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Socket.EndReceiveFrom Method

Ends a pending asynchronous read from a specific endpoint.

[Visual Basic]
Public Function EndReceiveFrom( _
   ByVal asyncResult As IAsyncResult, _
   ByRef endPoint As EndPoint _
) As Integer
[C#]
public int EndReceiveFrom(
 IAsyncResult asyncResult,
   ref EndPoint endPoint
);
[C++]
public: int EndReceiveFrom(
 IAsyncResult* asyncResult,
   EndPoint** endPoint
);
[JScript]
public function EndReceiveFrom(
   asyncResult : IAsyncResult,
 endPoint : EndPoint
) : int;

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.

Exceptions

Exception Type Condition
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.

Remarks

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 IPEndPoint.Address method to obtain the IP address and the IPEndPoint.Port method to obtain the port number.

Note   If you receive a SocketException, use SocketException.ErrorCode to obtain the specific error code. Once you have obtained this code, you can refer to the Windows Socket Version 2 API error code documentation in MSDN for a detailed description of the error.

Example

[Visual Basic, C#, C++] The following example ends a pending asynchronous read from a specific EndPoint.

[Visual Basic] 
Dim so As StateObject = CType(ar.AsyncState, StateObject)
Dim s As Socket = so.workSocket

' Creates a temporary EndPoint to pass to EndReceiveFrom.
Dim sender As New IPEndPoint(IPAddress.Any, 0)
Dim tempRemoteEP As EndPoint = CType(sender, EndPoint)

Dim read As Integer = s.EndReceiveFrom(ar, tempRemoteEP)


If read > 0 Then
   so.sb.Append(Encoding.ASCII.GetString(so.buffer, 0, read))
   s.BeginReceiveFrom(so.buffer, 0, StateObject.BUFFER_SIZE, 0, tempRemoteEP, New AsyncCallback(AddressOf Async_Send_Receive.ReceiveFrom_Callback), so)
Else
   If so.sb.Length > 1 Then
      'All the data has been read, so displays it to the console.
      Dim strContent As String
      strContent = so.sb.ToString()
      Console.WriteLine([String].Format("Read {0} byte from socket" + "data = {1} ", strContent.Length, strContent))
   End If
   s.Close()
End If 
   End Sub 'ReceiveFrom_Callback
   

[C#] 
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();
     
}

[C++] 
StateObject* so = __try_cast<StateObject*>(ar->AsyncState);
Socket* s = so->workSocket;

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

int read = s->EndReceiveFrom(ar, &tempRemoteEP); 

if (read > 0) {
    so->sb->Append(Encoding::ASCII->GetString(so->buffer, 0, read));
    s->BeginReceiveFrom(so->buffer, 0, StateObject::BUFFER_SIZE, SocketFlags::None, &tempRemoteEP,
        new AsyncCallback(0, &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 = so->sb->ToString();
        Console::WriteLine(S"Read {0} byte from socket data = {1}",
            __box(strContent->Length), strContent);
    }
    s->Close();
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework, Common Language Infrastructure (CLI) Standard

See Also

Socket Class | Socket Members | System.Net.Sockets Namespace | Including Asynchronous Calls

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