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NegotiateStream.BeginWrite Method

Begins an asynchronous write operation that writes Bytes from the specified buffer to the stream.

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

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


Type: System.Byte[]
A Byte array that supplies the bytes to be written to the stream.
Type: System.Int32
The zero-based location in buffer at which to begin reading bytes to be written to the stream.
Type: System.Int32
An Int32 value that specifies the number of bytes to read from buffer.
Type: System.AsyncCallback
An AsyncCallback delegate that references the method to invoke when the write operation is complete.
Type: System.Object
A user-defined object containing information about the write 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 write operation failed.

- or -

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


There is already a write operation in progress.


This object has been closed.


Authentication has not occurred.

If encryption, signing, or encryption and signing are enabled, this method reads the data from buffer, encrypts, signs, or encrypts and signs it, and transmits it using the underlying stream. If no security services such as data encryption or signing are in use, this method starts an asynchronous write 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 EndWrite 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 write operations. If you attempt to start a write operation while another write 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 beginning an asynchronous write operation.

// Request authentication.
NetworkStream clientStream = client.GetStream();
NegotiateStream authStream = new NegotiateStream(clientStream, false); 
// Pass the NegotiateStream as the AsyncState object 
// so that it is available to the callback delegate.
IAsyncResult ar = authStream.BeginAuthenticateAsClient(
    new AsyncCallback(EndAuthenticateCallback),
Console.WriteLine("Client waiting for authentication...");
// Wait until the result is available.
// Display the properties of the authenticated stream.
// Send a message to the server.
// Encode the test data into a byte array.
byte[] message = Encoding.UTF8.GetBytes("Hello from the client.");
ar = authStream.BeginWrite(message, 0, message.Length,
    new AsyncCallback(EndWriteCallback),

The following method is called when the operation completes.

// The following method is called when the write operation completes.
public static void EndWriteCallback (IAsyncResult ar)
    Console.WriteLine("Client ending write operation...");
    NegotiateStream authStream = (NegotiateStream) ar.AsyncState;

    // End the asynchronous operation.

.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.