get the (md5 hexdigest, md5 digest) of a file

def file_md5(fname):
    """ get the (md5 hexdigest, md5 digest) of a file """
    from dvc.progress import progress
    from dvc.istextfile import istextfile

    if os.path.exists(fname):
        hash_md5 = hashlib.md5()
        binary = not istextfile(fname)
        size = os.path.getsize(fname)
        bar = False
        if size >= LARGE_FILE_SIZE:
            bar = True
            msg = "Computing md5 for a large file {}. This is only done once."
            logger.info(msg.format(os.path.relpath(fname)))
            name = os.path.relpath(fname)
            total = 0

        with open(fname, "rb") as fobj:
            while True:
                data = fobj.read(LOCAL_CHUNK_SIZE)
                if not data:
                    break

                if bar:
                    total += len(data)
                    progress.update_target(name, total, size)

                if binary:
                    chunk = data
                else:
                    chunk = dos2unix(data)

                hash_md5.update(chunk)

        if bar:
            progress.finish_target(name)

        return (hash_md5.hexdigest(), hash_md5.digest())
    else:
        return (None, None)