samcli/local/apigw/path_converter.py

"""
Converter class that handles the conversion of paths from Api Gateway to Flask and back.
"""

import re

# The regex captures any path information before the {proxy+}. This is to support paths that have other params in
# them. Otherwise the regex will match the first { with the last +} giving incorrect results.
# Example: /id/{id}/user/{proxy+}. g<1> = '/id/{id}/user/' g<2> = 'proxy'
PROXY_PATH_PARAMS_ESCAPED = r"(.*/){(.*)\+}"

# The regex replaces what was captured with PROXY_PATH_PARAMS_ESCAPED to construct the full path with the {proxy+}
# replaces. The first group is anything before {proxy+}, while the second group is the name given to the proxy.
# Example: /id/{id}/user/{resource+}; g<1> = '/id/{id}/user/'; g<2> = 'resource'
FLASK_CAPTURE_ALL_PATH = r"\g<1><path:\g<2>>"

# The regex will replace the first group from FLASK_CAPTURE_ALL_PATH_REGEX into the proxy name part of the APIGW path.
# Example: /<path:resource>; g<1> = 'resource'; output = /{resource+}
PROXY_PATH_PARAMS = r"/{\g<1>+}"

# The regex will capture the name of the path for the APIGW Proxy path.
# Example: /<path:resource> is equivalent to the APIGW path /{resource+}
FLASK_CAPTURE_ALL_PATH_REGEX = r"/<path:(.*)>"

LEFT_BRACKET = "{"
RIGHT_BRACKET = "}"
LEFT_ANGLE_BRACKET = "<"
RIGHT_ANGLE_BRACKET = ">"

APIGW_TO_FLASK_REGEX = re.compile(PROXY_PATH_PARAMS_ESCAPED)
FLASK_TO_APIGW_REGEX = re.compile(FLASK_CAPTURE_ALL_PATH_REGEX)


class PathConverter:
    @staticmethod
    def convert_path_to_flask(path):
        """
        Converts a Path from an Api Gateway defined path to one that is accepted by Flask

        Examples:

        '/id/{id}' => '/id/<id>'
        '/{proxy+}' => '/<path:proxy>'

        :param str path: Path to convert to Flask defined path
        :return str: Path representing a Flask path
        """
        proxy_sub_path = APIGW_TO_FLASK_REGEX.sub(FLASK_CAPTURE_ALL_PATH, path)

        # Replace the '{' and '}' with '<' and '>' respectively
        return proxy_sub_path.replace(LEFT_BRACKET, LEFT_ANGLE_BRACKET).replace(RIGHT_BRACKET, RIGHT_ANGLE_BRACKET)

    @staticmethod
    def convert_path_to_api_gateway(path):
        """
        Converts a Path from a Flask defined path to one that is accepted by Api Gateway

        Examples:

        '/id/<id>' => '/id/{id}'
        '/<path:proxy>' => '/{proxy+}'

        :param str path: Path to convert to Api Gateway defined path
        :return str: Path representing an Api Gateway path
        """
        proxy_sub_path = FLASK_TO_APIGW_REGEX.sub(PROXY_PATH_PARAMS, path)

        # Replace the '<' and '>' with '{' and '}' respectively
        return proxy_sub_path.replace(LEFT_ANGLE_BRACKET, LEFT_BRACKET).replace(RIGHT_ANGLE_BRACKET, RIGHT_BRACKET)