AI edits: add calculator tool

[auto-swe]

This pull request contains AI-suggested changes:

add calculator tool

[codedaddy-reviewer]

Walkthrough

This Pull Request introduces a new Calculator tool designed to safely evaluate mathematical expressions within an agent ecosystem. It leverages Python's ast module to parse expressions into an Abstract Syntax Tree, rigorously validating each node to prevent the execution of arbitrary or malicious code, before compiling and evaluating the safe expression.

Changes

Cohort / File(s)	Summary
py-server/nodes/Agents/tools/tools.py	Implements the Calculator tool, including _is_safe_node for AST validation and safe_eval for secure expression evaluation.

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🔧 Key Implementation Details

Calculator Tool & Safe Evaluation

The core of this PR is the safe_eval function, which uses ast.parse to convert an input string into an Abstract Syntax Tree. This AST is then meticulously traversed by _is_safe_node to ensure only allowed arithmetic operations and numeric literals are present. This robust validation mechanism, coupled with a restricted eval environment, is crucial for mitigating security risks associated with executing user-provided expressions.

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Poem

Your Daddy reviews code with care and grace,
A Calculator tool now finds its place.
With AST parsed, and nodes held tight,
Safe math unfolds, in pure delight. 🐰✨

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Tip

🔮 Elevate AST Traversal with a Visitor Pattern

For more complex AST validations or transformations, consider using Python's ast.NodeVisitor or ast.NodeTransformer. This can lead to cleaner, more organized code than recursive functions, especially as your validation rules grow.

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✨ Finishing Touches

1. Consistent Error Messages: While the tool returns error strings, consider standardizing the format of these messages (e.g., "CalculatorError: [description]") to make them easier for agents or downstream systems to parse and handle programmatically.
2. Type Hinting for ast.AST: Ensure all functions interacting with AST nodes (like _is_safe_node) explicitly type hint ast.AST for better code clarity and static analysis.
3. Refine Docstrings: Expand docstrings for safe_eval and calculator_tool to include examples of usage and expected outputs/errors, further improving developer experience.

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Review Comments

📁 py-server/nodes/Agents/tools/tools.py

Comment on lines +30 to +35

🔴 MAJOR: Denial of Service (DoS) via uncontrolled exponentiation.

The _is_safe_node function explicitly allows the ast.Pow operator (**) without any checks on the magnitude of the base or exponent. An attacker can provide an expression like 2**10000000, which will cause the Python interpreter to calculate an extremely large integer, consuming significant CPU and memory resources and potentially leading to a denial of service.

Suggestion:

# Inside _is_safe_node, within the ast.BinOp block
elif isinstance(node.op, ast.Pow):
    # Add checks for base and exponent magnitude
    # This is a simplified example; a robust solution might involve
    # checking the values of node.left and node.right after they are
    # determined to be safe numbers, or limiting the result size.
    # For instance, if node.left and node.right are ast.Constant(value=N),
    # check if N is within a reasonable range.
    if isinstance(node.left, (ast.Constant, ast.Num)) and isinstance(node.right, (ast.Constant, ast.Num)):
        base = getattr(node.left, "value", getattr(node.left, "n", None))
        exponent = getattr(node.right, "value", getattr(node.right, "n", None))
        if isinstance(base, (int, float)) and isinstance(exponent, (int, float)):
            # Example: Disallow very large exponents or bases
            if abs(exponent) > 1000 or abs(base) > 1000000: # Adjust limits as needed
                return False # Too large, potential DoS
    return _is_safe_node(node.left) and _is_safe_node(node.right)

Rationale: Uncontrolled exponentiation is a known vector for resource exhaustion. Implementing checks on the magnitude of operands for ast.Pow is critical to prevent DoS attacks and ensure the calculator remains robust under malicious input.

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Comment on lines +20 to +25

🟡 MEDIUM: Potential Bug/Inaccuracy in _is_safe_node for ast.Num.

The _is_safe_node function attempts to handle both ast.Constant and ast.Num nodes for numeric values. However, the line isinstance(getattr(node, "value", None), (int, float, complex)) is incorrect for ast.Num nodes. ast.Num nodes store their value in the n attribute, not value. This means ast.Num nodes will always fail this check, potentially preventing the calculator from correctly evaluating numeric literals if the AST parser generates ast.Num nodes (which happens in Python versions prior to 3.8).

Suggestion:

# Inside _is_safe_node, within the ast.Constant/ast.Num check
elif isinstance(node, (ast.Constant, ast.Num)):
    # ast.Constant uses 'value', ast.Num uses 'n'
    node_value = getattr(node, "value", getattr(node, "n", None))
    return isinstance(node_value, (int, float, complex))

Rationale: Correctly handling ast.Num nodes ensures compatibility with older Python versions (if intended) and prevents unexpected failures when parsing numeric literals. The current implementation would incorrectly flag ast.Num nodes as unsafe.

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Comment on lines +95 to +98

🟡 MEDIUM: Overly Broad Exception Catch.

In calculator_tool, a generic except Exception as e: is used. While it returns an error string as intended for the tool, catching such a broad exception can mask specific underlying issues, making debugging harder. It's generally better to catch more specific exceptions (e.g., ValueError from safe_eval) or at least log the full traceback for unexpected errors before returning a generic message.

Suggestion:

# In calculator_tool function
try:
    result = safe_eval(expression)
    return str(result)
except ValueError as e: # Catch specific validation errors
    return f"Error: {e}"
except ZeroDivisionError: # Catch specific arithmetic errors
    return "Error: division by zero"
except Exception as e: # Catch any other unexpected errors and log them
    logger.error(f"Unexpected error in calculator_tool: {e}", exc_info=True) # Assuming a logger is available
    return f"Error: An unexpected issue occurred."

Rationale: Catching specific exceptions improves error handling clarity, makes debugging easier by differentiating expected errors from unexpected ones, and allows for more precise error messages to the user or agent. Logging unexpected exceptions is crucial for operational visibility.

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Comment on lines +36 to +45

🟢 LOW: Readability/Complexity of _is_safe_node for ast.BinOp.

The elif isinstance(node, ast.BinOp) block, particularly its long isinstance(node.op, (...)) check, is quite dense. While functional, it could benefit from refactoring to improve readability and maintainability.

Suggestion:

# Inside _is_safe_node
ALLOWED_BIN_OPS = (ast.Add, ast.Sub, ast.Mult, ast.Div, ast.Mod, ast.Pow, ast.FloorDiv)
ALLOWED_UNARY_OPS = (ast.UAdd, ast.USub)

# ...

elif isinstance(node, ast.BinOp):
    return isinstance(node.op, ALLOWED_BIN_OPS) and \
           _is_safe_node(node.left) and \
           _is_safe_node(node.right)
elif isinstance(node, ast.UnaryOp):
    return isinstance(node.op, ALLOWED_UNARY_OPS) and \
           _is_safe_node(node.operand)

Rationale: Using a tuple or set for allowed operators enhances readability, makes the code easier to modify if operators need to be added or removed, and reduces the visual clutter of a long isinstance check.

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Comment on lines +5 to +7

🟢 LOW: Docstring for _is_safe_node regarding ast.Num.

The docstring mentions Constant (Num in Python <3.8). Given that ast.Num is deprecated in Python 3.8 and removed in 3.9, and there's a bug in how ast.Num values are handled in the code, it would be beneficial to either clarify the target Python version for this module or remove the ast.Num check if the project exclusively targets Python 3.9+.

Suggestion:

# Update docstring
def _is_safe_node(node: ast.AST) -> bool:
    """
    Recursively checks if an AST node and its children are safe for evaluation.
    Allowed nodes include:
    - ast.Constant (for int, float, complex)
    - ast.BinOp with specific arithmetic operators (+, -, *, /, %, **, //)
    - ast.UnaryOp with specific unary operators (+, -)
    - ast.Expression (top-level wrapper)
    - ast.Paren (parenthesized expressions)

    Note: ast.Num (used in Python <3.8) is handled, but its usage is deprecated.
    """

Rationale: Clarifying the Python version compatibility in the docstring helps future developers understand the context and potential maintenance implications, especially when dealing with deprecated features.

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Comment on line +101

🟢 LOW: Missing Newline at End of File.

The file py-server/nodes/Agents/tools/tools.py is missing a newline character at the very end of the file. This is a common linting issue that can cause problems with some tools and version control systems.

Suggestion:

--- a/py-server/nodes/Agents/tools/tools.py
+++ b/py-server/nodes/Agents/tools/tools.py
@@ -98,3 +98,4 @@
     return Tool(name="Calculator", description=description, func=calculator_tool)
 
 CALCULATOR_TOOL = create_calculator_tool()
+

Rationale: A newline at the end of file is a POSIX standard and prevents issues with diff tools, cat commands, and some build systems.

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Comment on lines +55 to +80

🟢 LOW: Reliance on eval() (Anti-pattern).

Although safe_eval employs AST parsing and restricts built-ins to mitigate risks, using eval() is generally considered an anti-pattern from a security and robustness perspective. Ensuring absolute safety with eval() is complex. For arithmetic expressions, dedicated math expression parsing libraries or a custom AST traversal evaluator (without eval) could offer a more secure and maintainable approach, reducing the attack surface and complexity of the "safety" mechanism.

Suggestion:

# No direct code change for this specific PR, but a strategic consideration.
# If future security audits or performance requirements demand it,
# consider replacing the final `eval(compiled_code, {"__builtins__": None})`
# with a custom AST visitor that directly computes the result.
# Example (conceptual):
# class MathEvaluator(ast.NodeVisitor):
#     def visit_Constant(self, node): return node.value
#     def visit_BinOp(self, node):
#         left = self.visit(node.left)
#         right = self.visit(node.right)
#         if isinstance(node.op, ast.Add): return left + right
#         # ... handle other operators
#     # ... handle other allowed nodes
#
# Then, `MathEvaluator().visit(tree)` would replace `eval(...)`.

Rationale: While the current safe_eval is well-intentioned and robust for its design, the fundamental eval() function carries inherent risks. Exploring alternatives like a custom AST evaluator can provide an even stronger security posture by completely avoiding eval()'s execution capabilities and offering more granular control over expression evaluation. This is a long-term architectural consideration.

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Summary by CodeDaddy

• New Features

  • Introduced a Calculator tool for agents to perform safe mathematical evaluations.
  • Implemented safe_eval function leveraging Python's ast module for secure expression parsing and validation.
  • Developed _is_safe_node for rigorous AST node validation, allowing only arithmetic operations and numeric literals.

• Bug Fixes

  • (No explicit bug fixes in this PR, but several potential bugs/inaccuracies were identified in the review.)

• Improvements

  • Security: Enhanced security by using AST parsing to prevent arbitrary code execution.
  • Performance Considerations: The review highlighted potential performance overheads due to AST parsing, traversal, and compilation for each evaluation. Mitigation strategies like profiling and specialized libraries were suggested for future optimization if needed.
  • Code Quality: Suggestions for improving readability of _is_safe_node and refining docstrings were provided.

• Tests

  • Comprehensive unit test suggestions for _is_safe_node, safe_eval, and calculator_tool were provided, covering safe/unsafe operations, edge cases, and security bypass attempts.
  • Integration test scenarios with an AI agent were outlined to ensure the tool's functionality and error handling within the agent ecosystem.

• Documentation

  • Suggestions for clarifying docstrings regarding ast.Num compatibility were made.

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Actionable comments posted: 6

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📚 Tips

1. Prioritize Security Fixes: Address the ast.Pow DoS vulnerability immediately; it's a critical security flaw.
2. Automate Linting: Integrate linters (like Black, Flake8, or Ruff) into your CI/CD pipeline to catch issues like missing newlines and enforce code style automatically.
3. Test-Driven Development (TDD): Consider writing tests before the code for new features. This helps ensure comprehensive coverage and can guide implementation decisions.

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