add a retry if connect fails, and remove PanelNotFoundError

Author: Mike Prosser

src/nipanel/_panel.py

@@ -1,17 +1,16 @@
 from __future__ import annotations
 
 import sys
+import time
 from abc import ABC, abstractmethod
 from types import TracebackType
 from typing import TYPE_CHECKING, Optional, Type
 
-from grpc import RpcError, StatusCode
+from grpc import RpcError
 from ni.pythonpanel.v1.python_panel_service_pb2 import ConnectRequest, DisconnectRequest
 from ni.pythonpanel.v1.python_panel_service_pb2_grpc import PythonPanelServiceStub
 from ni_measurement_plugin_sdk_service.grpc.channelpool import GrpcChannelPool
 
-from nipanel._panel_not_found_error import PanelNotFoundError
-
 if TYPE_CHECKING:
     if sys.version_info >= (3, 11):
         from typing import Self
@@ -22,6 +21,8 @@
 class Panel(ABC):
     """This class allows you to connect to a panel and specify values for its controls."""
 
+    RETRY_WAIT_TIME = 1  # time in seconds to wait before retrying connection
+
     _channel_pool: GrpcChannelPool
     _stub: PythonPanelServiceStub | None
     _panel_id: str
@@ -32,6 +33,7 @@ class Panel(ABC):
     def __init__(self, panel_id: str, panel_uri: str) -> None:
         """Initialize the panel."""
         self._channel_pool = GrpcChannelPool()
+        self._stub = None
         self._panel_id = panel_id
         self._panel_uri = panel_uri
 
@@ -65,31 +67,22 @@ def connect(self) -> None:
         address = self._resolve_service_address()
         channel = self._channel_pool.get_channel(address)
         self._stub = PythonPanelServiceStub(channel)
-        connect_request = ConnectRequest(panel_id=self._panel_id, panel_uri=self._panel_uri)
 
+        connect_request = ConnectRequest(panel_id=self._panel_id, panel_uri=self._panel_uri)
         try:
             self._stub.Connect(connect_request)
-        except RpcError as e:
-            if e.code() == StatusCode.NOT_FOUND:
-                raise PanelNotFoundError(self._panel_id, self._panel_uri) from e
-            else:
-                raise
+        except RpcError:
+            # retry the connection if it fails, but only once
+            time.sleep(self.RETRY_WAIT_TIME)
+            self._stub.Connect(connect_request)
 
     def disconnect(self) -> None:
         """Disconnect from the panel (does not close the panel)."""
-        disconnect_request = DisconnectRequest(panel_id=self._panel_id)
-
         if self._stub is None:
             raise RuntimeError("connect() must be called before disconnect()")
 
-        try:
-            self._stub.Disconnect(disconnect_request)
-        except RpcError as e:
-            if e.code() == StatusCode.NOT_FOUND:
-                raise PanelNotFoundError(self._panel_id, self._panel_uri) from e
-            else:
-                raise
-
+        disconnect_request = DisconnectRequest(panel_id=self._panel_id)
+        self._stub.Disconnect(disconnect_request)
         self._stub = None
         self._channel_pool.close()
 

src/nipanel/_panel_not_found_error.py

@@ -1,5 +1,7 @@
 import grpc
+import pytest
 
+from tests.utils._fake_python_panel_servicer import FakePythonPanelServicer
 from tests.utils._port_panel import PortPanel
 
 
@@ -32,3 +34,30 @@ def test___with_panel___set_value___gets_same_value(
 
         # TODO: AB#3095681 - change asserted value to test_value
         assert panel.get_value("test_id") == "placeholder value"
+
+
+def test___new_panel___disconnect___raises_runtime_error(
+    fake_python_panel_service: tuple[grpc.Server, int],
+) -> None:
+    _, port = fake_python_panel_service
+    panel = PortPanel(port, "my_panel", "path/to/script")
+
+    with pytest.raises(RuntimeError):
+        panel.disconnect()
+
+
+def test___first_connect_fails___connect___gets_value(
+    fake_python_panel_service: tuple[grpc.Server, int],
+) -> None:
+    """Test that panel.connect() will automatically retry once."""
+    # Simulate a failure on the first connect attempt
+    FakePythonPanelServicer.fail_next_connect()
+    _, port = fake_python_panel_service
+    panel = PortPanel(port, "my_panel", "path/to/script")
+
+    panel.connect()
+
+    panel.set_value("test_id", "test_value")
+    # TODO: AB#3095681 - change asserted value to test_value
+    assert panel.get_value("test_id") == "placeholder value"
+    panel.disconnect()

tests/unit/test_panel.py

@@ -18,9 +18,13 @@ class FakePythonPanelServicer(PythonPanelServiceServicer):
     """Fake implementation of the PythonPanelServicer for testing."""
 
     _values = {"test_value": any_pb2.Any()}
+    _fail_next_connect = False
 
     def Connect(self, request: ConnectRequest, context: Any) -> ConnectResponse:  # noqa: N802
         """Just a trivial implementation for testing."""
+        if self._fail_next_connect:
+            self._fail_next_connect = False
+            raise ValueError("Simulate a failure to Connect.")
         return ConnectResponse()
 
     def Disconnect(  # noqa: N802
@@ -38,3 +42,8 @@ def SetValue(self, request: SetValueRequest, context: Any) -> SetValueResponse:
         """Just a trivial implementation for testing."""
         self._values[request.value_id] = request.value
         return SetValueResponse()
+
+    @classmethod
+    def fail_next_connect(cls) -> None:
+        """Set whether the Connect method should fail the next time it is called."""
+        cls._fail_next_connect = True