This documentation is archived and is not being maintained.

Socket.BeginReceive Method (Byte[], Int32, Int32, SocketFlags, AsyncCallback, Object)

Begins to asynchronously receive data from a connected Socket.

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

Public Function BeginReceive ( _
	buffer As Byte(), _
	offset As Integer, _
	size As Integer, _
	socketFlags As SocketFlags, _
	callback As AsyncCallback, _
	state As Object _
) As IAsyncResult
Dim instance As Socket
Dim buffer As Byte()
Dim offset As Integer
Dim size As Integer
Dim socketFlags As SocketFlags
Dim callback As AsyncCallback
Dim state As Object
Dim returnValue As IAsyncResult

returnValue = instance.BeginReceive(buffer, offset, size, socketFlags, callback, state)
public IAsyncResult BeginReceive (
	byte[] buffer, 
	int offset, 
	int size, 
	SocketFlags socketFlags, 
	AsyncCallback callback, 
	Object state
public function BeginReceive (
	buffer : byte[], 
	offset : int, 
	size : int, 
	socketFlags : SocketFlags, 
	callback : AsyncCallback, 
	state : Object
) : IAsyncResult



An array of type Byte that is the storage location for the received data.


The zero-based position in the buffer parameter at which to store the received data.


The number of bytes to receive.


A bitwise combination of the SocketFlags values.


An AsyncCallback delegate that references the method to invoke when the operation is complete.


A user-defined object that contains information about the receive operation. This object is passed to the EndReceive delegate when the operation is complete.

Return Value

An IAsyncResult that references the asynchronous read.

Exception typeCondition


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


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


Socket has been closed.


offset is less than 0.


offset is greater than the length of buffer.


size is less than 0.


size is greater than the length of buffer minus the value of the offset parameter.

The asynchronous BeginReceive operation must be completed by calling the EndReceive method. Typically, the method is invoked by the callback delegate.

This method does not block until the operation is complete. To block until the operation is complete, use one of the Receive method overloads.

To cancel a pending BeginReceive, call the Close method.

For detailed information about using the asynchronous programming model, see Calling Synchronous Methods Asynchronously.


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.


All I/O initiated by a given thread is canceled when that thread exits. A pending asynchronous operation can fail if the thread exits before the operation completes.


state is an instantiation of a user-defined class.


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


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.

The following code example begins to asynchronously receive data from a connected Socket.

Public Class StateObject
   Public workSocket As Socket = Nothing
   Public const BUFFER_SIZE As Integer = 1024
   Public buffer(BUFFER_SIZE) As byte
   Public sb As New StringBuilder()
End Class 'StateObject

Public Shared Sub Listen_Callback(ar As IAsyncResult)
   Dim s As Socket = CType(ar.AsyncState, Socket)
   Dim s2 As Socket = s.EndAccept(ar)
   Dim so2 As New StateObject()
   so2.workSocket = s2
   s2.BeginReceive(so2.buffer, 0, StateObject.BUFFER_SIZE, 0, New AsyncCallback(AddressOf Async_Send_Receive.Read_Callback), so2)
End Sub 'Listen_Callback

Socket s = (Socket)ar.get_AsyncState();
Socket s2 = s.EndAccept(ar);
StateObject so2 = new StateObject();
so2.workSocket = s2;
s2.BeginReceive(so2.buffer, 0, StateObject.BUFFER_SIZE,
    (SocketFlags)0, new AsyncCallback(Async_Send_Receive.Read_Callback),

Public Shared Sub Read_Callback(ar As IAsyncResult)
   Dim so As StateObject = CType(ar.AsyncState, StateObject)
   Dim s As Socket = so.workSocket
   Dim read As Integer = s.EndReceive(ar)
   If read > 0 Then, 0, read))
      s.BeginReceive(so.buffer, 0, StateObject.BUFFER_SIZE, 0, New AsyncCallback(AddressOf Async_Send_Receive.Read_Callback), so)
      If > 1 Then
         'All the data has been read, so displays it to the console
         Dim strContent As String
         strContent =
         Console.WriteLine([String].Format("Read {0} byte from socket" + "data = {1} ", strContent.Length, strContent))
      End If
   End If
End Sub 'Read_Callback

StateObject so = (StateObject)ar.get_AsyncState();
Socket s = so.workSocket;
int read = s.EndReceive(ar);

if (read > 0) {, 0, read));
    s.BeginReceive(so.buffer, 0, StateObject.BUFFER_SIZE,
        (SocketFlags)0, new AsyncCallback(Async_Send_Receive.
        Read_Callback), so);
else {
    if ( > 1) {
        //All of the data has been read, so displays it to the console
        String strContent;
        strContent =;
        Console.WriteLine(String.Format("Read {0} byte from socket"
            + "data = {1} ", (Int32)strContent.get_Length(), 

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0