NWConnection cancel

Question

Created Sep ’18

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Hi, i work on some application which should send data between devices, I implement that in Network Framwork instead of socket.

Everything works like it should, except one situation which i do not understand correctly.

When i open NWConnection to some endpoint, i can observe states - all works fine from setting uoo to ready.

I can send data between, without problems.

Now i want to solve in nice way situation when one side of connection is closed - manually or by an issue.

I do close connection by cancelCurrentEndpoint - there are no other endpoints on that connection - so as i expect State should change to cancelled, but it goes to failed on the device i close it with information that network is down.

I don't undersand why nothing happens on the endpoint this connection - no StateUpdate

When i use cancel() method, it works like expected - on my side of connection statusChange to cancelled.

I can make some code to send to all devices information about closing connection, but it is not solution i want.

Have someone got that issue and explain how those cancel - cancelEndPoint method works, on Apple Documentation there is nothing to read.

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Answer 1

DTS Engineer OP

Apple

Sep ’18

What transport protocol are you using (TCP or UDP)?

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Answer 2

jakajancar OP

Mar ’21

@HPmax, I know it's a "bit" late, but this should work if you are using plain TCP (no TLS). You must send() with data=nil and a context that has .isFinal=true (such as .finalMessage).

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Answer 3

anelad OP

Jan ’24

as an addition to @jakajancar's answer let me introduce an example code ;

Send a message to the connection you want to cancel; set contentContext: parameter to NWConnection.ContentContext.finalMessage, then cancel the connection:

connectionYouWantToCancel.send(content: nil, contentContext: .finalMessage, isComplete: true, completion: .idempotent)
connectionYouWantToCancel.cancel()

And read the message on the other device; check if the context is final

connectionOnTheOtherDevice.receiveMessage { (content, context, isComplete, error) in
    if let context = context, context.isFinal {
        connectionOnTheOtherDevice.cancel()
        // any other logic if needed.
        return
    }
        
    // other logic
}

At least I'm handling the problem this way without any delay or any unexpected behaviour.

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