Hi all,
I view many posts about this issue , the connected property does not tell us the current status of the socket.

based on couple of suggestions of msdn , and some article here , I try to write an helper method that will tell if the socket is connected or not , but it's not working good
continue to tell me that the socket is connectedeven if the other party already call shutdown(both) + close , or , even if the other party close the app itslef.
also I determine different behaviour when my app running behind NAT
when I run behind NAT , calling to socket.Receive(..) throw exception which was good forme to determine that it's already closed the connection , it doesn't throw nothing when I run the same code without NAT

Here is my code:

/// <summary>

/// Determine if the givven socket is connected or not

/// </summary>

/// <remarks>

/// There is a problem to based the Socket.Connected property since it's show the last operaion status: (from msdn)

/// The Connected property gets the connection state of the Socket as of the last I/O operation. When it returns false, the Socket was either never connected, or is no longer connected.

/// The value of the Connected property reflects the state of the connection as of the most recent operation. If you need to determine the current state of the connection, make a nonblocking, zero-byte Send call. If the call returns successfully or throws a WAEWOULDBLOCK error code (10035), then the socket is still connected; otherwise, the socket is no longer connected.

/// </remarks>

/// <seealso cref="http://groups.google.com/group/microsoft.public.dotnet.languages.csharp/browse_thread/thread/3cf03e0641731659/76e2563d28f1b256?lnk=st&q=c%23+determine+if+socket+connected&rnum=5#76e2563d28f1b256"/>

/// <seealso cref="http://windowssdk.msdn.microsoft.com/en-us/library/system.net.sockets.socket.connected.aspx"/>

/// <returns>Bool , True if connected , False if not</returns>

public static bool IsConnected(Socket checkSocket)

{

try

{

//if (checkSocket.GetSocketOption(SocketOptionLevel.Socket, SocketOptionName.KeepAlive, 1)[0].Equals(1))

// return checkSocket.Connected;

if (checkSocket.Connected == false)

return false;

//checkSocket.BeginSend(new byte[0], 0, 0, SocketFlags.None, null, null);

bool bSelectRead = checkSocket.Poll(1, SelectMode.SelectRead);

bool bSelectWrite = checkSocket.Poll(1, SelectMode.SelectWrite);

int available = checkSocket.Available;

//if (bSelectWrite && bSelectRead && available > 0)

if (bSelectWrite && bSelectRead)

{

//return true;

//checkSocket.BeginReceive(new byte[1], 0, 1, SocketFlags.Peek, null, null);

checkSocket.Receive(new byte[0], 0, 0, SocketFlags.Peek);

checkSocket.Send(new byte[0], 0, 0, SocketFlags.None);

return checkSocket.Connected;

}

else

return false;

}

catch (SocketException)

{

return false;

}

catch (ObjectDisposedException)

{

return false;

}

}





here is MS code , that also don't work - tell that the socket is connected even if the other party already close...

// This is how you can determine whether a socket is still connected.
bool blockingState = client.Blocking;
try
{
    byte [] tmp = new byte[1];

    client.Blocking = false;
    client.Send(tmp, 0, 0);
    Console.WriteLine("Connected!");
}
catch (SocketException e)
{
    // 10035 == WSAEWOULDBLOCK
    if (e.NativeErrorCode.Equals(10035))
        Console.WriteLine("Still Connected, but the Send would block");
    else
    {
        Console.WriteLine("Disconnected: error code {0}!", e.NativeErrorCode);
    }
}
finally
{
    client.Blocking = blockingState;
}

Console.WriteLine("Connected: {0}", client.Connected);

Hello, semedao!

s> based on couple of suggestions of msdn , and some article here , I try
s> to write an helper method that will tell if the socket is connected or
s> not , but it's not working good continue to tell me that the socket is
s> connectedeven if the other party already call shutdown(both) + close ,
s> or , even if the other party close the app itslef.

Until there is no network I/O you can't get peer's socket state.

s> also I determine different behaviour when my app running behind NAT when I
s> run behind NAT , calling to socket.Receive(..) throw exception which was
s> good forme to determine that it's already closed the connection , it
s> doesn't throw nothing when I run the same code without NAT

When you're behind NAT, NAT server can detect peer state and send you
RST packet that will notify that socket is not connected anymore.

[skipped]

There are following ways how to resolve:
- use SocketOptionName.KeepAlive
- develop custom keep-alive mechanism.

So... this method is something many developers need , there are noting in
..NET that already do it ?
Show quoteHide quote

Hello, semedao!

s> So... this method is something many developers need , there are noting
s> in .NET that already do it ?

If you're using plain sockets you have to do it yourself.

In order to make keep-alives work, specify KeepAliveTime and KeepAliveInterval
under windows registry
( http://support.microsoft.com/default.aspx?scid=kb;en-us;158474 ).
Computer restart may be required. 

In article <ODpi1sX3GHA.5***@TK2MSFTNGP02.phx.gbl>, Semedao wrote:
Semedao,

It's one of those yes and no situations. The Socket.Connected property tells
you if the local socket knows it's connected to the other end.
Unfortunately, the socket doesn't always know if it's connected due to the
way the TCP protocol is designed. The socket also only updates its
open/closed state when a Send or Receive operation is performed (see
http://windowssdk.msdn.microsoft.com/en-us/library/system.net.sockets.socket
_members.aspx). If you search this newsgroup, you'll find many threads
addressing this isuue.

Mike

Hi,
This is Charles from Microsoft Online Community Support. For this issue, I
noticed that Vadym and Mike had given you explanations. I think the replies
are reasonable. If you wanted to know exactly the connection status, I'm
afraid that you need to judge according to socket exception when you send
or receive data on the socket.

Could you please let me know the issue status and if you need further
research? If you have any other questions or concerns, please feel free to
let me know. It's my pleasure to be of assistance.

Sincerely,
Charles Wang
Microsoft Online Community Support

I understand this issue , so the only way is to inherit the socket and
override the send & receive method to throw some event of
connected/disconnected
thanks
Show quoteHide quote

Hi,
Appreciate your understanding and updating on this issue.

If you have any other questions or concerns, please feel free to let me
know. It's always my pleasure to be of assistance.

Sincerely,
Charles Wang
Microsoft Online Community Suppport

In article <e5QTxq74GHA.1***@TK2MSFTNGP04.phx.gbl>, Semedao wrote:
You don't need to override the Send and Receive methods to have errors
reported as events. The base methods already raise socket exceptions
(etc.).  What you do want to do is to ensure that your application has
a receive outstanding when you want to detect problems. When a  simple,
synchronous (server) application has finished processing one request,
it naturally uses the Receive mthod to get the next request so error
exceptions are raised at this point.

Mike

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