FIT文件CRC校验

校验FIT文件CRC代码做个记录，分为两步先校验头部然后再校验整个FIT文件。校验头部不是必需的看个人需要吧。为了偷懒使用Okio库，还有计算CRC的时候用的Garmin的FitSDK。

public class FitUtils {
    /**
     * 校验Fit文件，首先校验头部然后校验数据
     *
     * @param file
     * @return
     */
    public static boolean checkFitFile(File file) {
        BufferedSource source = null;
        try {
            final int MAX_HEADER_LEN = 14;
            source = Okio.buffer(Okio.source(file));
            byte[] header = new byte[MAX_HEADER_LEN - 2];
            header[0] = source.readByte();
            int headerLen = header[0];
            if (headerLen <= 0 || headerLen > MAX_HEADER_LEN)
                return false;
            source.read(header, 1, header.length - 1); //去除头长度和crc
            //验证头部
            if (headerLen == MAX_HEADER_LEN) {
                short fileCrc16 = source.readShortLe();
                if (fileCrc16 != 0) {    //FIT允许HEADER的CRC为0
                    int crc16 = getCRC16(header, 0, header.length);
                    if (crc16 != fileCrc16)
                        return false;
                }
            }
            //校验数据
            source.close();
            source = Okio.buffer(Okio.source(file));
            int crc16ForData = 0;
            for (int crcByte = 0; crcByte < file.length() - 2; crcByte++) {
                crc16ForData = CRC.get16(crc16ForData, source.readByte());
            }
            short originCRC16 = source.readShortLe();
            return originCRC16 == (short) crc16ForData;
        } catch (IOException e) {
            if (BuildConfig.DEBUG)
                e.printStackTrace();
        } finally {
            if (source != null) {
                try {
                    source.close();
                } catch (IOException e) {
                    if (BuildConfig.DEBUG)
                        e.printStackTrace();
                }
            }
        }
        return false;
    }
    public static short getCRC16(byte[] data, int offset, int len) {
        int crc16 = 0;
        for (int index = offset; index < (offset + len); index++) {
            crc16 = CRC.get16(crc16, data[index]);
        }
        return (short) crc16;
    }
}