fix 793: allow custom async iterator (#1041)

* fix 793

* custom async generator: implement pr notes

* custom async generator: cleanup dependencies

* update tests

* newline at end of tests

* fix linting

* Update tests/test_responses.py

Co-authored-by: Jamie Hewland <jhewland@gmail.com>

* Update tests/test_responses.py

Co-authored-by: Jamie Hewland <jhewland@gmail.com>

* fix naming for custom generator tests

* comply with pep 492

* Shift streaming tests to be in one place

Co-authored-by: witling <noreply@my.email>
Co-authored-by: Jamie Hewland <jhewland@gmail.com>

starlette/responses.py

@@ -1,6 +1,5 @@
 import hashlib
 import http.cookies
-import inspect
 import json
 import os
 import stat
@@ -204,7 +203,7 @@ def __init__(
         media_type: str = None,
         background: BackgroundTask = None,
     ) -> None:
-        if inspect.isasyncgen(content):
+        if isinstance(content, typing.AsyncIterable):
             self.body_iterator = content
         else:
             self.body_iterator = iterate_in_threadpool(content)

tests/test_responses.py

@@ -101,6 +101,44 @@ async def numbers_for_cleanup(start=1, stop=5):
     assert filled_by_bg_task == "6, 7, 8, 9"
 
 
+def test_streaming_response_custom_iterator():
+    async def app(scope, receive, send):
+        class CustomAsyncIterator:
+            def __init__(self):
+                self._called = 0
+
+            def __aiter__(self):
+                return self
+
+            async def __anext__(self):
+                if self._called == 5:
+                    raise StopAsyncIteration()
+                self._called += 1
+                return str(self._called)
+
+        response = StreamingResponse(CustomAsyncIterator(), media_type="text/plain")
+        await response(scope, receive, send)
+
+    client = TestClient(app)
+    response = client.get("/")
+    assert response.text == "12345"
+
+
+def test_streaming_response_custom_iterable():
+    async def app(scope, receive, send):
+        class CustomAsyncIterable:
+            async def __aiter__(self):
+                for i in range(5):
+                    yield str(i + 1)
+
+        response = StreamingResponse(CustomAsyncIterable(), media_type="text/plain")
+        await response(scope, receive, send)
+
+    client = TestClient(app)
+    response = client.get("/")
+    assert response.text == "12345"
+
+
 def test_sync_streaming_response():
     async def app(scope, receive, send):
         def numbers(minimum, maximum):