CcHex.java

/**
 * The MIT License (MIT)
 *
 * Copyright (c) 2014-2017 Yegor Bugayenko
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package org.takes.facets.auth.codecs;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import lombok.EqualsAndHashCode;
import org.takes.facets.auth.Identity;

/**
 * Hex codec.
 *
 * <p>The class is immutable and thread-safe.
 *
 * @author Yegor Bugayenko (yegor256@gmail.com)
 * @version $Id: 4e4de91cfa8aaef9755f908c86d2bc09d5f70f06 $
 * @since 0.1
 */
@EqualsAndHashCode
public final class CcHex implements Codec {

    /**
     * Length of chunk.
     */
    private static final int CHUNK = 4;

    /**
     * Backward mapping table.
     */
    private static final byte[] BACK = {
        -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1,
        0, 1, 2, 3, 4, 5, 6, 7,
        8, 9, -1, -1, -1, -1, -1, -1,
        -1, 0xa, 0xb, 0xc, 0xd, 0xe, 0xf,
    };

    /**
     * Forward mapping table.
     */
    private static final byte[] FWD = {
        '0', '1', '2', '3', '4', '5', '6', '7',
        '8', '9', 'A', 'B', 'C', 'D', 'E', 'F',
    };

    /**
     * Original codec.
     */
    private final Codec origin;

    /**
     * Ctor.
     * @param codec Original codec
     */
    public CcHex(final Codec codec) {
        this.origin = codec;
    }

    @Override
    public byte[] encode(final Identity identity) throws IOException {
        final byte[] raw = this.origin.encode(identity);
        final ByteArrayOutputStream out = new ByteArrayOutputStream();
        for (int idx = 0; idx < raw.length; ++idx) {
            if (idx > 0 && idx % CcHex.CHUNK == 0) {
                out.write('-');
            }
            // @checkstyle MagicNumberCheck (2 lines)
            out.write(CcHex.FWD[raw[idx] >> 4 & 0x0f]);
            out.write(CcHex.FWD[raw[idx] & 0x0f]);
        }
        return out.toByteArray();
    }

    @Override
    public Identity decode(final byte[] bytes) throws IOException {
        final ByteArrayOutputStream out = new ByteArrayOutputStream();
        int idx = 0;
        while (idx < bytes.length) {
            if (bytes[idx] == '-') {
                ++idx;
                continue;
            }
            if (idx > bytes.length - 2) {
                throw new DecodingException("not enough data");
            }
            out.write(
                // @checkstyle MagicNumberCheck (1 line)
                (CcHex.decode(bytes[idx]) << 4) + CcHex.decode(bytes[idx + 1])
            );
            idx += 2;
        }
        return this.origin.decode(out.toByteArray());
    }

    /**
     * Convert hex to number.
     * @param hex Hex number
     * @return Decoded
     */
    private static int decode(final int hex) {
        if (hex >= CcHex.BACK.length) {
            throw new DecodingException(
                String.format("invalid hex char: 0x%2x", hex)
            );
        }
        final int dec = CcHex.BACK[hex];
        if (dec < 0) {
            throw new DecodingException(
                String.format("invalid hex character: 0x%2x", hex)
            );
        }
        return dec;
    }

}