A learning experience with NetworkManager and zbus

Traveling heavily recently, I've become fatigued from typing all the WiFi passphrases. My phone can happily connect via a QR code. Why does my laptop required so much typing, I asked. So I proposed a simple project.

Researching how I might use my web-cam to connect to WiFi networks, I came across the Network Manager and Rust's Zbus article on rbs.io. I use NewtworkManager and I enjoy working with rust. I know next to nothing about DBus, but I thought some knowledge of hacking Linux networks couldn't do me any harm. Besides I had some free time.

The above article set me on the right path. The zbus documentation is still a little obscure in some salient details, however. Hopefully this post will help fill those in. The finished code is hosted in the scampi repo.

I first needed to generate a settings.rs with zbus-xmlgen as described in the above article. It is straightforward to create a connection by building the nested structures of HashMaps also described there. While that solution works, it is tedious, unsightly and doesn't make the most of rust's type system. Finding the issue for using DeserializeStruct with nested structs closed, I hoped there might now be a more ergonomic way forward.

With the help of the zbus book I managed to piece together a solution that feels a little more rust-like. Of course there are many pieces to the puzzle. You need serde and the zvariant::Type macro. But all that is gleaned fairly easily from the documentation, I think. The more salient discovery was that zbus allows declaring DBbus signatures on your types. This is done via a macro, like so:

#[zvariant(signature = "a{sa{sv}}")]`
struct MyType{..}

Declaring the correct signature(a{sa{sv}}) on the struct passed to NetworkManager's Settings.add_connection() allowed it to navigate Dbus's type system. Its children don't have any children of their own, so SerializedDict and DeserializeDict works fine on them.

For a more complete example you can have a look at the code.

I believe I could go further and replace some fields defined as String with more appropriate types, but it's one more thing to learn and I think this is good enough for now.

Originally published in my blog.