Released: Modify Headers 0.6.3

First reading about the “Modify Headers” extension I thought: That’s what I ‘m looking for.
But after installing the extension, it revealed to modify outging (request-) headers only. No possibility to modify or remove server-sided response headers. Yes, I should have read your extension-description more carefully, you mentioned it.
Ok, you may ask, why should I want to filter response headers? Answer: There are several reasons why you may want to filter server headers. One of them is to force caching in firefox.
Many servers send anti-cache headers, preventing firefox to cache documents and/or pictures, so there will always be a (full) reload when pushing the back button. That’s really annoying. Anti-cache headers may be AGE, CACHE-CONTROL, EXPIRES, ETAG, PRAGMA, VARY and even more headers.
I really would appreciate adding that feature.

Thank you! (for adding my request to the road map)

This may not be of interest for bloggers, but as all postings will be reviewed I’ll post it anyway
I made a small extension (BetterCache). It is a working demo concerning modification of response headers. You may use it in your own project:

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

RespHeaderObserver.prototype = {
observe: function(subject, topic, data) {
if (topic == “http-on-examine-response”) {
var headers = new Array();
headers[0] = “Age”;
headers[1] = “Cache-Control”;
headers[2] = “Date”;
headers[3] = “ETag”;
headers[4] = “Expires”;
headers[5] = “Last-Modified”;
headers[6] = “Pragma”;
headers[7] = “Vary”;
//headers[8] = “Set-Cookie”; //not anti-cache, but a better testpattern
var httpChannel = subject.QueryInterface(Components.interfaces.nsIHttpChannel);
//need to test every (above defined) header for existance. If not existant, getResponseHeader will throw an exception.
for(i = 0; i < headers.length; i++){
var headerval = “”;
var replacement = “”;
try{
headerval = httpChannel.getResponseHeader (headers[i]);
if(i == 6)//special case Pragma
replacement = headerval.replace(/no\-cache/g, “”);
httpChannel.setResponseHeader(headers[i], replacement, false);
//alert(headers[i]+’=’+headerval);
}catch(e){}//NS_ERROR_(header_)NOT_AVAILABLE
}
headers = null;
return;
}
},

register: function() {
var observerService = Components.classes[“@mozilla.org/observer-service;1”].getService(Components.interfaces.nsIObserverService);
observerService.addObserver(this, “http-on-examine-response”, false);
},
unregister: function() {
var observerService = Components.classes[“@mozilla.org/observer-service;1”].getService(Components.interfaces.nsIObserverService);
try{
observerService.removeObserver(this, “http-on-examine-response”);
}catch(e){}
}
}
//observer needs to be registered only once, so better use a XPT file
window.addEventListener(“load”, function(evnt) { observer = new RespHeaderObserver(); }, true);
window.addEventListener(“unload”, function(evnt) { observer.unregister(); }, true);

I think the best reason to be able to modify server side headers is… freedom.