Socket.ConnectAsync result get the socket error "InvalidArgument" for UDP

[iozcelik]

I use .net core 3.1 and creating a worker service.

I try to implement Socket.ConnectAsync both TCP and UDP. However UDP is not working as expected.

From documentation, it will be possibble. However, I am not successed.

If you are using a connection-oriented protocol, the ConnectAsync method starts an asynchronous request for a connection to the remote host. If you are using a connectionless protocol, ConnectAsync establishes a default remote host.

My code is simple:

var socket = new Socket(Endpoint.AddressFamily, SocketType.Dgram, ProtocolType.Udp);

var _connectEventArg = new SocketAsyncEventArgs();
_connectEventArg.RemoteEndPoint = Endpoint;
_connectEventArg.Completed += OnAsyncCompleted;

socket.ConnectAsync(_connectEventArg);

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[antonfirsov]

However UDP is not working as expected.

Can you elaborate on this? Do you get an error? If not, what is the behavior you find unexpected?
Your code looks fine. What is the value of Endpoint, where does it come from?

[iozcelik]

I add some screenshoot. And try to what I expect. First of all, I expect ConnectAsync must return true but it return false. Why?
From documentation:

true if the I/O operation is pending. The Completed event on the e parameter will be raised upon completion of the operation.

false if the I/O operation completed synchronously. In this case, The Completed event on the e parameter will not be raised and the e object passed as a parameter may be examined immediately after the method call returns to retrieve the result of the operation.

Secondly, _connectEventArg.SocketError give InvalidArgument error. Which given argument is invalid? I have only one endpoint argument.

Example code is here:

static void Main(string[] args) { 
       string address = "172.21.48.1";
       int port = 5858;
       var endpoint = new IPEndPoint(IPAddress.Parse(address), port);

       var socket = new Socket(endpoint.AddressFamily, SocketType.Dgram, ProtocolType.Udp);

       var _connectEventArg = new SocketAsyncEventArgs();
       _connectEventArg.RemoteEndPoint = endpoint;
       _connectEventArg.Completed += OnAsyncCompleted;

       var status = socket.ConnectAsync(_connectEventArg);
}

private static void OnAsyncCompleted(object sender, SocketAsyncEventArgs e) {
       Console.WriteLine(e.SocketError);
}

[wfurt]

This should be fixed by #33674.
Use 5.0 preview if you can @iozcelik
(You did not specify but I assume you are on Windows, right?)

[iozcelik]

Yes, working on Windows. I cant use .net 5 but thanks.

[wfurt]

You should be able to use socket.ConnectAsync(endpoint);