🐛 Fix stream item type lost when using `include_router()` (#15077)

Co-authored-by: Alexander Rauhut <[email protected]>
Co-authored-by: Sebastián Ramírez <[email protected]>

fastapi/routing.py

@@ -982,10 +982,11 @@ def _populate_api_route_state(
         generate_unique_id
     ),
     strict_content_type: bool | DefaultPlaceholder = Default(True),
+    stream_item_type: Any | None = None,
 ) -> None:
     route.path = path
     route.endpoint = endpoint
-    route.stream_item_type = None
+    route.stream_item_type = stream_item_type
     if isinstance(response_model, DefaultPlaceholder):
         return_annotation = get_typed_return_annotation(endpoint)
         if lenient_issubclass(return_annotation, Response):
@@ -1464,6 +1465,7 @@ class _EffectiveRouteContext:
                 include_context.included_router.strict_content_type,
                 include_context.strict_content_type,
             ),
+            stream_item_type=route.stream_item_type,
         )
         return context
 

tests/test_sse.py

@@ -64,7 +64,8 @@ async def sse_items_event():
 
 @app.get("/items/stream-mixed", response_class=EventSourceResponse)
 async def sse_items_mixed() -> AsyncIterable[Item]:
-    yield items[0]
+    for item in items:
+        yield item
     yield ServerSentEvent(data="custom-event", event="special")
     yield items[1]
 
@@ -96,6 +97,12 @@ async def stream_events():
     yield {"msg": "world"}
 
 
+@router.get("/events-typed", response_class=EventSourceResponse)
+async def stream_events_typed() -> AsyncIterable[Item]:
+    for item in items:
+        yield item
+
+
 app.include_router(router, prefix="/api")
 
 
@@ -274,6 +281,45 @@ def test_sse_on_router_included_in_app(client: TestClient):
     assert len(data_lines) == 2
 
 
+def test_sse_router_typed_stream(client: TestClient):
+    response = client.get("/api/events-typed")
+    assert response.status_code == 200
+    assert response.headers["content-type"] == "text/event-stream; charset=utf-8"
+    data_lines = [
+        line for line in response.text.strip().split("\n") if line.startswith("data: ")
+    ]
+    assert len(data_lines) == 3
+
+
+def test_sse_router_typed_openapi_schema(client: TestClient):
+    """Typed SSE endpoint on a router should preserve itemSchema with contentSchema."""
+    response = client.get("/openapi.json")
+    assert response.status_code == 200
+    paths = response.json()["paths"]
+    sse_response = paths["/api/events-typed"]["get"]["responses"]["200"]
+    assert sse_response == {
+        "description": "Successful Response",
+        "content": {
+            "text/event-stream": {
+                "itemSchema": {
+                    "type": "object",
+                    "properties": {
+                        "data": {
+                            "type": "string",
+                            "contentMediaType": "application/json",
+                            "contentSchema": {"$ref": "#/components/schemas/Item"},
+                        },
+                        "event": {"type": "string"},
+                        "id": {"type": "string"},
+                        "retry": {"type": "integer", "minimum": 0},
+                    },
+                    "required": ["data"],
+                }
+            }
+        },
+    }
+
+
 # Keepalive ping tests
 
 
@@ -325,3 +371,97 @@ def test_no_keepalive_when_fast(client: TestClient):
     assert response.status_code == 200
     # KEEPALIVE_COMMENT is ": ping\n\n".
     assert ": ping\n" not in response.text
+
+
+# default_response_class tests
+
+
+sse_schema_response = {
+    "description": "Successful Response",
+    "content": {
+        "text/event-stream": {
+            "itemSchema": {
+                "type": "object",
+                "properties": {
+                    "data": {
+                        "type": "string",
+                        "contentMediaType": "application/json",
+                        "contentSchema": {"$ref": "#/components/schemas/Item"},
+                    },
+                    "event": {"type": "string"},
+                    "id": {"type": "string"},
+                    "retry": {"type": "integer", "minimum": 0},
+                },
+                "required": ["data"],
+            }
+        }
+    },
+}
+
+
+# default_response_class on app
+
+default_app_app = FastAPI(default_response_class=EventSourceResponse)
+default_app_router = APIRouter()
+
+
+@default_app_router.get("/stream")
+async def default_app_stream() -> AsyncIterable[Item]:
+    for item in items:
+        yield item
+
+
+default_app_app.include_router(default_app_router, prefix="/api")
+
+
+def test_default_response_class_on_app_stream():
+    with TestClient(default_app_app) as client:
+        response = client.get("/api/stream")
+    assert response.status_code == 200
+    assert response.headers["content-type"] == "text/event-stream; charset=utf-8"
+    data_lines = [
+        line for line in response.text.strip().split("\n") if line.startswith("data: ")
+    ]
+    assert len(data_lines) == 3
+
+
+def test_default_response_class_on_app_openapi_schema():
+    assert (
+        default_app_app.openapi()["paths"]["/api/stream"]["get"]["responses"]["200"]
+        == sse_schema_response
+    )
+
+
+# default_response_class on parent router
+
+default_parent_app = FastAPI()
+parent_router = APIRouter(default_response_class=EventSourceResponse)
+child_router = APIRouter()
+
+
+@child_router.get("/stream")
+async def default_parent_stream() -> AsyncIterable[Item]:
+    for item in items:
+        yield item
+
+
+parent_router.include_router(child_router)
+default_parent_app.include_router(parent_router, prefix="/api")
+
+
+def test_default_response_class_on_parent_router_stream():
+    with TestClient(default_parent_app) as client:
+        response = client.get("/api/stream")
+    assert response.status_code == 200
+    assert response.headers["content-type"] == "text/event-stream; charset=utf-8"
+    data_lines = [
+        line for line in response.text.strip().split("\n") if line.startswith("data: ")
+    ]
+    assert len(data_lines) == 3
+
+
+def test_default_response_class_on_parent_router_openapi_schema():
+    assert (
+        default_parent_app.openapi()["paths"]["/api/stream"]["get"]["responses"]["200"]
+        == sse_schema_response
+    )

tests/test_stream_bare_type.py

@@ -1,13 +1,14 @@
 import json
 from typing import AsyncIterable, Iterable  # noqa: UP035 to test coverage
 
-from fastapi import FastAPI
+from fastapi import APIRouter, FastAPI
 from fastapi.testclient import TestClient
 from pydantic import BaseModel
 
 
 class Item(BaseModel):
     name: str
+    optional: str | None = None
 
 
 app = FastAPI()
@@ -23,6 +24,16 @@ def stream_bare_sync() -> Iterable:
     yield {"name": "bar"}
 
 
+router = APIRouter()
+
+
+@router.get("/events-jsonl", response_model_exclude_none=True)
+async def stream_events_jsonl() -> AsyncIterable[Item]:
+    yield Item(name="foo")
+
+
+app.include_router(router, prefix="/api")
+
 client = TestClient(app)
 
 
@@ -40,3 +51,24 @@ def test_stream_bare_sync_iterable():
     assert response.headers["content-type"] == "application/jsonl"
     lines = [json.loads(line) for line in response.text.strip().splitlines()]
     assert lines == [{"name": "bar"}]
+
+
+def test_jsonl_router_typed_stream():
+    response = client.get("/api/events-jsonl")
+    assert response.status_code == 200
+    assert response.headers["content-type"] == "application/jsonl"
+    lines = [json.loads(line) for line in response.text.strip().splitlines()]
+    assert lines == [{"name": "foo"}]
+
+
+def test_jsonl_router_typed_openapi_schema():
+    response = client.get("/openapi.json")
+    assert response.status_code == 200
+    paths = response.json()["paths"]
+    jsonl_response = paths["/api/events-jsonl"]["get"]["responses"]["200"]
+    assert jsonl_response == {
+        "description": "Successful Response",
+        "content": {
+            "application/jsonl": {"itemSchema": {"$ref": "#/components/schemas/Item"}}
+        },
+    }