import click


def split_http_header(header_string):
    """Splits a colon-separated string into header and value"""
    parts = tuple(part.strip() for part in header_string.split(":", 1))
    if len(parts) != 2 or any(part == '' for part in parts):
        msg = "Invalid header '{}'. Use colon to separate name and value".format(header_string)
        raise click.BadParameter(msg)
    return parts