Niall’s Weblog

While in general I appreciate very simple, no-nonsense user interfaces for applications that work efficiently on the console and so can be used via SSH, there are times when increased visualisation is very useful.

Specifically with regard to my BitTorrent client, Unworkable, the default user interface is exceedingly simple. Inspired by the ubiquitous scp program on UNIX, the idea is that it should be just as simple to download a file via BitTorrent as via SSH or FTP/HTTP. Indeed, I borrowed the progressmeter.c source code from OpenSSH (a great repository of nice code). Have a look at this screenshot of Unworkable running on Windows to get an idea of what it looks like.

While I’m pretty happy with the current console user interface, it is obviously very limited in how much information it can display. To overcome this, I have for a long time had an extremely verbose trace mechanism. Pass the -t option to Unworkable, and it will write a detailed log. This is incredibly useful for debugging, but it suffers from the opposite problem - information overload. Its quite difficult for a human to parse scrolling pages of ASCII text and spot patterns. It can take considerable analysis to determine exactly why the program is making the decisions it is. This is the main motivation for adding support for a graphical user interface - information can be much more easily distilled into graphs and other visualisations which make it much easier to understand, at a glance, what is going on. For some examples of the kind of things I have in mind, take a look at the Azureus screenshots page.

This brings me to the question of how to nicely add a GUI to my application. I strongly want to keep the existing simple, console interface, and don’t want to bloat the application with additional external dependencies for widget sets and so forth. I decided to go with an IPC mechanism, to split the GUI from Unworkable entirely. While considering IPC mechanisms, I figured why not simply use TCP/IP. While in general the GUI is going to be running on the same host as Unworkable, this at least gives the option for operation over a network.

So, I have added a simple “control server” to Unworkable, which currently has a fairly basic ASCII protocol. At the moment, communication is unidirectional - Unworkable only pushes out some event notification messages. There is no mechanism for clients to send instructions back, since this isn’t required for visualisation just yet and that is my first priority. I have started a client implementation in Python. “Why Python?”, you may ask. Python has pretty good networking support, good UI toolkit support and good multi-platform support. I’m also pretty experienced with the language, and I find it very fast to write applications with. Since the GUI itself performs practically no hard computation nor I/O, the performance penalties of a higher-level language are hardly a concern.

In closing, the formula of having the application split into a C program which does the performance-sensitive stuff, exposing a simple ASCII protocol over TCP/IP, while implementing the user interface in Python, permits maintaining a lean and efficient core application with a slick graphical user interface.

Tags: BitTorrent, C, OpenBSD, Python, Unworkable

This entry was posted on Saturday, December 22nd, 2007 at 2:07 am and is filed under BitTorrent, Python, Technical. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.