An example of nsIContentPolicy for firefox addon?

Question

I have read NsIContentPolicy and have searched whole Stackoverflow for a proper tutorial for implementing NsIContentPolicy, but all in vain. I know that Adblock uses NsICon

Answer 1

I am not aware of any good tutorial but I can give you some minimal example code:

Cu.import("resource://gre/modules/XPCOMUtils.jsm");
Cu.import("resource://gre/modules/Services.jsm");

let policy =
{
  classDescription: "Test content policy",
  classID: Components.ID("{12345678-1234-1234-1234-123456789abc}"),
  contractID: "@adblockplus.org/test-policy;1",
  xpcom_categories: ["content-policy"],

  init: function()
  {
    let registrar = Components.manager.QueryInterface(Ci.nsIComponentRegistrar);
    registrar.registerFactory(this.classID, this.classDescription, this.contractID, this);

    let catMan = Cc["@mozilla.org/categorymanager;1"].getService(Ci.nsICategoryManager);
    for each (let category in this.xpcom_categories)
      catMan.addCategoryEntry(category, this.contractID, this.contractID, false, true);

    onShutdown.add((function()
    {
      for each (let category in this.xpcom_categories)
        catMan.deleteCategoryEntry(category, this.contractID, false);

      // This needs to run asynchronously, see bug 753687
      Services.tm.currentThread.dispatch(function()
      {
        registrar.unregisterFactory(this.classID, this);
      }.bind(this), Ci.nsIEventTarget.DISPATCH_NORMAL);
    }).bind(this));
  },

  // nsIContentPolicy interface implementation
  shouldLoad: function(contentType, contentLocation, requestOrigin, node, mimeTypeGuess, extra)
  {
    dump("shouldLoad: " + contentType + " " +
                          (contentLocation ? contentLocation.spec : "null") + " " +
                          (requestOrigin ? requestOrigin.spec : "null") + " " +
                          node + " " +
                          mimeTypeGuess + "\n");
    return Ci.nsIContentPolicy.ACCEPT;
  },

  shouldProcess: function(contentType, contentLocation, requestOrigin, node, mimeTypeGuess, extra)
  {
    dump("shouldProcess: " + contentType + " " +
                            (contentLocation ? contentLocation.spec : "null") + " " +
                            (requestOrigin ? requestOrigin.spec : "null") + " " +
                            node + " " +
                            mimeTypeGuess + "\n");
    return Ci.nsIContentPolicy.ACCEPT;
  },

  // nsIFactory interface implementation
  createInstance: function(outer, iid)
  {
    if (outer)
      throw Cr.NS_ERROR_NO_AGGREGATION;
    return this.QueryInterface(iid);
  },

  // nsISupports interface implementation
  QueryInterface: XPCOMUtils.generateQI([Ci.nsIContentPolicy, Ci.nsIFactory])
};

policy.init();

This comes from the minimal content policy implementation I use to look at issues with the content policies implementation - it doesn't do anything other than dumping all content policies calls to the console (window.dump documentation). Obviously, in a real implementation the fields classDescription , classID and contractID should be changed to something proper. onShutdown belongs to the private framework I am using: this extension is restartless which is why it needs to register the component "manually" and will also run this code to remove it if it is shut down during a browser session.

You can also download the complete extension: testpolicy.xpi.