`trace_connect` is called twice

[erlend-aasland]

OS: macOS
pymodbus version 3.9.2

I supply the following dummy hook to the trace_connect argument during ModbusTcpServer instantiation:

def print_connect(connected):
    print("CONNECT:", connected)

Observed behaviour

Upon client connection (and subsequent disconnection), I get the following debug print on my console:

(venv) $ python ./server.py
CONNECT: True
CONNECT: True
CONNECT: False

Apparently, the callback is invoked twice upon connect, and once upon disconnect.

Expected behaviour

I would expect only a single callback invocation upon connect:

(venv) $ python ./server.py
CONNECT: True
CONNECT: False

Debugging

A quick, narrowed down, Git grep reveals the following invocations:

$ git grep -n 'self\.trace_connect('
pymodbus/server/base.py:64:            self.trace_connect(True)
pymodbus/transaction/transaction.py:205:        self.trace_connect(True)
pymodbus/transaction/transaction.py:209:        self.trace_connect(False)

It seems to me the invocation in server/base.py is superfluous, and should possibly be removed (?). OTOH, changing the behaviour would be a breaking change. OTOH again, this API is not exactly very well documented.

The superfluous invocation was added by @janiversen in commit bebccce, PR #2549, issue #2546.

[janiversen]

Pull requests are welcome.

If you want the API better documented, feel free to submit a PR. It is currently documented at the same level as other API calls.