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author | Peter Lamut <plamut@users.noreply.github.com> | 2020-06-09 20:48:10 +0200 |
---|---|---|
committer | GitHub <noreply@github.com> | 2020-06-09 18:48:10 +0000 |
commit | 74e0b0f8387207933c120af15b2bb5d175dd8f84 (patch) | |
tree | e8fe0a71fbfa6d2f59dece58a6b210f620111084 /google | |
parent | 945bafc47cfaf79f0947c970dba17dc8fbe3e197 (diff) | |
download | python-api-core-74e0b0f8387207933c120af15b2bb5d175dd8f84.tar.gz |
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)
Diffstat (limited to 'google')
-rw-r--r-- | google/api_core/grpc_helpers.py | 12 |
1 files changed, 9 insertions, 3 deletions
diff --git a/google/api_core/grpc_helpers.py b/google/api_core/grpc_helpers.py index fde6c33..b617ddf 100644 --- a/google/api_core/grpc_helpers.py +++ b/google/api_core/grpc_helpers.py @@ -62,14 +62,15 @@ def _wrap_unary_errors(callable_): class _StreamingResponseIterator(grpc.Call): - def __init__(self, wrapped): + def __init__(self, wrapped, prefetch_first_result=True): self._wrapped = wrapped # This iterator is used in a retry context, and returned outside after init. # gRPC will not throw an exception until the stream is consumed, so we need # to retrieve the first result, in order to fail, in order to trigger a retry. try: - self._stored_first_result = six.next(self._wrapped) + if prefetch_first_result: + self._stored_first_result = six.next(self._wrapped) except TypeError: # It is possible the wrapped method isn't an iterable (a grpc.Call # for instance). If this happens don't store the first result. @@ -141,7 +142,12 @@ def _wrap_stream_errors(callable_): def error_remapped_callable(*args, **kwargs): try: result = callable_(*args, **kwargs) - return _StreamingResponseIterator(result) + # Auto-fetching the first result causes PubSub client's streaming pull + # to hang when re-opening the stream, thus we need examine the hacky + # hidden flag to see if pre-fetching is disabled. + # https://github.com/googleapis/python-pubsub/issues/93#issuecomment-630762257 + prefetch_first = getattr(callable_, "_prefetch_first_result_", True) + return _StreamingResponseIterator(result, prefetch_first_result=prefetch_first) except grpc.RpcError as exc: six.raise_from(exceptions.from_grpc_error(exc), exc) |