def parse_cachecontrol(header):
    """Parse Cache-Control header

    https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9

    >>> parse_cachecontrol(b'public, max-age=3600') == {b'public': None,
    ...                                                 b'max-age': b'3600'}
    True
    >>> parse_cachecontrol(b'') == {}
    True

    """
    directives = {}
    for directive in header.split(b','):
        key, sep, val = directive.strip().partition(b'=')
        if key:
            directives[key.lower()] = val if sep else None
    return directives