Socket.EndSend Method (IAsyncResult)

Ends a pending asynchronous send.

Namespace: System.Net.Sockets
Assembly: System (in system.dll)

public int EndSend (
	IAsyncResult asyncResult
public int EndSend (
	IAsyncResult asyncResult
public function EndSend (
	asyncResult : IAsyncResult
) : int



An IAsyncResult that stores state information for this asynchronous operation.

Return Value

If successful, the number of bytes sent to the Socket; otherwise, an invalid Socket error.

Exception typeCondition


asyncResult is a null reference (Nothing in Visual Basic).


asyncResult was not returned by a call to the BeginSend method.


EndSend was previously called for the asynchronous send.


An error occurred when attempting to access the socket. See the Remarks section for more information.


The Socket has been closed.

EndSend completes the asynchronous send operation started in BeginSend.

Before calling BeginSend, you need to create a callback method that implements the AsyncCallback delegate. This callback method executes in a separate thread and is called by the system after BeginSend returns. The callback method must accept the IAsyncResult returned by the BeginSend method as a parameter.

Within the callback method, call the AsyncState method of the IAsyncResult parameter to obtain the sending Socket. After obtaining the Socket, you can call the EndSend method to successfully complete the send operation and return the number of bytes sent.

If you are using a connectionless protocol, EndSend will block until the datagram is sent. If you are using a connection-oriented protocol, EndSend will block until some of the buffer was sent. If the return value from EndSend indicates that the buffer was not completely sent, call the BeginSend method again, modifying the buffer to hold the unsent data.

There is no guarantee that the data you send will appear on the network immediately. To increase network efficiency, the underlying system may delay transmission until a significant amount of outgoing data is collected. A successful completion of the BeginSend method means that the underlying system has had room to buffer your data for a network send.


If you receive a SocketException, use the SocketException.ErrorCode property to obtain the specific error code. After you have obtained this code, refer to the Windows Sockets version 2 API error code documentation in the MSDN library for a detailed description of the error.


All I/O initiated by a given thread is canceled when that thread exits. A pending asynchronous operation can fail if the thread exits before the operation completes.


The successful completion of a send does not indicate that the data was successfully delivered. If no buffer space is available within the transport system to hold the data to be transmitted, send will block unless the socket has been placed in nonblocking mode.


This member outputs trace information when you enable network tracing in your application. For more information, see Network Tracing.

The following code example ends a pending asynchronous send.

StateObject so = (StateObject) ar.AsyncState;
Socket s = so.workSocket;

int send = s.EndSend(ar);

   Console.WriteLine("The size of the message sent was :" + send.ToString());


StateObject so = (StateObject)ar.get_AsyncState();
Socket s = so.workSocket;
int send = s.EndSend(ar);
Console.WriteLine("The size of the message sent was :"
    + ((Int32)send).ToString());

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0