transaction id check may be optional

[laurent-bohr]

Hi,

I update the version of pymodbus on my project and now for some connection with old modbus servers, the calls failed due to Modbus IO Exception: Modbus Error: [Input/Output] ERROR: request uses transaction id=1 but received 0.
The SCADA is not handling transactions ids, it was working fine before the update from 3.8.3 to 3.11.4.

The fixing of the issue #2709 is the root cause of my issue.

Can you have a configuration parameter to disable the check of the transaction id to be back compatibility ?

[janiversen]

The test and reject of wrong tid was done for a couple of reasons:

• a user requested it (and made a PR)
• without that check apps cannot make parallel requests.

Having said that, having a parameter at connection level to make it just a warning sounds like a nice idea.

a Pull Request is welcome.

Most SCADA system (which are client in sense of modbus) will demand a correct transaction Id, because they use parallel requests.