At the moment we have no formal method of accepting patches to the Snarl codebase. If you'd like to submit a patch, in the first instance raise a request on the developer forum and we'll guide you through the process.
The source code for Snarl is hosted on SourceForge using SVN. This link will take you to the landing page which allows you to browse the source tree and provides instructions on how to check the source code out.
The developer forum is focussed on supporting developers adding Snarl support to their applications. Registration is required to view and post to this forum.