Fix Webhook not working on Windows with Python 3.8+ (#2067)

* Fix start_webhook NotImplementedError on windows with python3.8

* Fine-tune and add tests.

* Minor fixes

* typos

* Make Codacy happy

Co-authored-by: n5y <41209360+n5y@users.noreply.github.com>

telegram/ext/updater.py

@@ -258,11 +258,15 @@ class Updater:
                 # Create & start threads
                 self.job_queue.start()
                 dispatcher_ready = Event()
+                polling_ready = Event()
                 self._init_thread(self.dispatcher.start, "dispatcher", ready=dispatcher_ready)
                 self._init_thread(self._start_polling, "updater", poll_interval, timeout,
-                                  read_latency, bootstrap_retries, clean, allowed_updates)
+                                  read_latency, bootstrap_retries, clean, allowed_updates,
+                                  ready=polling_ready)
 
+                self.logger.debug('Waiting for Dispatcher and polling to start')
                 dispatcher_ready.wait()
+                polling_ready.wait()
 
                 # Return the update queue so the main thread can insert updates
                 return self.update_queue
@@ -276,7 +280,8 @@ class Updater:
                       clean=False,
                       bootstrap_retries=0,
                       webhook_url=None,
-                      allowed_updates=None):
+                      allowed_updates=None,
+                      force_event_loop=False):
         """
         Starts a small http server to listen for updates via webhook. If cert
         and key are not provided, the webhook will be started directly on
@@ -284,6 +289,15 @@ class Updater:
         application. Else, the webhook will be started on
         https://listen:port/url_path
 
+        Note:
+            Due to an incompatibility of the Tornado library PTB uses for the webhook with Python
+            3.8+ on Windows machines, PTB will attempt to set the event loop to
+            :attr:`asyncio.SelectorEventLoop` and raise an exception, if an incompatible event loop
+            has already been specified. See this `thread`_ for more details. To suppress the
+            exception, set :attr:`force_event_loop` to :obj:`True`.
+
+            .. _thread: https://github.com/tornadoweb/tornado/issues/2608
+
         Args:
             listen (:obj:`str`, optional): IP-Address to listen on. Default ``127.0.0.1``.
             port (:obj:`int`, optional): Port the bot should be listening on. Default ``80``.
@@ -303,6 +317,8 @@ class Updater:
                 NAT, reverse proxy, etc. Default is derived from `listen`, `port` & `url_path`.
             allowed_updates (List[:obj:`str`], optional): Passed to
                 :attr:`telegram.Bot.set_webhook`.
+            force_event_loop (:obj:`bool`, optional): Force using the current event loop. See above
+                note for details. Defaults to :obj:`False`
 
         Returns:
             :obj:`Queue`: The update queue that can be filled from the main thread.
@@ -313,16 +329,23 @@ class Updater:
                 self.running = True
 
                 # Create & start threads
+                webhook_ready = Event()
+                dispatcher_ready = Event()
                 self.job_queue.start()
-                self._init_thread(self.dispatcher.start, "dispatcher"),
+                self._init_thread(self.dispatcher.start, "dispatcher", dispatcher_ready)
                 self._init_thread(self._start_webhook, "updater", listen, port, url_path, cert,
-                                  key, bootstrap_retries, clean, webhook_url, allowed_updates)
+                                  key, bootstrap_retries, clean, webhook_url, allowed_updates,
+                                  ready=webhook_ready, force_event_loop=force_event_loop)
+
+                self.logger.debug('Waiting for Dispatcher and Webhook to start')
+                webhook_ready.wait()
+                dispatcher_ready.wait()
 
                 # Return the update queue so the main thread can insert updates
                 return self.update_queue
 
     def _start_polling(self, poll_interval, timeout, read_latency, bootstrap_retries, clean,
-                       allowed_updates):  # pragma: no cover
+                       allowed_updates, ready=None):  # pragma: no cover
         # Thread target of thread 'updater'. Runs in background, pulls
         # updates from Telegram and inserts them in the update queue of the
         # Dispatcher.
@@ -354,6 +377,9 @@ class Updater:
             # broadcast it
             self.update_queue.put(exc)
 
+        if ready is not None:
+            ready.set()
+
         self._network_loop_retry(polling_action_cb, polling_onerr_cb, 'getting Updates',
                                  poll_interval)
 
@@ -410,7 +436,7 @@ class Updater:
         return current_interval
 
     def _start_webhook(self, listen, port, url_path, cert, key, bootstrap_retries, clean,
-                       webhook_url, allowed_updates):
+                       webhook_url, allowed_updates, ready=None, force_event_loop=False):
         self.logger.debug('Updater thread started (webhook)')
         use_ssl = cert is not None and key is not None
         if not url_path.startswith('/'):
@@ -448,7 +474,7 @@ class Updater:
             self.logger.warning("cleaning updates is not supported if "
                                 "SSL-termination happens elsewhere; skipping")
 
-        self.httpd.serve_forever()
+        self.httpd.serve_forever(force_event_loop=force_event_loop, ready=ready)
 
     @staticmethod
     def _gen_webhook_url(listen, port, url_path):

telegram/utils/webhookhandler.py

@@ -16,10 +16,13 @@
 #
 # You should have received a copy of the GNU Lesser Public License
 # along with this program.  If not, see [http://www.gnu.org/licenses/].
+import asyncio
+import os
 import sys
 import logging
 from telegram import Update
 from threading import Lock
+
 try:
     import ujson as json
 except ImportError:
@@ -41,13 +44,17 @@ class WebhookServer:
         self.server_lock = Lock()
         self.shutdown_lock = Lock()
 
-    def serve_forever(self):
+    def serve_forever(self, force_event_loop=False, ready=None):
         with self.server_lock:
-            IOLoop().make_current()
             self.is_running = True
             self.logger.debug('Webhook Server started.')
-            self.http_server.listen(self.port, address=self.listen)
+            self._ensure_event_loop(force_event_loop=force_event_loop)
             self.loop = IOLoop.current()
+            self.http_server.listen(self.port, address=self.listen)
+
+            if ready is not None:
+                ready.set()
+
             self.loop.start()
             self.logger.debug('Webhook Server stopped.')
             self.is_running = False
@@ -65,6 +72,42 @@ class WebhookServer:
         self.logger.debug('Exception happened during processing of request from %s',
                           client_address, exc_info=True)
 
+    def _ensure_event_loop(self, force_event_loop=False):
+        """If there's no asyncio event loop set for the current thread - create one."""
+        try:
+            loop = asyncio.get_event_loop()
+            if (not force_event_loop and os.name == 'nt' and sys.version_info >= (3, 8)
+                    and isinstance(loop, asyncio.ProactorEventLoop)):
+                raise TypeError('`ProactorEventLoop` is incompatible with '
+                                'Tornado. Please switch to `SelectorEventLoop`.')
+        except RuntimeError:
+            # Python 3.8 changed default asyncio event loop implementation on windows
+            # from SelectorEventLoop to ProactorEventLoop. At the time of this writing
+            # Tornado doesn't support ProactorEventLoop and suggests that end users
+            # change asyncio event loop policy to WindowsSelectorEventLoopPolicy.
+            # https://github.com/tornadoweb/tornado/issues/2608
+            # To avoid changing the global event loop policy, we manually construct
+            # a SelectorEventLoop instance instead of using asyncio.new_event_loop().
+            # Note that the fix is not applied in the main thread, as that can break
+            # user code in even more ways than changing the global event loop policy can,
+            # and because Updater always starts its webhook server in a separate thread.
+            # Ideally, we would want to check that Tornado actually raises the expected
+            # NotImplementedError, but it's not possible to cleanly recover from that
+            # exception in current Tornado version.
+            if (os.name == 'nt'
+                    and sys.version_info >= (3, 8)
+                    # OS+version check makes hasattr check redundant, but just to be sure
+                    and hasattr(asyncio, 'WindowsProactorEventLoopPolicy')
+                    and (isinstance(
+                         asyncio.get_event_loop_policy(),
+                         asyncio.WindowsProactorEventLoopPolicy))):  # pylint: disable=E1101
+                self.logger.debug(
+                    'Applying Tornado asyncio event loop fix for Python 3.8+ on Windows')
+                loop = asyncio.SelectorEventLoop()
+            else:
+                loop = asyncio.new_event_loop()
+            asyncio.set_event_loop(loop)
+
 
 class WebhookAppClass(tornado.web.Application):
 
@@ -88,35 +131,6 @@ class WebhookHandler(tornado.web.RequestHandler):
     def __init__(self, application, request, **kwargs):
         super().__init__(application, request, **kwargs)
         self.logger = logging.getLogger(__name__)
-        self._init_asyncio_patch()
-
-    def _init_asyncio_patch(self):
-        """set default asyncio policy to be compatible with tornado
-        Tornado 6 (at least) is not compatible with the default
-        asyncio implementation on Windows
-        Pick the older SelectorEventLoopPolicy on Windows
-        if the known-incompatible default policy is in use.
-        do this as early as possible to make it a low priority and overrideable
-        ref: https://github.com/tornadoweb/tornado/issues/2608
-        TODO: if/when tornado supports the defaults in asyncio,
-                remove and bump tornado requirement for py38
-        Copied from https://github.com/ipython/ipykernel/pull/456/
-        """
-        if sys.platform.startswith("win") and sys.version_info >= (3, 8):
-            import asyncio
-            try:
-                from asyncio import (
-                    WindowsProactorEventLoopPolicy,
-                    WindowsSelectorEventLoopPolicy,
-                )
-            except ImportError:
-                pass
-                # not affected
-            else:
-                if isinstance(asyncio.get_event_loop_policy(), WindowsProactorEventLoopPolicy):
-                    # WindowsProactorEventLoopPolicy is not compatible with tornado 6
-                    # fallback to the pre-3.8 default of Selector
-                    asyncio.set_event_loop_policy(WindowsSelectorEventLoopPolicy())
 
     def initialize(self, bot, update_queue, default_quote=None):
         self.bot = bot

tests/test_updater.py

@@ -16,11 +16,14 @@
 #
 # You should have received a copy of the GNU Lesser Public License
 # along with this program.  If not, see [http://www.gnu.org/licenses/].
+import asyncio
 import logging
 import os
 import signal
 import sys
-import asyncio
+import threading
+from contextlib import contextmanager
+
 from flaky import flaky
 from functools import partial
 from queue import Queue
@@ -36,37 +39,28 @@ import pytest
 from telegram import TelegramError, Message, User, Chat, Update, Bot
 from telegram.error import Unauthorized, InvalidToken, TimedOut, RetryAfter
 from telegram.ext import Updater, Dispatcher, DictPersistence
+from telegram.utils.webhookhandler import WebhookServer
 
 signalskip = pytest.mark.skipif(sys.platform == 'win32',
                                 reason='Can\'t send signals without stopping '
                                        'whole process on windows')
 
 
-if sys.platform.startswith("win") and sys.version_info >= (3, 8):
-    """set default asyncio policy to be compatible with tornado
-    Tornado 6 (at least) is not compatible with the default
-    asyncio implementation on Windows
-    Pick the older SelectorEventLoopPolicy on Windows
-    if the known-incompatible default policy is in use.
-    do this as early as possible to make it a low priority and overrideable
-    ref: https://github.com/tornadoweb/tornado/issues/2608
-    TODO: if/when tornado supports the defaults in asyncio,
-            remove and bump tornado requirement for py38
-    Copied from https://github.com/ipython/ipykernel/pull/456/
-    """
+ASYNCIO_LOCK = threading.Lock()
+
+
+@contextmanager
+def set_asyncio_event_loop(loop):
+    with ASYNCIO_LOCK:
         try:
-        from asyncio import (
-            WindowsProactorEventLoopPolicy,
-            WindowsSelectorEventLoopPolicy,
-        )
-    except ImportError:
-        pass
-        # not affected
-    else:
-        if type(asyncio.get_event_loop_policy()) is WindowsProactorEventLoopPolicy:
-            # WindowsProactorEventLoopPolicy is not compatible with tornado 6
-            # fallback to the pre-3.8 default of Selector
-            asyncio.set_event_loop_policy(WindowsSelectorEventLoopPolicy())
+            orig_lop = asyncio.get_event_loop()
+        except RuntimeError:
+            orig_lop = None
+        asyncio.set_event_loop(loop)
+        try:
+            yield
+        finally:
+            asyncio.set_event_loop(orig_lop)
 
 
 class TestUpdater:
@@ -203,6 +197,106 @@ class TestUpdater:
             assert not updater.httpd.is_running
             updater.stop()
 
+    def test_start_webhook_no_warning_or_error_logs(self, caplog, updater, monkeypatch):
+        monkeypatch.setattr(updater.bot, 'set_webhook', lambda *args, **kwargs: True)
+        monkeypatch.setattr(updater.bot, 'delete_webhook', lambda *args, **kwargs: True)
+        # prevent api calls from @info decorator when updater.bot.id is used in thread names
+        monkeypatch.setattr(updater.bot, 'bot', User(id=123, first_name='bot', is_bot=True))
+        monkeypatch.setattr(updater.bot, '_commands', [])
+
+        ip = '127.0.0.1'
+        port = randrange(1024, 49152)  # Select random port
+        with caplog.at_level(logging.WARNING):
+            updater.start_webhook(ip, port)
+            updater.stop()
+        assert not caplog.records
+
+    @pytest.mark.skipif(os.name != 'nt' or sys.version_info < (3, 8),
+                        reason='Workaround only relevant on windows with py3.8+')
+    def test_start_webhook_ensure_event_loop(self, updater, monkeypatch):
+        def serve_forever(self, force_event_loop=False, ready=None):
+            with self.server_lock:
+                self.is_running = True
+                self._ensure_event_loop(force_event_loop=force_event_loop)
+
+                if ready is not None:
+                    ready.set()
+
+        monkeypatch.setattr(WebhookServer, 'serve_forever', serve_forever)
+        monkeypatch.setattr(updater.bot, 'set_webhook', lambda *args, **kwargs: True)
+        monkeypatch.setattr(updater.bot, 'delete_webhook', lambda *args, **kwargs: True)
+
+        ip = '127.0.0.1'
+        port = randrange(1024, 49152)  # Select random port
+
+        with set_asyncio_event_loop(None):
+            updater._start_webhook(
+                ip,
+                port,
+                url_path='TOKEN',
+                cert=None,
+                key=None,
+                bootstrap_retries=0,
+                clean=False,
+                webhook_url=None,
+                allowed_updates=None)
+
+            assert isinstance(asyncio.get_event_loop(), asyncio.SelectorEventLoop)
+
+    @pytest.mark.skipif(os.name != 'nt' or sys.version_info < (3, 8),
+                        reason='Workaround only relevant on windows with py3.8+')
+    def test_start_webhook_force_event_loop_false(self, updater, monkeypatch):
+        monkeypatch.setattr(updater.bot, 'set_webhook', lambda *args, **kwargs: True)
+        monkeypatch.setattr(updater.bot, 'delete_webhook', lambda *args, **kwargs: True)
+
+        ip = '127.0.0.1'
+        port = randrange(1024, 49152)  # Select random port
+
+        with set_asyncio_event_loop(asyncio.ProactorEventLoop()):
+            with pytest.raises(TypeError, match='`ProactorEventLoop` is incompatible'):
+                updater._start_webhook(
+                    ip,
+                    port,
+                    url_path='TOKEN',
+                    cert=None,
+                    key=None,
+                    bootstrap_retries=0,
+                    clean=False,
+                    webhook_url=None,
+                    allowed_updates=None)
+
+    @pytest.mark.skipif(os.name != 'nt' or sys.version_info < (3, 8),
+                        reason='Workaround only relevant on windows with py3.8+')
+    def test_start_webhook_force_event_loop_true(self, updater, monkeypatch):
+        def serve_forever(self, force_event_loop=False, ready=None):
+            with self.server_lock:
+                self.is_running = True
+                self._ensure_event_loop(force_event_loop=force_event_loop)
+
+                if ready is not None:
+                    ready.set()
+
+        monkeypatch.setattr(WebhookServer, 'serve_forever', serve_forever)
+        monkeypatch.setattr(updater.bot, 'set_webhook', lambda *args, **kwargs: True)
+        monkeypatch.setattr(updater.bot, 'delete_webhook', lambda *args, **kwargs: True)
+
+        ip = '127.0.0.1'
+        port = randrange(1024, 49152)  # Select random port
+
+        with set_asyncio_event_loop(asyncio.ProactorEventLoop()):
+            updater._start_webhook(
+                ip,
+                port,
+                url_path='TOKEN',
+                cert=None,
+                key=None,
+                bootstrap_retries=0,
+                clean=False,
+                webhook_url=None,
+                allowed_updates=None,
+                force_event_loop=True)
+            assert isinstance(asyncio.get_event_loop(), asyncio.ProactorEventLoop)
+
     def test_webhook_ssl(self, monkeypatch, updater):
         monkeypatch.setattr(updater.bot, 'set_webhook', lambda *args, **kwargs: True)
         monkeypatch.setattr(updater.bot, 'delete_webhook', lambda *args, **kwargs: True)
@@ -267,33 +361,6 @@ class TestUpdater:
         assert q.get(False).message.default_quote is True
         updater.stop()
 
-    @pytest.mark.skipif(not (sys.platform.startswith("win") and sys.version_info >= (3, 8)),
-                        reason="only relevant on win with py>=3.8")
-    def test_webhook_tornado_win_py38_workaround(self, updater, monkeypatch):
-        updater._default_quote = True
-        q = Queue()
-        monkeypatch.setattr(updater.bot, 'set_webhook', lambda *args, **kwargs: True)
-        monkeypatch.setattr(updater.bot, 'delete_webhook', lambda *args, **kwargs: True)
-        monkeypatch.setattr('telegram.ext.Dispatcher.process_update', lambda _, u: q.put(u))
-
-        ip = '127.0.0.1'
-        port = randrange(1024, 49152)  # Select random port
-        updater.start_webhook(
-            ip,
-            port,
-            url_path='TOKEN')
-        sleep(.2)
-
-        try:
-            from asyncio import (WindowsSelectorEventLoopPolicy)
-        except ImportError:
-            pass
-            # not affected
-        else:
-            assert isinstance(asyncio.get_event_loop_policy(), WindowsSelectorEventLoopPolicy)
-
-        updater.stop()
-
     @pytest.mark.parametrize(('error',),
                              argvalues=[(TelegramError(''),)],
                              ids=('TelegramError',))