Function parse_list

src/websockets/headers.py:165–228

Parse a comma-separated list from ``header`` at the given position. This is appropriate for parsing values with the following grammar: 1#item ``parse_item`` parses one item. ``header`` is assumed not to start or end with whitespace. (This function is designed for pa

(
    parse_item: Callable[[str, int, str], tuple[T, int]],
    header: str,
    pos: int,
    header_name: str,
)

def parse_list(
    parse_item: Callable[[str, int, str], tuple[T, int]],
    header: str,
    pos: int,
    header_name: str,
) -> list[T]:
    """
    Parse a comma-separated list from ``header`` at the given position.

    This is appropriate for parsing values with the following grammar:

        1#item

    ``parse_item`` parses one item.

    ``header`` is assumed not to start or end with whitespace.

    (This function is designed for parsing an entire header value and
    :func:`~websockets.http.read_headers` strips whitespace from values.)

    Return a list of items.

    Raises:
        InvalidHeaderFormat: On invalid inputs.

    """
    # Per https://datatracker.ietf.org/doc/html/rfc7230#section-7, "a recipient
    # MUST parse and ignore a reasonable number of empty list elements";
    # hence while loops that remove extra delimiters.

    # Remove extra delimiters before the first item.
    while peek_ahead(header, pos) == ",":
        pos = parse_OWS(header, pos + 1)

    items = []
    while True:
        # Loop invariant: a item starts at pos in header.
        item, pos = parse_item(header, pos, header_name)
        items.append(item)
        pos = parse_OWS(header, pos)

        # We may have reached the end of the header.
        if pos == len(header):
            break

        # There must be a delimiter after each element except the last one.
        if peek_ahead(header, pos) == ",":
            pos = parse_OWS(header, pos + 1)
        else:
            raise InvalidHeaderFormat(header_name, "expected comma", header, pos)

        # Remove extra delimiters before the next item.
        while peek_ahead(header, pos) == ",":
            pos = parse_OWS(header, pos + 1)

        # We may have reached the end of the header.
        if pos == len(header):
            break