Handle legacy syntax for 'returning' a value

Author: inlined

src/firebase_functions/https_fn.py

@@ -353,11 +353,18 @@ class CallableRequest(_typing.Generic[_core.T]):
 _C2 = _typing.Callable[[CallableRequest[_typing.Any]], _typing.Any]
 
 class _IterWithReturn:
+    """ Utility class to capture return statements from a generator """
     def __init__(self, iterable):
         self.iterable = iterable
 
     def __iter__(self):
-        self.value = yield from self.iterable
+        try:
+            self.value = yield from self.iterable
+        except RuntimeError as e:
+            if isinstance(e.__cause__, StopIteration):
+                self.value = e.__cause__.value
+            else:
+                raise
 
 def _on_call_handler(func: _C2, request: Request,
                      enforce_app_check: bool) -> Response:

tests/test_https_fn.py

@@ -148,6 +148,15 @@ def yield_thrower(req: https_fn.CallableRequest[int]):
                 "Can't read anymore"
             )
 
+        @https_fn.on_call()
+        def legacy_yielder(req: https_fn.CallableRequest[int]):
+            yield from range(req.data)
+            # Prior to Python 3.3, this was the way "return" was handled
+            # Python 3.5 made this messy however because it converts
+            # raised StopIteration into a RuntimeError
+            # pylint: disable=stop-iteration-return
+            raise StopIteration("OK")
+
         with app.test_request_context("/"):
             environ = EnvironBuilder(
                 method="POST",
@@ -162,6 +171,20 @@ def yield_thrower(req: https_fn.CallableRequest[int]):
             self.assertEqual(response.status_code, 200)
             self.assertEqual(response.get_json(), { "result": "OK" })
 
+        with app.test_request_context("/"):
+            environ = EnvironBuilder(
+                method="POST",
+                json={
+                    "data": 5
+                }
+            ).get_environ()
+
+            request = Request(environ)
+            response = legacy_yielder(request)
+
+            self.assertEqual(response.status_code, 200)
+            self.assertEqual(response.get_json(), { "result": "OK" })
+
         with app.test_request_context("/"):
             environ = EnvironBuilder(
                 method="POST",