fix event loop bug with aiohttp 3.8

aio-libs/aiohttp#5572

pywebio/platform/aiohttp.py

@@ -13,7 +13,7 @@
 from .utils import make_applications, render_page, cdn_validation, deserialize_binary_event
 from ..session import CoroutineBasedSession, ThreadBasedSession, register_session_implement_for_target, Session
 from ..session.base import get_session_info_from_headers
-from ..utils import get_free_port, STATIC_PATH, iscoroutinefunction, isgeneratorfunction
+from ..utils import get_free_port, STATIC_PATH, iscoroutinefunction, isgeneratorfunction, func_params
 
 logger = logging.getLogger(__name__)
 
@@ -208,4 +208,9 @@ def start_server(applications, port=0, host='', debug=False,
     if remote_access:
         start_remote_access_service(local_port=port)
 
-    web.run_app(app, host=host, port=port)
+    if 'loop' in func_params(web.run_app):
+        # after aiohttp 3.8, aiohttp.web.run_app() create new loop by default, we need to pass current loop explicitly.
+        # see: https://github.com/aio-libs/aiohttp/pull/5572
+        web.run_app(app, host=host, port=port, loop=asyncio.get_event_loop())
+    else:
+        web.run_app(app, host=host, port=port)

pywebio/utils.py

@@ -378,3 +378,10 @@ def strip_space(text, n):
         for i in text.splitlines()
     )
     return '\n'.join(lines)
+
+
+def func_params(func):
+    """Return the parameter name list of the function
+    """
+    signature = inspect.signature(func)
+    return list(signature.parameters.keys())