sigma-rules/kql/ast.py

# Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
# or more contributor license agreements. Licensed under the Elastic License;
# you may not use this file except in compliance with the Elastic License.

import re
from string import Template

from eql.ast import BaseNode
from eql.errors import EqlCompileError
from eql.utils import is_number, is_string

__all__ = (
    "KqlNode",
    "Value",
    "Null",
    "Number",
    "Boolean",
    "List",
    "Expression",
    "String",
    "Wildcard",
    "NotValue",
    "OrValues",
    "AndValues",
    "AndExpr",
    "OrExpr",
    "NotExpr",
    "FieldComparison",
    "Field",
    "FieldRange",
    "NestedQuery",
    "Exists",
)


class KqlNode(BaseNode):
    def optimize(self, recursive=True):
        from .optimizer import Optimizer
        return Optimizer().walk(self)

    def _render(self):
        return BaseNode.render(self)

    def render(self, precedence=None, **kwargs):
        """Render an EQL node and add parentheses to support orders of operation."""
        rendered = self._render(**kwargs)
        if precedence is not None and self.precedence is not None and self.precedence > precedence:
            return '({})'.format(rendered)
        return rendered


class Value(KqlNode):
    __slots__ = "value",
    precedence = 1

    def __init__(self, value):
        self.value = value

    @classmethod
    def from_python(cls, value):
        if value is None:
            return Null()
        elif isinstance(value, bool):
            return Boolean(value)
        elif is_number(value):
            return Number(value)
        elif is_string(value):
            return String(value)
        else:
            raise EqlCompileError("Unknown type {} for value {}".format(type(value).__name__, value))


class Null(Value):
    def __init__(self, value=None):
        Value.__init__(self, None)

    def _render(self):
        return "null"


class Number(Value):
    def _render(self):
        return str(self.value)


class Boolean(Value):
    def _render(self):
        return 'true' if self.value else 'false'


class String(Value):
    unescapable = re.compile(r'^[^\\():<>"*{} \t\r\n]+$')
    escapes = {"\t": "\\t", "\r": "\\r", "\"": "\\\""}

    def _render(self):
        # pass through as-is since nothing needs to be escaped
        if self.unescapable.match(self.value) is not None:
            return str(self.value)

        regex = r"[{}]".format("".join(re.escape(s) for s in sorted(self.escapes)))
        return '"{}"'.format(re.sub(regex, lambda r: self.escapes[r.group()], self.value))


class Wildcard(Value):
    escapes = {"\t": "\\t", "\r": "\\r"}
    slash_escaped = r'''^\\():<>"*{} '''

    def _render(self):
        escaped = []
        for char in self.value:
            if char in self.slash_escaped:
                escaped.append("\\")
                escaped.append(char)
            elif char in self.escapes:
                escaped.append(self.escapes[char])
            else:
                escaped.append(char)
        return ''.join(escaped)


class List(KqlNode):
    __slots__ = "items",
    precedence = Value.precedence + 1
    operator = ""
    template = Template("$items")

    def __init__(self, items):
        self.items = items
        KqlNode.__init__(self)

    @property
    def delims(self):
        return {"items": " {} ".format(self.operator)}

    def __eq__(self, other):
        from .optimizer import Optimizer
        from functools import cmp_to_key
        if type(self) == type(other):
            a = list(self.items)
            b = list(other.items)
            a.sort(key=cmp_to_key(Optimizer.sort_key))
            b.sort(key=cmp_to_key(Optimizer.sort_key))
            return a == b

        return False


class NotValue(KqlNode):
    __slots__ = "value",
    template = Template("not $value")
    precedence = Value.precedence + 1

    def __init__(self, value):
        self.value = value
        KqlNode.__init__(self)


class AndValues(List):
    precedence = List.precedence + 1
    operator = "and"


class OrValues(List):
    precedence = AndValues.precedence + 1
    operator = "or"


class Field(KqlNode):
    __slots__ = "name",
    precedence = Value.precedence
    template = Template("$name")

    def __init__(self, name):
        self.name = name
        KqlNode.__init__(self)

    @property
    def path(self):
        return self.name.split(".")

    @classmethod
    def from_path(cls, path):
        dotted = ".".join(path)
        return cls(dotted)


class Expression(KqlNode):
    """Intermediate node for class hierarchy."""


class FieldRange(Expression, KqlNode):
    __slots__ = "field", "operator", "value",
    precedence = Field.precedence
    template = Template("$field $operator $value")

    def __init__(self, field, operator, value):
        self.field = field
        self.operator = operator
        self.value = value


class NestedQuery(Expression):
    __slots__ = "field", "expr",
    precedence = Field.precedence + 1
    template = Template("$field:{$expr}")

    def __init__(self, field, expr):
        self.field = field
        self.expr = expr


class FieldComparison(Expression):
    __slots__ = "field", "value",
    precedence = FieldRange.precedence
    template = Template("$field:$value")

    def __init__(self, field, value):
        self.field = field
        self.value = value


class Exists(KqlNode):
    __slots__ = tuple()
    precedence = FieldComparison.precedence
    template = Template("*")


class NotExpr(Expression):
    __slots__ = "expr",
    precedence = FieldComparison.precedence + 1
    template = Template("not $expr")

    def __init__(self, expr):
        self.expr = expr


class AndExpr(Expression, List):
    precedence = NotExpr.precedence + 1
    operator = "and"


class OrExpr(Expression, List):
    precedence = AndExpr.precedence + 1
    operator = "or"