Swank Deploys

SLIME and SWANK are incredible. Start a SWANK server in your application and Whammo! You've can connect to it from the comfort of Emacs. From there you can tinker with its insides to your heart's content. This is a beta-testing dream!

Except when it isn't. Recently I deployed a Common Lisp web application where I ran into some trouble.

Trouble The First: Connection Error

So say that my service is running on server.com and SWANK is listening on port 4040. Then to connect to it I have been using ssh port forwarding:

ssh -L 4040:localhost:4040 me@server.com

So that I can then do slime-connect with localhost and 4040 as its arguments.

You might be surprised, however if you were to have used the following ssh command, which lists the local host ip of, instead of localhost:

ssh -L 4040: me@server.com

For whatever reason, this fails: ssh reports a connection error. So, I had to use localhost explicitly.

Trouble The Second: SWANK-REQUIRE

The second, and more irksome issue comes up when I actually succeed at connecting via slime-connect: I immediately drop into the slime debugger. The issue seems to be that SWANK is trying to load some code upon connection. Obviously, it is not going to be able to load code unless that code is present and available on the server.

In order to get the required code into the deployed binary, I do the following prior to executing save-lisp-and-die:


I got the list of required modules directly from the SLIME debugger. I recompiled, redeployed, and ta-dah! It works!

#commonlisp #emacs