ai-agent-book 精选快照（<2MB 代码与文档，来自 github.com/bojieli/ai-agent-book）

chapter9/browser-use-rpa/browser-use/browser_use/browser/watchdogs/downloads_watchdog.py

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+"""Downloads watchdog for monitoring and handling file downloads."""
+
+import asyncio
+import json
+import os
+import tempfile
+from pathlib import Path
+from typing import TYPE_CHECKING, Any, ClassVar
+from urllib.parse import urlparse
+
+import anyio
+from bubus import BaseEvent
+from cdp_use.cdp.browser import DownloadProgressEvent, DownloadWillBeginEvent
+from cdp_use.cdp.target import SessionID, TargetID
+from pydantic import PrivateAttr
+
+from browser_use.browser.events import (
+	BrowserLaunchEvent,
+	BrowserStateRequestEvent,
+	BrowserStoppedEvent,
+	FileDownloadedEvent,
+	NavigationCompleteEvent,
+	TabClosedEvent,
+	TabCreatedEvent,
+)
+from browser_use.browser.watchdog_base import BaseWatchdog
+
+if TYPE_CHECKING:
+	pass
+
+
+class DownloadsWatchdog(BaseWatchdog):
+	"""Monitors downloads and handles file download events."""
+
+	# Events this watchdog listens to (for documentation)
+	LISTENS_TO: ClassVar[list[type[BaseEvent[Any]]]] = [
+		BrowserLaunchEvent,
+		BrowserStateRequestEvent,
+		BrowserStoppedEvent,
+		TabCreatedEvent,
+		TabClosedEvent,
+		NavigationCompleteEvent,
+	]
+
+	# Events this watchdog emits
+	EMITS: ClassVar[list[type[BaseEvent[Any]]]] = [
+		FileDownloadedEvent,
+	]
+
+	# Private state
+	_sessions_with_listeners: set[str] = PrivateAttr(default_factory=set)  # Track sessions that already have download listeners
+	_active_downloads: dict[str, Any] = PrivateAttr(default_factory=dict)
+	_pdf_viewer_cache: dict[str, bool] = PrivateAttr(default_factory=dict)  # Cache PDF viewer status by target URL
+	_download_cdp_session_setup: bool = PrivateAttr(default=False)  # Track if CDP session is set up
+	_download_cdp_session: Any = PrivateAttr(default=None)  # Store CDP session reference
+	_cdp_event_tasks: set[asyncio.Task] = PrivateAttr(default_factory=set)  # Track CDP event handler tasks
+	_cdp_downloads_info: dict[str, dict[str, Any]] = PrivateAttr(default_factory=dict)  # Map guid -> info
+	_use_js_fetch_for_local: bool = PrivateAttr(default=False)  # Guard JS fetch path for local regular downloads
+
+	async def on_BrowserLaunchEvent(self, event: BrowserLaunchEvent) -> None:
+		self.logger.debug(f'[DownloadsWatchdog] Received BrowserLaunchEvent, EventBus ID: {id(self.event_bus)}')
+		# Ensure downloads directory exists
+		downloads_path = self.browser_session.browser_profile.downloads_path
+		if downloads_path:
+			expanded_path = Path(downloads_path).expanduser().resolve()
+			expanded_path.mkdir(parents=True, exist_ok=True)
+			self.logger.debug(f'[DownloadsWatchdog] Ensured downloads directory exists: {expanded_path}')
+
+	async def on_TabCreatedEvent(self, event: TabCreatedEvent) -> None:
+		"""Monitor new tabs for downloads."""
+		# logger.info(f'[DownloadsWatchdog] TabCreatedEvent received for tab {event.target_id[-4:]}: {event.url}')
+
+		# Assert downloads path is configured (should always be set by BrowserProfile default)
+		assert self.browser_session.browser_profile.downloads_path is not None, 'Downloads path must be configured'
+
+		if event.target_id:
+			# logger.info(f'[DownloadsWatchdog] Found target for tab {event.target_id}, calling attach_to_target')
+			await self.attach_to_target(event.target_id)
+		else:
+			self.logger.warning(f'[DownloadsWatchdog] No target found for tab {event.target_id}')
+
+	async def on_TabClosedEvent(self, event: TabClosedEvent) -> None:
+		"""Stop monitoring closed tabs."""
+		pass  # No cleanup needed, browser context handles target lifecycle
+
+	async def on_BrowserStateRequestEvent(self, event: BrowserStateRequestEvent) -> None:
+		"""Handle browser state request events."""
+		cdp_session = self.browser_session.agent_focus
+		if not cdp_session:
+			return
+
+		url = await self.browser_session.get_current_page_url()
+		if not url:
+			return
+
+		target_id = cdp_session.target_id
+		self.event_bus.dispatch(
+			NavigationCompleteEvent(
+				event_type='NavigationCompleteEvent',
+				url=url,
+				target_id=target_id,
+				event_parent_id=event.event_id,
+			)
+		)
+
+	async def on_BrowserStoppedEvent(self, event: BrowserStoppedEvent) -> None:
+		"""Clean up when browser stops."""
+		# Cancel all CDP event handler tasks
+		for task in list(self._cdp_event_tasks):
+			if not task.done():
+				task.cancel()
+		# Wait for all tasks to complete cancellation
+		if self._cdp_event_tasks:
+			await asyncio.gather(*self._cdp_event_tasks, return_exceptions=True)
+		self._cdp_event_tasks.clear()
+
+		# Clean up CDP session
+		# CDP sessions are now cached and managed by BrowserSession
+		self._download_cdp_session = None
+		self._download_cdp_session_setup = False
+
+		# Clear other state
+		self._sessions_with_listeners.clear()
+		self._active_downloads.clear()
+		self._pdf_viewer_cache.clear()
+
+	async def on_NavigationCompleteEvent(self, event: NavigationCompleteEvent) -> None:
+		"""Check for PDFs after navigation completes."""
+		self.logger.debug(f'[DownloadsWatchdog] NavigationCompleteEvent received for {event.url}, tab #{event.target_id[-4:]}')
+
+		# Clear PDF cache for the navigated URL since content may have changed
+		if event.url in self._pdf_viewer_cache:
+			del self._pdf_viewer_cache[event.url]
+
+		# Check if auto-download is enabled
+		auto_download_enabled = self._is_auto_download_enabled()
+		if not auto_download_enabled:
+			return
+
+		# Note: Using network-based PDF detection that doesn't require JavaScript
+
+		target_id = event.target_id
+		self.logger.debug(f'[DownloadsWatchdog] Got target_id={target_id} for tab #{event.target_id[-4:]}')
+
+		is_pdf = await self.check_for_pdf_viewer(target_id)
+		if is_pdf:
+			self.logger.debug(f'[DownloadsWatchdog] 📄 PDF detected at {event.url}, triggering auto-download...')
+			download_path = await self.trigger_pdf_download(target_id)
+			if not download_path:
+				self.logger.warning(f'[DownloadsWatchdog] ⚠️ PDF download failed for {event.url}')
+
+	def _is_auto_download_enabled(self) -> bool:
+		"""Check if auto-download PDFs is enabled in browser profile."""
+		return self.browser_session.browser_profile.auto_download_pdfs
+
+	async def attach_to_target(self, target_id: TargetID) -> None:
+		"""Set up download monitoring for a specific target."""
+
+		# Define CDP event handlers outside of try to avoid indentation/scope issues
+		async def download_will_begin_handler(event: DownloadWillBeginEvent, session_id: SessionID | None):
+			self.logger.debug(f'[DownloadsWatchdog] Download will begin: {event}')
+			# Cache info for later completion event handling (esp. remote browsers)
+			guid = event.get('guid', '')
+			try:
+				suggested_filename = event.get('suggestedFilename')
+				assert suggested_filename, 'CDP DownloadWillBegin missing suggestedFilename'
+				self._cdp_downloads_info[guid] = {
+					'url': event.get('url', ''),
+					'suggested_filename': suggested_filename,
+					'handled': False,
+				}
+			except (AssertionError, KeyError):
+				pass
+			# Create and track the task
+			task = asyncio.create_task(self._handle_cdp_download(event, target_id, session_id))
+			self._cdp_event_tasks.add(task)
+			# Remove from set when done
+			task.add_done_callback(lambda t: self._cdp_event_tasks.discard(t))
+
+		async def download_progress_handler(event: DownloadProgressEvent, session_id: SessionID | None):
+			# Check if download is complete
+			if event.get('state') == 'completed':
+				file_path = event.get('filePath')
+				guid = event.get('guid', '')
+				if self.browser_session.is_local:
+					if file_path:
+						self.logger.debug(f'[DownloadsWatchdog] Download completed: {file_path}')
+						# Track the download
+						self._track_download(file_path)
+						# Mark as handled to prevent fallback duplicate dispatch
+						try:
+							if guid in self._cdp_downloads_info:
+								self._cdp_downloads_info[guid]['handled'] = True
+						except (KeyError, AttributeError):
+							pass
+					else:
+						# No local file path provided, local polling in _handle_cdp_download will handle it
+						self.logger.debug(
+							'[DownloadsWatchdog] No filePath in progress event (local); polling will handle detection'
+						)
+				else:
+					# Remote browser: do not touch local filesystem. Fallback to downloadPath+suggestedFilename
+					info = self._cdp_downloads_info.get(guid, {})
+					try:
+						suggested_filename = info.get('suggested_filename') or (Path(file_path).name if file_path else 'download')
+						downloads_path = str(self.browser_session.browser_profile.downloads_path or '')
+						effective_path = file_path or str(Path(downloads_path) / suggested_filename)
+						file_name = Path(effective_path).name
+						file_ext = Path(file_name).suffix.lower().lstrip('.')
+						self.event_bus.dispatch(
+							FileDownloadedEvent(
+								url=info.get('url', ''),
+								path=str(effective_path),
+								file_name=file_name,
+								file_size=0,
+								file_type=file_ext if file_ext else None,
+							)
+						)
+						self.logger.debug(f'[DownloadsWatchdog] ✅ (remote) Download completed: {effective_path}')
+					finally:
+						if guid in self._cdp_downloads_info:
+							del self._cdp_downloads_info[guid]
+
+		try:
+			downloads_path_raw = self.browser_session.browser_profile.downloads_path
+			if not downloads_path_raw:
+				# logger.info(f'[DownloadsWatchdog] No downloads path configured, skipping target: {target_id}')
+				return  # No downloads path configured
+
+			# Check if we already have a download listener on this session
+			# to prevent duplicate listeners from being added
+			# Note: Since download listeners are set up once per browser session, not per target,
+			# we just track if we've set up the browser-level listener
+			if self._download_cdp_session_setup:
+				self.logger.debug('[DownloadsWatchdog] Download listener already set up for browser session')
+				return
+
+			# logger.debug(f'[DownloadsWatchdog] Setting up CDP download listener for target: {target_id}')
+
+			# Use CDP session for download events but store reference in watchdog
+			if not self._download_cdp_session_setup:
+				# Set up CDP session for downloads (only once per browser session)
+				cdp_client = self.browser_session.cdp_client
+
+				# Set download behavior to allow downloads and enable events
+				downloads_path = self.browser_session.browser_profile.downloads_path
+				if not downloads_path:
+					self.logger.warning('[DownloadsWatchdog] No downloads path configured, skipping CDP download setup')
+					return
+				# Ensure path is properly expanded (~ -> absolute path)
+				expanded_downloads_path = Path(downloads_path).expanduser().resolve()
+				await cdp_client.send.Browser.setDownloadBehavior(
+					params={
+						'behavior': 'allow',
+						'downloadPath': str(expanded_downloads_path),  # Use expanded absolute path
+						'eventsEnabled': True,
+					}
+				)
+
+				# Register the handlers with CDP
+				cdp_client.register.Browser.downloadWillBegin(download_will_begin_handler)  # type: ignore[arg-type]
+				cdp_client.register.Browser.downloadProgress(download_progress_handler)  # type: ignore[arg-type]
+
+				self._download_cdp_session_setup = True
+				self.logger.debug('[DownloadsWatchdog] Set up CDP download listeners')
+
+			# No need to track individual targets since download listener is browser-level
+			# logger.debug(f'[DownloadsWatchdog] Successfully set up CDP download listener for target: {target_id}')
+
+		except Exception as e:
+			self.logger.warning(f'[DownloadsWatchdog] Failed to set up CDP download listener for target {target_id}: {e}')
+
+	def _track_download(self, file_path: str) -> None:
+		"""Track a completed download and dispatch the appropriate event.
+
+		Args:
+			file_path: The path to the downloaded file
+		"""
+		try:
+			# Get file info
+			path = Path(file_path)
+			if path.exists():
+				file_size = path.stat().st_size
+				self.logger.debug(f'[DownloadsWatchdog] Tracked download: {path.name} ({file_size} bytes)')
+
+				# Dispatch download event
+				from browser_use.browser.events import FileDownloadedEvent
+
+				self.event_bus.dispatch(
+					FileDownloadedEvent(
+						url=str(path),  # Use the file path as URL for local files
+						path=str(path),
+						file_name=path.name,
+						file_size=file_size,
+					)
+				)
+			else:
+				self.logger.warning(f'[DownloadsWatchdog] Downloaded file not found: {file_path}')
+		except Exception as e:
+			self.logger.error(f'[DownloadsWatchdog] Error tracking download: {e}')
+
+	async def _handle_cdp_download(
+		self, event: DownloadWillBeginEvent, target_id: TargetID, session_id: SessionID | None
+	) -> None:
+		"""Handle a CDP Page.downloadWillBegin event."""
+		downloads_dir = (
+			Path(
+				self.browser_session.browser_profile.downloads_path
+				or f'{tempfile.gettempdir()}/browser_use_downloads.{str(self.browser_session.id)[-4:]}'
+			)
+			.expanduser()
+			.resolve()
+		)  # Ensure path is properly expanded
+
+		# Initialize variables that may be used outside try blocks
+		unique_filename = None
+		file_size = 0
+		expected_path = None
+		download_result = None
+		download_url = event.get('url', '')
+		suggested_filename = event.get('suggestedFilename', 'download')
+		guid = event.get('guid', '')
+
+		try:
+			self.logger.debug(f'[DownloadsWatchdog] ⬇️ File download starting: {suggested_filename} from {download_url[:100]}...')
+			self.logger.debug(f'[DownloadsWatchdog] Full CDP event: {event}')
+
+			# Since Browser.setDownloadBehavior is already configured, the browser will download the file
+			# We just need to wait for it to appear in the downloads directory
+			expected_path = downloads_dir / suggested_filename
+
+			# Debug: List current directory contents
+			self.logger.debug(f'[DownloadsWatchdog] Downloads directory: {downloads_dir}')
+			if downloads_dir.exists():
+				files_before = list(downloads_dir.iterdir())
+				self.logger.debug(f'[DownloadsWatchdog] Files before download: {[f.name for f in files_before]}')
+
+			# Try manual JavaScript fetch as a fallback for local browsers (disabled for regular local downloads)
+			if self.browser_session.is_local and self._use_js_fetch_for_local:
+				self.logger.debug(f'[DownloadsWatchdog] Attempting JS fetch fallback for {download_url}')
+
+				unique_filename = None
+				file_size = None
+				download_result = None
+				try:
+					# Escape the URL for JavaScript
+					import json
+
+					escaped_url = json.dumps(download_url)
+
+					# Get the proper session for the frame that initiated the download
+					cdp_session = await self.browser_session.cdp_client_for_frame(event.get('frameId'))
+					assert cdp_session
+
+					result = await cdp_session.cdp_client.send.Runtime.evaluate(
+						params={
+							'expression': f"""
+						(async () => {{
+							try {{
+								const response = await fetch({escaped_url});
+								if (!response.ok) {{
+									throw new Error(`HTTP error! status: ${{response.status}}`);
+								}}
+								const blob = await response.blob();
+								const arrayBuffer = await blob.arrayBuffer();
+								const uint8Array = new Uint8Array(arrayBuffer);
+								return {{
+									data: Array.from(uint8Array),
+									size: uint8Array.length,
+									contentType: response.headers.get('content-type') || 'application/octet-stream'
+								}};
+							}} catch (error) {{
+								throw new Error(`Fetch failed: ${{error.message}}`);
+							}}
+						}})()
+						""",
+							'awaitPromise': True,
+							'returnByValue': True,
+						},
+						session_id=cdp_session.session_id,
+					)
+					download_result = result.get('result', {}).get('value')
+
+					if download_result and download_result.get('data'):
+						# Save the file
+						file_data = bytes(download_result['data'])
+						file_size = len(file_data)
+
+						# Ensure unique filename
+						unique_filename = await self._get_unique_filename(str(downloads_dir), suggested_filename)
+						final_path = downloads_dir / unique_filename
+
+						# Write the file
+						import anyio
+
+						async with await anyio.open_file(final_path, 'wb') as f:
+							await f.write(file_data)
+
+						self.logger.debug(f'[DownloadsWatchdog] ✅ Downloaded and saved file: {final_path} ({file_size} bytes)')
+						expected_path = final_path
+						# Emit download event immediately
+						file_ext = expected_path.suffix.lower().lstrip('.')
+						file_type = file_ext if file_ext else None
+						self.event_bus.dispatch(
+							FileDownloadedEvent(
+								url=download_url,
+								path=str(expected_path),
+								file_name=unique_filename or expected_path.name,
+								file_size=file_size or 0,
+								file_type=file_type,
+								mime_type=(download_result.get('contentType') if download_result else None),
+								from_cache=False,
+								auto_download=False,
+							)
+						)
+						# Mark as handled to prevent duplicate dispatch from progress/polling paths
+						try:
+							if guid in self._cdp_downloads_info:
+								self._cdp_downloads_info[guid]['handled'] = True
+						except (KeyError, AttributeError):
+							pass
+						self.logger.debug(
+							f'[DownloadsWatchdog] ✅ File download completed via CDP: {suggested_filename} ({file_size} bytes) saved to {expected_path}'
+						)
+						return
+					else:
+						self.logger.error('[DownloadsWatchdog] ❌ No data received from fetch')
+
+				except Exception as fetch_error:
+					self.logger.error(f'[DownloadsWatchdog] ❌ Failed to download file via fetch: {fetch_error}')
+
+			# For remote browsers, don't poll local filesystem; downloadProgress handler will emit the event
+			if not self.browser_session.is_local:
+				return
+		except Exception as e:
+			self.logger.error(f'[DownloadsWatchdog] ❌ Error handling CDP download: {type(e).__name__} {e}')
+
+		# If we reach here, the fetch method failed, so wait for native download
+		# Poll the downloads directory for new files
+		self.logger.debug(f'[DownloadsWatchdog] Checking if browser auto-download saved the file for us: {suggested_filename}')
+
+		# Get initial list of files in downloads directory
+		initial_files = set()
+		if Path(downloads_dir).exists():
+			for f in Path(downloads_dir).iterdir():
+				if f.is_file() and not f.name.startswith('.'):
+					initial_files.add(f.name)
+
+		# Poll for new files
+		max_wait = 20  # seconds
+		start_time = asyncio.get_event_loop().time()
+
+		while asyncio.get_event_loop().time() - start_time < max_wait:
+			await asyncio.sleep(5.0)  # Check every 5 seconds
+
+			if Path(downloads_dir).exists():
+				for file_path in Path(downloads_dir).iterdir():
+					# Skip hidden files and files that were already there
+					if file_path.is_file() and not file_path.name.startswith('.') and file_path.name not in initial_files:
+						# Check if file has content (> 4 bytes)
+						try:
+							file_size = file_path.stat().st_size
+							if file_size > 4:
+								# Found a new download!
+								self.logger.debug(
+									f'[DownloadsWatchdog] ✅ Found downloaded file: {file_path} ({file_size} bytes)'
+								)
+
+								# Determine file type from extension
+								file_ext = file_path.suffix.lower().lstrip('.')
+								file_type = file_ext if file_ext else None
+
+								# Dispatch download event
+								# Skip if already handled by progress/JS fetch
+								info = self._cdp_downloads_info.get(guid, {})
+								if info.get('handled'):
+									return
+								self.event_bus.dispatch(
+									FileDownloadedEvent(
+										url=download_url,
+										path=str(file_path),
+										file_name=file_path.name,
+										file_size=file_size,
+										file_type=file_type,
+									)
+								)
+								# Mark as handled after dispatch
+								try:
+									if guid in self._cdp_downloads_info:
+										self._cdp_downloads_info[guid]['handled'] = True
+								except (KeyError, AttributeError):
+									pass
+								return
+						except Exception as e:
+							self.logger.debug(f'[DownloadsWatchdog] Error checking file {file_path}: {e}')
+
+		self.logger.warning(f'[DownloadsWatchdog] Download did not complete within {max_wait} seconds')
+
+	async def _handle_download(self, download: Any) -> None:
+		"""Handle a download event."""
+		download_id = f'{id(download)}'
+		self._active_downloads[download_id] = download
+		self.logger.debug(f'[DownloadsWatchdog] ⬇️ Handling download: {download.suggested_filename} from {download.url[:100]}...')
+
+		# Debug: Check if download is already being handled elsewhere
+		failure = (
+			await download.failure()
+		)  # TODO: it always fails for some reason, figure out why connect_over_cdp makes accept_downloads not work
+		self.logger.warning(f'[DownloadsWatchdog] ❌ Download state - canceled: {failure}, url: {download.url}')
+		# logger.info(f'[DownloadsWatchdog] Active downloads count: {len(self._active_downloads)}')
+
+		try:
+			current_step = 'getting_download_info'
+			# Get download info immediately
+			url = download.url
+			suggested_filename = download.suggested_filename
+
+			current_step = 'determining_download_directory'
+			# Determine download directory from browser profile
+			downloads_dir = self.browser_session.browser_profile.downloads_path
+			if not downloads_dir:
+				downloads_dir = str(Path.home() / 'Downloads')
+			else:
+				downloads_dir = str(downloads_dir)  # Ensure it's a string
+
+			# Check if Playwright already auto-downloaded the file (due to CDP setup)
+			original_path = Path(downloads_dir) / suggested_filename
+			if original_path.exists() and original_path.stat().st_size > 0:
+				self.logger.debug(
+					f'[DownloadsWatchdog] File already downloaded by Playwright: {original_path} ({original_path.stat().st_size} bytes)'
+				)
+
+				# Use the existing file instead of creating a duplicate
+				download_path = original_path
+				file_size = original_path.stat().st_size
+				unique_filename = suggested_filename
+			else:
+				current_step = 'generating_unique_filename'
+				# Ensure unique filename
+				unique_filename = await self._get_unique_filename(downloads_dir, suggested_filename)
+				download_path = Path(downloads_dir) / unique_filename
+
+				self.logger.debug(f'[DownloadsWatchdog] Download started: {unique_filename} from {url[:100]}...')
+
+				current_step = 'calling_save_as'
+				# Save the download using Playwright's save_as method
+				self.logger.debug(f'[DownloadsWatchdog] Saving download to: {download_path}')
+				self.logger.debug(f'[DownloadsWatchdog] Download path exists: {download_path.parent.exists()}')
+				self.logger.debug(f'[DownloadsWatchdog] Download path writable: {os.access(download_path.parent, os.W_OK)}')
+
+				try:
+					self.logger.debug('[DownloadsWatchdog] About to call download.save_as()...')
+					await download.save_as(str(download_path))
+					self.logger.debug(f'[DownloadsWatchdog] Successfully saved download to: {download_path}')
+					current_step = 'save_as_completed'
+				except Exception as save_error:
+					self.logger.error(f'[DownloadsWatchdog] save_as() failed with error: {save_error}')
+					raise save_error
+
+				# Get file info
+				file_size = download_path.stat().st_size if download_path.exists() else 0
+
+			# Determine file type from extension
+			file_ext = download_path.suffix.lower().lstrip('.')
+			file_type = file_ext if file_ext else None
+
+			# Try to get MIME type from response headers if available
+			mime_type = None
+			# Note: Playwright doesn't expose response headers directly from Download object
+
+			# Check if this was a PDF auto-download
+			auto_download = False
+			if file_type == 'pdf':
+				auto_download = self._is_auto_download_enabled()
+
+			# Emit download event
+			self.event_bus.dispatch(
+				FileDownloadedEvent(
+					url=url,
+					path=str(download_path),
+					file_name=suggested_filename,
+					file_size=file_size,
+					file_type=file_type,
+					mime_type=mime_type,
+					from_cache=False,
+					auto_download=auto_download,
+				)
+			)
+
+			self.logger.debug(
+				f'[DownloadsWatchdog] ✅ Download completed: {suggested_filename} ({file_size} bytes) saved to {download_path}'
+			)
+
+			# File is now tracked on filesystem, no need to track in memory
+
+		except Exception as e:
+			self.logger.error(
+				f'[DownloadsWatchdog] Error handling download at step "{locals().get("current_step", "unknown")}", error: {e}'
+			)
+			self.logger.error(
+				f'[DownloadsWatchdog] Download state - URL: {download.url}, filename: {download.suggested_filename}'
+			)
+		finally:
+			# Clean up tracking
+			if download_id in self._active_downloads:
+				del self._active_downloads[download_id]
+
+	async def check_for_pdf_viewer(self, target_id: TargetID) -> bool:
+		"""Check if the current target is a PDF using network-based detection.
+
+		This method avoids JavaScript execution that can crash WebSocket connections.
+		Returns True if a PDF is detected and should be downloaded.
+		"""
+		self.logger.debug(f'[DownloadsWatchdog] Checking if target {target_id} is PDF viewer...')
+
+		# Get target info to get URL
+		cdp_client = self.browser_session.cdp_client
+		targets = await cdp_client.send.Target.getTargets()
+		target_info = next((t for t in targets['targetInfos'] if t['targetId'] == target_id), None)
+		if not target_info:
+			self.logger.warning(f'[DownloadsWatchdog] No target info found for {target_id}')
+			return False
+
+		page_url = target_info.get('url', '')
+
+		# Check cache first
+		if page_url in self._pdf_viewer_cache:
+			cached_result = self._pdf_viewer_cache[page_url]
+			self.logger.debug(f'[DownloadsWatchdog] Using cached PDF check result for {page_url}: {cached_result}')
+			return cached_result
+
+		try:
+			# Method 1: Check URL patterns (fastest, most reliable)
+			url_is_pdf = self._check_url_for_pdf(page_url)
+			if url_is_pdf:
+				self.logger.debug(f'[DownloadsWatchdog] PDF detected via URL pattern: {page_url}')
+				self._pdf_viewer_cache[page_url] = True
+				return True
+
+			# Method 2: Check network response headers via CDP (safer than JavaScript)
+			header_is_pdf = await self._check_network_headers_for_pdf(target_id)
+			if header_is_pdf:
+				self.logger.debug(f'[DownloadsWatchdog] PDF detected via network headers: {page_url}')
+				self._pdf_viewer_cache[page_url] = True
+				return True
+
+			# Method 3: Check Chrome's PDF viewer specific URLs
+			chrome_pdf_viewer = self._is_chrome_pdf_viewer_url(page_url)
+			if chrome_pdf_viewer:
+				self.logger.debug(f'[DownloadsWatchdog] Chrome PDF viewer detected: {page_url}')
+				self._pdf_viewer_cache[page_url] = True
+				return True
+
+			# Not a PDF
+			self._pdf_viewer_cache[page_url] = False
+			return False
+
+		except Exception as e:
+			self.logger.warning(f'[DownloadsWatchdog] ❌ Error checking for PDF viewer: {e}')
+			self._pdf_viewer_cache[page_url] = False
+			return False
+
+	def _check_url_for_pdf(self, url: str) -> bool:
+		"""Check if URL indicates a PDF file."""
+		if not url:
+			return False
+
+		url_lower = url.lower()
+
+		# Direct PDF file extensions
+		if url_lower.endswith('.pdf'):
+			return True
+
+		# PDF in path
+		if '.pdf' in url_lower:
+			return True
+
+		# PDF MIME type in URL parameters
+		if any(
+			param in url_lower
+			for param in [
+				'content-type=application/pdf',
+				'content-type=application%2fpdf',
+				'mimetype=application/pdf',
+				'type=application/pdf',
+			]
+		):
+			return True
+
+		return False
+
+	def _is_chrome_pdf_viewer_url(self, url: str) -> bool:
+		"""Check if this is Chrome's internal PDF viewer URL."""
+		if not url:
+			return False
+
+		url_lower = url.lower()
+
+		# Chrome PDF viewer uses chrome-extension:// URLs
+		if 'chrome-extension://' in url_lower and 'pdf' in url_lower:
+			return True
+
+		# Chrome PDF viewer internal URLs
+		if url_lower.startswith('chrome://') and 'pdf' in url_lower:
+			return True
+
+		return False
+
+	async def _check_network_headers_for_pdf(self, target_id: TargetID) -> bool:
+		"""Infer PDF via navigation history/URL; headers are not available post-navigation in this context."""
+		try:
+			import asyncio
+
+			# Get CDP session
+			temp_session = await self.browser_session.get_or_create_cdp_session(target_id, focus=False)
+
+			# Get navigation history to find the main resource
+			history = await asyncio.wait_for(
+				temp_session.cdp_client.send.Page.getNavigationHistory(session_id=temp_session.session_id), timeout=3.0
+			)
+
+			current_entry = history.get('entries', [])
+			if current_entry:
+				current_index = history.get('currentIndex', 0)
+				if 0 <= current_index < len(current_entry):
+					current_url = current_entry[current_index].get('url', '')
+
+					# Check if the URL itself suggests PDF
+					if self._check_url_for_pdf(current_url):
+						return True
+
+			# Note: CDP doesn't easily expose response headers for completed navigations
+			# For more complex cases, we'd need to set up Network.responseReceived listeners
+			# before navigation, but that's overkill for most PDF detection cases
+
+			return False
+
+		except Exception as e:
+			self.logger.debug(f'[DownloadsWatchdog] Network headers check failed (non-critical): {e}')
+			return False
+
+	async def trigger_pdf_download(self, target_id: TargetID) -> str | None:
+		"""Trigger download of a PDF from Chrome's PDF viewer.
+
+		Returns the download path if successful, None otherwise.
+		"""
+		self.logger.debug(f'[DownloadsWatchdog] trigger_pdf_download called for target_id={target_id}')
+
+		if not self.browser_session.browser_profile.downloads_path:
+			self.logger.warning('[DownloadsWatchdog] ❌ No downloads path configured, cannot save PDF download')
+			return None
+
+		downloads_path = self.browser_session.browser_profile.downloads_path
+		self.logger.debug(f'[DownloadsWatchdog] Downloads path: {downloads_path}')
+
+		try:
+			# Create a temporary CDP session for this target without switching focus
+			import asyncio
+
+			self.logger.debug(f'[DownloadsWatchdog] Creating CDP session for PDF download from target {target_id}')
+			temp_session = await self.browser_session.get_or_create_cdp_session(target_id, focus=False)
+
+			# Try to get the PDF URL with timeout
+			result = await asyncio.wait_for(
+				temp_session.cdp_client.send.Runtime.evaluate(
+					params={
+						'expression': """
+				(() => {
+					// For Chrome's PDF viewer, the actual URL is in window.location.href
+					// The embed element's src is often "about:blank"
+					const embedElement = document.querySelector('embed[type="application/x-google-chrome-pdf"]') ||
+										document.querySelector('embed[type="application/pdf"]');
+					if (embedElement) {
+						// Chrome PDF viewer detected - use the page URL
+						return { url: window.location.href };
+					}
+					// Fallback to window.location.href anyway
+					return { url: window.location.href };
+				})()
+				""",
+						'returnByValue': True,
+					},
+					session_id=temp_session.session_id,
+				),
+				timeout=5.0,  # 5 second timeout to prevent hanging
+			)
+			pdf_info = result.get('result', {}).get('value', {})
+
+			pdf_url = pdf_info.get('url', '')
+			if not pdf_url:
+				self.logger.warning(f'[DownloadsWatchdog] ❌ Could not determine PDF URL for download {pdf_info}')
+				return None
+
+			# Generate filename from URL
+			pdf_filename = os.path.basename(pdf_url.split('?')[0])  # Remove query params
+			if not pdf_filename or not pdf_filename.endswith('.pdf'):
+				parsed = urlparse(pdf_url)
+				pdf_filename = os.path.basename(parsed.path) or 'document.pdf'
+				if not pdf_filename.endswith('.pdf'):
+					pdf_filename += '.pdf'
+
+			self.logger.debug(f'[DownloadsWatchdog] Generated filename: {pdf_filename}')
+
+			# Check if already downloaded by looking in the downloads directory
+			downloads_dir = str(self.browser_session.browser_profile.downloads_path)
+			if os.path.exists(downloads_dir):
+				existing_files = os.listdir(downloads_dir)
+				if pdf_filename in existing_files:
+					self.logger.debug(f'[DownloadsWatchdog] PDF already downloaded: {pdf_filename}')
+					return None
+
+			self.logger.debug(f'[DownloadsWatchdog] Starting PDF download from: {pdf_url[:100]}...')
+
+			# Download using JavaScript fetch to leverage browser cache
+			try:
+				# Properly escape the URL to prevent JavaScript injection
+				escaped_pdf_url = json.dumps(pdf_url)
+
+				result = await asyncio.wait_for(
+					temp_session.cdp_client.send.Runtime.evaluate(
+						params={
+							'expression': f"""
+					(async () => {{
+						try {{
+							// Use fetch with cache: 'force-cache' to prioritize cached version
+							const response = await fetch({escaped_pdf_url}, {{
+								cache: 'force-cache'
+							}});
+							if (!response.ok) {{
+								throw new Error(`HTTP error! status: ${{response.status}}`);
+							}}
+							const blob = await response.blob();
+							const arrayBuffer = await blob.arrayBuffer();
+							const uint8Array = new Uint8Array(arrayBuffer);
+							
+							// Check if served from cache
+							const fromCache = response.headers.has('age') || 
+											 !response.headers.has('date');
+											 
+							return {{ 
+								data: Array.from(uint8Array),
+								fromCache: fromCache,
+								responseSize: uint8Array.length,
+								transferSize: response.headers.get('content-length') || 'unknown'
+							}};
+						}} catch (error) {{
+							throw new Error(`Fetch failed: ${{error.message}}`);
+						}}
+					}})()
+					""",
+							'awaitPromise': True,
+							'returnByValue': True,
+						},
+						session_id=temp_session.session_id,
+					),
+					timeout=10.0,  # 10 second timeout for download operation
+				)
+				download_result = result.get('result', {}).get('value', {})
+
+				if download_result and download_result.get('data') and len(download_result['data']) > 0:
+					# Ensure unique filename
+					downloads_dir = str(self.browser_session.browser_profile.downloads_path)
+					# Ensure downloads directory exists
+					os.makedirs(downloads_dir, exist_ok=True)
+					unique_filename = await self._get_unique_filename(downloads_dir, pdf_filename)
+					download_path = os.path.join(downloads_dir, unique_filename)
+
+					# Save the PDF asynchronously
+					async with await anyio.open_file(download_path, 'wb') as f:
+						await f.write(bytes(download_result['data']))
+
+					# Verify file was written successfully
+					if os.path.exists(download_path):
+						actual_size = os.path.getsize(download_path)
+						self.logger.debug(
+							f'[DownloadsWatchdog] PDF file written successfully: {download_path} ({actual_size} bytes)'
+						)
+					else:
+						self.logger.error(f'[DownloadsWatchdog] ❌ Failed to write PDF file to: {download_path}')
+						return None
+
+					# Log cache information
+					cache_status = 'from cache' if download_result.get('fromCache') else 'from network'
+					response_size = download_result.get('responseSize', 0)
+					self.logger.debug(
+						f'[DownloadsWatchdog] ✅ Auto-downloaded PDF ({cache_status}, {response_size:,} bytes): {download_path}'
+					)
+
+					# Emit file downloaded event
+					self.logger.debug(f'[DownloadsWatchdog] Dispatching FileDownloadedEvent for {unique_filename}')
+					self.event_bus.dispatch(
+						FileDownloadedEvent(
+							url=pdf_url,
+							path=download_path,
+							file_name=unique_filename,
+							file_size=response_size,
+							file_type='pdf',
+							mime_type='application/pdf',
+							from_cache=download_result.get('fromCache', False),
+							auto_download=True,
+						)
+					)
+
+					# No need to detach - session is cached
+					return download_path
+				else:
+					self.logger.warning(f'[DownloadsWatchdog] No data received when downloading PDF from {pdf_url}')
+					return None
+
+			except Exception as e:
+				self.logger.warning(f'[DownloadsWatchdog] Failed to auto-download PDF from {pdf_url}: {type(e).__name__}: {e}')
+				return None
+
+		except TimeoutError:
+			self.logger.debug('[DownloadsWatchdog] PDF download operation timed out')
+			return None
+		except Exception as e:
+			self.logger.error(f'[DownloadsWatchdog] Error in PDF download: {type(e).__name__}: {e}')
+			return None
+
+	@staticmethod
+	async def _get_unique_filename(directory: str, filename: str) -> str:
+		"""Generate a unique filename for downloads by appending (1), (2), etc., if a file already exists."""
+		base, ext = os.path.splitext(filename)
+		counter = 1
+		new_filename = filename
+		while os.path.exists(os.path.join(directory, new_filename)):
+			new_filename = f'{base} ({counter}){ext}'
+			counter += 1
+		return new_filename
+
+
+# Fix Pydantic circular dependency - this will be called from session.py after BrowserSession is defined