Add CancellationToken overloads to Socket.ConnectAsync and Socket.AcceptAsync

[tmds]

CancellationTokens were added to SendAsync and ReceiveAsync in PR dotnet/corefx#36516

This for adding overloads to ConnectAsync and AcceptAsync:

class SocketTaskExtensions
{
   public static ValueTask ConnectAsync (this Socket socket, EndPoint remoteEP, CancellationToken cancellationToken);
   public static ValueTask ConnectAsync (this Socket socket, IPAddress address, int port, CancellationToken cancellationToken);
   public static ValueTask ConnectAsync (this Socket socket, IPAddress[] addresses, int port, CancellationToken cancellationToken);
   public static ValueTask ConnectAsync (this Socket socket, string host, int port, CancellationToken cancellationToken);
   public static ValueTask<Socket> AcceptAsync (this Socket socket, CancellationToken cancellationToken);
   public static ValueTask<Socket> AcceptAsync (this Socket socket, Socket acceptSocket, CancellationToken cancellationToken);

   // existing methods:
   // public static Task ConnectAsync (this Socket socket, EndPoint remoteEP);
   // public static Task ConnectAsync (this Socket socket, IPAddress address, int port);
   // public static Task ConnectAsync (this Socket socket, IPAddress[] addresses, int port);
   // public static Task ConnectAsync (this Socket socket, string host, int port);
   // public static Task<Socket> AcceptAsync (this Socket socket);
   // public static Task<Socket> AcceptAsync (this Socket socket, Socket acceptSocket);
}

class Socket
{
   public static void CancelAcceptAsync(SocketAsyncEventArgs e);

   // existing methods:
   // public bool AcceptAsync (SocketAsyncEventArgs e);
   // public bool ConnectAsync (SocketAsyncEventArgs e);
   // public static void CancelConnectAsync (SocketAsyncEventArgs e);
}

class TcpClient
{
   public ValueTask ConnectAsync (string host, int port, CancellationToken cancellationToken);
   public ValueTask ConnectAsync (IPAddress address, int port, CancellationToken cancellationToken);
   public ValueTask ConnectAsync (IPAddress[] addresses, int port, CancellationToken cancellationToken);

   // existing methods:
   // public Task ConnectAsync (string host, int port);
   // public Task ConnectAsync (IPAddress address, int port);
   // public Task ConnectAsync (IPAddress[] addresses, int port);
}

class TcpListener
{
   public ValueTask<Socket> AcceptSocketAsync (CancellationToken cancellationToken);
   public ValueTask<TcpClient> AcceptTcpClientAsync (CancellationToken cancellationToken);

   // existing methods:
   // public Task<Socket> AcceptSocketAsync ();
   // public Task<TcpClient> AcceptTcpClientAsync ();
}

CC @stephentoub

[stephentoub]

CancellationTokens were added to SendAsync and ReceiveAsync in dotnet/corefx#36516

FWIW, they were actually added in .NET Core 2.1, but the tokens were only checked prior to initiating the call. dotnet/corefx#36516 plumbed them all the way down.

[tmds]

ah ok.

I took a look what is possible with current APIs:
A ConnectAsync(SocketAsyncEventArgs) can be canceled using CancelConnectAsync(SocketAsyncEventArgs).
There is no API to cancel an AcceptAsync.

[clairernovotny]

Does this include UdpClient? I just looked at the surface area for the type in NET Standard 2.1 and did not see a SendAsync or RecieveAsync method with a CancellationToken overload. It would be useful there too.

[tmds]

Does this include UdpClient? I just looked at the surface area for the type in NET Standard 2.1 and did not see a SendAsync or RecieveAsync method with a CancellationToken overload. It would be useful there too.

Those are not included (currently). Adding them to UdpClient is mostly for convenience. You can use the CancellationToken overloads via the UdpClient.Client (which gives you the Socket).

[karelz]

TODO: Looks also into other APIs on Sockets as mentioned in #19592

[tmds]

public static ValueTask<Socket> AcceptAsync (this Socket socket, Socket acceptSocket, CancellationToken cancellationToken);

This one will throw PNSE on non-Windows:

runtime/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Unix.cs

Lines 106 to 110 in 35fe82c

	// AcceptSocket is not supported on Unix.
	if (acceptSocket != null)
	{
	throw new PlatformNotSupportedException(SR.PlatformNotSupported_AcceptSocket);
	}

[xsacha]

Slightly unrelated: Does this mean AcceptTcpClientAsync (as a layer on top of Socket) won't work unless we use Windows? What is the alternative?

[tmds]

@xsacha only the overloads that pass in an existing socket as an acceptSocket argument don't work on non-Windows. AcceptTcpClientAsync doesn't do that.