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Server behaviour in closing a connection
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Phuong Nguyen
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08/31/2021 - 01:16
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Hi,

what would be proper behaviour of OPCUA server in processing CloseSecureChannelRequest? In OPC Spec Part 6 V1.04, Section 7.1.4 Closing a connection, it does not explicitly state what the server should do rather than “…releasing all resources allocated for the channel”.

Figure 15 of the OPC Spec Part 6, however, illustrates that Transport Connection module of the server initiates closing socket. Should this be done explicitly by calling, for example, socket_close after having released all resources related to the closed secure channel?

If this is the case and socket is configured with linger of, say, 2 minutes, the socket would end up in TIME_WAIT state after the socket is closed gracefully. During this time the socket cannot be used for other connection. Do you have any suggestions for handling socket in this case?

Thank you so much!

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Randy Armstrong
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09/01/2021 - 07:09
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The server closing the socket should trigger a socket closed event on the client.

The client would them close the socket which would completely release resources before the linger time expires.

A misbehaving client could leave the socket open. If this is an issue for your server then you can reduce the linger timeout.

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Phuong Nguyen
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09/02/2021 - 00:20
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OK. Thank you for the explanation/confirmation and suggestion. I assume then that value of linger timeout is also implementation specific. 

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