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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.codec.binary;

import org.apache.commons.codec.CodecPolicy;

/**
 * Provides Base16 encoding and decoding.
 *
 * 

* This class is thread-safe. *

*

* This implementation strictly follows RFC 4648, and as such unlike * the {@link Base32} and {@link Base64} implementations, * it does not ignore invalid alphabet characters or whitespace, * neither does it offer chunking or padding characters. *

*

* The only additional feature above those specified in RFC 4648 * is support for working with a lower-case alphabet in addition * to the default upper-case alphabet. *

* * @see RFC 4648 - 8. Base 16 Encoding * * @since 1.15 */ public class Base16 extends BaseNCodec { /** * BASE16 characters are 4 bits in length. * They are formed by taking an 8-bit group, * which is converted into two BASE16 characters. */ private static final int BITS_PER_ENCODED_BYTE = 4; private static final int BYTES_PER_ENCODED_BLOCK = 2; private static final int BYTES_PER_UNENCODED_BLOCK = 1; /** * This array is a lookup table that translates Unicode characters drawn from the "Base16 Alphabet" (as specified * in Table 5 of RFC 4648) into their 4-bit positive integer equivalents. Characters that are not in the Base16 * alphabet but fall within the bounds of the array are translated to -1. */ private static final byte[] UPPER_CASE_DECODE_TABLE = { // 0 1 2 3 4 5 6 7 8 9 A B C D E F -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 00-0f -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 10-1f -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 20-2f 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, -1, -1, -1, -1, -1, -1, // 30-3f 0-9 -1, 10, 11, 12, 13, 14, 15 // 40-46 A-F }; /** * This array is a lookup table that translates 4-bit positive integer index values into their "Base16 Alphabet" * equivalents as specified in Table 5 of RFC 4648. */ private static final byte[] UPPER_CASE_ENCODE_TABLE = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' }; /** * This array is a lookup table that translates Unicode characters drawn from the a lower-case "Base16 Alphabet" * into their 4-bit positive integer equivalents. Characters that are not in the Base16 * alphabet but fall within the bounds of the array are translated to -1. */ private static final byte[] LOWER_CASE_DECODE_TABLE = { // 0 1 2 3 4 5 6 7 8 9 A B C D E F -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 00-0f -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 10-1f -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 20-2f 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, -1, -1, -1, -1, -1, -1, // 30-3f 0-9 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 40-4f -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 50-5f -1, 10, 11, 12, 13, 14, 15 // 60-66 a-f }; /** * This array is a lookup table that translates 4-bit positive integer index values into their "Base16 Alphabet" * lower-case equivalents. */ private static final byte[] LOWER_CASE_ENCODE_TABLE = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' }; /** Mask used to extract 4 bits, used when decoding character. */ private static final int MASK_4BITS = 0x0f; /** * Decode table to use. */ private final byte[] decodeTable; /** * Encode table to use. */ private final byte[] encodeTable; /** * Creates a Base16 codec used for decoding and encoding. */ public Base16() { this(false); } /** * Creates a Base16 codec used for decoding and encoding. * * @param lowerCase if {@code true} then use a lower-case Base16 alphabet. */ public Base16(final boolean lowerCase) { this(lowerCase, DECODING_POLICY_DEFAULT); } /** * Creates a Base16 codec used for decoding and encoding. * * @param lowerCase if {@code true} then use a lower-case Base16 alphabet. * @param decodingPolicy Decoding policy. */ public Base16(final boolean lowerCase, final CodecPolicy decodingPolicy) { super(BYTES_PER_UNENCODED_BLOCK, BYTES_PER_ENCODED_BLOCK, 0, 0, PAD_DEFAULT, decodingPolicy); if (lowerCase) { this.encodeTable = LOWER_CASE_ENCODE_TABLE; this.decodeTable = LOWER_CASE_DECODE_TABLE; } else { this.encodeTable = UPPER_CASE_ENCODE_TABLE; this.decodeTable = UPPER_CASE_DECODE_TABLE; } } @Override void decode(final byte[] data, int offset, final int length, final Context context) { if (context.eof || length < 0) { context.eof = true; if (context.ibitWorkArea != 0) { validateTrailingCharacter(); } return; } final int dataLen = Math.min(data.length - offset, length); final int availableChars = (context.ibitWorkArea != 0 ? 1 : 0) + dataLen; // small optimisation to short-cut the rest of this method when it is fed byte-by-byte if (availableChars == 1 && availableChars == dataLen) { context.ibitWorkArea = decodeOctet(data[offset]) + 1; // store 1/2 byte for next invocation of decode, we offset by +1 as empty-value is 0 return; } // we must have an even number of chars to decode final int charsToProcess = availableChars % BYTES_PER_ENCODED_BLOCK == 0 ? availableChars : availableChars - 1; final byte[] buffer = ensureBufferSize(charsToProcess / BYTES_PER_ENCODED_BLOCK, context); int result; int i = 0; if (dataLen < availableChars) { // we have 1/2 byte from previous invocation to decode result = (context.ibitWorkArea - 1) << BITS_PER_ENCODED_BYTE; result |= decodeOctet(data[offset++]); i = 2; buffer[context.pos++] = (byte)result; // reset to empty-value for next invocation! context.ibitWorkArea = 0; } while (i < charsToProcess) { result = decodeOctet(data[offset++]) << BITS_PER_ENCODED_BYTE; result |= decodeOctet(data[offset++]); i += 2; buffer[context.pos++] = (byte)result; } // we have one char of a hex-pair left over if (i < dataLen) { context.ibitWorkArea = decodeOctet(data[i]) + 1; // store 1/2 byte for next invocation of decode, we offset by +1 as empty-value is 0 } } private int decodeOctet(final byte octet) { int decoded = -1; if ((octet & 0xff) < decodeTable.length) { decoded = decodeTable[octet]; } if (decoded == -1) { throw new IllegalArgumentException("Invalid octet in encoded value: " + (int)octet); } return decoded; } @Override void encode(final byte[] data, final int offset, final int length, final Context context) { if (context.eof) { return; } if (length < 0) { context.eof = true; return; } final int size = length * BYTES_PER_ENCODED_BLOCK; if (size < 0) { throw new IllegalArgumentException("Input length exceeds maximum size for encoded data: " + length); } final byte[] buffer = ensureBufferSize(size, context); final int end = offset + length; for (int i = offset; i < end; i++) { final int value = data[i]; final int high = (value >> BITS_PER_ENCODED_BYTE) & MASK_4BITS; final int low = value & MASK_4BITS; buffer[context.pos++] = encodeTable[high]; buffer[context.pos++] = encodeTable[low]; } } /** * Returns whether or not the {@code octet} is in the Base16 alphabet. * * @param octet The value to test. * * @return {@code true} if the value is defined in the the Base16 alphabet {@code false} otherwise. */ @Override public boolean isInAlphabet(final byte octet) { return (octet & 0xff) < decodeTable.length && decodeTable[octet] != -1; } /** * Validates whether decoding allows an entire final trailing character that cannot be * used for a complete byte. * * @throws IllegalArgumentException if strict decoding is enabled */ private void validateTrailingCharacter() { if (isStrictDecoding()) { throw new IllegalArgumentException("Strict decoding: Last encoded character is a valid base 16 alphabet" + "character but not a possible encoding. " + "Decoding requires at least two characters to create one byte."); } } }




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