How to use zbus to list block devices? - rust

Question

I want to list all the available block devices in the system using a dbus implementation called zbus.
The UDisks2 documentation mentions a method call on org.freedesktop.UDisks2.Manager interface called GetBlockDevices which accepts IN a{sv} options, OUT ao block_objects for method parameters.
Using zbus, I write:
use std::error::Error;
use std::result::Result;
use zbus::{Connection, Proxy};
fn main() -> Result<(), Box<dyn Error>> {
let connection = Connection::new_system()?;
let p = Proxy::new(
&connection,
"org.freedesktop.UDisks2",
"/org/freedesktop/UDisks2/Manager",
"org.freedesktop.UDisks2.Manager",
)?;
let resp: Vec<zvariant::ObjectPath> = p.call("GetBlockDevices", &std::collections::HashMap::<String, zvariant::Value>::new())?;
dbg!(resp);
Ok(())
}
As far as I understand, zvariant Values represent a DBus Variant. However I get the following error:
error: implementation of `serde::de::Deserialize` is not general enough
--> src/main.rs:13:45
|
13 | let resp: Vec<zvariant::ObjectPath> = p.call("GetBlockDevices", &std::collections::HashMap::<String, zvariant::Value>::new())?;
| ^^^^ implementation of `serde::de::Deserialize` is not general enough
|
::: /home/adnan338/.cargo/registry/src/github.com-1ecc6299db9ec823/serde-1.0.115/src/de/mod.rs:531:1
|
531 | / pub trait Deserialize<'de>: Sized {
532 | | /// Deserialize this value from the given Serde deserializer.
533 | | ///
534 | | /// See the [Implementing `Deserialize`][impl-deserialize] section of the
... |
569 | | }
570 | | }
| |_- trait `serde::de::Deserialize` defined here
|
= note: `std::vec::Vec<zvariant::object_path::ObjectPath<'_>>` must implement `serde::de::Deserialize<'0>`, for any lifetime `'0`...
= note: ...but `std::vec::Vec<zvariant::object_path::ObjectPath<'_>>` actually implements `serde::de::Deserialize<'1>`, for some specific lifetime `'1`
What's causing this and how can I avoid this error?

Answer 1

Firstly, thanks for trying out our crate. The issue is that zbus::Proxy::call expects the return value to be an owned one, while you're deserializing to an unowned type. Both of the the following work:
// OwnedObjectPath require zvariant >= 2.2.0
let resp: Vec<zvariant::OwnedObjectPath> = p.call(
"GetBlockDevices",
&std::collections::HashMap::<String, zvariant::Value>::new(),
)?;
let resp = p.call_method(
"GetBlockDevices",
&std::collections::HashMap::<String, zvariant::Value>::new(),
)?;
let resp: Vec<zvariant::ObjectPath> = resp.body()?;