    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      https://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017
    018package org.apache.commons.codec.binary;
    019
    020import java.util.Objects;
    021
    022import org.apache.commons.codec.CodecPolicy;
    023
    024/**
    025 * Provides Base16 encoding and decoding.
    026 *
    027 * <p>
    028 * This class is thread-safe.
    029 * </p>
    030 * <p>
    031 * This implementation strictly follows RFC 4648, and as such unlike the {@link Base32} and {@link Base64} implementations, it does not ignore invalid alphabet
    032 * characters or whitespace, neither does it offer chunking or padding characters.
    033 * </p>
    034 * <p>
    035 * 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
    036 * alphabet.
    037 * </p>
    038 *
    039 * @see <a href="https://tools.ietf.org/html/rfc4648#section-8">RFC 4648 - 8. Base 16 Encoding</a>
    040 * @since 1.15
    041 */
    042public class Base16 extends BaseNCodec {
    043
    044    /**
    045     * BASE16 characters are 4 bits in length. They are formed by taking an 8-bit group, which is converted into two BASE16 characters.
    046     */
    047    private static final int BITS_PER_ENCODED_BYTE = 4;
    048    private static final int BYTES_PER_ENCODED_BLOCK = 2;
    049    private static final int BYTES_PER_UNENCODED_BLOCK = 1;
    050
    051    /**
    052     * 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
    053     * positive integer equivalents. Characters that are not in the Base16 alphabet but fall within the bounds of the array are translated to -1.
    054     */
    055    // @formatter:off
    056    private static final byte[] UPPER_CASE_DECODE_TABLE = {
    057            //  0   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
    058            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 00-0f
    059            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 10-1f
    060            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 20-2f
    061             0,  1,  2,  3,  4,  5,  6,  7,  8,  9, -1, -1, -1, -1, -1, -1, // 30-3f 0-9
    062            -1, 10, 11, 12, 13, 14, 15                                      // 40-46 A-F
    063    };
    064    // @formatter:on
    065
    066    /**
    067     * 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
    068     * 4648.
    069     */
    070    private static final byte[] UPPER_CASE_ENCODE_TABLE = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
    071
    072    /**
    073     * This array is a lookup table that translates Unicode characters drawn from the a lower-case "Base16 Alphabet" into their 4-bit positive integer
    074     * equivalents. Characters that are not in the Base16 alphabet but fall within the bounds of the array are translated to -1.
    075     */
    076    // @formatter:off
    077    private static final byte[] LOWER_CASE_DECODE_TABLE = {
    078            //  0   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
    079            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 00-0f
    080            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 10-1f
    081            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 20-2f
    082             0,  1,  2,  3,  4,  5,  6,  7,  8,  9, -1, -1, -1, -1, -1, -1, // 30-3f 0-9
    083            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 40-4f
    084            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 50-5f
    085            -1, 10, 11, 12, 13, 14, 15                                      // 60-66 a-f
    086    };
    087    // @formatter:on
    088
    089    /**
    090     * This array is a lookup table that translates 4-bit positive integer index values into their "Base16 Alphabet" lower-case equivalents.
    091     */
    092    private static final byte[] LOWER_CASE_ENCODE_TABLE = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
    093
    094    /** Mask used to extract 4 bits, used when decoding character. */
    095    private static final int MASK_4BITS = 0x0f;
    096
    097    /**
    098     * Decode table to use.
    099     */
    100    private final byte[] decodeTable;
    101
    102    /**
    103     * Encode table to use.
    104     */
    105    private final byte[] encodeTable;
    106
    107    /**
    108     * Constructs a Base16 codec used for decoding and encoding.
    109     */
    110    public Base16() {
    111        this(false);
    112    }
    113
    114    /**
    115     * Constructs a Base16 codec used for decoding and encoding.
    116     *
    117     * @param lowerCase if {@code true} then use a lower-case Base16 alphabet.
    118     */
    119    public Base16(final boolean lowerCase) {
    120        this(lowerCase, DECODING_POLICY_DEFAULT);
    121    }
    122
    123    /**
    124     * Constructs a Base16 codec used for decoding and encoding.
    125     *
    126     * @param lowerCase      if {@code true} then use a lower-case Base16 alphabet.
    127     * @param encodeTable    the encode table.
    128     * @param decodingPolicy Decoding policy.
    129     */
    130    private Base16(final boolean lowerCase, final byte[] encodeTable, final CodecPolicy decodingPolicy) {
    131        super(BYTES_PER_UNENCODED_BLOCK, BYTES_PER_ENCODED_BLOCK, 0, 0, PAD_DEFAULT, decodingPolicy);
    132        Objects.requireNonNull(encodeTable, "encodeTable");
    133        this.encodeTable = encodeTable;
    134        this.decodeTable = encodeTable == LOWER_CASE_ENCODE_TABLE ? LOWER_CASE_DECODE_TABLE : UPPER_CASE_DECODE_TABLE;
    135    }
    136
    137    /**
    138     * Constructs a Base16 codec used for decoding and encoding.
    139     *
    140     * @param lowerCase      if {@code true} then use a lower-case Base16 alphabet.
    141     * @param decodingPolicy Decoding policy.
    142     */
    143    public Base16(final boolean lowerCase, final CodecPolicy decodingPolicy) {
    144        this(lowerCase, lowerCase ? LOWER_CASE_ENCODE_TABLE : UPPER_CASE_ENCODE_TABLE, decodingPolicy);
    145    }
    146
    147    @Override
    148    void decode(final byte[] data, int offset, final int length, final Context context) {
    149        if (context.eof || length < 0) {
    150            context.eof = true;
    151            if (context.ibitWorkArea != 0) {
    152                validateTrailingCharacter();
    153            }
    154            return;
    155        }
    156        final int dataLen = Math.min(data.length - offset, length);
    157        final int availableChars = (context.ibitWorkArea != 0 ? 1 : 0) + dataLen;
    158        // small optimization to short-cut the rest of this method when it is fed byte-by-byte
    159        if (availableChars == 1 && availableChars == dataLen) {
    160            // store 1/2 byte for next invocation of decode, we offset by +1 as empty-value is 0
    161            context.ibitWorkArea = decodeOctet(data[offset]) + 1;
    162            return;
    163        }
    164        // we must have an even number of chars to decode
    165        final int charsToProcess = availableChars % BYTES_PER_ENCODED_BLOCK == 0 ? availableChars : availableChars - 1;
    166        final int end = offset + dataLen;
    167        final byte[] buffer = ensureBufferSize(charsToProcess / BYTES_PER_ENCODED_BLOCK, context);
    168        int result;
    169        if (dataLen < availableChars) {
    170            // we have 1/2 byte from previous invocation to decode
    171            result = context.ibitWorkArea - 1 << BITS_PER_ENCODED_BYTE;
    172            result |= decodeOctet(data[offset++]);
    173            buffer[context.pos++] = (byte) result;
    174            // reset to empty-value for next invocation!
    175            context.ibitWorkArea = 0;
    176        }
    177        final int loopEnd = end - 1;
    178        while (offset < loopEnd) {
    179            result = decodeOctet(data[offset++]) << BITS_PER_ENCODED_BYTE;
    180            result |= decodeOctet(data[offset++]);
    181            buffer[context.pos++] = (byte) result;
    182        }
    183        // we have one char of a hex-pair left over
    184        if (offset < end) {
    185            // store 1/2 byte for next invocation of decode, we offset by +1 as empty-value is 0
    186            context.ibitWorkArea = decodeOctet(data[offset]) + 1;
    187        }
    188    }
    189
    190    private int decodeOctet(final byte octet) {
    191        int decoded = -1;
    192        if ((octet & 0xff) < decodeTable.length) {
    193            decoded = decodeTable[octet];
    194        }
    195        if (decoded == -1) {
    196            throw new IllegalArgumentException("Invalid octet in encoded value: " + (int) octet);
    197        }
    198        return decoded;
    199    }
    200
    201    @Override
    202    void encode(final byte[] data, final int offset, final int length, final Context context) {
    203        if (context.eof) {
    204            return;
    205        }
    206        if (length < 0) {
    207            context.eof = true;
    208            return;
    209        }
    210        final int size = length * BYTES_PER_ENCODED_BLOCK;
    211        if (size < 0) {
    212            throw new IllegalArgumentException("Input length exceeds maximum size for encoded data: " + length);
    213        }
    214        final byte[] buffer = ensureBufferSize(size, context);
    215        final int end = offset + length;
    216        for (int i = offset; i < end; i++) {
    217            final int value = data[i];
    218            final int high = value >> BITS_PER_ENCODED_BYTE & MASK_4BITS;
    219            final int low = value & MASK_4BITS;
    220            buffer[context.pos++] = encodeTable[high];
    221            buffer[context.pos++] = encodeTable[low];
    222        }
    223    }
    224
    225    /**
    226     * Returns whether or not the {@code octet} is in the Base16 alphabet.
    227     *
    228     * @param octet The value to test.
    229     * @return {@code true} if the value is defined in the Base16 alphabet {@code false} otherwise.
    230     */
    231    @Override
    232    public boolean isInAlphabet(final byte octet) {
    233        return (octet & 0xff) < decodeTable.length && decodeTable[octet] != -1;
    234    }
    235
    236    /**
    237     * Validates whether decoding allows an entire final trailing character that cannot be used for a complete byte.
    238     *
    239     * @throws IllegalArgumentException if strict decoding is enabled
    240     */
    241    private void validateTrailingCharacter() {
    242        if (isStrictDecoding()) {
    243            throw new IllegalArgumentException("Strict decoding: Last encoded character is a valid base 16 alphabet character but not a possible encoding. " +
    244                    "Decoding requires at least two characters to create one byte.");
    245        }
    246    }
    247}