IWMSCacheProxy.QueryCacheMissPolicy (Visual Basic .NET)

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IWMSCacheProxy.QueryCacheMissPolicy (Visual Basic .NET)

The server calls the QueryCacheMissPolicy method to query the cache plug-in for a cache-miss policy.

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.

pCachePluginContext

[in] Object containing a cache plug-in context.

lQueryType

[in] Member of the WMS_CACHE_QUERY_TYPE_FLAGS enumeration type that indicates why the server called IWMSCacheProxy.QueryCache. This must be a bitwise OR of one or more 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 WMS_CACHE_QUERY_LOCAL_EVENT 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.

[in] pCallback

IWMSCacheProxyCallback object containing the callback function. The cache plug-in calls IWMSCacheProxyCallback.OnQueryCacheMissPolicy to respond to a call to QueryCache.

[in] varContext

Object containing a value defined by the server to identify which call to QueryCacheMissPolicy the plug-in is responding to when it calls IWMSCacheProxyCallback.OnQueryCacheMissPolicy. You must pass this value back unaltered.

Return Values

This method does not return a value.

Remarks

A proxy server must call QueryCache on the cache plug-in and receive a cache miss before it calls QueryCacheMissPolicy. A custom cache plug-in can use the WMS_CACHE_QUERY_TYPE_FLAGS enumeration type in the lQueryType parameter to direct the implementation of a cache-miss policy.

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

• IWMSCacheProxy Object (Visual Basic .NET)

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