SslStream.BeginRead(Byte[], Int32, Int32, AsyncCallback, Object) Metodo

public:
 override IAsyncResult ^ BeginRead(cli::array <System::Byte> ^ buffer, int offset, int count, AsyncCallback ^ asyncCallback, System::Object ^ asyncState);

public override IAsyncResult BeginRead(byte[] buffer, int offset, int count, AsyncCallback asyncCallback, object asyncState);

override this.BeginRead : byte[] * int * int * AsyncCallback * obj -> IAsyncResult

Public Overrides Function BeginRead (buffer As Byte(), offset As Integer, count As Integer, asyncCallback As AsyncCallback, asyncState As Object) As IAsyncResult

Parametri

Valori restituiti

Oggetto IAsyncResult che indica lo stato dell'operazione asincrona.

Eccezioni

Esempio

Nell'esempio di codice seguente viene illustrato l'avvio di un'operazione di lettura asincrona.

// readData and buffer holds the data read from the server.
// They is used by the ReadCallback method.
static StringBuilder readData = new StringBuilder();
static byte [] buffer = new byte[2048];

' readData and buffer holds the data read from the server.
' They is used by the ReadCallback method.
Shared readData As New StringBuilder()
Shared buffer As Byte() = New Byte(2048) {}

static void WriteCallback(IAsyncResult ar)
{
    SslStream stream = (SslStream) ar.AsyncState;
    try
    {
        Console.WriteLine("Writing data to the server.");
        stream.EndWrite(ar);
        // Asynchronously read a message from the server.
        stream.BeginRead(buffer, 0, buffer.Length,
            new AsyncCallback(ReadCallback),
            stream);
    }
    catch (Exception writeException)
    {
        e = writeException;
        complete = true;
        return;
    }
}

Shared Sub WriteCallback(ar As IAsyncResult)
    Dim stream = CType(ar.AsyncState, SslStream)
    Try
        Console.WriteLine("Writing data to the server.")
        stream.EndWrite(ar)
        ' Asynchronously read a message from the server.
        stream.BeginRead(buffer, 0, buffer.Length, New AsyncCallback(AddressOf ReadCallback), stream)
    Catch writeException As Exception
        e = writeException
        complete = True
        Return
    End Try
End Sub

Al termine della lettura viene chiamato il metodo seguente.

static void ReadCallback(IAsyncResult ar)
{
    // Read the  message sent by the server.
    // The end of the message is signaled using the
    // "<EOF>" marker.
    SslStream stream = (SslStream) ar.AsyncState;
    int byteCount = -1;
    try
    {
        Console.WriteLine("Reading data from the server.");
        byteCount = stream.EndRead(ar);
        // Use Decoder class to convert from bytes to UTF8
        // in case a character spans two buffers.
        Decoder decoder = Encoding.UTF8.GetDecoder();
        char[] chars = new char[decoder.GetCharCount(buffer,0, byteCount)];
        decoder.GetChars(buffer, 0, byteCount, chars,0);
        readData.Append (chars);
        // Check for EOF or an empty message.
        if (readData.ToString().IndexOf("<EOF>") == -1 && byteCount != 0)
        {
            // We are not finished reading.
            // Asynchronously read more message data from  the server.
            stream.BeginRead(buffer, 0, buffer.Length,
                new AsyncCallback(ReadCallback),
                stream);
        }
        else
        {
            Console.WriteLine("Message from the server: {0}", readData.ToString());
        }
    }
    catch (Exception readException)
    {
        e = readException;
        complete = true;
        return;
    }
    complete = true;
}

Shared Sub ReadCallback(ar As IAsyncResult)
    ' Read the  message sent by the server.
    ' The end of the message is signaled using the
    ' "<EOF>" marker.
    Dim stream = CType(ar.AsyncState, SslStream)
    Dim byteCount As Integer
    Try
        Console.WriteLine("Reading data from the server.")
        byteCount = stream.EndRead(ar)
        ' Use Decoder class to convert from bytes to UTF8
        ' in case a character spans two buffers.
        Dim decoder As Decoder = Encoding.UTF8.GetDecoder()
        Dim chars = New Char(decoder.GetCharCount(buffer, 0, byteCount)) {}
        decoder.GetChars(buffer, 0, byteCount, chars, 0)
        readData.Append(chars)
        ' Check for EOF or an empty message.
        If readData.ToString().IndexOf("<EOF>") = -1 AndAlso byteCount <> 0 Then
            ' We are not finished reading.
            ' Asynchronously read more message data from  the server.
            stream.BeginRead(buffer, 0, buffer.Length, New AsyncCallback(AddressOf ReadCallback), stream)
        Else
            Console.WriteLine("Message from the server: {0}", readData.ToString())
        End If
    Catch readException As Exception
        e = readException
        complete = True
        Return
    End Try
    complete = True
End Sub

Commenti

Se la crittografia e la firma sono abilitate, l'operazione di lettura legge i dati dal flusso sottostante, controlla l'integrità dei dati e/o la decrittografa. L'operazione di lettura asincrona deve essere completata chiamando il EndRead metodo . In genere, il metodo viene richiamato dal asyncCallback delegato.

Questo metodo non blocca al termine dell'operazione. Per bloccare fino al completamento dell'operazione, usare il Read metodo .

Per informazioni dettagliate sull'uso del modello di programmazione asincrona, vedere Chiamata asincrona di metodi sincroni

La SslStream classe non supporta più operazioni di lettura simultanee.

Non è possibile chiamare questo metodo fino a quando non è stata eseguita correttamente l'autenticazione. Per autenticare chiamare uno dei AuthenticateAsClientmetodi , o BeginAuthenticateAsClient, AuthenticateAsServer. BeginAuthenticateAsServer