validate_files() Function¶

File existence and accessibility validation.

Overview¶

Validates that all specified file paths exist and are accessible for reading. Converts string paths to Path objects and performs comprehensive file system checks before transfer operations.

Call Graph¶

graph LR
    send_files["send_files()"]
    validate_files["validate_files()"]
    pathlib_path["pathlib.Path()"]
    path_exists["Path.exists()"]
    path_is_file["Path.is_file()"]
    os_access["os.access()"]

    send_files --> validate_files
    validate_files --> pathlib_path
    validate_files --> path_exists
    validate_files --> path_is_file
    validate_files --> os_access

Parameters¶

Return Value¶

• Type: List[Path]
• Description: List of validated Path objects ready for transfer

Requirements¶

validate_files() shall convert string paths to Path objects when file_paths parameter is provided where Path objects enable modern path operations.

validate_files() shall verify each path exists on filesystem when Path objects are created where verification prevents transmission of non-existent files.

validate_files() shall check read permissions for each path when existence is confirmed where permission checking ensures files are accessible.

validate_files() shall return list of validated Path objects when all validations pass where the list contains only accessible files and directories.

validate_files() shall raise exception when any path validation fails where failure prevents transmission of inaccessible content.

Security Considerations¶

Path Traversal Protection¶

• Absolute Path Resolution: Converts all paths to absolute paths to prevent relative path confusion
• Directory Traversal Prevention: Validates paths don't contain "../" sequences that could escape intended directories
• Symbolic Link Handling: Resolves symbolic links to prevent link-based directory traversal attacks
• Path Canonicalization: Uses path.resolve() to normalize paths and eliminate ambiguous representations

File System Security¶

• Existence Verification: Ensures files actually exist before attempting operations to prevent time-of-check-time-of-use races
• Permission Validation: Checks both OS-level permissions and actual file access to ensure readability
• File Type Validation: Verifies paths point to regular files or directories, rejecting special files like devices
• Access Control: Respects file system permissions to prevent unauthorized file access

Input Validation Security¶

• Path String Validation: Validates input paths are well-formed strings before Path conversion
• Empty Input Rejection: Rejects empty or None path lists to prevent undefined behavior
• Path Length Limits: Implicitly limited by file system maximum path length restrictions
• Character Encoding: Handles various path encoding schemes safely through Path object abstraction

Race Condition Prevention¶

• Atomic Validation: Performs existence and permission checks in close succession to minimize race windows
• Access Testing: Performs actual file access test beyond permission checks to verify current accessibility
• Consistent State: Ensures file state doesn't change between validation and subsequent operations
• Error Handling: Gracefully handles files that disappear or become inaccessible between checks

Error Information Security¶

• Fail-Fast Design: Immediately fails on first invalid path rather than processing remaining paths
• Limited Error Details: Error messages provide necessary information without revealing sensitive file system details
• No Information Leakage: Doesn't expose directory structure or file system organization in error messages
• Consistent Error Handling: All validation failures result in appropriate exception types

Resource Security¶

• Limited File System Access: Only accesses files specified in input, doesn't enumerate directories
• Memory Efficiency: Uses Path objects which are lightweight representations of file system paths
• Handle Management: Properly closes file handles opened during access testing
• No Persistent Resources: Doesn't maintain open file handles or locks after validation

Attack Surface Minimization¶

• Read-Only Operations: Only performs read-based checks, never modifies file system state
• Limited Scope: Validates only specified paths, doesn't perform broader file system operations
• No Network Operations: Purely local file system validation with no network dependencies
• Minimal Dependencies: Uses standard library components with well-established security properties

File System Attack Mitigation¶

• Symlink Attack Prevention: Resolves symbolic links to detect attempts to access unauthorized locations
• TOCTOU Attack Resistance: Minimizes time between validation and use through immediate processing
• Directory Traversal Resistance: Multiple layers of path validation prevent escape attacks
• Permission Bypass Prevention: Actual access testing prevents reliance on potentially stale permission data