Bug when breaking a line

[LoopholesInTheHeart]

When you successfully connect and send data, receive data, this is normal.
Unplugging the network cable and sending data again will return an error, which is normal.
However, when you plug the network cable back in, no error will be returned because "err_no" is 0,
This bug occurs in -> If (err) {return err_no; }

Another problem is that when the wire is broken and reconnected, there is no check to see if the content of the protocol frame returned is correct