Sync fastapi docs from b5ca1324 on 2025-12-07

tests/test_dependency_after_yield_streaming.py

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+from contextlib import contextmanager
+from typing import Any, Generator
+
+import pytest
+from fastapi import Depends, FastAPI
+from fastapi.responses import StreamingResponse
+from fastapi.testclient import TestClient
+from typing_extensions import Annotated
+
+
+class Session:
+    def __init__(self) -> None:
+        self.data = ["foo", "bar", "baz"]
+        self.open = True
+
+    def __iter__(self) -> Generator[str, None, None]:
+        for item in self.data:
+            if self.open:
+                yield item
+            else:
+                raise ValueError("Session closed")
+
+
+@contextmanager
+def acquire_session() -> Generator[Session, None, None]:
+    session = Session()
+    try:
+        yield session
+    finally:
+        session.open = False
+
+
+def dep_session() -> Any:
+    with acquire_session() as s:
+        yield s
+
+
+def broken_dep_session() -> Any:
+    with acquire_session() as s:
+        s.open = False
+        yield s
+
+
+SessionDep = Annotated[Session, Depends(dep_session)]
+BrokenSessionDep = Annotated[Session, Depends(broken_dep_session)]
+
+app = FastAPI()
+
+
+@app.get("/data")
+def get_data(session: SessionDep) -> Any:
+    data = list(session)
+    return data
+
+
+@app.get("/stream-simple")
+def get_stream_simple(session: SessionDep) -> Any:
+    def iter_data():
+        yield from ["x", "y", "z"]
+
+    return StreamingResponse(iter_data())
+
+
+@app.get("/stream-session")
+def get_stream_session(session: SessionDep) -> Any:
+    def iter_data():
+        yield from session
+
+    return StreamingResponse(iter_data())
+
+
+@app.get("/broken-session-data")
+def get_broken_session_data(session: BrokenSessionDep) -> Any:
+    return list(session)
+
+
+@app.get("/broken-session-stream")
+def get_broken_session_stream(session: BrokenSessionDep) -> Any:
+    def iter_data():
+        yield from session
+
+    return StreamingResponse(iter_data())
+
+
+client = TestClient(app)
+
+
+def test_regular_no_stream():
+    response = client.get("/data")
+    assert response.json() == ["foo", "bar", "baz"]
+
+
+def test_stream_simple():
+    response = client.get("/stream-simple")
+    assert response.text == "xyz"
+
+
+def test_stream_session():
+    response = client.get("/stream-session")
+    assert response.text == "foobarbaz"
+
+
+def test_broken_session_data():
+    with pytest.raises(ValueError, match="Session closed"):
+        client.get("/broken-session-data")
+
+
+def test_broken_session_data_no_raise():
+    client = TestClient(app, raise_server_exceptions=False)
+    response = client.get("/broken-session-data")
+    assert response.status_code == 500
+    assert response.text == "Internal Server Error"
+
+
+def test_broken_session_stream_raise():
+    # Can raise ValueError on Pydantic v2 and ExceptionGroup on Pydantic v1
+    with pytest.raises((ValueError, Exception)):
+        client.get("/broken-session-stream")
+
+
+def test_broken_session_stream_no_raise():
+    """
+    When a dependency with yield raises after the streaming response already started
+    the 200 status code is already sent, but there's still an error in the server
+    afterwards, an exception is raised and captured or shown in the server logs.
+    """
+    with TestClient(app, raise_server_exceptions=False) as client:
+        response = client.get("/broken-session-stream")
+        assert response.status_code == 200
+        assert response.text == ""