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Socket.EndSendFile Method

Ends a pending asynchronous send of a file.

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

public void EndSendFile(
	IAsyncResult asyncResult


Type: System.IAsyncResult
An IAsyncResult object that stores state information for this asynchronous operation.


Windows NT is required for this method.


The Socket object has been closed.


asyncResult is empty.


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


EndSendFile was previously called for the asynchronous BeginSendFile.


An error occurred when attempting to access the socket. See remarks section below.

EndSendFile completes the asynchronous send operation started in BeginSendFile.

Before calling BeginSendFile, you must create a callback method that implements the AsyncCallback delegate. This callback method executes in a separate thread and is called by the system after BeginSendFile returns. The callback method must accept the IAsyncResult object returned by the BeginSendFile 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 EndSendFile method to successfully complete the send operation.

If you are using a connectionless protocol, EndSendFile blocks until the datagram is sent. If you are using a connection-oriented protocol, EndSendFile blocks until the entire file is sent. 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 BeginSendFile 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.


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

The following code example creates and connects a socket for asynchronous communication and begins sending the file "text.txt" asynchronously to the remote host. The callback delegate calls EndSendFile to complete the transmission.

public static void AsynchronousFileSend()
    // Send a file to a remote device.

    // Establish the remote endpoint for the socket.
    IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());
    IPAddress ipAddress = ipHostInfo.AddressList[0];
    IPEndPoint remoteEP = new IPEndPoint(ipAddress, 11000);

    // Create a TCP/IP socket.
    Socket client = new Socket(AddressFamily.InterNetwork,
        SocketType.Stream, ProtocolType.Tcp);

    // Connect to the remote endpoint.
        new AsyncCallback(ConnectCallback), client);

    // Wait for connect.

    // There is a text file test.txt in the root directory.
    string fileName = "C:\\test.txt";

    // Send file fileName to the remote device.
    client.BeginSendFile(fileName, new AsyncCallback(FileSendCallback), client);

    // Release the socket.

private static void FileSendCallback(IAsyncResult ar)
    // Retrieve the socket from the state object.
    Socket client = (Socket) ar.AsyncState;

    // Complete sending the data to the remote device.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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