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grid-x / modbus

BSD 3-Clause "New" or "Revised" License
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Bug fix: connection stuck forever with mismatched transaction ID #32

Closed wz2b closed 3 years ago

wz2b commented 4 years ago

connection) you might go to send the next poll and immediately receive the previous response. The result is a mismatch in the transaction ID from which the connection will never recover. There are a few ways to mitigate this, including receiving the response in a loop, but since this modbus tcp implementation is completely synchronous the simplest thing to do is to simply flush the receive buffer immediately prior to sending the next poll.

wz2b commented 4 years ago

Another approach here would be to read the response in a loop. If the transaction ID is not the one you expected, go around the loop again. The reason I didn't do that is it's more intrusive of a code change, but if somebody feels strongly that's a better way to solve this let me know.

frzifus commented 4 years ago

hey @wz2b thanks for your contribution, i will have a look in the next days. What might help is a unittest that shows the behaviour.

wz2b commented 4 years ago

hey @wz2b thanks for your contribution, i will have a look in the next days. What might help is a unittest that shows the behaviour.

I think that to really test it would require mocking the TCP stream, wouldn't it? The behavior I would want to see would be send it a mismatched transaction id and see that it closes the connection, fails that transaction, then starts over at transaction id 1 with a new connection. I'm not really sure how to approach this in go.

guelfey commented 3 years ago

see #36.