Recently I tried out the minimalist dwm window manager. I don’t know yet if I’ll stick with it, but it gave me a nice excuse to hack a bit of Go.
Like most window managers, dwm has a status bar that can show useful information like time and date, battery status etc. It uses a simple and clever approach to set the contents of the status bar: it’s simply the title of the normally invisible X root window. So all we need is a simple utility that periodically generates a string and sets it as the root window title.
dwm comes with a little C program that does just that, dwmstatus. I thought it’d be a fun little exercise to do the same in Go, using Andrew Gallant’s xgb package. It was a pleasure to use, works as advertised and closely follows the XGB protocol so that all the documentation out there still applies.
The result is github.com/thomas11/dwmstatus, with a whopping 54 lines of code. That’s a lot shorter than the 128 lines of the C version, although that one also displays some default content which mine does not. Two things stood out to me that made the Go implementation clear and easy to write.
The time package has a great API that uses channels where
appropriate. The Tick function returns a channel that keeps sending
the current time in the given interval. That let’s us write the
periodic updates to the status bar like this:
c := time.Tick(interval)
for now := range c {
genTitle(now, &status)
// ...
}
Functions are first-class values in Go. That offers a simple and convenient way of separating the core functionality of dwmstatus, periodically updating the root window title, from generating the actual status bar content, where each user might wish to show different things. In the Go version I defined a type that’s simply a function that, given the current time and a buffer, writes the new status bar content into the buffer. The main entry function of dwmstatus accepts such a function and calls it for each update, without knowing anything about it:
type GenTitleFunc func(now time.Time, b *bytes.Buffer)
...
// Start the process of updating the status bar. genTitle will
// be called repeatedly in the given interval.
func Run(interval time.Duration, genTitle GenTitleFunc) {
// ...
}
There’s a sample implementation of GenTitleFunc in dwmstatus/main.go
that I use on my Linux system to show time and date and the battery
status.