Creating a Channel Agent

The example below demonstrates how to write and use a channel agent. A channel agent can be written in any scripting language with an installed scripting engine. The agent uses the COM objects passed to its namespace during a refresh cycle to update the channel content. Any channel in a project can have an agent refresh its content during the refresh cycle.

This example agent will scan a specified folder for all Microsoft® Word files and include them as content in a channel during a refresh cycle. In this case, the project is set up using a Windows Scripting Host Script (WSH). The top-level Channel object is configured to run the agent as a "customagent" meaning that the RefreshScript property will point to the script's location on the file system.

In the first code segment, a Windows Scripting Host (WSH) script is shown that creates an instance of the Project class. It then sets the top-level Channel object's RefreshType property to "userscript" (that is, custom agent that the programmer specifies). It sets a few hypothetical options for the custom agent, and then executes the refresh cycle on the project.
In the second code sample, the hypothetical custom agent is listed. In this example, the agent will scan the directory specified in the RefreshOptions collection under the key "DocsDir." In that directory, it will add all Word documents it encounters into the Channel object as Item objects. This example could be used to keep subscribers abreast of, say, the latest specifications or memos present in the directory specified.

It should be stressed that this example is for illustration purposes only. Usually, it would be easier to build the Project object and Channel using one of the administrative tools such as MMC or WebAdmin. However, for testing purposes, the procedure listed below is quite useful.

Building the Channel and Running the Refresh Cycle

(VBScript and Windows Scripting Host)

' File: sample.vbs
' This WSH script builds a Project object, sets up the
'  top level channel object's refresh information, 
'  and runs the refresh cycle on the project
'   
'   It will scan the specified directory for all 
'    word documents (.doc) and automatically incorporate
'    them into the channel

Option Explicit Dim Project Dim Channel Dim Options ' Set up the Project with useful info Set Project = CreateObject("Push.Project") Project.Name="Test Project" Project.CDFFile="c:\channels\LatestSpecs.cdf" Project.Schedule.Startdate=#1/1/1998 19:00:00# Project.Schedule.IntervalTime = 360 ' suggest to subscribers that they 'check in' ' every 6 hours for new content Set Channel = Project.Channel Set Options = Channel.RefreshOptions ' Some useful (and hypothetical) Bibliographic info Channel.Base = "file://\\somemachine\TechSpecs\" Channel.Title="The Latest Specs on Widgets" Channel.Abstract="This channel contains all the latest specification documents for the Widget research" Channel.Authors.Add "Dr. John Doe" Channel.Authors.Add "Dr. Jane Doe" ' Set up the refresh information Channel.RefreshType="USERSCRIPT" ' here we will specify a custom script ' that is listed below. The path to the ' agent script is "c:\agentscripts\CustomTechRefresh" Channel.RefreshScript="c:\scripts\CustomTechRefresh" Options("DocsDir") = "c:\TechSpecs" ' this option specifies where to find the .doc files ' Now we run the refresh explicitly Project.Refresh ' finished adding the items. Let's Schedule the refresh ' on the server for every 6 hours call Project.SetTask("SomeUser",720,0) Project.Task.Update "password" ' task should now be scheduled. The refresh cycle ' will occur every 6 hours starting a 12 am midnight ' every day Project.Save "TestProject" ' save the project

The Channel Agent

The code listed below is the channel agent that runs on behalf of the channel to update the content. Notice the use of the built-in channel and options objects. These objects are automatically included in the namespace of the script when the refresh cycle runs and the scripts execute. They need not be created, and can be used as if they were intrinsic objects of the script. This is the same as within an ASP script, where the script writer can refer to the Response or Application object without having to create it explicitly.

The Active Channel Server object names are listed in bold in the example below.

' File: c:\scripts\CustomTechRefresh
'
'  This script is an agent called by a Push.Channel object
'   to refresh its content.  It checks first to make sure
'   a valid "DocDir" option is passed, and if so, does the 
'   following:
'    deletes all items marked with "DeleteonFresh" set to TRUE
'    Scans the directory for .doc files
'    Adds any it finds as items to the Channel object on whose
'    behalf the agent is being run.

If not util.IsValidData(Options("DocDir"), vbString ) Then
  RaiseError("A valid string was not passed to the agent")
End If

Set fs = createobject("Scripting.FileSystemObject")
set folder = fs.GetFolder(Options("DocDir"))
For each File in folder.files
  NameExt = split(File.Name,".")
  If UBound(NameExt) > 0 Then
    If NameExt(UBound(NameExt)) = "doc" Then
      Set Item = Channel.AddItem
      Item.HREF=File.Name
      Item.Title=File.Name
    End If
   End If
Next