IWMSCacheProxyServerCallback.OnGetContentInformation (C#)

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

void IWMSCacheProxyServerCallback.OnGetContentInformation(
  int lHr,
  IWMSContext pContentInfo,
  object varContext
);

Arguments

	[in] int indicating whether the call to IWMSCacheProxyServer.GetContentInformation succeeded.
	[in] IWMSContextIWMSContext Object (C#) containing a Cache Content Information Context. The context includes a variable named WMS_CACHE_CONTENT_INFORMATION_CONTENT_TYPE, which can be zero to indicate on-demand content, or one of the values in the following table, or a bitwise OR of both values.

Value	Description
WMS_CACHE_CONTENT_TYPE_BROADCAST	The content is a broadcast.
WMS_CACHE_CONTENT_TYPE_PLAYLIST	The content is a playlist.

[in] object containing a value defined by the plug-in when it called IWMSCacheProxyServer.GetContentInformation. 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 OnGetContentInformation.

Return Value

This method does not return a value. To report an error, the plug-in can throw a COMException object to the server. If the plug-in uses the IWMSEventLogIWMSEventLog Object (C#) to log error information, it is recommended that it throw NS_E_PLUGIN_ERROR_REPORTED (0xC00D157D). 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 object to send custom error information to the Windows Event Viewer, throwing NS_E_PLUGIN_ERROR_REPORTED stops the server from also logging to the event viewer. For more information about plug-in error information, see Identifying Plug-in Errors.

Remarks

Cache proxy plug-ins generally call GetContentInformation when performing any of the following operations:

• Rolling over to a different protocol

• Establishing a cache-miss policy

• Processing a prestuff request

In each case, the plug-in must get more information about the content before it can proceed. For example, to establish a cache-miss policy, the plug-in must determine whether the content is a broadcast, a playlist, or on demand. Also, before prestuffing content, it must determine whether the content can be cached.

Example

using Microsoft.WindowsMediaServices.Interop;
using System.Runtime.InteropServices;

void IWMSCacheProxyServerCallback.OnGetContentInformation(
            int lHr,
            IWMSContext pContentInfo,
            object varContext
            )
{
  try
  {
    int nFlag=0;
    bool bAddCacheItem = false;
    int nRetHr = lHr;

    // Retrieve the user-defined ContentInfo object from the
    // varContext parameter.
    ContentInfo ci = (ContentInfo)varContext;


    // If this function is called from AddCacheItem(), lExpiration
    // will not be zero, and you can call DownloadContent().
    if(ci.lExpiration!=0)
    {
      bAddCacheItem=true;
      lHr=0;
    }


    // Download the content if the server indicates that your
    // plug-in's call to GetContentInformation() succeeded.
    if(lHr==0)
    {
      // Call a user-defined function, GetContentInfoFromContext(),
      // to retrieve cache content information from the pContentInfo
      // parameter. The context contains a reference to an
      // IWMSDataContainerVersion object that the plug-in can use
      // to retrieve content information. 
       GetContentInfoFromContext(pContentInfo, ref ci);

      // Determine whether the content can be downloaded.
      nFlag = ci.CacheFlags & (int)WMS_DATA_CONTAINER_VERSION_CACHE_FLAGS.WMS_DATA_CONTAINER_VERSION_ALLOW_PROXY_CACHING;

      
      if((nFlag!=0)||(bAddCacheItem))
      {
        // Identify a cache URL.
        if((!bAddCacheItem)||(bAddCacheItem && (ci.CacheUrl==null)))
        {
          ci.CacheUrl = "c:\\WMSCache\\test";
        }
        // Call a user-defined function, IsDownloadInProgress(), to
        // determine whether there is a download in progress.
        if(!IsDownloadInProgress(ci))
        {
          // If there is no current download, call a user-defined
          // function, AddForDownload(), to add cache content
          // information to the DataSet object.  
          AddForDownload(ci);

          // Download the content.
          CacheProxyServer.DownloadContent(ci.OriginUrl,
                                           ci.CacheUrl,
                                           0,0,0,0,
                                           this,
                                           null,
                                           this,
                                           ci);
        }
        else
        {
          // Debugging is already in progress.
        }
      }

      // If the content is a broadcast, do not download it, but
      // store the content information in the DataSet with an empty
      // cache URL.
      if((ci.ContentType & 1)!=0)
      {
        UpdateTable(ci);
      }
    }

    // The server returned E_ACCESSDENIED in response to the
    // plug-in's call to GetContentInformation().
    else
    {
      if(lHr==-2147024891)
      nRetHr=0;
    }

    // Determine whether stream splitting is allowed.
    WMS_CACHE_QUERY_MISS_RESPONSE MissResponse = WMS_CACHE_QUERY_MISS_RESPONSE.WMS_CACHE_QUERY_MISS_PLAY_ON_DEMAND;
    nFlag = ci.CacheFlags & (int)WMS_DATA_CONTAINER_VERSION_CACHE_FLAGS.WMS_DATA_CONTAINER_VERSION_ALLOW_STREAM_SPLITTING;

    // If the stream can be split, broadcast the content.
    // Otherwise, play the content on demand.
    if(nFlag!=0)
    {
       MissResponse = WMS_CACHE_QUERY_MISS_RESPONSE.WMS_CACHE_QUERY_MISS_PLAY_BROADCAST;
    }

    // Request that the server proxy the content on demand.
    if(ci.CacheProxyCallback!=null)
    {
      ci.CacheProxyCallback.OnQueryCacheMissPolicy((int)nRetHr,MissResponse
                    ,ci.OriginUrl,null,pContentInfo,ci.varContext);
    }
  }

  catch(Exception e)
  {
    throw new COMException();
  }

  return;
}

Requirements

Reference: Add a reference to Microsoft.WindowsMediaServices.

Namespace: Microsoft.WindowsMediaServices.Interop.

Assembly: Microsoft.WindowsMediaServices.dll.

Library: WMSServerTypeLib.dll.

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

See Also

Concepts

IWMSCacheProxyServerCallback Object (C#)