Fix ConnectAsync not throwing exception for already connected Socket

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

@@ -789,6 +789,11 @@ public void Connect(EndPoint remoteEP)
                 throw new InvalidOperationException(SR.net_sockets_mustnotlisten);
             }
 
+            if (_isConnected)
+            {
+                throw new SocketException((int)SocketError.IsConnected);
+            }
+
             ValidateBlockingMode();
 
             if (NetEventSource.IsEnabled)
@@ -842,6 +847,11 @@ public void Connect(IPAddress address, int port)
                 throw new ArgumentOutOfRangeException(nameof(port));
             }
 
+            if (_isConnected)
+            {
+                throw new SocketException((int)SocketError.IsConnected);
+            }
+
             ValidateForMultiConnect(isMultiEndpoint: false); // needs to come before CanTryAddressFamily call
 
             if (!CanTryAddressFamily(address.AddressFamily))
@@ -917,6 +927,11 @@ public void Connect(IPAddress[] addresses, int port)
                 throw new NotSupportedException(SR.net_invalidversion);
             }
 
+            if (_isConnected)
+            {
+                throw new SocketException((int)SocketError.IsConnected);
+            }
+
             ValidateForMultiConnect(isMultiEndpoint: true); // needs to come before CanTryAddressFamily call
 
             ExceptionDispatchInfo lastex = null;
@@ -2074,6 +2089,11 @@ public IAsyncResult BeginConnect(EndPoint remoteEP, AsyncCallback callback, obje
                 throw new InvalidOperationException(SR.net_sockets_mustnotlisten);
             }
 
+            if (_isConnected)
+            {
+                throw new SocketException((int)SocketError.IsConnected);
+            }
+
 
             DnsEndPoint dnsEP = remoteEP as DnsEndPoint;
             if (dnsEP != null)
@@ -2154,6 +2174,11 @@ public IAsyncResult BeginConnect(string host, int port, AsyncCallback requestCal
                 throw new InvalidOperationException(SR.net_sockets_mustnotlisten);
             }
 
+            if (_isConnected)
+            {
+                throw new SocketException((int)SocketError.IsConnected);
+            }
+
             IPAddress parsedAddress;
             if (IPAddress.TryParse(host, out parsedAddress))
             {
@@ -2201,6 +2226,11 @@ public IAsyncResult BeginConnect(IPAddress address, int port, AsyncCallback requ
                 throw new ArgumentOutOfRangeException(nameof(port));
             }
 
+            if (_isConnected)
+            {
+                throw new SocketException((int)SocketError.IsConnected);
+            }
+
             ValidateForMultiConnect(isMultiEndpoint: false); // needs to be called before CanTryAddressFamily
 
             if (!CanTryAddressFamily(address.AddressFamily))
@@ -2243,6 +2273,11 @@ public IAsyncResult BeginConnect(IPAddress[] addresses, int port, AsyncCallback
                 throw new InvalidOperationException(SR.net_sockets_mustnotlisten);
             }
 
+            if (_isConnected)
+            {
+                throw new SocketException((int)SocketError.IsConnected);
+            }
+
             ValidateForMultiConnect(isMultiEndpoint: true);
 
             // Set up the result to capture the context.  No need for a lock.
@@ -3804,6 +3839,11 @@ public bool ConnectAsync(SocketAsyncEventArgs e)
                 throw new InvalidOperationException(SR.net_sockets_mustnotlisten);
             }
 
+            if (_isConnected)
+            {
+                throw new SocketException((int)SocketError.IsConnected);
+            }
+
             // Prepare SocketAddress.
             EndPoint endPointSnapshot = e.RemoteEndPoint;
             DnsEndPoint dnsEP = endPointSnapshot as DnsEndPoint;

src/System.Net.Sockets/tests/FunctionalTests/Connect.cs

@@ -44,9 +44,7 @@ public async Task Connect_MultipleIPAddresses_Success(IPAddress listenAt)
             }
         }
 
-        [OuterLoop] // TODO: Issue #11345
         [Fact]
-        [ActiveIssue(22765, TestPlatforms.AnyUnix)]
         public async Task Connect_OnConnectedSocket_Fails()
         {
             int port;