DecodingUtils.java

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2013 Alexandre Normand
 *
 * 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 NONINFRINGEMENT. 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.glukit.dexcom.sync;

import com.google.common.base.Joiner;
import com.google.common.primitives.UnsignedInts;
import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.xml.bind.DatatypeConverter;
import java.util.List;

import static com.google.common.collect.Lists.newArrayList;
import static java.lang.String.format;
import static org.glukit.dexcom.sync.ResponseReader.TRAILER_SIZE;

/**
 * Some useful methods for decoding.
 *
 * @author alexandre.normand
 */
public final class DecodingUtils {
  private static Logger LOGGER = LoggerFactory.getLogger(DecodingUtils.class);

  public static final int CRC16_SIZE = 2;

  private static int[] CRC16_TABLE = new int[]{
          0, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7, 0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad,
          0xe1ce, 0xf1ef, 0x1231, 0x210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6, 0x9339, 0x8318, 0xb37b, 0xa35a,
          0xd3bd, 0xc39c, 0xf3ff, 0xe3de, 0x2462, 0x3443, 0x420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485, 0xa56a, 0xb54b,
          0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d, 0x3653, 0x2672, 0x1611, 0x630, 0x76d7, 0x66f6, 0x5695, 0x46b4,
          0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc, 0x48c4, 0x58e5, 0x6886, 0x78a7, 0x840, 0x1861,
          0x2802, 0x3823, 0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b, 0x5af5, 0x4ad4, 0x7ab7,
          0x6a96, 0x1a71, 0xa50, 0x3a33, 0x2a12, 0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
          0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0xc60, 0x1c41, 0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a,
          0xbd0b, 0x8d68, 0x9d49, 0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0xe70, 0xff9f, 0xefbe, 0xdfdd,
          0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78, 0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f,
          0x1080, 0xa1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067, 0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c,
          0xe37f, 0xf35e, 0x2b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256, 0xb5ea, 0xa5cb, 0x95a8, 0x8589,
          0xf56e, 0xe54f, 0xd52c, 0xc50d, 0x34e2, 0x24c3, 0x14a0, 0x481, 0x7466, 0x6447, 0x5424, 0x4405, 0xa7db, 0xb7fa,
          0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c, 0x26d3, 0x36f2, 0x691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
          0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab, 0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x8e1,
          0x3882, 0x28a3, 0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a, 0x4a75, 0x5a54, 0x6a37,
          0x7a16, 0xaf1, 0x1ad0, 0x2ab3, 0x3a92, 0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9, 0x7c26,
          0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0xcc1, 0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9,
          0x9ff8, 0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0xed1, 0x1ef0};

  public static int getCrc16(byte[] bytes, int offset, int length) {
    int contentSize = length - offset;
    byte[] content = new byte[contentSize];
    System.arraycopy(bytes, offset, content, 0, contentSize);

    int value = 0;
    for (byte element : content) {
      value = unsignedShort((value << 8) ^ CRC16_TABLE[((value >>> 8) ^ element) & 0xff]);
    }
    return value;
  }

  public static int unsignedShort(int value) {
    return (short) value & 0xFFFF;
  }

  public static void validateCrc(int receiverCrc, byte[] content) {
    LOGGER.debug(format("Validating that [%s] matches crc value [%s]", toHexString(content),
            UnsignedInts.toString(receiverCrc)));

    int expectedCrc = DecodingUtils.getCrc16(content, 0, content.length - TRAILER_SIZE);

    if (receiverCrc != expectedCrc) {
      throw new IllegalStateException(format("Invalid crc, expected [%s], received [%s]",
              UnsignedInts.toString(expectedCrc), UnsignedInts.toString((receiverCrc))));
    }
  }

  /**
   * Takes a string like 0A 0F 05 and converts it into a byte array.
   *
   * @param hexString hex string, can contain spaces
   * @return the byte array
   */
  public static byte[] fromHexString(String hexString) {
    String hexStringWithoutSpaces = StringUtils.remove(hexString, " ");
    return DatatypeConverter.parseHexBinary(hexStringWithoutSpaces);
  }

  /**
   * Prints a space delimited hex string of a byte array.
   *
   * @param value the bytes
   * @return the hex string such as "01 01" for a byte array of two elements ([1 1]).
   */
  public static String toHexString(byte[] value) {
    List<String> hexChars = newArrayList();

    for (byte element : value) {
      hexChars.add(String.format("%02x", element));
    }

    return Joiner.on(" ").join(hexChars);
  }
}