Wie kann ich den HTTP-Antworttext in einer Firefox-Erweiterung ändern? Ich habe einen Beobachter für http-on-exam-response und ein nsIStreamListener-Objekt mit dem folgenden Code eingerichtet. Wie kann ich die geänderte Antwort an den Firefox-Browser zurückschieben, nachdem ich die Daten erhalten, analysiert und geändert habe? Angenommen, ich gehe mit aktivierter Erweiterung zu Google.com. Die Erweiterung sollte die Antwort abfangen und jedes Vorkommen von "google" in "goggle" ändern. Wenn die Seite geladen wird, sieht der Benutzer überall "Brille".

function TmSteroidsObserver()
{
  this.register();
}


TmSteroidsObserver.prototype = {
  observe: function(subject, topic, data) {

    if (topic == "http-on-examine-response") {

    }
    else if (topic == "http-on-modify-request") {
       var channel = subject.QueryInterface(Components.interfaces.nsIChannel);
       var listener = new StreamListener(channel);
    }

  },

  register: function() {
    var observerService = Components.classes["@mozilla.org/observer-service;1"]
                                .getService(Components.interfaces.nsIObserverService);
    observerService.addObserver(listener, "http-on-modify-request", false);
    observerService.addObserver(listener, "http-on-examine-response", false);
  },

  unregister: function() {
    var observerService = Components.classes["@mozilla.org/observer-service;1"]
                            .getService(Components.interfaces.nsIObserverService);
    observerService.removeObserver(this, "http-on-modify-request");
    observerService.removeObserver(this, "http-on-examine-response");
  },

  QueryInterface : function(aIID) {
    if (aIID.equals(Components.interfaces.nsISupports) ||
        aIID.equals(Components.interfaces.nsIObserver))
      return this;
    throw Components.results.NS_NOINTERFACE;
  }

}

function StreamListener(channel) {

    channel.notificationCallbacks = listener;
    channel.asyncOpen(listener, null);

}

StreamListener.prototype = {
  mData: "",
  mChannel: null,

  // nsIStreamListener
  onStartRequest: function (aRequest, aContext) {
    this.mData = "";
  },

  onDataAvailable: function (aRequest, aContext, aStream, aSourceOffset, aLength) {
    var scriptableInputStream = 
      Components.classes["@mozilla.org/scriptableinputstream;1"]
        .createInstance(Components.interfaces.nsIScriptableInputStream);
    scriptableInputStream.init(aStream);

    this.mData += scriptableInputStream.read(aLength);
  },

  onStopRequest: function (aRequest, aContext, aStatus) {
    if (Components.isSuccessCode(aStatus)) {
      // request was successfull
      this.mCallbackFunc(this.mData);
    } else {
      // request failed
      this.mCallbackFunc(null);
    }

    this.mChannel = null;
  },

  // nsIChannelEventSink
  onChannelRedirect: function (aOldChannel, aNewChannel, aFlags) {
    // if redirecting, store the new channel
    this.mChannel = aNewChannel;
  },

  // nsIInterfaceRequestor
  getInterface: function (aIID) {
    try {
      return this.QueryInterface(aIID);
    } catch (e) {
      throw Components.results.NS_NOINTERFACE;
    }
  },

  // nsIProgressEventSink (not implementing will cause annoying exceptions)
  onProgress : function (aRequest, aContext, aProgress, aProgressMax) { },
  onStatus : function (aRequest, aContext, aStatus, aStatusArg) { },

  // nsIHttpEventSink (not implementing will cause annoying exceptions)
  onRedirect : function (aOldChannel, aNewChannel) { },

  // we are faking an XPCOM interface, so we need to implement QI
  QueryInterface : function(aIID) {
    if (aIID.equals(Components.interfaces.nsISupports) ||
        aIID.equals(Components.interfaces.nsIInterfaceRequestor) ||
        aIID.equals(Components.interfaces.nsIChannelEventSink) || 
        aIID.equals(Components.interfaces.nsIProgressEventSink) ||
        aIID.equals(Components.interfaces.nsIHttpEventSink) ||
        aIID.equals(Components.interfaces.nsIStreamListener))
      return this;

    throw Components.results.NS_NOINTERFACE;
  }
};