Socket.EndReceiveFrom(IAsyncResult, EndPoint) Method

Definition

Ends a pending asynchronous read from a specific endpoint.

public:
 int EndReceiveFrom(IAsyncResult ^ asyncResult, System::Net::EndPoint ^ % endPoint);
public:
 int EndReceiveFrom(IAsyncResult ^ result, System::Net::EndPoint ^ % end_point);
public int EndReceiveFrom (IAsyncResult asyncResult, ref System.Net.EndPoint endPoint);
public int EndReceiveFrom (IAsyncResult result, ref System.Net.EndPoint end_point);
member this.EndReceiveFrom : IAsyncResult * EndPoint -> int
member this.EndReceiveFrom : IAsyncResult * EndPoint -> int
Public Function EndReceiveFrom (asyncResult As IAsyncResult, ByRef endPoint As EndPoint) As Integer
Public Function EndReceiveFrom (result As IAsyncResult, ByRef end_point As EndPoint) As Integer

Parameters

asyncResultresult
IAsyncResult

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

endPointend_point
EndPoint

The source EndPoint.

Returns

Int32

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

Exceptions

asyncResult is null.

EndReceiveFrom(IAsyncResult, EndPoint) was previously called for the asynchronous read.

An error occurred when attempting to access the socket.

The Socket has been closed.

Examples

The following code example ends a pending asynchronous read from a specific EndPoint.

StateObject^ so = safe_cast<StateObject^>(ar->AsyncState);
Socket^ s = so->workSocket;

// Creates a temporary EndPoint to pass to EndReceiveFrom.
IPEndPoint^ sender = gcnew IPEndPoint( IPAddress::Any,0 );
EndPoint^ tempRemoteEP = safe_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, gcnew 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 = so->sb->ToString();
      Console::WriteLine( "Read {0} byte from socket" +
         " data = {1}", strContent->Length, strContent );
   }
   s->Close();
}
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();
}
   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

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 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 for a detailed description of the error.

Note

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

Applies to