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

 
System_CAPS_noteNote

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Begins to asynchronously receive data from a connected Socket.

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

<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)>
Public Function BeginReceive (
	buffer As Byte(),
	offset As Integer,
	size As Integer,
	socketFlags As SocketFlags,
	callback As AsyncCallback,
	state As Object
) As IAsyncResult

Parameters

buffer
Type: System.Byte()

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

offset
Type: System.Int32

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

size
Type: System.Int32

The number of bytes to receive.

socketFlags
Type: System.Net.Sockets.SocketFlags

A bitwise combination of the SocketFlags values.

callback
Type: System.AsyncCallback

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

state
Type: System.Object

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

Type: System.IAsyncResult

An IAsyncResult that references the asynchronous read.

Exception Condition
ArgumentNullException

buffer is null.

SocketException

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

ObjectDisposedException

Socket has been closed.

ArgumentOutOfRangeException

offset is less than 0.

-or-

offset is greater than the length of buffer.

-or-

size is less than 0.

-or-

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.

System_CAPS_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.

System_CAPS_noteNote

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.

System_CAPS_noteNote

state is an instantiation of a user-defined class.

System_CAPS_noteNote

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

System_CAPS_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.

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)
   allDone.Set()
   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

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
      so.sb.Append(Encoding.ASCII.GetString(so.buffer, 0, read))
      s.BeginReceive(so.buffer, 0, StateObject.BUFFER_SIZE, 0, New AsyncCallback(AddressOf Async_Send_Receive.Read_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 'Read_Callback

.NET Framework
Available since 1.1
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