AttributeError: '_SubHandler' object has no attribute 'status_change_notification'

[mahadi]

Hello,

i am using the sync client in a python application and during disconnect/reconnect tests i found the following issue:

When i stop the server i get:

Exception calling status change handler
Traceback (most recent call last):
  File "asyncua/client/client.py", line 457, in _monitor_server_loop
    _ = await self.nodes.server_state.read_value()
  File "asyncua/common/node.py", line 179, in read_value
    result = await self.read_data_value()
  File "asyncua/common/node.py", line 190, in read_data_value
    return await self.read_attribute(ua.AttributeIds.Value, None, raise_on_bad_status)
  File "asyncua/common/node.py", line 304, in read_attribute
    result = await self.session.read(params)
  File "asyncua/client/ua_client.py", line 397, in read
    data = await self.protocol.send_request(request)
  File "asyncua/client/ua_client.py", line 163, in send_request
    raise ConnectionError("Connection is closed") from None
ConnectionError: Connection is closed

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "asyncua/common/subscription.py", line 173, in _call_status
    if asyncio.iscoroutinefunction(self._handler.status_change_notification):
AttributeError: '_SubHandler' object has no attribute 'status_change_notification'

My subscription handler provides the method:

class SubscriptionHandler(object):

    """
    Subscription Handler. To receive events from server for a subscription
    data_change and event methods are called directly from receiving thread.
    Do not do expensive, slow or network operation there. Create another
    thread if you need to do such a thing
    """

    def __init__(self, producer: OPCUAHandler):
        self.producer: OPCUAHandler = producer

    def datachange_notification(self, node, val, data):
        ...

    def status_change_notification(self, status: ua.StatusChangeNotification):
        logger.info(f"Received a StatusChangeNotification: {status}")

and the class is used for the subscription from within my OPCUAHandler class:

sub_handler = SubscriptionHandler(self)
fast_sub = self.client.create_subscription(500, sub_handler)

I tried to trace it down:
In sync.py there is a _SubHandler implemented

class _SubHandler:
    def __init__(self, tloop, sync_handler):
        self.tloop = tloop
        self.sync_handler = sync_handler

    def datachange_notification(self, node, val, data):
        self.sync_handler.datachange_notification(SyncNode(self.tloop, node), val, data)

    def event_notification(self, event):
        self.sync_handler.event_notification(event)

which wraps my sync Subhandler, but it doesnt implement the status_change_notification method.

So it seems, that this part is missing in _SubHandler:

    def status_change_notification(self, status: ua.StatusChangeNotification):
        self.sync_handler.status_change_notification(status)

but even if i implement this the same error is thrown.

In sync.py create_subscription the handler is properly passed

    def create_subscription(self, period, handler):
        coro = self.aio_obj.create_subscription(period, _SubHandler(self.tloop, handler))
        aio_sub = self.tloop.post(coro)
        return Subscription(self.tloop, aio_sub)

so i think i am missing something here. Do you have a hint what is going wrong?

[mahadi]

I found that there was an issue in the past with the same symptoms: #1176
It is reported to be fixed on the main branch. I am also using 1.0.1 and i applied the manual fix already. So it seems to be an issue of the sync client only?

[mahadi]

I found why my modification did not make it work: I am using WSL2 and PyCharm for this project and i made these changes from within PyCharm. But it turned out that PyCharm (probably in combination with WSL2 file access) does not write the changes to the source file. Performing the change manually in WSL2 suceeded and the Exception could be eliminated.

[mahadi]

I added a PR to fix this issue: #1258