HexUtil.java

/*
 * Copyright (c) 2016 OBiBa. All rights reserved.
 *
 * This program and the accompanying materials
 * are made available under the terms of the GNU Public License v3.0.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package org.obiba.core.util;

/**
 * Copied from http://www.koders.com/java/fid03708253E2C24FCEF72C90AE2948739B84F7026F.aspx
 */
@SuppressWarnings({ "UnusedDeclaration", "MagicNumber" })
final public class HexUtil {

  private HexUtil() {
  }

  /**
   * Converts a byte array into a string of upper case hex chars.
   *
   * @param bs A byte array
   * @param off The index of the first byte to read
   * @param length The number of bytes to read.
   * @return the string of hex chars.
   */
  public static String bytesToHex(byte[] bs, int off, int length) {
    StringBuffer sb = new StringBuffer(length * 2);
    bytesToHexAppend(bs, off, length, sb);
    return sb.toString();
  }

  public static void bytesToHexAppend(byte[] bs, int off, int length, StringBuffer sb) {
    sb.ensureCapacity(sb.length() + length * 2);
    for(int i = off; i < off + length && i < bs.length; i++) {
      sb.append(Character.forDigit(bs[i] >>> 4 & 0xf, 16));
      sb.append(Character.forDigit(bs[i] & 0xf, 16));
    }
  }

  public static String bytesToHex(byte... bs) {
    return bytesToHex(bs, 0, bs.length);
  }

  public static byte[] hexToBytes(String s) {
    return hexToBytes(s, 0);
  }

  public static byte[] hexToBytes(String s, int off) {
    byte[] bs = new byte[off + (1 + s.length()) / 2];
    hexToBytes(s, bs, off);
    return bs;
  }

  /**
   * Converts a String of hex characters into an array of bytes.
   *
   * @param s A string of hex characters (upper case or lower) of even length.
   * @param out A byte array of length at least s.length()/2 + off
   * @param off The first byte to write of the array
   */
  public static void hexToBytes(String s, byte[] out, int off) throws NumberFormatException, IndexOutOfBoundsException {
    int slen = s.length();
    String filledString = s;
    if(slen % 2 != 0) {
      filledString = '0' + s;
    }

    if(out.length < off + slen / 2) {
      throw new IndexOutOfBoundsException(
          "Output buffer too small for input (" + out.length + "<" + (off + slen / 2) + ")");
    }

    // Safe to assume the string is even length
    byte b1, b2;
    for(int i = 0; i < slen; i += 2) {
      b1 = (byte) Character.digit(filledString.charAt(i), 16);
      b2 = (byte) Character.digit(filledString.charAt(i + 1), 16);
      if(b1 < 0 || b2 < 0) {
        throw new NumberFormatException();
      }
      out[off + i / 2] = (byte) (b1 << 4 | b2);
    }
  }

}