Auto-reconnect to OPC-UA server

RCUSCC/RCUSCC/RCUSCC.py

@@ -26,6 +26,8 @@ import sys
 import opcua
 import traceback
 import numpy
+import time
+from threading import Thread
 
 from functools import wraps
 import socket
@@ -41,10 +43,10 @@ def fault_on_opcua_error(func):
     def opcua_error_wrapper(self, *args, **kwargs):
         try:
             return func(self, *args, **kwargs)
-        except socket.error as e:
-            self.error_stream("Communication with the OPC-UA server %s:%d failed.  Trace: %s" % (self.OPC_Server_Name, self.OPC_Server_Port, traceback.format_exc()))
+        except Exception as e:
+            self.error_stream("Communication with the OPC-UA server %s:%d failed. Reconnecting. Trace: %s" % (self.OPC_Server_Name, self.OPC_Server_Port, traceback.format_exc()))
             self.set_state(DevState.FAULT)
-            self._disconnect()
+            self._reconnect_opcua()
 
             return None
 
@@ -53,6 +55,35 @@ def fault_on_opcua_error(func):
 
 __all__ = ["RCUSCC", "main"]
 
+class BackgroundConnector(Thread):
+    """
+      Run a function in the background, until it succeeds.
+    """
+
+    def __init__(self, connect_func, try_interval=2, debug_stream=print):
+        super().__init__(daemon=True)
+
+        self.connect_func = connect_func
+        self.try_interval = try_interval
+        self.debug_stream = debug_stream
+        self.connecting = True
+        self.connected = False
+
+    def try_connect(self):
+        try:
+            self.connect_func()
+            self.connected = True
+        except socket.error as e:
+            self.debug_stream("Could not connect: %s" % (e,))
+        finally:
+            self.connecting = False
+
+    def run(self):
+        while not self.connected:
+            self.try_connect()
+            if not self.connected:
+                time.sleep(self.try_interval)
+
 
 class RCUSCC(Device):
     """
@@ -174,8 +205,41 @@ class RCUSCC(Device):
 
             return DummyNode()
 
+    def _reconnect_opcua(self):
+        """
+          Connect or reconnect to the OPC-UA server.
+        """
+
+        if self.opcua_connector:
+            if self.opcua_connector.connecting:
+              # don't try twice in parallel
+              return
+            
+            # reap previous instance
+            self.debug_stream("reaping previous connector")
+            self.opcua_connector.join()
+
+        self.debug_stream("disconnecting (if connected)")
+        self._disconnect()
+        self.debug_stream("connecting")
+        self.opcua_connector = BackgroundConnector(self._init_opcua)
+        self.opcua_connector.start()
 
-    def _connect(self):
+    def _wait_opcua_connect(self):
+        """
+          Wait until an OPC-UA connection is established.
+        """
+
+        if not self.opcua_connector:
+            # start connecting if not already
+            self._reconnect_opcua()
+
+        self.opcua_connector.join()
+
+        if not self.opcua_connector.connected:
+            raise Exception("Could not connect to OPC-UA server")
+
+    def _init_opcua(self):
         self.debug_stream("Connecting to OPC-UA server %s:%d...", self.OPC_Server_Name, self.OPC_Server_Port)
 
         self.client = opcua.Client("opc.tcp://{}:{}/".format(self.OPC_Server_Name, self.OPC_Server_Port), self.OPC_Time_Out) # timeout in seconds
@@ -191,7 +255,6 @@ class RCUSCC(Device):
         self.obj_node = self.client.get_objects_node()
         self.pcc_node = self.obj_node.get_child(["{}:PCC".format(self.name_space_index)])
 
-    def _extract_pcc_nodes(self):
         self.debug_stream("Mapping OPC-UA MP/CP to attributes...")
 
         # 2020-11-27, thomas
@@ -242,6 +305,9 @@ class RCUSCC(Device):
         # PROTECTED REGION ID(RCUSCC.init_device) ENABLED START #
         self.set_state(DevState.INIT)
 
+        # Thread to connect to OPC-UA in the background
+        self.opcua_connector = None
+
         # Init the dict that contains attribute to OPC-UA MP/CP mappings.
         self.attribute_mapping = {}
 
@@ -284,8 +350,7 @@ class RCUSCC(Device):
         # Set defaults to property values.
 
         try:
-            self._connect()
-            self._extract_pcc_nodes()
+            self._wait_opcua_connect()
 
             self.set_state(DevState.ON)
         except Exception as e:
@@ -306,6 +371,8 @@ class RCUSCC(Device):
                 self.client.close_secure_channel()
         except Exception as e:
             self.warn_stream("Disconnect from OPC-UA server %s:%d failed.  Trace: %s" % (self.OPC_Server_Name, self.OPC_Server_Port, traceback.format_exc()))
+        finally:
+            self.client = None
 
     def delete_device(self):
         """Hook to delete resources allocated in init_device.