Add scan cancellation feature

- Replace subprocess.run() with Popen for cancellable processes
- Add cancel() method to SneakyScanner with process termination
- Track running scanners in registry for stop signal delivery
- Handle ScanCancelledError to set scan status to 'cancelled'
- Add POST /api/scans/<id>/stop endpoint
- Add 'cancelled' as valid scan status
- Add Stop button to scans list and detail views
- Show cancelled status with warning badge in UI

app/web/jobs/scan_job.py

@@ -7,6 +7,7 @@ updating database status and handling errors.
 
 import json
 import logging
+import threading
 import traceback
 from datetime import datetime
 from pathlib import Path
@@ -14,13 +15,49 @@ from pathlib import Path
 from sqlalchemy import create_engine
 from sqlalchemy.orm import sessionmaker
 
-from src.scanner import SneakyScanner
+from src.scanner import SneakyScanner, ScanCancelledError
 from web.models import Scan, ScanProgress
 from web.services.scan_service import ScanService
 from web.services.alert_service import AlertService
 
 logger = logging.getLogger(__name__)
 
+# Registry for tracking running scanners (scan_id -> SneakyScanner instance)
+_running_scanners = {}
+_running_scanners_lock = threading.Lock()
+
+
+def get_running_scanner(scan_id: int):
+    """Get a running scanner instance by scan ID."""
+    with _running_scanners_lock:
+        return _running_scanners.get(scan_id)
+
+
+def stop_scan(scan_id: int, db_url: str) -> bool:
+    """
+    Stop a running scan.
+
+    Args:
+        scan_id: ID of the scan to stop
+        db_url: Database connection URL
+
+    Returns:
+        True if scan was cancelled, False if not found or already stopped
+    """
+    logger.info(f"Attempting to stop scan {scan_id}")
+
+    # Get the scanner instance
+    scanner = get_running_scanner(scan_id)
+    if not scanner:
+        logger.warning(f"Scanner for scan {scan_id} not found in registry")
+        return False
+
+    # Cancel the scanner
+    scanner.cancel()
+    logger.info(f"Cancellation signal sent to scan {scan_id}")
+
+    return True
+
 
 def create_progress_callback(scan_id: int, session):
     """
@@ -186,6 +223,11 @@ def execute_scan(scan_id: int, config_id: int, db_url: str = None):
         # Initialize scanner with database config
         scanner = SneakyScanner(config_id=config_id)
 
+        # Register scanner in the running registry
+        with _running_scanners_lock:
+            _running_scanners[scan_id] = scanner
+        logger.debug(f"Scan {scan_id}: Registered in running scanners registry")
+
         # Create progress callback
         progress_callback = create_progress_callback(scan_id, session)
 
@@ -220,6 +262,19 @@ def execute_scan(scan_id: int, config_id: int, db_url: str = None):
 
         logger.info(f"Scan {scan_id}: Completed successfully")
 
+    except ScanCancelledError:
+        # Scan was cancelled by user
+        logger.info(f"Scan {scan_id}: Cancelled by user")
+
+        scan = session.query(Scan).filter_by(id=scan_id).first()
+        if scan:
+            scan.status = 'cancelled'
+            scan.error_message = 'Scan cancelled by user'
+            scan.completed_at = datetime.utcnow()
+            if scan.started_at:
+                scan.duration = (datetime.utcnow() - scan.started_at).total_seconds()
+            session.commit()
+
     except FileNotFoundError as e:
         # Config file not found
         error_msg = f"Configuration file not found: {str(e)}"
@@ -249,6 +304,12 @@ def execute_scan(scan_id: int, config_id: int, db_url: str = None):
             logger.error(f"Scan {scan_id}: Failed to update error status in database: {str(db_error)}")
 
     finally:
+        # Unregister scanner from registry
+        with _running_scanners_lock:
+            if scan_id in _running_scanners:
+                del _running_scanners[scan_id]
+                logger.debug(f"Scan {scan_id}: Unregistered from running scanners registry")
+
         # Always close the session
         session.close()
         logger.info(f"Scan {scan_id}: Background job completed, session closed")