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What's with ping(), and how do I use it?

The question: What's with client.ping(), and how do I use it?

The answer:

Well, I guess to start off, the question is in reality a bit more advanced than what I've wrote above, but more or less it's "what the heck do I do with ping() and why doesn't work as I expect for what I want to do".

So, the first thing I will start off with is what ping() is all about. Ping in the normal network world is used to find a node on a network and how long it takes to get there and back. These packets are sent at high priority so there is less delay etc. I'm not going into too much detail on this of course, but what I can say is that FMS's client.ping() on the server side is just about the same.

What is happening behind the scenes when you call ping() on the client is the server is sending out some packets to the client at a high priority. Higher than all the other data that could be going back and forth. If it gets a response, true comes back. Not quite the same as the "normal" ping that we all know and love, but more or less you are knocking on the door and seeing if somebody answers. ping() doesn't really care how long that takes.

So, the next part of this question is "what would you use this for?". Well, a lot of people want to use it to see if a client is alive on the server. Why would you use ping for that? Well, supposedly it's the fastest way to tell. You're probably wondering "compared to what?".

Which leads us to the next question, "why would you want to know if somebody was connected up to the server if the client object still exists?"

Aha! now that is the key question here I think. In FCS1.0 and 1.5 (throughout all the updates too) there was the problem of "ghost clients". These clients would sit in the application objects that the server had yet to figure out they are gone. There are a few reasons for this of course, there could be a stay-alive going on here, where a router or something is just keeping the connection there. There is also the problem with IE in where even if you close the window, the connection to the server stays open. You can even still be sending your video and audio to the application if you didn't close it first and just closed the browser window!! Imagine that! I heard a story about how one guy's connection stayed up for over an hour with his vid and aud being broadcasted to a chat. I'm sure there are other instances of this.. It gets solved by closing ALL of the browser windows you have open of IE. Odd bug.. not sure who to blame, I guess Microsoft.

There was also the problem in where if you were doing nothing on the application, the app would disconnect you, although you'd still be there.. it's a really weird problem and it sucked, so you had to make your own "stay-alive" code to keep users connected when there was no data going back and forth in the application. Some people used ping() in this instance.

So, what does this mean to a developer of FMS apps? Well, you need to know if users are actually there and if they are going to stay there when nothing is going on. In FMS2, I've actually yet to see the problem of the user getting disconnected when nothing is going on in the app. This is a good thing :) Nice to see it fixed. There are less instances of ghost users, but they are there, especially in busier applications.

What do you do? Do you use ping() to see if they are there? My answer is to suggest "no". The reason is that ping() can return true even when the client is no longer connected. The router or something in the middle actually returns that the client is there (I don't actually know exactly what is happening here, I do know that ping() will return true even though the client isn't there).

So, this makes ping() a bit crappy. My suggestion to solve not only the worry to make sure clients stay alive in the app, and also to check if they are there is to call a function in the SWF file.

This is reasonably simple because all you need to do is create a function on the netConnection object.

myNC = new NetConnection();

myNC.checkForOnline = function(){
return "yes, I'm still here";

Then on the server side you just call that on all clients every 30 seconds or so (this will depend on your app of course). If the call returns an error, or nothing, or the wrong string then you know that either the client is not there or is a rogue user that has connected up to your application. The good side effect here is that you are adding a bit of security to your application. Security is always good :) Once you have discovered that the call failed or returned no string or the wrong string, you disconnect them and delete the client object.

That's about it. All about ping() and why it's not really that beneficial to use it :)

Posted by: Graeme Bull on May 23, 2006

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