feat(sound): use cosmic-settings-daemon's varlink API

pages/sound/src/lib.rs

@@ -0,0 +1,58 @@
+// Copyright 2026 System76 <info@system76.com>
+// SPDX-License-Identifier: GPL-3.0-only
+
+pub mod model;
+use std::sync::Arc;
+
+pub use cosmic_settings_audio_client as audio_client;
+use futures::{SinkExt, StreamExt};
+
+pub async fn subscribe<T>(
+    mut emitter: futures::channel::mpsc::Sender<T>,
+    apply_fn: fn(Message) -> T,
+) {
+    loop {
+        let mut client = match audio_client::connect().await {
+            Ok(client) => client,
+            Err(why) => {
+                if let audio_client::zlink::Error::Io(ref why) = why
+                    && why.kind() == std::io::ErrorKind::NotFound
+                {
+                    tracing::error!("cosmic-settings-daemon varlink service not found.");
+                } else {
+                    tracing::error!(
+                        ?why,
+                        "failed to connect to cosmic-settings's varlink service"
+                    );
+                }
+
+                tokio::time::sleep(std::time::Duration::from_secs(3)).await;
+                continue;
+            }
+        };
+
+        if let Ok(Ok(mut stream)) = client.recv_events().await {
+            _ = emitter
+                .send(apply_fn(Message::Client(Arc::new(client))))
+                .await;
+            while let Some(message) = stream.next().await {
+                match message {
+                    Ok(event) => {
+                        _ = emitter.send(apply_fn(Message::Subscription(event))).await;
+                    }
+                    Err(why) => {
+                        tracing::error!(?why, "event error");
+                    }
+                }
+            }
+        }
+    }
+}
+
+#[derive(Clone, Debug)]
+pub enum Message {
+    /// Connection to `com.system76.CosmicSettings`.
+    Client(Arc<audio_client::Client>),
+    /// Messages from the varlink audio client,
+    Subscription(audio_client::Event),
+}