import re
from typing import List, Union
from moto.dynamodb.exceptions import (
InvalidExpressionAttributeNameKey,
InvalidTokenException,
)
class Token:
_TOKEN_INSTANCE = None
MINUS_SIGN = "-"
PLUS_SIGN = "+"
EQUAL_SIGN = "="
OPEN_ROUND_BRACKET = "("
CLOSE_ROUND_BRACKET = ")"
COMMA = ","
SPACE = " "
NEW_LINE = "\n"
DOT = "."
OPEN_SQUARE_BRACKET = "["
CLOSE_SQUARE_BRACKET = "]"
SPECIAL_CHARACTERS = [
MINUS_SIGN,
PLUS_SIGN,
EQUAL_SIGN,
OPEN_ROUND_BRACKET,
CLOSE_ROUND_BRACKET,
COMMA,
SPACE,
NEW_LINE,
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: Union[int, str], value: str):
assert (
token_type in self.SPECIAL_CHARACTERS
or token_type in self.PLACEHOLDER_NAMES
)
self.type = token_type
self.value = value
def __repr__(self) -> str:
if isinstance(self.type, int):
return f'Token("{self.PLACEHOLDER_NAMES[self.type]}", "{self.value}")'
else:
return f'Token("{self.type}", "{self.value}")'
def __eq__(self, other: "Token") -> bool: # type: ignore[override]
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: str) -> bool:
return character.isalnum() or character in ("_", ":", "#")
@classmethod
def is_possible_token_boundary(cls, character: str) -> bool:
return (
character in Token.SPECIAL_CHARACTERS
or not cls.is_simple_token_character(character)
)
@classmethod
def is_expression_attribute(cls, input_string: str) -> bool:
return re.compile("^[a-zA-Z0-9][a-zA-Z0-9_]*$").match(input_string) is not None
@classmethod
def is_expression_attribute_name(cls, input_string: str) -> bool:
"""
https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.ExpressionAttributeNames.html
An expression attribute name must begin with a pound sign (#), and be followed by one or more alphanumeric
characters.
"""
return (
input_string.startswith("#")
and re.compile("^[a-zA-Z0-9_]+$").match(input_string[1:]) is not None
)
@classmethod
def is_expression_attribute_value(cls, input_string: str) -> bool:
return re.compile("^:[a-zA-Z0-9_]*$").match(input_string) is not None
def raise_unexpected_token(self) -> None:
"""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: str):
self.input_expression_str = input_expression_str
self.token_list: List[Token] = []
self.staged_characters = ""
@classmethod
def make_list(cls, input_expression_str: str) -> List[Token]:
assert isinstance(input_expression_str, str)
return ExpressionTokenizer(input_expression_str)._make_list()
def add_token(self, token_type: Union[int, str], token_value: str) -> None:
self.token_list.append(Token(token_type, token_value))
def add_token_from_stage(self, token_type: int) -> None:
self.add_token(token_type, self.staged_characters)
self.staged_characters = ""
@classmethod
def is_numeric(cls, input_str: str) -> bool:
return re.compile("[0-9]+").match(input_str) is not None
def process_staged_characters(self) -> None:
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) -> List[Token]:
"""
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 in [Token.SPACE, Token.NEW_LINE]:
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