fix(routing): preserve stream metadata in include_router

fastapi/routing.py

@@ -1794,6 +1794,15 @@ class APIRouter(routing.Router):
                         self.strict_content_type,
                     ),
                 )
+                new_route = self.routes[-1]
+                if isinstance(new_route, APIRoute) and route.stream_item_type is not None:
+                    new_route.stream_item_type = route.stream_item_type
+                    new_route.stream_item_field = create_model_field(
+                        name=f"StreamItem_{new_route.unique_id}",
+                        type_=new_route.stream_item_type,
+                        mode="serialization",
+                    )
+                    new_route.app = request_response(new_route.get_route_handler())
             elif isinstance(route, routing.Route):
                 methods = list(route.methods or [])
                 self.add_route(

tests/test_sse.py

@@ -91,9 +91,9 @@ router = APIRouter()
 
 
 @router.get("/events", response_class=EventSourceResponse)
-async def stream_events():
-    yield {"msg": "hello"}
-    yield {"msg": "world"}
+async def stream_events() -> AsyncIterable[Item]:
+    yield items[0]
+    yield items[1]
 
 
 app.include_router(router, prefix="/api")
@@ -256,6 +256,17 @@ def test_data_and_raw_data_mutually_exclusive():
 
 
 def test_sse_on_router_included_in_app(client: TestClient):
+    route = next(r for r in app.routes if getattr(r, "path", None) == "/api/events")
+    assert route.stream_item_type is Item
+    assert route.stream_item_field is not None
+
+    openapi = app.openapi()
+    item_schema = openapi["paths"]["/api/events"]["get"]["responses"]["200"][
+        "content"
+    ]["text/event-stream"]["itemSchema"]
+    assert "contentSchema" in item_schema["properties"]["data"]
+    assert "Item" in openapi["components"]["schemas"]
+
     response = client.get("/api/events")
     assert response.status_code == 200
     assert response.headers["content-type"] == "text/event-stream; charset=utf-8"