feat: allow disabling response stream pre-fetch (#30)
Closes #25.
This PR adds the ability to disable automatically pre-fetching the first item of a stream returned by `*-Stream` gRPC callables. This hook will be used in PubSub to fix the [stalled stream issue](https://github.com/googleapis/python-pubsub/issues/93), while also not affecting Firestore, since the default behavior is preserved.
I realize the fix is far from ideal, but it's the least ugly among the approaches I tried, e.g. somehow passing the flag through `ResumableBidiRpc` (it's a messy rabbit hole). On the PubSub side monkeypatching the generated SubscriberClient will be needed, but it's a (relatively) clean one-liner:
```patch
diff --git google/cloud/pubsub_v1/gapic/subscriber_client.py google/cloud/pubsub_v1/gapic/subscriber_client.py
index e98a686..1d6c058 100644
--- google/cloud/pubsub_v1/gapic/subscriber_client.py
+++ google/cloud/pubsub_v1/gapic/subscriber_client.py
@@ -1169,6 +1169,8 @@ class SubscriberClient(object):
default_timeout=self._method_configs["StreamingPull"].timeout,
client_info=self._client_info,
)
+ # TODO: explain this monkeypatch!
+ self.transport.streaming_pull._prefetch_first_result_ = False
return self._inner_api_calls["streaming_pull"](
requests, retry=retry, timeout=timeout, metadata=metadata
```
If/when we merge this, we should also release it, and then we can add `!= 1.17.0` to the `google-api-core` version pin in PubSub.
### PR checklist
- [x] Make sure to open an issue as a [bug/issue](https://github.com/googleapis/python-api-core/issues/new/choose) before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
- [x] Ensure the tests and linter pass
- [x] Code coverage does not decrease (if any source code was changed)
- [x] Appropriate docs were updated (if necessary)
2 files changed