Upload tracking with Perlbal

Brad Fitzpatrick brad at danga.com
Sat Nov 5 00:06:03 PST 2005

In the latest version or two of Perlbal, Perlbal can now help you show a
progress bar to users during uploads.

Here's how you configure your Perlbal:

# Make a service that listens for UDP progress packets.  With a single
# Perlbal, these packets are only from itself.  Sorry, I didn't optimize
# for the single host case.

  SET role = upload_tracker
  SET listen =
ENABLE uptrack

# Then configure your web_proxy service to send those packets once a
# second per connection (if the upload actually is requested being
# tracked)

  SET role = reverse_proxy
  SET upload_status_listeners =,

Then use this JavaScript library:


And on your page, use JavaScript to intercept the form submit event and
change the form's target to an in-page iframe and kick-off the library
doing its tracking (using XmlHttpRequest), calling your callback.  (If the
client doesn't have javascript, your form submit goes through

Here's an example:


var uptrack; // our Perlbal upload tracker object, if defined

// called from iframe's content on complete, with a URL of where we should go:
function onUploadComplete (destURL) {
    window.location = destURL;

// called by the perlbal upload tracker library:  (we pass it this function below)
function uploadCallback (data) {
    if (! (data && data.total)) return;
    var percent = Math.floor(data.done * 100 / data.total);
    $("UploadBarInside").style.width = percent + "%";
    var status = Math.floor(data.done / 1024) + " kB / " + Math.floor(data.total / 1024) + " kB, " + percent + "% complete";
    $("UploadStatus").innerHTML = status;

function submitForm () {
    if (uptrack) uptrack.stopTracking();

    var frm = $("WebUpload");

    frm.target = "upiframe"; // change target to our iframe

    // create the actual Perlbal upload tracker object:
    uptrack = new UploadTracker(frm, uploadCallback);

    $("UploadStatus").innerHTML = "Uploading, please wait...";
    $("UploadBar").style.display = "block";
    return true;


Here's the patch I just did for fotobilder with almost that exact same code above:



- Brad

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