directly return an image from Tapestry

[Chuck Kring]

Hi everybody,

I need to create a watchdog on a page that reloads the entire page when 
I detect the server has restarted.  

So far, my approach is to retrieve and image from the Tapestry web app 
by setting an image src field, then reloading or not based upon onload 
vs.onerror event handlers.   This tests the webapp and server and I can 
reload the page if I receive an onload after an onerror event.

In other words....

var img = new Image();
img.onerror = imageFailed;
img.onload = imageLoaded;
failed = false;
setTimeout( doPoll, 10000);

doPoll(){
   img.src = location.locationhost + "/t/testpage/" + Date.UTC();   // 
to prevent image caching
}

imageFailed()
{
   failed = true;
   setTimeout( doPoll, 10000);
}
imageLoaded()
{
   if( failed == true ){
       location.reload(true);
   } else {
      setTimeOut(doPoll, 10000);
   }
}

I *think* I need to create a Tapestry page that returns an Asset or 
StreamResponse.   I don't want to handle this as an event on the watched 
page because I'm not sure how Tapestry will handle the event if the 
server has restarted.

So, it is possible for a Tapestry page to return a streamresponse?  Or 
is there a better way to do this?    I hesitate to use Ajax requests 
because I'm not sure that I'll be able to differentiate between the 
server not up yet and Tapestry not knowing what to do with old Ajax 
requests from another session.  Images seem easy from the Javascript 
side but I'm not sure how to handle this in tapestry.

Regards,

Chuck Kring


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