CODEWITHSUNDEEP
javascriptapachefirefoxxmlhttprequestfirefox-addon
Matt
Matt

Reputation: 303

addEventListener("load",...) causing too many XmlHttpRequests?

Suppose I have the following JavaScript code running in a Firefox plugin, which should perform an XmlHttpRequest on a page load:

function my_fun(){

var xmlHttpConnection = new XMLHttpRequest();
    xmlHttpConnection.open('GET', globalUrl+'/call_this.php', true);
    xmlHttpConnection.onreadystatechange=function(){
        if (xmlHttpConnection.readyState == 4 && xmlHttpConnection.status == 200) {
            var serverResponse = xmlHttpConnection.responseText;
            do_stuff();
            clearTimeout(xmlHttpTimeout);
            xmlHttpConnection.abort();
       }
 };

 xmlHttpConnection.send(null);
 xmlHttpTimeout = setTimeout(function (){
                                 do_other_stuff();
                                 xmlHttpConnection.abort();
                                 clearTimeout(xmlHttpTimeout);
                             },5000);
}

container.addEventListener("load", my_fun, true);

When my_fun() is called, the access logs for my Apache server look something like this:

<client-ip> - - [06/Nov/2014:10:40:04 -0500] "GET /call_this.php HTTP/1.1" 200 1 "-" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Firefox/31.0"

Further suppose I have 4 client connections on my server. Within the span 1 second, this line can show up in the access log dozens (sometimes over 50) of times simultaneously, and the pings sometimes come from just 1 client. Most times, the number of pings per second is lower than 5, but there are occasional spikes caused by call_this.php.

Why would this happen? I suspect something is wrong with container.addEventListener("load", my_fun, true);. Does this over count the number of loads, e.g., if a page contains multiple hidden URL's that are loaded? If so, how can I fix this? (Edit: Would an observer service be better?)

Upvotes: 0

Views: 237

Answers (2)

Matt
Matt

Reputation: 303

Found the answer. I do believe there is a problem with the event listener. But since the above code is in a Firefox plugin, a good approach is to use Mozilla observers. The following observer significantly reduced the number of pings to the server (empirically tested).

Special thanks goes to Noitidart, who supplied a similar solution to a different problem.

var myObserver = {
register: function() {
    var observerService = Components.classes["@mozilla.org/observer-service;1"]
    .getService(Components.interfaces.nsIObserverService);
    observerService.addObserver(this, TOPIC_MODIFY_REQUEST, false);
},
    //observe function to capture the changed event
    observe : function(aSubject, aTopic, aData) {
        if (TOPIC_MODIFY_REQUEST == aTopic ) {
            var url;
            aSubject.QueryInterface(Components.interfaces.nsIHttpChannel);

            url = aSubject.URI.spec;
            url = encodeURIComponent(url);

            var oHttp = aSubject.QueryInterface(Components.interfaces.nsIHttpChannel);
            if (oHttp.loadFlags & Components.interfaces.nsIHttpChannel.LOAD_INITIAL_DOCUMENT_URI) {
                //is top level load
                my_fun(); //Same function as in original question
            }
        }
    }       
} 

myObserver.register();

Upvotes: 1

sergio0983
sergio0983

Reputation: 1278

Yes. something looks wrong to me:

Check this line:

container.addEventListener("load", function(){my_fun();}, true);

or change function declaration: 

function my_fun(){
...

for

my_fun = function(){
...

Upvotes: 2

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