Facebook Application Tab not showing content

I'm started off developing a facebook application. One of the requirements is to have a 'profile tab'. Our web application is hosted on my local machine (for now), my /etc/hosts file has we开发者_如何学JAVAbapp.xyz going to 127.0.0.1. (i.e. I can use webapp.xyz as a domain name for my web app and everything works locally).

I have set up webapp.xyz/facebook/ as the Canvas URL and tab as the Tab URL. My webapp handles this correctly and print a simple hello world output. If I go to http://apps.facebook.com/MYAPPNAME/tab, I see my hello world output. I can also see the access logs on my local machine.

I have added the application to a page, and added the profile tab. I can see the tab there, but when I click on it, there is nothing, just an empty page. I see the 'throbber' flashing for a second then an empty page. I see no access logs on my local machine. Firebug tells me there is no iframe in the middle (the big empty white space). What's going on?

I found the solution to this. You can't have 'local' applications that work as facebook tabs. Facebook's server's POST to your URL and parse and clean the data there, so your web application need to be globally reachable.

I solved this by setting up SSH tunnels to a host I controlled and changing the Facebook application to that URL & port.