The Tor Browser / file revision

 // SJS file for CSP mochitests

 Components.utils.import("resource://gre/modules/NetUtil.jsm");

 function loadHTMLFromFile(path) {

   // Load the HTML to return in the response from file.

   // Since it's relative to the cwd of the test runner, we start there and

   // append to get to the actual path of the file.

   var testHTMLFile =

     Components.classes["@mozilla.org/file/directory_service;1"].

     getService(Components.interfaces.nsIProperties).

     get("CurWorkD", Components.interfaces.nsILocalFile);

   var dirs = path.split("/");

   for (var i = 0; i < dirs.length; i++) {

     testHTMLFile.append(dirs[i]);

   }

   var testHTMLFileStream =

     Components.classes["@mozilla.org/network/file-input-stream;1"].

     createInstance(Components.interfaces.nsIFileInputStream);

   testHTMLFileStream.init(testHTMLFile, -1, 0, 0);

   var testHTML = NetUtil.readInputStreamToString(testHTMLFileStream, testHTMLFileStream.available());

   return testHTML;

 }

 function handleRequest(request, response)

 {

   var query = {};

   request.queryString.split('&').forEach(function (val) {

     var [name, value] = val.split('=');

     query[name] = unescape(value);

   });

   var csp = unescape(query['csp']);

   var file = unescape(query['file']);

   // avoid confusing cache behaviors

   response.setHeader("Cache-Control", "no-cache", false);

   // Deliver the CSP policy encoded in the URI

   response.setHeader("Content-Security-Policy", csp, false);

   // Send HTML to test allowed/blocked behaviors

   response.setHeader("Content-Type", "text/html", false);

   response.write(loadHTMLFromFile(file));

 }