Subscribing to a ProSys OPCUA server node id using the namespace uri

[KishanKishore]

I am trying to connect to a ProSys OPCUA server's node using the nodeId: nsu=http://www.prosysopc.com/OPCUA/SimulationNodes/;i=1001. When executing the following code:

from asyncua import Client
client = Client("opc.tcp://localhost:53530/OPCUA/SimulationServer")
await client.connect()
node = client.get_node("nsu=http://www.prosysopc.com/OPCUA/SimulationNodes/;i=1001")
print(await node.get_access_level())

I get the following error:

Received an error: MessageAbort(error:StatusCode(BadDecodingError), reason:Bad_DecodingError (code=0x80070000, description="Unexpected NodeId Encoding Byte -126"))
Received an error: MessageAbort(error:StatusCode(BadDecodingError), reason:Bad_DecodingError (code=0x80070000, description="Unexpected NodeId Encoding Byte -126"))
Exception raised while parsing message from server
Traceback (most recent call last):
  File "/Users/kishan/Documents/Configuration/edge-sdk/lib/python3.7/site-packages/asyncua/client/ua_client.py", line 169, in _call_callback
    self._callbackmap[request_id].set_result(body)
KeyError: 0

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/kishan/Documents/Configuration/edge-sdk/lib/python3.7/site-packages/asyncua/client/ua_client.py", line 81, in _process_received_data
    self._process_received_message(msg)
  File "/Users/kishan/Documents/Configuration/edge-sdk/lib/python3.7/site-packages/asyncua/client/ua_client.py", line 105, in _process_received_message
    self._call_callback(0, ua.UaStatusCodeError(msg.Error.value))
  File "/Users/kishan/Documents/Configuration/edge-sdk/lib/python3.7/site-packages/asyncua/client/ua_client.py", line 171, in _call_callback
    raise ua.UaError(f"No request found for request id: {request_id}, pending are {self._callbackmap.keys()}")
asyncua.ua.uaerrors._base.UaError: No request found for request id: 0, pending are dict_keys([4])
---------------------------------------------------------------------------
ConnectionError                           Traceback (most recent call last)
<ipython-input-25-d3da8efff58d> in async-def-wrapper()

~/Documents/Configuration/edge-sdk/lib/python3.7/site-packages/asyncua/common/node.py in get_access_level(self)
    113         Get the access level attribute of the node as a set of AccessLevel enum values.
    114         """
--> 115         result = await self.read_attribute(ua.AttributeIds.AccessLevel)
    116         return ua.AccessLevel.parse_bitfield(result.Value.Value)
    117

~/Documents/Configuration/edge-sdk/lib/python3.7/site-packages/asyncua/common/node.py in read_attribute(self, attr)
    298         params = ua.ReadParameters()
    299         params.NodesToRead.append(rv)
--> 300         result = await self.server.read(params)
    301         result[0].StatusCode.check()
    302         return result[0]

~/Documents/Configuration/edge-sdk/lib/python3.7/site-packages/asyncua/client/ua_client.py in read(self, parameters)
    359         request = ua.ReadRequest()
    360         request.Parameters = parameters
--> 361         data = await self.protocol.send_request(request)
    362         response = struct_from_binary(ua.ReadResponse, data)
    363         self.logger.debug(response)

~/Documents/Configuration/edge-sdk/lib/python3.7/site-packages/asyncua/client/ua_client.py in send_request(self, request, timeout, message_type)
    148         except Exception:
    149             if self.state != self.OPEN:
--> 150                 raise ConnectionError("Connection is closed") from None
    151
    152             raise

ConnectionError: Connection is closed

What am I doing incorrectly here? If I try the same with ns=3;i=1001, it works as expected.

Here are some screenshots from my local OPCUA server/client for reference:

[AndreasHeine]

client.get_node(ua.NodeId.from_string(...))

opcua-asyncio/asyncua/ua/uatypes.py

Line 464 in 7d7841b

def _from_string(string):

should return a expanded node id?

opcua-asyncio/asyncua/ua/uatypes.py

Line 584 in 7d7841b

class ExpandedNodeId(NodeId):

[AndreasHeine]

in 0.9.14 we dont differenciate between NodeId class and ExpandedNodeId class

Latest:

opcua-asyncio/asyncua/ua/uatypes.py

Line 464 in 7a86b03

ExpandedNodeId = NodeId

Master:

opcua-asyncio/asyncua/ua/uatypes.py

Line 584 in 7d7841b

class ExpandedNodeId(NodeId):

[KishanKishore]

Should I raise an issue in the issues section?

[AndreasHeine]

@KishanKishore working on a fix: #589

[AndreasHeine]

the decode error happens because the field order is different in NodeId and ExpandedNodeId now i made the order right an some other errors occure... need to fix them as well... hang on ;)

[KishanKishore]

Thanks @AndreasHeine for the help!

[oroulet]

@KishanKishore My current conclusion is that you cannot use an ExpandedNode in a ReadRequest. see the last comments in #589 . You are welcome to prove me otherwise. Maybe try another client implementation and make ReadRequest that works with an ExpandedNodeId

[KishanKishore]

@oroulet Thanks for the reply. Has this been mentioned somewhere in the specification ? I went through some articles regarding the different types of node id representation but none of them mentioned about this restriction. I will go through the comments in the PR as well.

I will try to use a different implementation as well.

[oroulet]

I am not 100% sure but i notice that some structures explicitly support expandedNodeId so i understand that the others do not.