add support for async server function

Author: mconflitti-pbc

shiny/_app.py

@@ -6,7 +6,7 @@
 from contextlib import AsyncExitStack, asynccontextmanager
 from inspect import signature
 from pathlib import Path
-from typing import Any, Callable, Mapping, Optional, TypeVar, cast
+from typing import Any, Awaitable, Callable, Mapping, Optional, TypeVar, cast
 
 import starlette.applications
 import starlette.exceptions
@@ -57,8 +57,8 @@ class App:
         returns a UI definition, if you need the UI definition to be created dynamically
         for each pageview.
     server
-        A function which is called once for each session, ensuring that each session is
-        independent.
+        A sync or async function which is called once for each session, ensuring that
+        each session is independent.
     static_assets
         Static files to be served by the app. If this is a string or Path object, it
         must be a directory, and it will be mounted at `/`. If this is a dictionary,
@@ -104,13 +104,13 @@ def server(input: Inputs, output: Outputs, session: Session):
     """
 
     ui: RenderedHTML | Callable[[Request], Tag | TagList]
-    server: Callable[[Inputs, Outputs, Session], None]
+    server: Callable[[Inputs, Outputs, Session], Awaitable[None] | None]
 
     def __init__(
         self,
         ui: Tag | TagList | Callable[[Request], Tag | TagList] | Path,
         server: (
-            Callable[[Inputs], None] | Callable[[Inputs, Outputs, Session], None] | None
+            Callable[[Inputs], Awaitable[None] | None] | Callable[[Inputs, Outputs, Session], Awaitable[None] | None] | None
         ),
         *,
         static_assets: Optional[str | Path | Mapping[str, str | Path]] = None,

shiny/session/_session.py

@@ -633,7 +633,9 @@ def verify_state(expected_state: ConnectionState) -> None:
                             self._manage_inputs(message_obj["data"])
 
                             with session_context(self):
-                                self.app.server(self.input, self.output, self)
+                                result = self.app.server(self.input, self.output, self)
+                                if isinstance(result, Awaitable):
+                                    await result
 
                         elif message_obj["method"] == "update":
                             verify_state(ConnectionState.Running)