IWMSCacheProxyCallback.OnQueryCache (Visual Basic .NET)
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IWMSCacheProxyCallback.OnQueryCache (Visual Basic .NET)
The OnQueryCache method is called by the cache plug-in to respond when the server calls IWMSCacheProxy.QueryCache.
Syntax
Parameters
lHr
[in] Integer indicating whether the call to IWMSCacheProxy.QueryCache was successful.
Response
[in] Member of the WMS_CACHE_QUERY_RESPONSE enumeration type indicating the response of the cache plug-in. This must be one of the following values.
| Value | Description |
| WMS_CACHE_QUERY_HIT_PLAY_ON_DEMAND | The requested content is in the cache and is current. Therefore, it may be streamed from the cache or proxied from an upstream server. Each client request requires a separate connection. |
| WMS_CACHE_QUERY_HIT_PLAY_BROADCAST | The requested content is in the cache and is current. Therefore, it may be streamed from the cache or proxied from an upstream server. A single stream can be split to multiple downstream clients. |
| WMS_CACHE_QUERY_HIT_PROCESS_REQUEST | The requested content is in the cache. The server must process the request and send information about the result to the downstream client. This response is only valid if the server has called QueryCache and specified either WMS_CACHE_QUERY_GET_CONTENT_INFO or WMS_CACHE_QUERY_CACHE_EVENT. |
| WMS_CACHE_QUERY_MISS | The requested content is not in the cache or is not current. |
bstrCacheUrl
[in] String containing the cache URL.
pContentInfo
[in] IWMSContext object containing a content description context.
pCachePluginContext
[in] Object containing information defined by the cache plug-in. The server does not use this information. It passes the pointer back to the plug-in when it calls IWMSCacheProxy.QueryCacheMissPolicy.
varContext
[in] Object containing a value defined by the server to identify which call to IWMSCacheProxy.QueryCache the plug-in is responding to when it calls OnQueryCache. You must pass this value back unaltered.
Return Values
This method does not return a value.
If this method fails, it throws an exception.
| Number | Description |
| 0x80070057 | The content information context identified by the pContentInfo parameter does not exist, and the plug-in returned WMS_CACHE_QUERY_HIT_PLAY_ON_DEMAND in the Response parameter. |
| 0x80070057 | The VarContext parameter does not contain a valid reference. |
| 0x80070057 | The plug-in returned WMS_CACHE_QUERY_HIT_PROCESS_REQUEST in the Response parameter when the server called QueryCache and specified WMS_CACHE_QUERY_GET_CONTENT_INFO or WMS_CACHE_QUERY_CACHE_EVENT. |
Example Code
Imports Microsoft.WindowsMediaServices.Interop
Imports System.Runtime.InteropServices
Public Sub QueryCacheMissPolicy(ByVal OriginUrl As String, _
ByVal UserContext As IWMSContext, _
ByVal CommandContext As IWMSCommandContext, _
ByVal PresentationContext As IWMSContext, _
ByVal CachePluginContext As Object, _
ByVal lQueryType As Integer, _
ByVal Callback As IWMSCacheProxyCallback, _
ByVal varContext As Object) _
Implements IWMSCacheProxy.QueryCacheMissPolicy
Dim nOpenFlag As Integer
Dim nGCI As Integer
Dim nReverseProxy As Integer
Dim ci As ContentInfo
Dim ciRP As ContentInfo
Dim Response As WMS_CACHE_QUERY_MISS_RESPONSE
Dim ContentInfoContext As IWMSContext
Try
nOpenFlag = WMS_CACHE_QUERY_TYPE_FLAGS.WMS_CACHE_QUERY_OPEN
nGCI = lQueryType And WMS_CACHE_QUERY_TYPE_FLAGS.WMS_CACHE_QUERY_GET_CONTENT_INFO
nReverseProxy = lQueryType & WMS_CACHE_QUERY_TYPE_FLAGS.WMS_CACHE_QUERY_REVERSE_PROXY
' The ContentInfo class is user-defined and includes
' information about a cached item.
ci = New ContentInfo(OriginUrl, Nothing)
' An open request was issued.
If (nOpenFlag And lQueryType) <> 0 Then
' Retrieve content information for the normal proxy mode.
If nReverseProxy = 0 Then
ci.CacheProxyCallback = Callback
ci.varContext = varContext
CacheProxyServer.GetContentInformation(OriginUrl, _
PresentationContext, _
Nothing, _
Nothing, _
Me, _
ci)
Else
' Reverse proxy mode:
' Map the requested URL to the reverse proxy URL.
' The call to the user-defined GetContentInfo() searches
' a reverse proxy ContentInfo object for a
' "ReverseProxy" string.
ciRP = Nothing
GetContentInfo(OriginUrl, ciRP)
Response = WMS_CACHE_QUERY_MISS_RESPONSE.WMS_CACHE_QUERY_MISS_PLAY_BROADCAST
If (ciRP.ContentType And 1) = 0 Then
' Play the content as a broadcast stream.
Response = WMS_CACHE_QUERY_MISS_RESPONSE.WMS_CACHE_QUERY_MISS_PLAY_BROADCAST
Else
' Play the content on demand.
Response = WMS_CACHE_QUERY_MISS_RESPONSE.WMS_CACHE_QUERY_MISS_PLAY_ON_DEMAND
End If
' Create a content information context. The
' GetContentInfoContext() function is user-defined.
ContentInfoContext = Nothing
GetContentInfoContext(ci, ContentInfoContext)
' Call OnQueryCacheMissPolicy().
Callback.OnQueryCacheMissPolicy(0, _
Response, _
ciRP.CacheUrl, _
Nothing, _
ContentInfoContext, _
varContext)
End If
End If
If (nGCI And lQueryType) <> 0 Then
' Forward the request upstream.
Response = WMS_CACHE_QUERY_MISS_RESPONSE.WMS_CACHE_QUERY_MISS_FORWARD_REQUEST
ContentInfoContext = Nothing
GetContentInfoContext(ci, ContentInfoContext)
Callback.OnQueryCacheMissPolicy(0, _
Response, _
OriginUrl, _
Nothing, _
ContentInfoContext, _
varContext)
End If
' A downstream cache proxy server propagated a remote
' cache proxy event. Forward the event to an upstream server.
If (lQueryType And WMS_CACHE_QUERY_TYPE_FLAGS.WMS_CACHE_QUERY_CACHE_EVENT) <> 0 Then
Callback.OnQueryCacheMissPolicy(0, _
Response, _
Nothing, _
Me, _
Nothing, _
varContext)
End If
Catch
Throw New COMException()
End Try
End Sub
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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