One of the most frustrating things I found early on when working on facebook applications, was that there was no simple way to create a local development environment. Because so many of the features of the platform existed only when the code was executed THROUGH the facebook proxy (fbml parsing, fb:ref cache content, etc), I found myself in an almost endless cycle of “svn commit”, “svn up” on the test server. Although I could have reduced this to a single step using a capistrano deployment task, or (heavens forbid) simply edited the code in place on the server using VI, I wasn’t happy with either of these options.

By happy coincidence, I spent the day hacking away on FB apps with my friend Ben Savage, who showed me how *he* does it – he simply port forwards port 4100 on his local router into his laptop, and then sets the facebook application to use his current outside IP:4100 as the app url.

I didn’t like this for a few reasons – first, it requires admin access to the router, a no-go from Starbucks. Second, I don’t like having to change my facebook application settings every time I change offices. So I decided to try using an ssh tunnel.

After mucking about a bit, I got it working! Here’s what I had to do (and yes, it’s pretty ugly and you probably want to do this on a non-critical junk proxy box you’ve got somewhere):

Changes to /etc/ssh/sshd_config

1. You have to make the ssh connection as root in order to bind to a privileged port (it’s probably trivial to use a non-privileged port for this, but I couldn’t be bothered). So you need to enabled root logins, by adding/changing
PermitRootLogin yes
2. In order to bind to a network address other than localhost on the remote server, you need
GatewayPorts yes

Then you simply run this from console on your local machine:

ssh root@mytunnelbox.com -p22 -N -R *:8090/localhost/80

This will forward port 8090 on your remote server to port 80 on your local workstation, via ssh tunnel. I don’t usually bother to fork into the background, because it’s nice to be able to ctrl-c to finish up.

Now get into your facebook developer application (you probably want to create a test application for this), and change the Callback URL to mytunnelbox.com:8090/. (You’ll only have to do this the first time).

Voila! Local development facebook application work – from Starbucks or anywhere else!