chore: allow forking control flow in route (#1375)

Author: pavelfeldman

playwright/_impl/_browser_context.py

@@ -262,7 +262,12 @@ async def route(
     ) -> None:
         self._routes.insert(
             0,
-            RouteHandler(URLMatcher(self._options.get("baseURL"), url), handler, times),
+            RouteHandler(
+                URLMatcher(self._options.get("baseURL"), url),
+                handler,
+                True if self._dispatcher_fiber else False,
+                times,
+            ),
         )
         if len(self._routes) == 1:
             await self._channel.send(

playwright/_impl/_connection.py

@@ -293,6 +293,9 @@ def dispatch(self, msg: ParsedMessagePayload) -> None:
         try:
             if self._is_sync:
                 for listener in object._channel.listeners(method):
+                    # Each event handler is a potentilly blocking context, create a fiber for each
+                    # and switch to them in order, until they block inside and pass control to each
+                    # other and then eventually back to dispatcher as listener functions return.
                     g = greenlet(listener)
                     g.switch(self._replace_guids_with_channels(params))
             else:

playwright/_impl/_helper.py

@@ -37,6 +37,8 @@
 )
 from urllib.parse import urljoin
 
+from greenlet import greenlet
+
 from playwright._impl._api_structures import NameValue
 from playwright._impl._api_types import Error, TimeoutError
 
@@ -208,23 +210,34 @@ def __init__(
         self,
         matcher: URLMatcher,
         handler: RouteHandlerCallback,
+        is_sync: bool,
         times: Optional[int] = None,
     ):
         self.matcher = matcher
         self.handler = handler
         self._times = times if times else math.inf
         self._handled_count = 0
+        self._is_sync = is_sync
 
     def matches(self, request_url: str) -> bool:
         return self.matcher.matches(request_url)
 
     def handle(self, route: "Route", request: "Request") -> None:
-        self._handled_count += 1
-        result = cast(
-            Callable[["Route", "Request"], Union[Coroutine, Any]], self.handler
-        )(route, request)
-        if inspect.iscoroutine(result):
-            asyncio.create_task(result)
+        def impl() -> None:
+            self._handled_count += 1
+            result = cast(
+                Callable[["Route", "Request"], Union[Coroutine, Any]], self.handler
+            )(route, request)
+            if inspect.iscoroutine(result):
+                asyncio.create_task(result)
+
+        # As with event handlers, each route handler is a potentially blocking context
+        # so it needs a fiber.
+        if self._is_sync:
+            g = greenlet(impl)
+            g.switch()
+        else:
+            impl()
 
     @property
     def is_active(self) -> bool:

playwright/_impl/_page.py

@@ -236,17 +236,21 @@ def _on_frame_detached(self, frame: Frame) -> None:
         self.emit(Page.Events.FrameDetached, frame)
 
     def _on_route(self, route: Route, request: Request) -> None:
-        for handler_entry in self._routes:
-            if handler_entry.matches(request.url):
-                try:
-                    handler_entry.handle(route, request)
-                finally:
-                    if not handler_entry.is_active:
-                        self._routes.remove(handler_entry)
-                        if len(self._routes) == 0:
-                            asyncio.create_task(self._disable_interception())
-                return
-        self._browser_context._on_route(route, request)
+        # Make this artificially async so that we could chain routes.
+        async def inner_route() -> None:
+            for handler_entry in self._routes:
+                if handler_entry.matches(request.url):
+                    try:
+                        handler_entry.handle(route, request)
+                    finally:
+                        if not handler_entry.is_active:
+                            self._routes.remove(handler_entry)
+                            if len(self._routes) == 0:
+                                asyncio.create_task(self._disable_interception())
+                    return
+            self._browser_context._on_route(route, request)
+
+        asyncio.create_task(inner_route())
 
     def _on_binding(self, binding_call: "BindingCall") -> None:
         func = self._bindings.get(binding_call._initializer["name"])
@@ -578,6 +582,7 @@ async def route(
             RouteHandler(
                 URLMatcher(self._browser_context._options.get("baseURL"), url),
                 handler,
+                True if self._dispatcher_fiber else False,
                 times,
             ),
         )

playwright/sync_api/_context_manager.py

@@ -60,10 +60,14 @@ def __enter__(self) -> SyncPlaywright:
             self._watcher = ThreadedChildWatcher()
             asyncio.set_child_watcher(self._watcher)  # type: ignore
 
+        # Create a new fiber for the protocol dispatcher. It will be pumping events
+        # until the end of times. We will pass control to that fiber every time we
+        # block while waiting for a response.
         def greenlet_main() -> None:
             self._loop.run_until_complete(self._connection.run_as_sync())
 
         dispatcher_fiber = greenlet(greenlet_main)
+
         self._connection = Connection(
             dispatcher_fiber,
             create_remote_object,
@@ -77,9 +81,11 @@ def callback_wrapper(playwright_impl: Playwright) -> None:
             self._playwright = SyncPlaywright(playwright_impl)
             g_self.switch()
 
+        # Switch control to the dispatcher, it'll fire an event and pass control to
+        # the calling greenlet.
         self._connection.call_on_object_with_known_name("Playwright", callback_wrapper)
-
         dispatcher_fiber.switch()
+
         playwright = self._playwright
         playwright.stop = self.__exit__  # type: ignore
         return playwright