def extract_headers(event):
    """
    Returns the headers from the request

    The format is: a dict of {name: value_list} where value_list is an iterable of all header values.

    Supports regular and multivalue headers.
    """
    headers = event.get('headers') or {}
    multi_headers = (event.get('multiValueHeaders') or {}).copy()
    for h in set(headers.keys()):
        if h not in multi_headers:
            multi_headers[h] = [headers[h]]

    return multi_headers