[9.0] Guard against empty Accept address (#111366)

* guard agains empty Accept address

* remove assert

* add comment

---------

Co-authored-by: wfurt <tweinfurt@yahoo.com>

Author: github-actions[bot]

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

@@ -3602,15 +3602,15 @@ internal void InternalSetBlocking(bool desired)
         }
 
         // CreateAcceptSocket - pulls unmanaged results and assembles them into a new Socket object.
-        internal Socket CreateAcceptSocket(SafeSocketHandle fd, EndPoint remoteEP)
+        internal Socket CreateAcceptSocket(SafeSocketHandle fd, EndPoint? remoteEP)
         {
             // Internal state of the socket is inherited from listener.
             Debug.Assert(fd != null && !fd.IsInvalid);
             Socket socket = new Socket(fd, loadPropertiesFromHandle: false);
             return UpdateAcceptSocket(socket, remoteEP);
         }
 
-        internal Socket UpdateAcceptSocket(Socket socket, EndPoint remoteEP)
+        internal Socket UpdateAcceptSocket(Socket socket, EndPoint? remoteEP)
         {
             // Internal state of the socket is inherited from listener.
             socket._addressFamily = _addressFamily;

src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.Unix.cs

@@ -35,7 +35,6 @@ private void CompleteAcceptOperation(IntPtr acceptedFileDescriptor, Memory<byte>
             _acceptedFileDescriptor = acceptedFileDescriptor;
             if (socketError == SocketError.Success)
             {
-                Debug.Assert(socketAddress.Length > 0);
                 _acceptAddressBufferCount = socketAddress.Length;
             }
             else
@@ -348,9 +347,10 @@ private SocketError FinishOperationAccept(SocketAddress remoteSocketAddress)
             new ReadOnlySpan<byte>(_acceptBuffer, 0, _acceptAddressBufferCount).CopyTo(remoteSocketAddress.Buffer.Span);
             remoteSocketAddress.Size = _acceptAddressBufferCount;
 
+            // on macOS accept can sometimes return empty remote address even when it returns successfully.
             Socket acceptedSocket = _currentSocket!.CreateAcceptSocket(
                 SocketPal.CreateSocket(_acceptedFileDescriptor),
-                _currentSocket._rightEndPoint!.Create(remoteSocketAddress));
+                remoteSocketAddress.Size > 0 ? _currentSocket._rightEndPoint!.Create(remoteSocketAddress) : null);
             if (_acceptSocket is null)
             {
                 // Store the accepted socket