webdrop-bridge/docs/ARCHITECTURE.md

Architecture Guide

High-Level Design

┌──────────────────────────────────────────────────────────┐
│ Application Layer (UI)                                   │
│ ┌────────────────────────────────────────────────────────┤
│ │ QMainWindow (main_window.py)                           │
│ │ ├─ QWebEngineView (web app container)                 │
│ │ └─ DragInterceptor (drag handling)                    │
│ └────────────────────────────────────────────────────────┘
│              ↓ Events (dragEnterEvent, etc.)
├──────────────────────────────────────────────────────────┤
│ Business Logic Layer (Core)                              │
│ ┌────────────────────────────────────────────────────────┤
│ │ PathValidator (security & validation)                 │
│ │ DragInterceptor (drag/drop conversion)               │
│ │ Config (configuration management)                    │
│ └────────────────────────────────────────────────────────┘
│              ↓ Platform APIs
├──────────────────────────────────────────────────────────┤
│ Platform Layer (OS Integration)                          │
│ ┌────────────────────────────────────────────────────────┤
│ │ QUrl (Windows: CF_HDROP, macOS: NSFilenamesPboardType)│
│ │ QMimeData (cross-platform mime data)                 │
│ │ QDrag (native drag-drop implementation)              │
│ └────────────────────────────────────────────────────────┘

Module Organization

src/webdrop_bridge/core/

Purpose: Core business logic, independent of UI

Key Components:

• validator.py: Path validation against whitelist
• drag_interceptor.py: Drag event handling and conversion
• config.py: Configuration management
• errors.py: Custom exception classes

Dependencies: None (only stdlib + pathlib)

src/webdrop_bridge/ui/

Purpose: User interface components using Qt/PySide6

Key Components:

• main_window.py: Main application window
• widgets.py: Reusable custom widgets
• styles.py: UI styling and themes

Dependencies: PySide6, core/

src/webdrop_bridge/utils/

Purpose: Shared utilities and helpers

Key Components:

• logging.py: Logging configuration
• constants.py: Application constants
• helpers.py: General-purpose helper functions

Dependencies: stdlib only

Data Flow

Drag-and-Drop Operation

User in Web App
    ↓
[dragstart event] → JavaScript sets dataTransfer.text = "Z:\path\file.txt"
    ↓
[dragend event] → Drag leaves WebEngine widget
    ↓
DragInterceptor.dragEnterEvent() triggered
    ↓
Extract text from QMimeData
    ↓
PathValidator.is_valid_file(path)
    ├─ is_allowed(path) → Check whitelist
    └─ path.exists() and path.is_file() → File system check
    ↓
If valid:
    → Create QUrl.fromLocalFile(path)
    → Create new QMimeData with URLs
    → QDrag.exec() → Native file drag
    ↓
If invalid:
    → event.ignore()
    → Log warning
    ↓
OS receives native file drag
    ↓
InDesign/Word receives file handle

Security Model

Path Validation Strategy

1. Whitelist-based: Only allow configured root directories
2. Absolute path resolution: Prevent directory traversal attacks
3. Symlink handling: Resolve to real path before checking
4. File existence check: Don't drag non-existent files
5. Type verification: Only allow regular files

# Example allowed roots
ALLOWED_ROOTS = [
    Path("Z:/"),              # Network share
    Path("C:/Users/Public"),  # Windows public folder
]

# Example validation
path = Path(r"Z:\projects\file.psd")
→ Resolve: Z:\projects\file.psd
→ Check: starts with Z:\? YES
→ Check: file exists? YES
→ Check: is regular file? YES
→ Result: ALLOW

Web Engine Security

• LocalContentCanAccessFileUrls: Enabled (required for drag)
• LocalContentCanAccessRemoteUrls: Disabled (prevent phishing)
• Certificate validation: Enforced for HTTPS

Performance Considerations

Drag Operation Timing

Event         Time (ms)  Critical Path
─────────────────────────────────────
dragenter     <1        ✓ Must be fast
validation    <10       ✓ Keep fast
QUrl creation <1        
QDrag.exec()  <50       ✓ Start quickly
─────────────────────────
TOTAL         <50       ✓ Imperceptible

Memory Management

• Web engine: ~100-150 MB baseline
• Drag interceptor: Minimal overhead
• Logging: Rotated to prevent growth
• File cache: None (on-demand validation)

Testing Strategy

Unit Testing

validator.py
├─ test_is_allowed()
├─ test_is_valid_file()
└─ test_symlink_handling()

config.py
├─ test_load_from_env()
├─ test_default_values()
└─ test_validation()

drag_interceptor.py
├─ test_dragEnterEvent()
├─ test_invalid_path_rejected()
└─ test_file_drag_created()

Integration Testing

end_to_end.py
├─ test_app_startup()
├─ test_webapp_loads()
├─ test_complete_drag_workflow()
└─ test_invalid_path_handling()

Extension Points

Adding New Handlers

# Future: Support for additional file types or sources
class HandlerRegistry:
    def register(self, source_type: str, handler: Handler):
        self.handlers[source_type] = handler
    
    def handle(self, data: QMimeData) -> Optional[QMimeData]:
        for handler in self.handlers.values():
            if handler.can_handle(data):
                return handler.handle(data)
        return None

Custom Validators

# Future: Pluggable validation rules
class ValidatorPlugin(ABC):
    @abstractmethod
    def validate(self, path: Path) -> bool:
        pass

class FileSizeValidator(ValidatorPlugin):
    def __init__(self, max_size: int):
        self.max_size = max_size
    
    def validate(self, path: Path) -> bool:
        return path.stat().st_size <= self.max_size

Deployment Architecture

Single-File Executable

WebDropBridge.exe (built with PyInstaller)
├─ Python runtime
├─ PySide6 libraries
├─ Qt libraries
├─ Embedded web app (index.html)
└─ Bundled resources (icons, etc.)

Size: ~100-120 MB
Startup: <1 second

Portable Deployment

• Single executable: No installation required
• No registry entries: Clean removal
• Relative paths: Can run from any directory
• Configuration: .env file per instance

Platform Differences

Windows

• Drag Format: CF_HDROP (file paths)
• File URLs: file:///C:/path/to/file
• Paths: Backslash \ (converted to forward /)
• Permissions: Admin privileges not required

macOS

• Drag Format: NSFilenamesPboardType (same as Windows, different implementation)
• File URLs: file:///Users/username/path/to/file
• Paths: Forward slash / (native)
• Permissions: May require accessibility permissions

Monitoring & Debugging

Debug Logging

# Enable debug logging
LOG_LEVEL=DEBUG

# Output
2026-01-28 14:32:15 - webdrop_bridge - DEBUG - DragInterceptor: dragEnterEvent triggered
2026-01-28 14:32:15 - webdrop_bridge - DEBUG - PathValidator: Checking Z:\file.psd
2026-01-28 14:32:15 - webdrop_bridge - INFO - File dragged: Z:\file.psd

Performance Profiling

import cProfile
import pstats

profiler = cProfile.Profile()
profiler.enable()
# ... drag operation ...
profiler.disable()
stats = pstats.Stats(profiler)
stats.print_stats()

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For more details, see DEVELOPMENT_PLAN.md