| # |
| # Copyright (c) 2023 Project CHIP Authors |
| # |
| # Licensed under the Apache License, Version 2.0 (the 'License'); |
| # you may not use this file except in compliance with the License. |
| # You may obtain a copy of the License at |
| # |
| # http://www.apache.org/licenses/LICENSE-2.0 |
| # |
| # Unless required by applicable law or agreed to in writing, software |
| # distributed under the License is distributed on an 'AS IS' BASIS, |
| # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| # See the License for the specific language governing permissions and |
| # limitations under the License. |
| |
| import unicodedata |
| from typing import List |
| |
| _COMMENT_CHARACTER = '#' |
| _VALUE_SEPARATOR = '=' |
| _VALUE_DISABLED = '0' |
| _VALUE_ENABLED = '1' |
| _CONTROL_CHARACTER_IDENTIFIER = 'C' |
| |
| |
| class InvalidPICSConfigurationError(Exception): |
| "Raised when the configured pics entry can not be parsed." |
| pass |
| |
| |
| class InvalidPICSConfigurationValueError(Exception): |
| "Raised when the configured pics value is not an authorized value." |
| pass |
| |
| |
| class InvalidPICSParsingError(Exception): |
| "Raised when a parsing error occured." |
| pass |
| |
| |
| class PICSChecker(): |
| """Class to compute a PICS expression""" |
| |
| def __init__(self, pics_file: str): |
| self.__pics = {} |
| self.__expression_index = 0 |
| |
| if pics_file is not None: |
| self.__pics = self.__parse(pics_file) |
| |
| def check(self, pics) -> bool: |
| if pics is None: |
| return True |
| |
| self.__expression_index = 0 |
| tokens = self.__tokenize(pics) |
| return self.__evaluate_expression(tokens, self.__pics) |
| |
| def __parse(self, pics_file: str): |
| pics = {} |
| with open(pics_file) as f: |
| line = f.readline() |
| while line: |
| preprocessed_line = self.__preprocess_input(line) |
| if preprocessed_line: |
| items = preprocessed_line.split(_VALUE_SEPARATOR) |
| # There should always be one key and one value, nothing else. |
| if len(items) != 2: |
| raise InvalidPICSConfigurationError( |
| f'Invalid expression: {line}') |
| |
| key, value = items |
| if value != _VALUE_DISABLED and value != _VALUE_ENABLED: |
| raise InvalidPICSConfigurationValueError( |
| f'Invalid expression: {line}') |
| |
| pics[key] = value == _VALUE_ENABLED |
| |
| line = f.readline() |
| return pics |
| |
| def __evaluate_expression(self, tokens: List[str], pics: dict): |
| leftExpr = self.__evaluate_sub_expression(tokens, pics) |
| if self.__expression_index >= len(tokens): |
| return leftExpr |
| |
| token = tokens[self.__expression_index] |
| |
| if token == ')': |
| return leftExpr |
| |
| token = tokens[self.__expression_index] |
| |
| if token == '&&': |
| self.__expression_index += 1 |
| rightExpr = self.__evaluate_expression(tokens, pics) |
| return leftExpr and rightExpr |
| |
| if token == '||': |
| self.__expression_index += 1 |
| rightExpr = self.__evaluate_expression(tokens, pics) |
| return leftExpr or rightExpr |
| |
| raise InvalidPICSParsingError(f'Unknown token: {token}') |
| |
| def __evaluate_sub_expression(self, tokens: List[str], pics: dict): |
| token = tokens[self.__expression_index] |
| if token == '(': |
| self.__expression_index += 1 |
| expr = self.__evaluate_expression(tokens, pics) |
| if tokens[self.__expression_index] != ')': |
| raise KeyError('Missing ")"') |
| |
| self.__expression_index += 1 |
| return expr |
| |
| if token == '!': |
| self.__expression_index += 1 |
| expr = self.__evaluate_sub_expression(tokens, pics) |
| return not expr |
| |
| token = self.__normalize(token) |
| self.__expression_index += 1 |
| |
| if pics.get(token) is None: |
| # By default, let's consider that if a PICS item is not defined, it is |false|. |
| # It allows to create a file that only contains enabled features. |
| return False |
| |
| return pics.get(token) |
| |
| def __tokenize(self, expression: str): |
| token = '' |
| tokens = [] |
| |
| for c in expression: |
| if c == ' ' or c == '\t' or c == '\n': |
| pass |
| elif c == '(' or c == ')' or c == '!': |
| if token: |
| tokens.append(token) |
| token = '' |
| tokens.append(c) |
| elif c == '&' or c == '|': |
| if token and token[-1] == c: |
| token = token[:-1] |
| if token: |
| tokens.append(token) |
| token = '' |
| tokens.append(c + c) |
| else: |
| token += c |
| else: |
| token += c |
| |
| if token: |
| tokens.append(token) |
| token = '' |
| |
| return tokens |
| |
| def __preprocess_input(self, value: str): |
| value = self.__remove_comments(value) |
| value = self.__remove_control_characters(value) |
| value = self.__remove_whitespaces(value) |
| value = self.__make_lowercase(value) |
| return value |
| |
| def __remove_comments(self, value: str) -> str: |
| return value if not value else value.split(_COMMENT_CHARACTER, 1)[0] |
| |
| def __remove_control_characters(self, value: str) -> str: |
| return ''.join(c for c in value if unicodedata.category(c)[0] != _CONTROL_CHARACTER_IDENTIFIER) |
| |
| def __remove_whitespaces(self, value: str) -> str: |
| return value.replace(' ', '') |
| |
| def __make_lowercase(self, value: str) -> str: |
| return value.lower() |
| |
| def __normalize(self, token: str): |
| # Convert to all-lowercase so people who mess up cases don't have things |
| # break on them in subtle ways. |
| token = self.__make_lowercase(token) |
| |
| # TODO strip off "(Additional Context)" bits from the end of the code. |
| return token |