IWMSCacheProxyServerCallback.OnGetContentInformation (Visual Basic .NET)
The OnGetContentInformation method is called by the server to respond when a cache plug-in calls IWMSCacheProxyServer.GetContentInformation.
IWMSCacheProxyServerCallback.OnGetContentInformation( lHr As Int32,
pContentInfo As IWMSContext,
varContext As Object
)
Arguments
Int32 indicating whether the call to IWMSCacheProxyServer.GetContentInformation succeeded. |
|
IWMSContextIWMSContext Object (Visual Basic .NET) 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. |
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
Imports Microsoft.WindowsMediaServices.Interop
Imports System.Runtime.InteropServices
Public Sub OnGetContentInformation(ByVal lHr As Integer, _
ByVal ContentInformation As IWMSContext, _
ByVal varContext As Object) _
Implements IWMSCacheProxyServerCallback.OnGetContentInformation
Dim nFlag As Integer
Dim bAddCacheItem As Boolean
Dim nRetHr As Integer
Dim ci As ContentInfo
Dim bDownloadInProgress As Boolean
Dim MissResponse As WMS_CACHE_QUERY_MISS_RESPONSE
Try
' Set default values.
nFlag = 0
bAddCacheItem = False
nRetHr = 0
' Retrieve the user-defined ContentInfo object from the
' varContext parameter. The ContentInfo object describes
' an item of cached content.
ci = varContext
' If this function is called from AddCacheItem(), lExpiration
' will not be zero, and you can call DownloadContent().
If ci.lExpiration <> 0 Then
bAddCacheItem = True
lHr = 0
End If
' Download the content if the server indicates that your
' plug-in's call to GetContentInformation() succeeded.
If lHr = 0 Then
' 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(ContentInformation, ci)
' Determine whether the content can be downloaded
nFlag = ci.CacheFlags And WMS_DATA_CONTAINER_VERSION_CACHE_FLAGS.WMS_DATA_CONTAINER_VERSION_ALLOW_PROXY_CACHING
If (nFlag <> 0) Or (bAddCacheItem = True) Then
' Identify a Cache URL.
If ((Not bAddCacheItem) Or (bAddCacheItem And ci.CacheUrl = "")) Then
ci.CacheUrl = "C:\WMSCache\Test"
End If
' Call a user-defined function, IsDownloadInProgress(), to
' determine whether there is a download in progress.
bDownloadInProgress = IsDownloadInProgress(ci)
If bDownloadInProgress = False Then
' 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 by calling
' IWMSCacheProxyServer.DownloadContent().
CacheProxyServer.DownloadContent(ci.OriginUrl, _
ci.CacheUrl, _
0, 0, 0, 0, _
Me, _
Nothing, _
ci)
Else
' Debugging is already in progress.
End If
' 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 And 1) <> 0 Then
UpdateTable(ci)
End If
End If
Else
' The server returned E_ACCESSDENIED in response to the
' plug-in's call to GetContentInformation().
If lHr = -2147024891 Then
nRetHr = 0
End If
End If
' Determine whether stream splitting is allowed.
nFlag = ci.CacheFlags And 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 Then
MissResponse = WMS_CACHE_QUERY_MISS_RESPONSE.WMS_CACHE_QUERY_MISS_PLAY_BROADCAST
End If
' Call IWMSCacheProxyCallback.OnQueryCacheMissPolicy.
ci.CacheProxyCallback.OnQueryCacheMissPolicy(nRetHr, MissReponse, ci.OriginUrl, Nothing, ContentInformation, ci.varContext) Then
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.