fix(client/grpc): use SyncGrpcClient._create_channel in sync paths

src/bentoml/_internal/client/grpc.py

@@ -512,7 +512,11 @@ def wait_until_server_ready(
     ) -> None:
         protocol_version = kwargs.get("protocol_version", LATEST_PROTOCOL_VERSION)
 
-        with GrpcClient._create_channel(
+        # Use SyncGrpcClient._create_channel — the wrapper class GrpcClient does
+        # not define _create_channel, and the AsyncGrpcClient version returns an
+        # async channel that is incompatible with the sync ``with`` below.
+        # See bentoml/BentoML#4683.
+        with SyncGrpcClient._create_channel(
             f"{host}:{port}",
             ssl=kwargs.get("ssl", False),
             ssl_client_credentials=kwargs.get("ssl_client_credentials", None),
@@ -725,7 +729,13 @@ def run():
             raise BentoMLException("\n".join(exception_message))
         pb, _ = import_generated_stubs(protocol_version)
 
-        with GrpcClient._create_channel(
+        # Use ``cls._create_channel`` — the wrapper class ``GrpcClient`` does
+        # not define ``_create_channel``, and the ``AsyncGrpcClient`` version
+        # returns an async channel that is incompatible with the sync ``with``
+        # below. Using ``cls`` (rather than hardcoding ``SyncGrpcClient``) lets
+        # subclasses of ``SyncGrpcClient`` override the channel factory.
+        # See bentoml/BentoML#4683.
+        with cls._create_channel(
             server_url.replace(r"localhost", "0.0.0.0"),
             ssl=kwargs.get("ssl", False),
             ssl_client_credentials=kwargs.get("ssl_client_credentials", None),

tests/unit/_internal/client/test_grpc_sync_create_channel.py

@@ -0,0 +1,73 @@
+"""Regression test for #4263 / #4683: SyncGrpcClient mistakenly calls
+``GrpcClient._create_channel`` (which doesn't exist), instead of its own
+``SyncGrpcClient._create_channel``.
+
+Before the fix, both ``SyncGrpcClient.from_url`` and
+``SyncGrpcClient.wait_until_server_ready`` raised
+``AttributeError: type object 'GrpcClient' has no attribute '_create_channel'``.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+pytest.importorskip("grpc")
+
+
+def test_sync_grpc_client_has_create_channel() -> None:
+    # The wrapper class ``GrpcClient`` does NOT define ``_create_channel`` —
+    # only ``SyncGrpcClient`` and ``AsyncGrpcClient`` do. Sync code paths
+    # MUST resolve ``_create_channel`` via ``SyncGrpcClient``.
+    from bentoml._internal.client.grpc import GrpcClient
+    from bentoml._internal.client.grpc import SyncGrpcClient
+
+    assert not hasattr(GrpcClient, "_create_channel"), (
+        "GrpcClient is a thin wrapper and intentionally has no "
+        "_create_channel. Sync paths must use SyncGrpcClient._create_channel."
+    )
+    assert hasattr(SyncGrpcClient, "_create_channel")
+
+
+def test_sync_grpc_client_create_channel_returns_sync_channel() -> None:
+    # ``SyncGrpcClient._create_channel`` must return a *sync* channel that
+    # supports ``with ... as channel``. Using the async ``aio.insecure_channel``
+    # returns a channel that only supports ``async with``, breaking sync paths.
+    from bentoml._internal.client.grpc import SyncGrpcClient
+
+    channel = SyncGrpcClient._create_channel("127.0.0.1:65530")
+    try:
+        assert hasattr(channel, "__enter__"), (
+            "SyncGrpcClient._create_channel must return a sync context manager."
+        )
+    finally:
+        # ``grpc.insecure_channel`` exposes ``close`` synchronously.
+        channel.close()
+
+
+def test_sync_grpc_client_wait_until_server_ready_no_attribute_error() -> None:
+    # Regression for #4683: ``wait_until_server_ready`` was calling
+    # ``GrpcClient._create_channel`` (which doesn't exist) and crashed with
+    # AttributeError before it ever attempted a connection.
+    from bentoml._internal.client.grpc import SyncGrpcClient
+
+    with pytest.raises(Exception) as excinfo:
+        SyncGrpcClient.wait_until_server_ready("127.0.0.1", 65531, timeout=1)
+    # Whatever happens, it must NOT be an AttributeError on _create_channel.
+    assert not (
+        isinstance(excinfo.value, AttributeError)
+        and "_create_channel" in str(excinfo.value)
+    ), f"Regression: {excinfo.value!r}"
+
+
+def test_sync_grpc_client_from_url_no_attribute_error(monkeypatch) -> None:
+    # Regression for #4683: ``SyncGrpcClient.from_url`` crashed with
+    # ``AttributeError: type object 'GrpcClient' has no attribute
+    # '_create_channel'`` because it called the wrong class's classmethod.
+    from bentoml._internal.client.grpc import SyncGrpcClient
+
+    with pytest.raises(Exception) as excinfo:
+        SyncGrpcClient.from_url("127.0.0.1:65532")
+    assert not (
+        isinstance(excinfo.value, AttributeError)
+        and "_create_channel" in str(excinfo.value)
+    ), f"Regression: {excinfo.value!r}"