FAQ

How to use a struct as a dictionary?

Since the use of a dictionary, specifically one with strings as keys and variants as value (i-e a{sv}) is very common in the D-Bus world and use of HashMaps isn’t as convenient and type-safe as a struct, you might find yourself wanting to use a struct as a dictionary.

zvariant provides convenient macros for making this possible: SerializeDict and DeserializeDict. You’ll also need to tell Type macro to treat the type as a dictionary using the signature attribute. Here is a simple example:

#![allow(unused)]
fn main() {
use zbus::{
    dbus_proxy, dbus_interface, fdo::Result,
    zvariant::{DeserializeDict, SerializeDict, Type},
};

#[derive(DeserializeDict, SerializeDict, Type)]
// `Type` treats `dict` is an alias for `a{sv}`.
#[zvariant(signature = "dict")]
pub struct Dictionary {
    field1: u16,
    #[zvariant(rename = "another-name")]
    field2: i64,
    optional_field: Option<String>,
}

#[dbus_proxy(
    interface = "org.zbus.DictionaryGiver",
    default_path = "/org/zbus/DictionaryGiver",
    default_service = "org.zbus.DictionaryGiver",
)]
trait DictionaryGiver {
    fn give_me(&self) -> Result<Dictionary>;
}

struct DictionaryGiverInterface;

#[dbus_interface(interface = "org.zbus.DictionaryGiver")]
impl DictionaryGiverInterface {
    fn give_me(&self) -> Result<Dictionary> {
        Ok(Dictionary {
            field1: 1,
            field2: 4,
            optional_field: Some(String::from("blah")),
        })
    }
}
}

Why do async tokio API calls from interface methods not work?

Many of the tokio (and tokio-based) APIs assume the tokio runtime to be driving the async machinery and since by default, zbus runs the ObjectServer in its own internal runtime thread, it’s not possible to use these APIs from interface methods. Moreover, by default zbus relies on async-io crate to communicate with the bus, which uses its own thread.

Not to worry, though! You can enable tight integration between tokio and zbus by enabling tokio feature and disabling async-io feature:

# Sample Cargo.toml snippet.
[dependencies]
zbus = { version = "2", default-features = false, features = ["tokio"] }