Filters

You might have static files that are not formatted to view from a web browser. However, these files could be viewed if they were modified, for example, by including HTML tags. Filters are programs that a programmer at your site writes to make the necessary modifications. Modifications can range in magnitude from simply adding a single line of text to creating a completely different file.

For example, BookManager files contain tags a web browser cannot process. A programmer can code a filter to translate the files from BookManager format to HTML format.

How Filters Work

When a web browser user requests a file that requires a filter, VM:Webgateway allocates a worker and invokes the filter on the worker. VM:Webgateway passes information about the requested file (file data, HTTP headers, and filter variables) to the filter. The filter makes modifications to the file and returns the reformatted file to VM:Webgateway. If character set translation needs to be performed, VM:Webgateway performs translation on the file returned from the filter, and then delivers the reformatted file to the web browser.

Adding Filters to VM:Webgateway

When you have determined that you need a particular filter, a programmer must code a filter, and a VM:Webgateway system administrator must make it available for VM:Webgateway to use. A programmer must code the filter as a CMS Pipelines stage. The system administrator must:

• Place the filter on a minidisk or directory accessed by the VM:Webgateway SVM.
• Configure one or more filetype definitions to use the filter.

If your site does not currently use worker machines, your VM:Webgateway system administrator must also configure worker machines. Filters only run on worker machines.