ALSA: better card enumeration (#916)

- better device name
- list physical devices
- inject most common virtual ones (default, pipewire, pulse, ...)

Author: abique

src/host/alsa/enumerate.rs

@@ -5,42 +5,79 @@ use std::sync::{Arc, Mutex};
 
 /// ALSA's implementation for `Devices`.
 pub struct Devices {
-    hint_iter: alsa::device_name::HintIter,
+    builtin_pos: usize,
+    card_iter: alsa::card::Iter,
 }
 
 impl Devices {
     pub fn new() -> Result<Self, DevicesError> {
         Ok(Devices {
-            hint_iter: alsa::device_name::HintIter::new_str(None, "pcm")?,
+            builtin_pos: 0,
+            card_iter: alsa::card::Iter::new(),
         })
     }
 }
 
 unsafe impl Send for Devices {}
 unsafe impl Sync for Devices {}
 
+const BUILTINS: [&'static str; 5] = ["default", "pipewire", "pulse", "jack", "oss"];
+
 impl Iterator for Devices {
     type Item = Device;
 
     fn next(&mut self) -> Option<Device> {
+        while self.builtin_pos < BUILTINS.len() {
+            let pos = self.builtin_pos;
+            self.builtin_pos += 1;
+            let name = BUILTINS[pos];
+
+            if let Ok(handles) = DeviceHandles::open(&name) {
+                return Some(Device {
+                    name: name.to_string(),
+                    pcm_id: name.to_string(),
+                    handles: Arc::new(Mutex::new(handles)),
+                });
+            }
+        }
+
         loop {
-            match self.hint_iter.next() {
-                None => return None,
-                Some(hint) => {
-                    let name = match hint.name {
-                        None => continue,
-                        // Ignoring the `null` device.
-                        Some(name) if name == "null" => continue,
-                        Some(name) => name,
-                    };
+            let Some(res) = self.card_iter.next() else {
+                return None;
+            };
+            let Ok(card) = res else { continue };
+
+            let ctl_id = format!("hw:{}", card.get_index());
+            let Ok(ctl) = alsa::Ctl::new(&ctl_id, false) else {
+                continue;
+            };
+            let Ok(cardinfo) = ctl.card_info() else {
+                continue;
+            };
+            let Ok(card_name) = cardinfo.get_name() else {
+                continue;
+            };
 
-                    if let Ok(handles) = DeviceHandles::open(&name) {
-                        return Some(Device {
-                            name,
-                            handles: Arc::new(Mutex::new(handles)),
-                        });
-                    }
-                }
+            // Using plughw adds the ALSA plug layer, which can do sample type conversion,
+            // sample rate convertion, ...
+            // It is convenient, but at the same time not suitable for pro-audio as it hides
+            // the actual device capabilities and perform audio manipulation under your feet,
+            // for example sample rate conversion, sample format conversion, adds dummy channels,
+            // ...
+            // For now, many hardware only support 24bit / 3 bytes, which isn't yet supported by
+            // cpal. So we have to enable plughw (unfortunately) for maximum compatibility.
+            const USE_PLUGHW: bool = true;
+            let pcm_id = if USE_PLUGHW {
+                format!("plughw:{}", card.get_index())
+            } else {
+                ctl_id
+            };
+            if let Ok(handles) = DeviceHandles::open(&pcm_id) {
+                return Some(Device {
+                    name: card_name.to_string(),
+                    pcm_id: pcm_id.to_string(),
+                    handles: Arc::new(Mutex::new(handles)),
+                });
             }
         }
     }
@@ -50,6 +87,7 @@ impl Iterator for Devices {
 pub fn default_input_device() -> Option<Device> {
     Some(Device {
         name: "default".to_owned(),
+        pcm_id: "default".to_owned(),
         handles: Arc::new(Mutex::new(Default::default())),
     })
 }
@@ -58,6 +96,7 @@ pub fn default_input_device() -> Option<Device> {
 pub fn default_output_device() -> Option<Device> {
     Some(Device {
         name: "default".to_owned(),
+        pcm_id: "default".to_owned(),
         handles: Arc::new(Mutex::new(Default::default())),
     })
 }

src/host/alsa/mod.rs

@@ -185,10 +185,10 @@ struct DeviceHandles {
 impl DeviceHandles {
     /// Create `DeviceHandles` for `name` and try to open a handle for both
     /// directions. Returns `Ok` if either direction is opened successfully.
-    fn open(name: &str) -> Result<Self, alsa::Error> {
+    fn open(pcm_id: &str) -> Result<Self, alsa::Error> {
         let mut handles = Self::default();
-        let playback_err = handles.try_open(name, alsa::Direction::Playback).err();
-        let capture_err = handles.try_open(name, alsa::Direction::Capture).err();
+        let playback_err = handles.try_open(pcm_id, alsa::Direction::Playback).err();
+        let capture_err = handles.try_open(pcm_id, alsa::Direction::Capture).err();
         if let Some(err) = capture_err.and(playback_err) {
             Err(err)
         } else {
@@ -202,7 +202,7 @@ impl DeviceHandles {
     /// `Option` is guaranteed to be `Some(..)`.
     fn try_open(
         &mut self,
-        name: &str,
+        pcm_id: &str,
         stream_type: alsa::Direction,
     ) -> Result<&mut Option<alsa::PCM>, alsa::Error> {
         let handle = match stream_type {
@@ -211,7 +211,7 @@ impl DeviceHandles {
         };
 
         if handle.is_none() {
-            *handle = Some(alsa::pcm::PCM::new(name, stream_type, true)?);
+            *handle = Some(alsa::pcm::PCM::new(pcm_id, stream_type, true)?);
         }
 
         Ok(handle)
@@ -221,10 +221,10 @@ impl DeviceHandles {
     /// If the handle is not yet opened, it will be opened and stored in `self`.
     fn get_mut(
         &mut self,
-        name: &str,
+        pcm_id: &str,
         stream_type: alsa::Direction,
     ) -> Result<&mut alsa::PCM, alsa::Error> {
-        Ok(self.try_open(name, stream_type)?.as_mut().unwrap())
+        Ok(self.try_open(pcm_id, stream_type)?.as_mut().unwrap())
     }
 
     /// Take ownership of the `alsa::PCM` handle for a specific `stream_type`.
@@ -237,6 +237,7 @@ impl DeviceHandles {
 #[derive(Clone)]
 pub struct Device {
     name: String,
+    pcm_id: String,
     handles: Arc<Mutex<DeviceHandles>>,
 }
 
@@ -251,7 +252,7 @@ impl Device {
             .handles
             .lock()
             .unwrap()
-            .take(&self.name, stream_type)
+            .take(&self.pcm_id, stream_type)
             .map_err(|e| (e, e.errno()));
 
         let handle = match handle_result {
@@ -308,7 +309,7 @@ impl Device {
     ) -> Result<VecIntoIter<SupportedStreamConfigRange>, SupportedStreamConfigsError> {
         let mut guard = self.handles.lock().unwrap();
         let handle_result = guard
-            .get_mut(&self.name, stream_t)
+            .get_mut(&self.pcm_id, stream_t)
             .map_err(|e| (e, e.errno()));
 
         let handle = match handle_result {