Use Iterable instead Iterator on iterate_in_threadpool (#2362)

* Fixed AsyncContentStream to be AsyncIterator

* Updating isinstance check too

* Standardizing on Iterable/AsyncIterable

* Moved iterate_in_threadpool to make an iter internally

* Added test of iterate_in_threadpool accepting an Iterable

* Renamed arg to iterator, and fixed type hint in return to be AsyncIterator

---------

Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com>

starlette/concurrency.py

@@ -55,10 +55,11 @@ def _next(iterator: typing.Iterator[T]) -> T:
 
 
 async def iterate_in_threadpool(
-    iterator: typing.Iterator[T],
+    iterator: typing.Iterable[T],
 ) -> typing.AsyncIterator[T]:
+    as_iterator = iter(iterator)
     while True:
         try:
-            yield await anyio.to_thread.run_sync(_next, iterator)
+            yield await anyio.to_thread.run_sync(_next, as_iterator)
         except _StopIteration:
             break

starlette/responses.py

@@ -204,7 +204,7 @@ def __init__(
 
 
 Content = typing.Union[str, bytes]
-SyncContentStream = typing.Iterator[Content]
+SyncContentStream = typing.Iterable[Content]
 AsyncContentStream = typing.AsyncIterable[Content]
 ContentStream = typing.Union[AsyncContentStream, SyncContentStream]
 

tests/test_concurrency.py

@@ -4,7 +4,7 @@
 import pytest
 
 from starlette.applications import Starlette
-from starlette.concurrency import run_until_first_complete
+from starlette.concurrency import iterate_in_threadpool, run_until_first_complete
 from starlette.requests import Request
 from starlette.responses import Response
 from starlette.routing import Route
@@ -40,3 +40,12 @@ def endpoint(request: Request) -> Response:
 
     resp = client.get("/")
     assert resp.content == b"data"
+
+
+@pytest.mark.anyio
+async def test_iterate_in_threadpool() -> None:
+    class CustomIterable:
+        def __iter__(self):
+            yield from range(3)
+
+    assert [v async for v in iterate_in_threadpool(CustomIterable())] == [0, 1, 2]