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NegotiateStream.BeginRead Method

Begins an asynchronous read operation that reads data from the stream and stores it in the specified array.

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

[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)]
public override IAsyncResult BeginRead(
	byte[] buffer,
	int offset,
	int count,
	AsyncCallback asyncCallback,
	Object asyncState


Type: System.Byte[]
A Byte array that receives the bytes read from the stream.
Type: System.Int32
The zero-based location in buffer at which to begin storing the data read from this stream.
Type: System.Int32
The maximum number of bytes to read from the stream.
Type: System.AsyncCallback
An AsyncCallback delegate that references the method to invoke when the read operation is complete.
Type: System.Object
A user-defined object containing information about the read operation. This object is passed to the asyncCallback delegate when the operation completes.

Return Value

Type: System.IAsyncResult
An IAsyncResult object indicating the status of the asynchronous operation.


buffer is null.


offset is less than 0.

- or -

offset is greater than the length of buffer.

- or -

offset plus count is greater than the length of buffer.


The read operation failed.

- or -

Encryption is in use, but the data could not be decrypted.


There is already a read operation in progress.


This object has been closed.


Authentication has not occurred.

If encryption, signing, or encryption and signing are enabled, the read operation reads the data from the underlying stream, checks the integrity of the data, and decrypts it. If no security services such as data encryption or signing are in use, this method starts an asynchronous read operation on the underlying stream.

This method is asynchronous and does not block while the operation completes. To block until the operation completes, use the Read method.

The asynchronous read operation must be completed by calling the EndRead method. Typically, the method is invoked by the asyncCallback delegate. For detailed information about using the asynchronous programming model, see Calling Synchronous Methods Asynchronously

The NegotiateStream class does not support multiple simultaneous read operations. If you attempt to start a read operation while another read operation is already executing on the same stream, a NotSupportedException exception will be thrown.

You cannot call this method until you have successfully authenticated. To authenticate, call one of the AuthenticateAsClient, BeginAuthenticateAsClient, AuthenticateAsServer, or BeginAuthenticateAsServer methods.


The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

The following code example demonstrates starting an asynchronous read operation. This code example is part of a larger example provided for the NegotiateStream class.

public static void AuthenticateClient(TcpClient clientRequest)
    NetworkStream stream = clientRequest.GetStream(); 
    // Create the NegotiateStream.
    NegotiateStream authStream = new NegotiateStream(stream, false); 
    // Save the current client and NegotiateStream instance 
    // in a ClientState object.
    ClientState cState = new ClientState(authStream, clientRequest);
    // Listen for the client authentication request.
    authStream.BeginAuthenticateAsServer (
        new AsyncCallback(EndAuthenticateCallback),
    // Wait until the authentication completes.
    authStream.BeginRead(cState.Buffer, 0, cState.Buffer.Length, 
           new AsyncCallback(EndReadCallback), 
    // Finished with the current client.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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