Example of a PagePark plug-in

filter.js

//translate a url in this form: http://my.this.how/davewiner/example.opml  
//to a file path like this: /root/apps/littleoutliner/publicFiles/users/davewiner/myOutlines/example.opml

exports.filter = filter; 

const folder = "/root/apps/littleoutliner/publicFiles/users/";

function filter (options, callback) {
	var url = options.httpRequest.url;
	var splits = url.split ("?");
	url = splits [0];
	splits = url.split ("/");
	var f = folder + splits [1] + "/myOutlines/" + splits [2];
	options.serveLocalFile (f);
	}

More info here.

scripting/Scripting-News#158 (comment)