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Socket.EndReceiveFrom Method

Ends a pending asynchronous read from a specific endpoint.

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

public int EndReceiveFrom (
	IAsyncResult asyncResult,
	ref EndPoint endPoint
)
public int EndReceiveFrom (
	IAsyncResult asyncResult, 
	/** @ref */ EndPoint endPoint
)
Not applicable.

Parameters

asyncResult

An IAsyncResult that stores state information and any user defined data for this asynchronous operation.

endPoint

The source EndPoint.

Return Value

If successful, the number of bytes received. If unsuccessful, returns 0.

Exception typeCondition

ArgumentNullException

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

ArgumentException

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

InvalidOperationException

EndReceiveFrom was previously called for the asynchronous read.

SocketException

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

ObjectDisposedException

The Socket has been closed.

The EndReceiveFrom method completes the asynchronous read operation started in the BeginReceiveFrom method.

Before calling BeginReceiveFrom, 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 BeginReceiveFrom returns. The callback method must accept the IAsyncResult returned by the BeginReceiveFrom method as a parameter.

Within the callback method, call the AsyncState method of the IAsyncResult to obtain the state object passed to the BeginReceiveFrom method. Extract the receiving Socket from this state object. After obtaining the Socket, you can call the EndReceiveFrom method to successfully complete the read operation and return the number of bytes read.

The EndReceiveFrom method will block until data is available. If you are using a connectionless protocol, EndReceiveFrom will read the first enqueued datagram available in the incoming network buffer. If you are using a connection-oriented protocol, the EndReceiveFrom method will read as much data as is available up to the number of bytes you specified in the size parameter of the BeginReceiveFrom method. If the remote host shuts down the Socket connection with the Shutdown method, and all available data has been received, the EndReceiveFrom method will complete immediately and return zero bytes. To obtain the received data, call the AsyncState method of the IAsyncResult object, and extract the buffer contained in the resulting state object. To identify the originating host, extract the EndPoint and cast it to an IPEndPoint. Use the System.Net.IPEndPoint.Address method to obtain the IP address and the System.Net.IPEndPoint.Port method to obtain the port number.

NoteNote:

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.

NoteNote:

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 read from a specific EndPoint.

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

   // Creates a temporary EndPoint to pass to EndReceiveFrom.
   IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
EndPoint tempRemoteEP = (EndPoint)sender;

   int read = s.EndReceiveFrom(ar, ref tempRemoteEP); 


if (read > 0) {
        so.sb.Append(Encoding.ASCII.GetString(so.buffer, 0, read));
        s.BeginReceiveFrom(so.buffer, 0, StateObject.BUFFER_SIZE, 0, ref tempRemoteEP,
                                 new AsyncCallback(Async_Send_Receive.ReceiveFrom_Callback), so);
}
else{
     if (so.sb.Length > 1) {
          //All the data has been read, so displays it to the console.
          string strContent;
          strContent = so.sb.ToString();
          Console.WriteLine(String.Format("Read {0} byte from socket" + 
                             "data = {1} ", strContent.Length, strContent));
     }
     s.Close();
     
}

StateObject so = (StateObject)ar.get_AsyncState();
Socket s = so.workSocket;
// Creates a temporary EndPoint to pass to EndReceiveFrom.
IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
EndPoint tempRemoteEP = (EndPoint)sender;
int read = s.EndReceiveFrom(ar, tempRemoteEP);

if (read > 0) {
    so.sb.Append(Encoding.get_ASCII().GetString(so.buffer, 0, read));
    s.BeginReceiveFrom(so.buffer, 0, StateObject.BUFFER_SIZE,
        (SocketFlags)0, tempRemoteEP,
        new AsyncCallback(Async_Send_Receive.ReceiveFrom_Callback), so);
}
else {
    if (so.sb.get_Length() > 1) {
        //All the data has been read, so displays it to the console.
        String strContent;
        strContent = so.sb.ToString();
        Console.WriteLine(String.Format("Read {0} byte from socket"
            + "data = {1} ", (Int32)(strContent.get_Length()),
            strContent));
    }
    s.Close();
}

Windows 98, Windows Server 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 Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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