tools/secure_path_utils.py

"""
Secure path utilities to prevent path injection attacks.

This module provides secure alternatives to os.path operations that validate
and sanitize file paths to prevent directory traversal and other path-based attacks.
"""

import logging
import os
import re
from pathlib import Path
from typing import Optional, Union

logger = logging.getLogger(__name__)


def sanitize_filename(filename: str, max_length: int = 255) -> str:
    """
    Sanitize a filename to prevent path injection attacks.

    Args:
        filename: The filename to sanitize
        max_length: Maximum length of the sanitized filename

    Returns:
        A sanitized filename safe for use in file operations

    Raises:
        ValueError: If the filename cannot be sanitized safely
    """
    if not filename or not isinstance(filename, str):
        raise ValueError("Filename must be a non-empty string")

    # Remove any path separators and normalize
    filename = os.path.basename(filename)

    # Remove or replace dangerous characters
    # Keep alphanumeric, dots, hyphens, underscores, spaces, parentheses, brackets, and other safe chars
    # Only remove truly dangerous characters like path separators and control chars
    sanitized = re.sub(r'[<>:"|?*\x00-\x1f]', "_", filename)

    # Remove multiple consecutive dots (except for file extensions)
    sanitized = re.sub(r"\.{2,}", ".", sanitized)

    # Remove leading/trailing dots and spaces
    sanitized = sanitized.strip(". ")

    # Ensure it's not empty after sanitization
    if not sanitized:
        sanitized = "sanitized_file"

    # Truncate if too long, preserving extension
    if len(sanitized) > max_length:
        name, ext = os.path.splitext(sanitized)
        max_name_length = max_length - len(ext)
        sanitized = name[:max_name_length] + ext

    return sanitized


def secure_path_join(base_path: Union[str, Path], *path_parts: str) -> Path:
    """
    Safely join paths while preventing directory traversal attacks.

    Args:
        base_path: The base directory path
        *path_parts: Additional path components to join

    Returns:
        A Path object representing the safe joined path

    Raises:
        ValueError: If any path component contains dangerous characters
        PermissionError: If the resulting path would escape the base directory
    """
    base_path = Path(base_path).resolve()

    # Sanitize each path part - only sanitize if it contains dangerous patterns
    sanitized_parts = []
    for part in path_parts:
        if not part:
            continue
        # Only sanitize if the part contains dangerous patterns
        if re.search(r'[<>:"|?*\x00-\x1f]|\.{2,}', part):
            sanitized_part = sanitize_filename(part)
        else:
            sanitized_part = part
        sanitized_parts.append(sanitized_part)

    # Join the paths
    result_path = base_path
    for part in sanitized_parts:
        result_path = result_path / part

    # Resolve the final path
    result_path = result_path.resolve()

    # Security check: ensure the result is within the base directory
    try:
        result_path.relative_to(base_path)
    except ValueError:
        raise PermissionError(f"Path would escape base directory: {result_path}")

    return result_path


def secure_file_write(
    base_path: Union[str, Path],
    filename: str,
    content: str,
    mode: str = "w",
    encoding: Optional[str] = None,
    **kwargs,
) -> None:
    """
    Safely write content to a file within a base directory with path validation.

    Args:
        base_path: The base directory under which to write the file
        filename: The target file name or relative path (untrusted)
        content: The content to write
        mode: File open mode (default: 'w')
        encoding: Text encoding (default: None for binary mode)
        **kwargs: Additional arguments for open()
    """
    # Use secure_path_join to ensure the final path is within base_path and to sanitize filename
    file_path = secure_path_join(base_path, filename)

    # Ensure the parent directory exists AFTER joining and securing the final path
    file_path.parent.mkdir(parents=True, exist_ok=True)

    # Write the file
    open_kwargs = {"mode": mode}
    if encoding:
        open_kwargs["encoding"] = encoding
    open_kwargs.update(kwargs)

    with open(file_path, **open_kwargs) as f:
        f.write(content)


def secure_file_read(
    base_path: Union[str, Path],
    filename: str,
    mode: str = "r",
    encoding: Optional[str] = None,
    **kwargs,
) -> str:
    """
    Safely read content from a file within a base directory with path validation.

    Args:
        base_path: The base directory under which to read the file
        filename: The target file name or relative path (untrusted)
        mode: File open mode (default: 'r')
        encoding: Text encoding (default: None for binary mode)
        **kwargs: Additional arguments for open()

    Returns:
        The file content
    """
    # Use secure_path_join to ensure the final path is within base_path and to sanitize filename
    file_path = secure_path_join(base_path, filename)

    # Validate the path exists and is a file
    if not file_path.exists():
        raise FileNotFoundError(f"File not found: {file_path}")

    if not file_path.is_file():
        raise ValueError(f"Path is not a file: {file_path}")

    # Read the file
    open_kwargs = {"mode": mode}
    if encoding:
        open_kwargs["encoding"] = encoding
    open_kwargs.update(kwargs)

    with open(file_path, **open_kwargs) as f:
        return f.read()


def validate_path_safety(
    path: Union[str, Path], base_path: Optional[Union[str, Path]] = None
) -> bool:
    """
    Validate that a path is safe and doesn't contain dangerous patterns.

    Args:
        path: The path to validate
        base_path: Optional base path to check against

    Returns:
        True if the path is safe, False otherwise
    """
    try:
        path = Path(path)

        # Check for dangerous patterns
        path_str = str(path)

        # Check for directory traversal patterns
        dangerous_patterns = [
            "..",  # Parent directory
            "//",  # Double slashes
            "\\",  # Backslashes (on Unix systems)
        ]

        for pattern in dangerous_patterns:
            if pattern in path_str:
                return False

        # If base path is provided, ensure the path is within it
        if base_path:
            base_path = Path(base_path).resolve()
            path = path.resolve()
            try:
                path.relative_to(base_path)
            except ValueError:
                return False

        return True

    except Exception:
        return False


# Backward compatibility functions that maintain the same interface as os.path
def secure_join(*paths: str) -> str:
    """
    Secure alternative to os.path.join that prevents path injection.

    Args:
        *paths: Path components to join

    Returns:
        A safe joined path string
    """
    if not paths:
        return ""

    # Use the first path as base, others as components
    base_path = Path(paths[0])
    path_parts = paths[1:]

    # Only use secure_path_join if there are potentially dangerous patterns
    if any(re.search(r'[<>:"|?*\x00-\x1f]|\.{2,}', part) for part in path_parts):
        result_path = secure_path_join(base_path, *path_parts)
        return str(result_path)
    else:
        # Use normal path joining for safe paths
        return str(Path(*paths))


def secure_basename(path: str) -> str:
    """
    Secure alternative to os.path.basename that sanitizes the result.

    Args:
        path: The path to get the basename from

    Returns:
        A sanitized basename
    """
    basename = os.path.basename(path)
    # Only sanitize if the basename contains dangerous patterns
    if re.search(r'[<>:"|?*\x00-\x1f]|\.{2,}', basename):
        return sanitize_filename(basename)
    else:
        return basename