import re import sys from moto.dynamodb2.exceptions import ( InvalidTokenException, InvalidExpressionAttributeNameKey, ) class Token(object): _TOKEN_INSTANCE = None MINUS_SIGN = "-" PLUS_SIGN = "+" SPACE_SIGN = " " EQUAL_SIGN = "=" OPEN_ROUND_BRACKET = "(" CLOSE_ROUND_BRACKET = ")" COMMA = "," SPACE = " " DOT = "." OPEN_SQUARE_BRACKET = "[" CLOSE_SQUARE_BRACKET = "]" SPECIAL_CHARACTERS = [ MINUS_SIGN, PLUS_SIGN, SPACE_SIGN, EQUAL_SIGN, OPEN_ROUND_BRACKET, CLOSE_ROUND_BRACKET, COMMA, SPACE, DOT, OPEN_SQUARE_BRACKET, CLOSE_SQUARE_BRACKET, ] # Attribute: an identifier that is an attribute ATTRIBUTE = 0 # Place holder for attribute name ATTRIBUTE_NAME = 1 # Placeholder for attribute value starts with : ATTRIBUTE_VALUE = 2 # WhiteSpace shall be grouped together WHITESPACE = 3 # Placeholder for a number NUMBER = 4 PLACEHOLDER_NAMES = { ATTRIBUTE: "Attribute", ATTRIBUTE_NAME: "AttributeName", ATTRIBUTE_VALUE: "AttributeValue", WHITESPACE: "Whitespace", NUMBER: "Number", } def __init__(self, token_type, value): assert ( token_type in self.SPECIAL_CHARACTERS or token_type in self.PLACEHOLDER_NAMES ) self.type = token_type self.value = value def __repr__(self): if isinstance(self.type, int): return 'Token("{tt}", "{tv}")'.format( tt=self.PLACEHOLDER_NAMES[self.type], tv=self.value ) else: return 'Token("{tt}", "{tv}")'.format(tt=self.type, tv=self.value) def __eq__(self, other): return self.type == other.type and self.value == other.value class ExpressionTokenizer(object): """ Takes a string and returns a list of tokens. While attribute names in DynamoDB must be between 1 and 255 characters long there are no other restrictions for attribute names. For expressions however there are additional rules. If an attribute name does not adhere then it must be passed via an ExpressionAttributeName. This tokenizer is aware of the rules of Expression attributes. We consider a Token as a tuple which has the tokenType From https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.ExpressionAttributeNames.html 1) If an attribute name begins with a number or contains a space, a special character, or a reserved word, you must use an expression attribute name to replace that attribute's name in the expression. => So spaces,+,- or other special characters do identify tokens in update expressions 2) When using a dot (.) in an attribute name you must use expression-attribute-names. A dot in an expression will be interpreted as a separator in a document path 3) For a nested structure if you want to use expression_attribute_names you must specify one per part of the path. Since for members of expression_attribute_names the . is part of the name """ @classmethod def is_simple_token_character(cls, character): return character.isalnum() or character in ("_", ":", "#") @classmethod def is_possible_token_boundary(cls, character): return ( character in Token.SPECIAL_CHARACTERS or not cls.is_simple_token_character(character) ) @classmethod def is_expression_attribute(cls, input_string): return re.compile("^[a-zA-Z0-9][a-zA-Z0-9_]*$").match(input_string) is not None @classmethod def is_expression_attribute_name(cls, input_string): """ https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.ExpressionAttributeNames.html An expression attribute name must begin with a pound sign (#), and be followed by one or more alphanumeric characters. """ return input_string.startswith("#") and cls.is_expression_attribute( input_string[1:] ) @classmethod def is_expression_attribute_value(cls, input_string): return re.compile("^:[a-zA-Z0-9_]*$").match(input_string) is not None def raise_unexpected_token(self): """If during parsing an unexpected token is encountered""" if len(self.token_list) == 0: near = "" else: if len(self.token_list) == 1: near = self.token_list[-1].value else: if self.token_list[-1].type == Token.WHITESPACE: # Last token was whitespace take 2nd last token value as well to help User orientate near = self.token_list[-2].value + self.token_list[-1].value else: near = self.token_list[-1].value problematic_token = self.staged_characters[0] raise InvalidTokenException(problematic_token, near + self.staged_characters) def __init__(self, input_expression_str): self.input_expression_str = input_expression_str self.token_list = [] self.staged_characters = "" @classmethod def is_py2(cls): return sys.version_info[0] == 2 @classmethod def make_list(cls, input_expression_str): if cls.is_py2(): pass else: assert isinstance(input_expression_str, str) return ExpressionTokenizer(input_expression_str)._make_list() def add_token(self, token_type, token_value): self.token_list.append(Token(token_type, token_value)) def add_token_from_stage(self, token_type): self.add_token(token_type, self.staged_characters) self.staged_characters = "" @classmethod def is_numeric(cls, input_str): return re.compile("[0-9]+").match(input_str) is not None def process_staged_characters(self): if len(self.staged_characters) == 0: return if self.staged_characters.startswith("#"): if self.is_expression_attribute_name(self.staged_characters): self.add_token_from_stage(Token.ATTRIBUTE_NAME) else: raise InvalidExpressionAttributeNameKey(self.staged_characters) elif self.is_numeric(self.staged_characters): self.add_token_from_stage(Token.NUMBER) elif self.is_expression_attribute(self.staged_characters): self.add_token_from_stage(Token.ATTRIBUTE) elif self.is_expression_attribute_value(self.staged_characters): self.add_token_from_stage(Token.ATTRIBUTE_VALUE) else: self.raise_unexpected_token() def _make_list(self): """ Just go through characters if a character is not a token boundary stage it for adding it as a grouped token later if it is a tokenboundary process staged characters and then process the token boundary as well. """ for character in self.input_expression_str: if not self.is_possible_token_boundary(character): self.staged_characters += character else: self.process_staged_characters() if character == Token.SPACE: if ( len(self.token_list) > 0 and self.token_list[-1].type == Token.WHITESPACE ): self.token_list[-1].value = ( self.token_list[-1].value + character ) else: self.add_token(Token.WHITESPACE, character) elif character in Token.SPECIAL_CHARACTERS: self.add_token(character, character) elif not self.is_simple_token_character(character): self.staged_characters += character self.raise_unexpected_token() else: raise NotImplementedError( "Encountered character which was not implemented : " + character ) self.process_staged_characters() return self.token_list