0;
532 
533             // Overflow-conscious:
534             // x + y > z  ==  x + y - z > 0
535             
536         } else if (context.pos + size - context.buffer.length > 0) {
537             return resizeBuffer(context, context.pos + size);
538         }
539         
540         return context.buffer;
541     }
542 
543     /**
544      * Returns the decoding behavior policy.
545      * 
546      * <p>
547      * The default is lenient. If the decoding policy is strict, then decoding will raise an
548      * {@link IllegalArgumentException} if trailing bits are not part of a valid encoding. Decoding will compose
549      * trailing bits into 8-bit bytes and discard the remainder.
550      * </p>
551      *
552      * @return true if using strict decoding
553      * @since 1.15
554      */
555     public CodecPolicy getCodecPolicy() {
556         return this.decodingPolicy;
557     }
558 
559     /**
560      * Get the default buffer size. Can be overridden.
561      *
562      * @return the default buffer size.
563      */
564     protected int getDefaultBufferSize() {
565         return DEFAULT_BUFFER_SIZE;
566     }
567 
568     /**
569      * Calculates the amount of space needed to encode the supplied array.
570      *
571      * @param pArray byte[] array which will later be encoded
572      *
573      * @return amount of space needed to encoded the supplied array.
574      * Returns a long since a max-len array will require &gt; Integer.MAX_VALUE
575      */
576     public long getEncodedLength(final byte[] pArray) {
577         
578         // Calculate non-chunked size - rounded up to allow for padding
579         // cast to long is needed to avoid possibility of overflow
580         long len = ((pArray.length + this.unencodedBlockSize-1)  / this.unencodedBlockSize) * (long) this.encodedBlockSize;
581         
582         if (this.lineLength > 0) { // We're using chunking
583             // Round up to nearest multiple
584             len += ((len + this.lineLength-1) / this.lineLength) * this.chunkSeparatorLength;
585         }
586         
587         return len;
588     }
589 
590     /**
591      * Returns true if this object has buffered data for reading.
592      *
593      * @param context the context to be used
594      * @return true if there is data still available for reading.
595      */
596     public boolean hasData(final Context context) {  // package protected for access from I/O streams
597         return context.buffer != null;
598     }
599 
600     /**
601      * Returns whether or not the {@code octet} is in the current alphabet.
602      * Does not allow whitespace or pad.
603      *
604      * @param value The value to test
605      *
606      * @return {@code true} if the value is defined in the current alphabet, {@code false} otherwise.
607      */
608     protected abstract boolean isInAlphabet(byte value);
609 
610     /**
611      * Tests a given byte array to see if it contains only valid characters within the alphabet.
612      * The method optionally treats whitespace and pad as valid.
613      *
614      * @param arrayOctet byte array to test
615      * @param allowWSPad if {@code true}, then whitespace and PAD are also allowed
616      *
617      * @return {@code true} if all bytes are valid characters in the alphabet or if the byte array is empty;
618      *         {@code false}, otherwise
619      */
620     public boolean isInAlphabet(final byte[] arrayOctet, final boolean allowWSPad) {
621         
622         for (final byte octet : arrayOctet) {
623             if (
624                 !this.isInAlphabet(octet)
625                 && (!allowWSPad || (octet != this.pad)
626                 && !isWhiteSpace(octet))
627             ) {
628                 return false;
629             }
630         }
631         
632         return true;
633     }
634 
635     /**
636      * Tests a given String to see if it contains only valid characters within the alphabet.
637      * The method treats whitespace and PAD as valid.
638      *
639      * @param basen String to test
640      * @return {@code true} if all characters in the String are valid characters in the alphabet or if
641      *         the String is empty; {@code false}, otherwise
642      * @see #isInAlphabet(byte[], boolean)
643      */
644     public boolean isInAlphabet(final String basen) {
645         return this.isInAlphabet(StringUtils.getBytesUtf8(basen), true);
646     }
647 
648     /**
649      * Returns true if decoding behavior is strict. Decoding will raise an {@link IllegalArgumentException} if trailing
650      * bits are not part of a valid encoding.
651      *
652      * <p>
653      * The default is false for lenient decoding. Decoding will compose trailing bits into 8-bit bytes and discard the
654      * remainder.
655      * </p>
656      *
657      * @return true if using strict decoding
658      * @since 1.15
659      */
660     public boolean isStrictDecoding() {
661         return this.decodingPolicy == CodecPolicy.STRICT;
662     }
663 
664     /**
665      * Extracts buffered data into the provided byte[] array, starting at position bPos, up to a maximum of bAvail
666      * bytes. Returns how many bytes were actually extracted.
667      * <p>
668      * Package protected for access from I/O streams.
669      *
670      * @param b
671      *            byte[] array to extract the buffered data into.
672      * @param bPos
673      *            position in byte[] array to start extraction at.
674      * @param bAvail
675      *            amount of bytes we're allowed to extract. We may extract fewer (if fewer are available).
676      * @param context
677      *            the context to be used
678      * @return The number of bytes successfully extracted into the provided byte[] array.
679      */
680     private int readResults(final byte[] b, final int bPos, final int bAvail, final Context context) {
681         
682         if (context.buffer != null) {
683             
684             final int len = Math.min(this.available(context), bAvail);
685             System.arraycopy(context.buffer, context.readPos, b, bPos, len);
686             context.readPos += len;
687             
688             if (context.readPos >= context.pos) {
689                 context.buffer = null; // so hasData() will return false, and this method can return -1
690             }
691             
692             return len;
693         }
694         
695         return context.eof ? EOF : 0;
696     }
697 
698     /**
699      * Holds thread context so classes can be thread-safe.
700      *
701      * This class is not itself thread-safe; each thread must allocate its own copy.
702      *
703      * @since 1.7
704      */
705     protected static class Context {
706 
707         /**
708          * Place holder for the bytes we're dealing with for our based logic.
709          * Bitwise operations store and extract the encoding or decoding from this variable.
710          */
711         protected int ibitWorkArea;
712 
713         /**
714          * Place holder for the bytes we're dealing with for our based logic.
715          * Bitwise operations store and extract the encoding or decoding from this variable.
716          */
717         protected long lbitWorkArea;
718 
719         /**
720          * Buffer for streaming.
721          */
722         protected byte[] buffer;
723 
724         /**
725          * Position where next character should be written in the buffer.
726          */
727         protected int pos;
728 
729         /**
730          * Position where next character should be read from the buffer.
731          */
732         protected int readPos;
733 
734         /**
735          * Boolean flag to indicate the EOF has been reached. Once EOF has been reached, this object becomes useless,
736          * and must be thrown away.
737          */
738         protected boolean eof;
739 
740         /**
741          * Variable tracks how many characters have been written to the current line. Only used when encoding. We use
742          * it to make sure each encoded line never goes beyond lineLength (if lineLength &gt; 0).
743          */
744         protected int currentLinePos;
745 
746         /**
747          * Writes to the buffer only occur after every 3/5 reads when encoding, and every 4/8 reads when decoding. This
748          * variable helps track that.
749          */
750         protected int modulus;
751 
752         /**
753          * Returns a String useful for debugging (especially within a debugger.)
754          *
755          * @return a String useful for debugging.
756          */
757         @SuppressWarnings("boxing") // OK to ignore boxing here
758         @Override
759         public String toString() {
760             return String.format(
761                 "%s[buffer=%s, currentLinePos=%s, eof=%s, ibitWorkArea=%s, lbitWorkArea=%s, modulus=%s, pos=%s, readPos=%s]",
762                 this.getClass().getSimpleName(),
763                 Arrays.toString(this.buffer),
764                 this.currentLinePos,
765                 this.eof,
766                 this.ibitWorkArea,
767                 this.lbitWorkArea,
768                 this.modulus,
769                 this.pos,
770                 this.readPos
771             );
772         }
773     }
774 }
775