Add no_mixer alternative for volume control

src/config.rs

@@ -81,6 +81,7 @@ static VOLUME_CONTROLLER_VALUES: &[&str] = &[
     "alsa",
     #[cfg(feature = "alsa_backend")]
     "alsa_linear",
+    "none",
 ];
 
 #[derive(Clone, Copy, Debug, Deserialize, PartialEq, Eq, StructOpt)]
@@ -90,6 +91,7 @@ pub enum VolumeController {
     AlsaLinear,
     #[serde(rename = "softvol")]
     SoftVolume,
+    None,
 }
 
 impl FromStr for VolumeController {
@@ -100,6 +102,7 @@ impl FromStr for VolumeController {
             "alsa" => Ok(VolumeController::Alsa),
             "alsa_linear" => Ok(VolumeController::AlsaLinear),
             "softvol" => Ok(VolumeController::SoftVolume),
+            "none" => Ok(VolumeController::None),
             _ => unreachable!(),
         }
     }

src/main.rs

@@ -17,6 +17,7 @@ mod config;
 mod dbus_mpris;
 mod error;
 mod main_loop;
+mod no_mixer;
 mod process;
 mod setup;
 mod utils;

src/no_mixer.rs

@@ -0,0 +1,23 @@
+use librespot_playback::mixer::{AudioFilter, Mixer, MixerConfig};
+
+pub struct NoMixer {}
+
+impl Mixer for NoMixer {
+    fn open(_: Option<MixerConfig>) -> NoMixer {
+        NoMixer {}
+    }
+
+    fn start(&self) {}
+
+    fn stop(&self) {}
+
+    fn volume(&self) -> u16 {
+        0
+    }
+
+    fn set_volume(&self, _volume: u16) {}
+
+    fn get_audio_filter(&self) -> Option<Box<dyn AudioFilter + Send>> {
+        None
+    }
+}

src/setup.rs

@@ -32,6 +32,11 @@ pub(crate) fn initial_state(config: config::SpotifydConfig) -> main_loop::MainLo
                 Box::new(|| Box::new(mixer::softmixer::SoftMixer::open(None)) as Box<dyn Mixer>)
                     as Box<dyn FnMut() -> Box<dyn Mixer>>
             }
+            config::VolumeController::None => {
+                info!("Using no volume controller.");
+                Box::new(|| Box::new(crate::no_mixer::NoMixer::open(None)) as Box<dyn Mixer>)
+                    as Box<dyn FnMut() -> Box<dyn Mixer>>
+            }
             _ => {
                 info!("Using alsa volume controller.");
                 let linear = matches!(
@@ -53,10 +58,17 @@ pub(crate) fn initial_state(config: config::SpotifydConfig) -> main_loop::MainLo
     };
 
     #[cfg(not(feature = "alsa_backend"))]
-    let mut mixer = {
-        info!("Using software volume controller.");
-        Box::new(|| Box::new(mixer::softmixer::SoftMixer::open(None)) as Box<dyn Mixer>)
-            as Box<dyn FnMut() -> Box<dyn Mixer>>
+    let mut mixer = match config.volume_controller {
+        config::VolumeController::None => {
+            info!("Using no volume controller.");
+            Box::new(|| Box::new(crate::no_mixer::NoMixer::open(None)) as Box<dyn Mixer>)
+                as Box<dyn FnMut() -> Box<dyn Mixer>>
+        }
+        _ => {
+            info!("Using software volume controller.");
+            Box::new(|| Box::new(mixer::softmixer::SoftMixer::open(None)) as Box<dyn Mixer>)
+                as Box<dyn FnMut() -> Box<dyn Mixer>>
+        }
     };
 
     let cache = config.cache;