IWMSCacheProxyServerCallback.OnGetContentInformation (C#)
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IWMSCacheProxyServerCallback.OnGetContentInformation (C#)
The OnGetContentInformation method is called by the server to respond when a cache plug-in calls IWMSCacheProxyServer::GetContentInformation.
Syntax
Parameters
lHr
[in] int indicating whether the call to IWMSCacheProxyServer.GetContentInformation succeeded.
pContentInfo
[in] IWMSContext object 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. |
varContext
[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 Values
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 IWMSEventLog object 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 Code
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
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