'parse WRITE_ANDX message to extract the FID and raw bytes
return fid (file handle to be written) and the raw bytes: return fid,rawbytes)
-1 and \'\' if err'

def PARSE_WRITE_ANDX(self, data):

    try:
        (wct, andxcmd, rsrv1, andxoffset, fid, offset, rsrv2) = struct.unpack('<BBBHHII', data[:15])
        (writemode, remaining, datalenhigh, datalenlow, dataoffset) = struct.unpack('<HHHHH', data[15:25])
        (highoffset, bytecount, padding) = struct.unpack('<IHB', data[25:32])
        rawbytes = data[32:((32 + datalenlow) + (datalenhigh * 65536))]
        return (fid, rawbytes)
    except:
        return ((-1), '')
