python_psuedo_code.py

def get_memento_url(input_url, memento_datetime):
    """
        Given an original URL and a target datetime,
        recursively search for the appropriate Memento URL.
    """

    global original_url
    is_timegate = False

    # START
    # HEAD URI-Q with Accept-Datetime value
    # Go to TEST-0
    response = get_headers(input_url,
		headers={'Accept-Datetime':memento_datetime})

    # FOLLOW
    # URI-Q = Location (value of HTTP header)
    # Go to START
    def follow():
        return get_memento_url(response.headers['Location'], memento_datetime)

    # TEST-0
    # IF the response from URI-Q contains "Vary: accept-datetime"
    #    SET TG-FLAG=TRUE
    #    SET URI-R=URI-Q
    # Go to TEST-1
    if 'accept-datetime' in response.headers['Vary']:
	is_timegate=True
	original_url = input_url

    # TEST-1
    # Is URI-Q a Memento?
    #         YES =>
    #                 TG-FLAG=FALSE
    #                 SET URI-R=blank
    #                 Is the response from URI-Q a 3XX?
    #                        YES => Go to FOLLOW
    #                        NO   => STOP SUCCESS
    #         NO => Go to TEST-2
    if 'Memento-Datetime' in response.headers:
	is_timegate = False
	original_url = None
	if response.response_code.startswith('3'):
	    return follow()
	else:
	    return input_url

    # TEST-2 (the poor man's version)
    # Is the response from URI-Q a 3XX?
    #         YES => Go to FOLLOW
    #         NO   => Go to TEST-3
    if response.response_code.startswith('3'):
	return follow()

    # TEST-2 (the rich man's version)
    # Is the response from URI-Q a 3XX?
    #         YES =>
    #                 Is TG-FLAG=TRUE?
    #                         YES => Go to FOLLOW
    #                         NO   => CASE O1 302 O2. How does the
					user agent handle this?
    #         NO => Go to TEST-3
    if response.response_code.startswith('3'):
	if is_timegate:
	    return follow()
	else:
	    raise NotImplementedError()

    # TEST-3
    # Is TG-FLAG=TRUE AND Is the response from URI-Q a 4XX or 5XX?
    #         YES => CASE TimeGate or Memento error. How does the user
			agent handle this?
    #         NO   => Go to TEST-4
    if is_timegate and (response.response_code.startswith('4') or
		response.response_code.startswith('5')):
	# TimeGate or Memento error
	raise HttpError()

    # TEST-4
    # Does the response from URI-Q have a "timegate" link pointing at URI-G?
    #    SET TG-FLAG=TRUE
    #    SET URI-R=URI-Q
    #    YES => SET URI-Q=URI-G
    #    NO   => SET URI-Q=URI of the user agent's preferred TimeGate
    #    Go to START
    is_timegate = True
    original_url = input_url
    new_input_url = response.links.get('timegate', DEFAULT_TIMEGATE+input_url)
    return get_memento_url(new_input_url, memento_datetime)