IWMSCacheProxyServerCallback::OnCompareContentInformation

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IWMSCacheProxyServerCallback::OnCompareContentInformation

The OnCompareContentInformation method is called by the server to respond when a cache plug-in calls IWMSCacheProxyServer::CompareContentInformation.

Syntax

  HRESULT OnCompareContentInformation(
  
  HRESULT
  
  lHr
  ,
  
  WMS_CACHE_VERSION_COMPARE_RESPONSE
  
  CompareResponse
  ,
  
  IWMSContext*
  
  pNewContentInfo
  ,
  
  VARIANT
  
  varContext
  
  );

Parameters

lHr

[in] HRESULT indicating whether the call to IWMSCacheProxyServer::CompareContentInformation succeeded.

CompareResponse

[in] Member of the WMS_CACHE_VERSION_COMPARE_RESPONSE enumeration type indicating the server response. This must be one of the following values.

Value Description
WMS_CACHE_VERSION_FAIL_TO_CHECK_VERSION There was a problem in checking the version. The cache plug-in should either delete the cached content, or try to compare versions again.
WMS_CACHE_VERSION_CACHE_STALE The content is out of date. The cache plug-in must delete the cached content.
WMS_CACHE_VERSION_CACHE_UP_TO_DATE The content is current. The content can be streamed.

pNewContentInfo

[in] Pointer to an IWMSContext interface containing a content description context. The context is associated with the URL passed when the plug-in calls CompareContentInformation.

varContext

[in] VARIANT containing a value defined by the plug-in when it called IWMSCacheProxyServer::CompareContentInformation. For example, your plug-in can use this parameter to persist state information. The server does not alter this value and passes it back when calling OnCompareContentInformation.

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.

Example Code

HRESULT STDMETHODCALLTYPE 
CCachePlugin::OnCompareContentInformation(
               long lHr,
               WMS_CACHE_VERSION_COMPARE_RESPONSE CompareResponse,
               IWMSContext *pReserved,
               VARIANT varContext
               )
{
    HRESULT hr = (HRESULT) lHr;
    WMS_CACHE_QUERY_RESPONSE OpenResponse;
    CCacheEntry *pCacheEntry = NULL;
    CComBSTR bstrCacheUrl;
    IWMSContext* pContentInfo = NULL;
    CComBSTR bstrUrl;

    // The call to CompareContentInformation() failed 
    if( FAILED( hr ) )
    {      
        goto callback;
    }

    // The call to CompareContentInformation() did not fail.
    // Specify the time at which version information was checked.
    // SetVersionCheckTime() is user-defined.
    pCacheEntry->SetVersionCheckTime( CCacheDatabase::GetTimeNow() );

    // Retrieve the cache URL.
    if( NULL != pCacheEntry )
    {
        pCacheEntry->GetCacheUrl( &bstrCacheUrl );
    }

    switch ( CompareResponse )
    {
    case WMS_CACHE_VERSION_CACHE_UP_TO_DATE:
        OpenResponse = WMS_CACHE_QUERY_HIT_PLAY_ON_DEMAND;
        break;

    case WMS_CACHE_VERSION_CACHE_STALE:
        hr = pCacheDatabase.DeleteEntry( pCacheEntry );
        pCacheEntry = NULL;
        OpenResponse = WMS_CACHE_QUERY_MISS;
        break;

    case WMS_CACHE_VERSION_FAIL_TO_CHECK_VERSION:
        OpenResponse = WMS_CACHE_QUERY_MISS;
        hr = S_OK;
        break;
    }
    

callback:
    // Call OnQueryCache() with a URL and a cache hit or miss.
    hr = m_pCacheProxyCallback->OnQueryCache(
                                  hr,
                                  OpenResponse,
                                  bstrCacheUrl,
                                  (IUnknown *) pCachePluginContext,
                                  varContext
                                  );

    return( hr );
}

Requirements

Header: streamcache.h.

Library: WMSServerTypeLib.dll.

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

See Also

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