void dumpBytes(const unsigned char * data, int len, char *outBuf) {
    sprintf(outBuf, "%d bytes:\n", len);
    char * tmp=outBuf + strlen(outBuf);
    for (int j=0; j<len; j++) {
        if (j % 16 == 0) {
            sprintf(tmp, "%04X:", j);
            tmp+=5;
        }
        sprintf(tmp, " %02X", data[j]);
        tmp += 3;
        if (j % 8 == 7)
            *tmp++ = ' ';
        if (j % 16 == 15 || j == len - 1) {
            *tmp++ = ' ';
            for (int k = j - j % 16; k <= j; k++) {
                *tmp++ = (data[k] <= 32 ? '.' : data[k]);
                if (k % 16 == 7)
                    *tmp++ = ' ';
            }
            *tmp++ = '\n';
        }
    }
    *tmp++ = '\n';
    *tmp++ = 0;
}