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IWMSDataContainerCallback::OnRead

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IWMSDataContainerCallback::OnRead

The OnRead method returns the results of the IWMSDataContainer::Read method call.

Syntax

  HRESULT OnRead(
  HRESULT  hr,
  DWORD  dwActualBytesTransferred,
  DWORD  dwChangeType,
  QWORD  qwChangeParameter,
  QWORD  qwContext
);

Parameters

hr

[in] HRESULT containing the result of the IWMSDataContainer::Read method call.

dwActualBytesTransferred

[in] DWORD containing the number of bytes of data transferred.

dwChangeType

[in] DWORD reserved for future use. Set this parameter to NULL.

qwChangeParameter

[in] QWORD reserved for future use. Set this parameter to NULL.

qwContext

[in] QWORD containing a value defined by the server to identify which IWMSDataContainer::Read request the plug-in is responding to when it calls OnRead. The plug-in must pass this value back unaltered.

Return Values

If the method succeeds, the plug-in must return S_OK. To report an error, the plug-in can return any HRESULT other than S_OK. If the plug-in uses the IWMSEventLog interface to log error information directly to the Windows Event Viewer, it is recommended that it return NS_E_PLUGIN_ERROR_REPORTED. Typically, the server attempts to make plug-in error information available to the server object model, the Windows Event Viewer, and the troubleshooting list in the details pane of the Windows Media Services MMC. However, if the plug-in uses the IWMSEventLog interface to send custom error information to the Windows Event Viewer, returning NS_E_PLUGIN_ERROR_REPORTED stops the server from also logging to the event viewer. For more information about retrieving plug-in error information, see Identifying Plug-in Errors.

Remarks

It is recommended that, if possible, your plug-in read at least one second of data before calling this method.

Example Code

The following example applies only to data contained in a file.

HRESULT STDMETHODCALLTYPE 
CDataContainer::Read( 
                        BYTE *pbBuffer,
                        QWORD qwReadPosition,
                        DWORD dwMaxDataSize,
                        IWMSDataContainerCallback *pCallback,
                        QWORD qwContext
                        )
{
    HRESULT hr = S_OK;
    BOOL fSuccess = FALSE;

    // TODO: Allocate (not shown) and initialize an OVERLAPPED 
    // structure. The pOverLapped variable is a pointer to 
    // this structure. See the CreateFile() documentation in the 
    // MSDN library for more information.
    // If you opened the container by using the 
    // FILE_FLAG_OVERLAPPED flag, an OVERLAPPED structure is 
    // required for a read operation.
    pOverlapped->Offset = LODWORD( qwReadPosition );
    pOverlapped ->OffsetHigh = ( LONG ) HIDWORD( qwReadPosition );
    pOverlapped ->hEvent = NULL;

    // Read the file.
    fSuccess = ReadFile( 
                    m_hFile, 
                    pbBuffer, 
                    dwMaxDataSize, 
                    &m_dwBytesTransferred ),
                    ( LPOVERLAPPED ) pOverLapped
                    );

    // TODO: Specify HRESULT for read operation.

    // Respond to the server.
    hr = m_pCallback->OnRead( 
                             hr,
                             m_dwBytesTransferred,
                             0,
                             0,
                             qwContext );

    return( S_OK );
}

Requirements

Header: datacontainer.h.

Library: WMSServerTypeLib.dll.

Platform: Windows Server 2003, Enterprise Edition; Windows Server 2003, Datacenter Edition; Windows Server 2008.

See Also

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