def METHOD_NAME(search_string, default_fields):
    """
    All input defaults to doing an infix search for each term.
    (This may later change to some kind of fuzzy matching).
    This is also available via the main ESQuery class.
    """
    if not search_string:
        return match_all()
    # Parse user input into individual search terms
    r = re.compile(r'\w+')
    tokens = r.findall(search_string)
    query_string = "*{}*".format("* *".join(tokens))
    # TODO: add support for searching date ranges.
    return {
        "query_string": {
            "query": query_string,
            "default_operator": "AND",
            "fields": default_fields,
        }
    }