IWMSCacheProxy.QueryCache (C#)
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IWMSCacheProxy.QueryCache (C#)
The QueryCache method is called by the server to direct the cache plug-in to search the cache for specific content.
Syntax
Parameters
bstrOriginUrl
[in] string containing the origin URL.
pUserContext
[in] IWMSContext object containing the user context.
pCommandContext
[in] IWMSCommandContext object containing the command context.
pPresentationContext
[in] IWMSContext object containing the presentation context.
lQueryType
[in] Member of the WMS_CACHE_QUERY_TYPE_FLAGS enumeration type that indicates why the server called IWMSCacheProxy.QueryCache. This must be one of the following values.
| Value | Description |
| WMS_CACHE_QUERY_OPEN | A client using a downstream proxy requested content. |
| WMS_CACHE_QUERY_GET_CONTENT_INFO | A downstream proxy requested information about content cached on the remote computer. |
| WMS_CACHE_QUERY_CACHE_EVENT | A cache event notice is being sent upstream. If the WMS_CACHE_QUERY_LOCAL_EVENT flag is set, the cache event was generated by the local computer. Otherwise, it was sent by a downstream proxy server. |
| WMS_CACHE_QUERY_REVERSE_PROXY | A downstream server is configured to be a reverse proxy server. If a cache proxy plug-in supports reverse proxy, it can use this flag to determine whether it must map client requests to an upstream server farm. |
| WMS_CACHE_QUERY_LOCAL_EVENT | The local server is generating an event to send upstream. |
pCallback
[in] IWMSCacheProxyCallback object containing the callback function. The cache plug-in calls IWMSCacheProxyCallback.OnQueryCache to respond to a call to QueryCache.
varContext
[in] object containing a value defined by the server to identify which call to QueryCache the plug-in is responding to when it calls IWMSCacheProxyCallback.OnQueryCache. You must pass this value back unaltered.
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.
Example Code
using Microsoft.WindowsMediaServices.Interop;
using System.Runtime.InteropServices;
void IWMSCacheProxy.QueryCache(string bstrOriginUrl ,
IWMSContext pUserContext ,
IWMSCommandContext pCommandContext ,
IWMSContext pPresentationContext ,
int lQueryType ,
IWMSCacheProxyCallback pCallback ,
object varContext )
{
try
{
int nFlag = (int)WMS_CACHE_QUERY_TYPE_FLAGS.WMS_CACHE_QUERY_OPEN;
int nOpen = lQueryType & nFlag;
int nGCI = lQueryType & ((int)WMS_CACHE_QUERY_TYPE_FLAGS.WMS_CACHE_QUERY_GET_CONTENT_INFO);
int nReverseProxy = lQueryType & ((int)WMS_CACHE_QUERY_TYPE_FLAGS.WMS_CACHE_QUERY_REVERSE_PROXY);
// Either a get content information (GCI) or an open call is made.
if((nOpen!=0)||(nGCI!=0))
{
// Allocate a content information context.
IWMSContext Context;
WMS_CACHE_QUERY_RESPONSE Response = WMS_CACHE_QUERY_RESPONSE.WMS_CACHE_QUERY_MISS;
// The ContentInfo object is user-defined. It contains
// information about an item of cached content.
ContentInfo ci;
GetContentInfo(bstrOriginUrl,out ci);
ci.CacheProxyCallback = pCallback;
ci.varContext = varContext;
// Retrieve the new content information context.
GetContentInfoContext(ci,out Context);
bool bQueryCache = true;
bool bOnDemand = true;
// This is not a reverse proxy, and content has been cached.
if((ci.CacheUrl!=null) && (nReverseProxy==0))
{
// Convert the current time to UTC time.
DateTime now = DateTime.Now;
now = now.ToUniversalTime();
// If the content has not expired, declare a cache hit.
if(ci.ExpirationTime > now)
{
// The content is a broadcast. Declare a cache
// hit and set the cache policy to play the broadcast.
if((ci.ContentType & 1 )!=0)
{
Response = WMS_CACHE_QUERY_RESPONSE.WMS_CACHE_QUERY_HIT_PLAY_BROADCAST;
bOnDemand = false;
}
// The content is on demand. Declare a cache
// hit and set the cache policy to play the content on demand.
else
{
Response = WMS_CACHE_QUERY_RESPONSE.WMS_CACHE_QUERY_HIT_PLAY_ON_DEMAND;
bOnDemand = true;
}
}
// The content has expired.
else
{
if(nOpen!=0)
{
bQueryCache = false;
}
}
}
// The content has not expired. Call OnQueryCache() and send the
// Response parameter and the content information context
// back to the server.
if(bQueryCache)
{
// Retrieve the cache URL from the user-defined content
// information object.
string CacheUrl = ci.CacheUrl;
if(bOnDemand)
{
CacheUrl = string.Format("file://{0}",ci.CacheUrl);
}
pCallback.OnQueryCache( 0,
Response,
CacheUrl,
Context,
null,
varContext);
}
// The content has expired. Call CompareContentInformation (for
// open requests only).
else
{
CacheProxyServer.CompareContentInformation(bstrOriginUrl,
Context,
pPresentationContext,
this,
null,
this,
(object)ci);
}
}
// The request is not a GCI or open call. Determine what the
// request is.
else
{
// Determine whether the call is for event propagation.
int nCacheEvent = lQueryType & ((int)WMS_CACHE_QUERY_TYPE_FLAGS.WMS_CACHE_QUERY_CACHE_EVENT);
int nLocalEvent = lQueryType & ((int)WMS_CACHE_QUERY_TYPE_FLAGS.WMS_CACHE_QUERY_LOCAL_EVENT);
if((nCacheEvent | nLocalEvent)!=0)
{
// Declare a cache miss and ask the server to
// forward the request.
WMS_CACHE_QUERY_RESPONSE Response = WMS_CACHE_QUERY_RESPONSE.WMS_CACHE_QUERY_MISS;
pCallback.OnQueryCache( 0,
Response,
bstrOriginUrl,
null,
null,
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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