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Socket.BeginSendFile Method (String, AsyncCallback, Object)

Sends the file fileName to a connected Socket object using the UseDefaultWorkerThread flag.

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

[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)]
public IAsyncResult BeginSendFile(
	string fileName,
	AsyncCallback callback,
	Object state
)

Parameters

fileName
Type: System.String

A string that contains the path and name of the file to send. This parameter can be null.

callback
Type: System.AsyncCallback

The AsyncCallback delegate.

state
Type: System.Object

An object that contains state information for this request.

Return Value

Type: System.IAsyncResult
An IAsyncResult object that represents the asynchronous send.

ExceptionCondition
ObjectDisposedException

The Socket object has been closed.

NotSupportedException

The socket is not connected to a remote host.

FileNotFoundException

The file fileName was not found.

SocketException

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

This overload sends the file fileName to the connected socket. If fileName is in the local directory, it may be identified with just the name of the file; otherwise, the full path and name of the file must be specified. Wildcards ("..\\myfile.txt") and UNC share names ("\\\\shared directory\\myfile.txt") are supported. If the file is not found, the exception FileNotFoundException is thrown.

This method uses the TransmitFile function found in the Windows Sockets 2 API. For more information about the TransmitFile function and its flags, see the Windows Sockets documentation in the MSDN Library.

The BeginSendFile method starts an asynchronous send operation to the remote host established in the Connect, BeginConnect, Accept, or BeginAccept methods. BeginSendFile throws an exception if you do not first call Accept, BeginAccept, Connect, or BeginConnect. Calling the BeginSendFile method enables you to send a file within a separate execution thread.

To complete the operation, you can create a callback method that is invoked by the AsyncCallback delegate parameter. To do this, at the very minimum, the state parameter must contain the Socket object being used for communication. If your callback needs more information, you can create a class or structure to hold the Socket and the other required information. Pass an instance of this custom object to the BeginSendFile method through the state parameter.

Your callback method must invoke the EndSendFile method. When your application calls BeginSendFile, the system uses a separate thread to execute the specified callback method, and blocks on EndSendFile until the Socket sends the entire file or throws an exception. For additional information on writing callback methods see Callback Sample.

Although intended for connection-oriented protocols, BeginSendFile also works for connectionless protocols, provided that you first call the Connect or BeginConnect method to establish a default remote host. With connectionless protocols, you must be sure that the size of your file does not exceed the maximum packet size of the underlying service provider. If it does, the datagram is not sent and BeginSendFile throws a SocketException exception.

NoteNote

If you receive a SocketException exception, 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.

NoteNote

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

NoteNote

The execution context (the security context, the impersonated user, and the calling context) is cached for the asynchronous Socket methods. After the first use of a particular context (a specific asynchronous Socket method, a specific Socket instance, and a specific callback), subsequent uses of that context will see a performance improvement.

NoteNote

The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

The following code example creates and connects a socket for asynchronous communication. First, the file "text.txt" is sent 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.
    client.BeginConnect(remoteEP, 
        new AsyncCallback(ConnectCallback), client);

    // Wait for connect.
    connectDone.WaitOne();

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

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

    // Release the socket.
    client.Shutdown(SocketShutdown.Both);
    client.Close();
}


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.
    client.EndSendFile(ar);
    sendDone.Set();
}

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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